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Environmental characteristics within a region often form site-specific agro-ecological responses to management. Using 92 fall-stockpiled tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] field trials in North Carolina and surrounding states, our objective was to test the influence of two management factors (forage utilization and pasture age) and two environmental factors (elevation and soil textural gradients) on soil properties at 0-to-10-cm depth, surface residue carbon (C) and nitrogen (N) contents, and absolute forage mass and nutritive values and their responses to N fertilization. Soil organic C and N fractions (i.e., total, particulate, and mineralizable) were greater (a) with improved (rotational stocking) than conventional (haying and/or continuous grazing) forage utilization, (b) in older pastures, (c) at higher elevation, and (d) with finer texture. Soil chemical properties were variably affected by these factors, and soil-test P was not affected. Surface residue N tended to be greater with improved than conventional forage utilization, but surface residue C was not affected by any of the factors. Crude protein was greater and dry matter yield response to N fertilizer was lower with improved than with conventional forage utilization. Forage mass was lower and nutritive values were greater at higher elevation. Soil organic C and total soil N sequestration rates during a 25-yr period were 0.75 Mg C ha−1 yr−1 and 75 kg N ha−1 yr−1, respectively. Elevation and soil texture imparted strong environmental controls on a diversity of soil properties, but management factors mostly affected surface-soil organic C and N fractions, which helped sustain forage productivity and nutritive value with lower N fertilizer input.
- body weight
- crude protein
- dry matter
- major land resource area
- neutral-detergent fiber
- near-infrared spectroscopy.
Tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] is a perennial cool-season forage that grows well throughout the eastern United States (Ball, Lacefield, & Hoveland, 2019). It tolerates soil acidity but responds positively to liming (Belesky & Fedders, 1995). It appears to accumulate N from deep in the soil, from recycled plant material, and possibly from other environmental sources (Giddens, Adams, & Dawson, 1971), resulting in significant accumulation of surface soil organic matter (Franzluebbers, Endale, Buyer, & Stuedemann, 2012; Franzluebbers et al., 1999). It is responsive to N fertilizer (Poore, Benson, Scott, & Green, 2000), but soil may provide sufficient N once pastures are mature (Franzluebbers, Pehim-Limbu, & Poore, 2018; Franzluebbers & Poore, 2020). It persists for decades (Franzluebbers, Stuedemann, Schomberg, & Wilkinson, 2000) and is a well-known forage for conservation plantings on hillsides and roadways (Bennett, 1979). Its persistence is related to the presence of the fungal endophyte Neotyphodium coenophialum, which also produces toxic ergot alkaloids that can cause animal health disorders (Stuedemann & Hoveland, 1988). Discovery and dissemination of novel endophytes that produce low or no ergot alkaloids (Bouton et al., 2002) have created new opportunities for cool-season production with greater animal gain in the southeastern United States (Drewnoski, Oliphant, Poore, Green, & Hockett, 2009; Watson et al., 2004).
Despite the fact that tall fescue is grown widely throughout the eastern United States, and particularly in the transition zone of the southeastern United States (Rouquette & Aiken, 2020), there have been only a few descriptions of how this ubiquitous forage alters soil properties and surface residue. Additionally, forage mass and nutritive value characteristics have not been comprehensively evaluated across a diversity of locations and with different management approaches. Individual field studies have assessed tall fescue influence on soil organic C and N fractions (Franzluebbers, Endale, Buyer, & Stuedemann, 2012; Franzluebbers et al., 1999; Handayani, Coyne, & Phillips, 2011), macronutrient concentrations (Schomberg, Stuedemann, Franzluebbers, & Wilkinson, 2000; West, Mallarino, Wedin, & Marx, 1989), forage production (Burns, Fisher, & Rottinghaus, 2006; Nave, Barbero, Boyer, Corbin, & Bates, 2016), and forage nutritive value (Balasko, 1977; Kallenbach, Bishop-Hurley, Massie, Rottinghaus, & West, 2003; Rayburn, Blaser, & Wolf, 1979), but little synthesis has occurred across locations or regions.
The objective of this study was to evaluate the effects of farm management characteristics (i.e., forage utilization and pasture age) and environmental gradients (i.e., elevation as affected by physiographic region and a diversity of soil textures) on surface-soil properties, surface residue C and N, forage mass, and forage nutritive value and its response to N fertilization across numerous locations in North Carolina and surrounding states.
2 MATERIALS AND METHODS
2.1 Experimental conditions
A total of 92 fall-stockpiled tall fescue trials were conducted in Georgia, South Carolina, North Carolina, Virginia, and West Virginia during 2015, 2016, and 2018 (Franzluebbers & Poore, 2020; Franzluebbers et al., 2018). These trials assessed forage mass and nutritive value responses to N fertilizer applied in late summer, as related to soil N availability. The hypothesis was that initial soil conditions would modify the extent of forage responses to N fertilization. Fields were distributed in 37 counties of five states and situated on four soil orders and 20 subgroups (Table 1). Mean annual temperature among sites was 13.9 ± 1.5 °C, and mean annual precipitation was 1,141 ± 97 mm.
|Soil subgroup||Location (state–county)|
|Fluvaquentic Eutrudepts||VA -Goochland|
|Typic Hapludalfs||NC–Davidson; VA – Pulaski|
|Ultic Hapludalfs||NC–Rowan; VA–Carroll, Fauquier, Loudoun|
|NC–Alexander, Ashe, Clay, Davidson, Guilford, Haywood, Rockingham, Stanly|
|Aquic Hapludults||NC–Durham, Granville, Rowan, Wayne|
|Typic Kanhapludults||GA–Madison, Oglethorpe, Oconee, Wilkes|
|NC–Durham, Granville, Guilford, Haywood, Orange, Person, Randolph, Rockingham, Rowan, Stanly, Surry, Wake, Wilkes, Yadkin|
|VA–Culpeper, Dinwiddie, Halifax, Madison|
|Aquic Paleudults||NC–Johnston, Pender|
|Typic Endoaquults||NC–Pender, Wayne|
- Tall fescue pasture age and forage utilization affected soil organic C and N fractions.
- Pasture age and forage utilization rarely altered forage nutritive value.
- Soil textural and elevation gradients influenced a diversity of soil properties.
- Soil organic C and total soil N were sequestered as a function of pasture age.
- Particulate organic C and N were ∼40% greater with improved than conventional grazing.
Forage utilization: Fields were classified as either (a) conventional or (b) improved. Conventional pasture management was with typical haying and/or grazing with continuous stocking (n = 28 fields). Hayed fields were those typically cut for hay once or twice per year but not hayed in the fall season of testing. Continuous stocking was typical for the region of allowing livestock free access through much of the year on a pasture. These conventional pasture management practices were contrasted with an improved forage utilization strategy of rotational stocking (n = 64 fields), which could be typified as pasture stocked with cattle for a period of a few days to several weeks and at least 1 mo of rest between grazing periods. Most farmers were striving for reduced hay feeding by adopting fall stockpiling. Detailed historical management for each field was not readily available, but the distinction between these two general approaches was clear. Most tall fescue fields had wild-type endophyte (n = 76 fields), and 16 fields were with novel endophyte. Presence of endophyte and toxicity was not determined, so we did not assess this factor. Nine of the novel-endophyte fields were in conventional management, typically for hay production.
Pasture age: Through farmer interviews, age of pasture was recorded. Statistical distribution of pasture age in ranked order was <10 yr in Quartile 1, 10–28 yr in Quartile 2, 28–40 yr in Quartile 3, and >40 yr in Quartile 4.
Elevation: Fields were located on Google Earth, and elevation was recorded. Broadly, fields were in Coastal Plain (n = 6 fields), Piedmont (n = 67 fields), and Appalachian (n = 19 fields) physiographic regions. These physiographic regions were summary groups for several individual major land resource areas (MLRAs), including the Central Allegheny Plateau (MLRA 126), Southern Appalachian Ridges and Valleys (MLRA 128), Southern Blue Ridge (MLRA 130B), Southern Coastal Plain (MLRA 133A), Southern Piedmont (MLRA 136), Carolina and Georgia Sandhills (MLRA 137), and Atlantic Coast Flatwoods (MLRA 153A). Statistical distribution of elevation in ranked order was 14–164 m in Quartile 1, 164–216 m in Quartile 2, 216–321 m in Quartile 3, and 321–855 m in Quartile 4.
Soil texture index: Fraction of soil as clay (0.220 ± 0.072 kg kg−1) was divided by fraction of soil as sand (0.461 ± 0.156 kg kg−1) to create a soil texture index. Fine-textured soils had larger values than coarse-textured soils. Statistical distribution of this index in ranked order was 0.10–0.32 in Quartile 1, 0.32–0.48 in Quartile 2, 0.48–0.75 in Quartile 3, and 0.75–1.90 in Quartile 4.
Fields were selected that had >67% tall fescue composition, although botanical composition was not quantified and the general characteristics of each field were reported elsewhere (Franzluebbers & Poore, 2021). Field trials were established in September and harvested 125 ± 17 d later in December–January. The experimental design of each field trial consisted of (a) four N fertilizer rates (0, 45, 90, and 134 kg N ha−1) replicated four times in a randomized block design in 2015 and 2016 (total area of 12 by 24 m with individual plot size of 3 by 6 m) and (b) four N fertilizer rates (0, 45, 90, and 134 kg N ha−1) combined with four P fertilizer rates (0, 45, 90, and 134 kg P2O5 ha−1) in a Latin-square in 2018 (total area of 18 by 36 m within individual plot size of 4.5 by 9 m). No trials were conducted in 2017. In all trials, 16 plots were present. Fertilizer sources were urea in 2015 and 2016 and urea stabilized with N-(n-Butyl) thiophosphoric triamide and triple super phosphate in 2018. Fertilizer was applied from 19 Aug. to 4 Sept. 2015, 30 Aug. to 15 Sept. 2016, and 23 Aug. to 27 Sept. 2018. Forage mass and nutritive value characteristics were reported elsewhere (Franzluebbers & Poore, 2020; Franzluebbers et al., 2018, 2021) and summarized in Table 2.
|Forage characteristic||Percentile limit|
|Forage mass, Mg DM ha−1||1.47||2.44||3.06||3.98|
|Moisture at harvest, g kg−1||417||548||639||748|
|Crude protein, g kg−1 DM||87||116||127||148|
|Neutral detergent fiber, g kg−1 DM||545||604||626||662|
|Acid detergent fiber, g kg−1 DM||303||355||380||414|
|Lignin, g kg−1 DM||45||61||71||93|
|Relative feed value, kg−1 N||79||89||94||113|
|Response to unit of N fertilizer|
|Forage mass, kg DM kg−1 N||−1.7||1.2||2.7||7.2|
|Moisture at harvest, g kg−1 DM kg−1 N||−0.01||0.21||0.34||0.68|
|Crude protein, g kg−1 DM kg−1 N||0.008||0.015||0.020||0.027|
|Neutral detergent fiber, g kg−1 DM kg−1 N||−0.39||−0.18||−0.12||−0.04|
|Acid detergent fiber, g kg−1 DM kg−1 N||−0.26||−0.14||−0.09||−0.01|
|Lignin, g kg−1 DM kg−1 N||−0.08||−0.03||−0.01||0.02|
|Relative feed value, kg−1 N||0.01||0.03||0.04||0.08|
2.2 Soil and plant analyses
On the same day as fertilization, initial sward condition was estimated by collecting forage from ≥4-cm height from a composite of two 0.25-m2 areas immediately outside of the test area (generally at diagonally opposite corners) and determining dry mass and C and N concentrations. Additionally, surface residue was collected in a 0.08-m2 area in each of the cut 0.25-m2 areas and composited. Surface residue was considered all organic material from ground level to 4-cm height after shearing off plant material at soil level. This may have included older decomposing plant material, dung, detritus, and basal stems of plants. Organic material was scraped from the soil surface, and soil contamination was estimated based on declining C concentration of material (Franzluebbers, 2020a). However, residue C and N were calculated on an area basis, so soil contamination would have been inconsequential. Both forage and surface residue samples were oven-dried at 55 °C for ≥3 d to constant mass. Samples were ground and analyzed for total C and N concentrations with a CN combustion analyzer (TruMac, Leco Corp.).
Soil was typically sampled in each field trial on the same day as and just prior to fertilization (late August/early September), although in 2015 and 2016 some fields were sampled within 2 wk prior to fertilization. Within each of four areas of a field trial (6 by 12 m blocks in 2015 and 2016 and 9 by 18 m blocks in 2018), eight soil cores (4 cm diameter) at depth of 0–10 cm were composited in a paper bag and within 12 h of collection were placed in an oven at 55 °C to dry until constant mass. Bulk density was calculated from dry mass and volume (1,005 cm3) of cores from each plot. Soil samples were homogenized by gently crushing with a pestle over a sieve with 4.75-mm openings. Stones and pieces of organic residue not passing the screen were discarded. Some soil properties from samples collected in 2015 and 2016 were first reported in Franzluebbers et al. (2018) and from samples collected in 2018 in Franzluebbers and Poore (2020).
Total organic C and N were determined by dry combustion on the CN analyzer from a 0.5-1 g subsample that was ground to a fine powder in ball mill. Soil pH was <7.0 (except on four fields), so total C was assumed as organic C. The C/N ratio of the four fields with pH = 7.1 ± 0.1 was no greater than that of the other fields. Particulate organic C and N fractions were determined from a 50-g subsample shaken with 100 ml of 0.1 mol L−1 Na4P2O7 for 16 h, diluted in a 1-L volumetric cylinder with deionized water, mixed with a plunger 10 times, and allowed to settle for exactly 5 h to obtain solution density for calculating clay concentration. The entire mixture was poured over a screen with 0.053-mm openings to collect the sand fraction, which was dried (55 °C for 24 h past visual dryness) and weighed. The sand fraction containing particulate organic matter was ball milled and analyzed for C and N with dry combustion as described for total organic C and N. Soil C and N mineralization and microbial biomass C were determined from the following sequence of steps: two 50-g subsamples were weighed into 60-ml glass jars, wetted to 50% water-filled pore space, and placed into a 1-L canning jar along with a vial containing 10 ml of 1 mol L−1 NaOH to trap CO2 and a vial of water to maintain humidity. Sealed jars were incubated at 25 °C in the dark for 24 d. The alkali trap was replaced at 3 and 10 d of incubation, and CO2–C from the screw-cap–sealed vial was determined by titration with 1 mol L−1 HCl with vigorous stirring in the presence of BaCl2 (that precipitated to form BaCO3) to a phenolphthalein endpoint. At 10 d, one of the subsamples was removed from the incubation jar and fumigated with CHCl3 under vacuum for 1 d. Vapors were removed, and the sample placed into a separate canning jar along with vials of alkali and water, and incubated at 25 °C for 10 d. Basal soil respiration was calculated from the assumed linear rate of C mineralization from 10 to 24 d of incubation. Potential C mineralization was calculated from cumulative CO2–C evolution of 0-to-3-d, 3-to-10-d, and 10-to-24-d periods. Soil-test biological activity was from CO2 evolved during the 0-to-3-d period. Net N mineralization was determined from the difference in inorganic N concentrations between 0 and 24 d of incubation. Inorganic N (NH4–N + NO2–N + NO3–N) was determined from the filtered extract of a 10-g subsample of dried (55 °C for 3 d) and sieved (≤2 mm) soil that was shaken with 20 ml of 2 mol L−1 KCl for 30 min using salicylate-nitroprusside and hydrazine autoanalyzer techniques (Bundy & Meisinger, 1994). Net nitrification was calculated as the percentage of total mineralized N that could be attributed to an increase in nitrate-N during the 24-d incubation.
Routine soil chemical properties were determined by the North Carolina Department of Agriculture Soil Testing Laboratory using standard techniques. Analysis of P, K, Ca, Mg, S, Mn, Cu, and Zn was from 2.5 ml of soil extracted with 25 ml of Mehlich-3 solution (Mehlich, 1984a) and determination with argon plasma emission spectroscopy. Cation exchange capacity was from summation of base cations (Ca2+, Mg2+, K+) and acidity (Al3+, H+). Nutrient values were reported as g m−3, which would be equivalent to mg kg−1 if soil density were 1.0 Mg m−3. Weight of a 10-ml scoop of soil was used to calculate sieved density, which was 1.18 ± 0.12 Mg m−3 among fields. Soil pH was in 1:1 soil to 0.01 mol L−1 CaCl2 and reported as a water pH by addition of 0.6 pH units. Humic matter was from NaOH digestion and colorimetric determination (Mehlich, 1984b).
Stockpiled forage was harvested with a rotary mower with rear vacuum bag having a cutting width of 0.5-m (Troy-Bilt, 159 cc). Forage was collected from the central 10 m2 in 2015 and 2016 and 14 m2 of each plot in 2018 (35–56% of plot area). Only forage ≥10-cm height was collected in 2015. In subsequent years, forage ≥10-cm height was collected first, and then a second harvest at 5-cm height on the same day was collected (5-to-10-cm layer). Forage was collected in a 60-L tub and weighed in the field (nearest 0.01 kg) on a portable balance. A representative subsample (70–300 g) was collected and weighed at field moisture. Subsamples were then oven-dried at 55 °C for ≥3 d to constant weight to determine forage dry matter (DM) and moisture contents at time of harvest.
Dried forage samples were ground in a Wiley mill to ≤1 mm particle size. All forage samples were scanned with near-infrared spectroscopy (NIRS; Model 5000 with WinISI version 1.5 software, Foss North America, Inc.). Nitrogen-treatment results were presented elsewhere (Franzluebbers & Poore, 2020; Franzluebbers et al., 2018, 2021). A calibration dataset for forage nutritive value was established from 275 tall fescue samples collected in 2015 and 2016 (out of 1,168 total samples available). Spectra were analyzed for outliers (‘H’ > 3.0) prior to sample selection for chemical determinations. An ‘H’ statistic of 0.6 was used to select samples with different spectra. Forage constituents of C and N concentration were determined for the 275 samples using a Leco TruMac (Leco Corp.). Forage constituents of lignin, amylase-treated neutral-detergent fiber (NDF), and acid-detergent fiber were chemically determined for the 275 samples by Cumberland Valley Analytical Services. Both sets of chemical analyses were used for calibration with NIRS. Additional forage constituents of acid detergent insoluble protein (protein in the acid-insoluble fraction associated with lignin), P, K, Ca, and Mg concentration were estimated with NIRS from purchased equations representing hay and fresh forage from a library of 334–1,230 calibration samples (Foss) (Table 3). The combined analysis across all 3 yr was from 92 field trials with 2,608 samples.
|C, g kg−1||415||493||3|
|N, g kg−1||7.5||33.9||0.4|
|P, g kg−1||0.6||5.6||0.4|
|Ca, g kg−1||0||24||2|
|K, g kg−1||1||49||5|
|Mg, g kg−1||<1||54||1|
|Dry matter, g kg−1||904||953||6|
|Acid detergent fiber, g kg−1||228||497||8|
|Neutral detergent fiber, g kg−1||441||757||12|
|Lignin, g kg−1||9||119||4|
|Acid-detergent insoluble protein, g kg−1||0||18||2|
|Relative feed value||53||138||3|
2.3 Statistical analyses
Farm collaborators were interviewed to characterize management of each field (e.g., age of pasture, planted species, style of grazing management, routine fertilizer inputs, and any unique features). Response variables of soil, surface residue, and forage properties were tested for significance to four broad farm characteristics (i.e., management according to forage utilization and pasture age and environmental according to elevation and soil texture index). Soil and surface residue properties were independent of N fertilization because sampling occurred prior to fertilizer application. For forage properties at ≥10-cm-height, both (a) mean forage nutritive value of each field and (b) response of forage nutritive value to N fertilization on each field were tested against farm characteristics. Rates of N fertilizer were the same for all sites of all years, but P fertilizer was only a variable with equal distribution among N fertilizer rates in the third year. Only mean values for a field were used (n = 92), including for forage mass and nutritive value responses to N fertilization after calculation of regression responses to N fertilization (Franzluebbers & Poore, 2020; Franzluebbers et al., 2018, 2021).
Analysis of variation was conducted with SAS version 9.4 (SAS Institute Inc.) using the stepwise procedure with an entry level of P ≤ .05 to identify significant variables of interest. A small but significant correlation was found between elevation and soil texture index (r = .21; P = .04). Those significant variables selected were then manually placed into simple or multiple linear regressions to determine magnitude of effects, accounting for covarying effects. Forage utilization was numerically transformed into 0 for conventional and 1 for improved so that all four factors had equal opportunity to be selected in the stepwise procedure. Therefore, fixed effects were the four farm factors, and random effects were the multiple fields (n = 92). Fields were independent because only a couple of fields had testing on the same paddock in different years. If forage utilization was significant in the stepwise procedure, then simple means for this factor were calculated and reported. All other farm characteristics were reported as linear regression coefficients. Linear and nonlinear regressions were computed and plotted with SigmaPlot v. 14.0. Soil organic C and N sequestration rates were based on contents of soil organic C and N at 10-cm depth after adjustment for measured bulk density.
3 RESULTS AND DISCUSSION
3.1 Forage utilization strategy
Surface residue C (i.e., all living and dead organic C below 4 cm to mineral surface soil) was similar (2.23 ± 1.13 Mg C ha−1) between conventional (i.e., haying and/or continuous stocking) and improved (i.e., rotational stocking) forage utilization strategies. Surface residue N tended to be greater for improved than conventional forage utilization (113 and 90 kg N ha−1, respectively; P = .08). Initial forage mass (2.17 ± 1.07 Mg ha−1) and crude protein (CP) (128 ± 26 g kg−1 DM) at the beginning of the stockpile period were not different among forage utilization strategies. Therefore, end-of-summer condition of pastures was similar in forage mass, but marginally greater surface residue N content of rotationally grazed pastures may have reflected a longer-term impact of the conservation management axiom of “take half–leave half.” Although each producer would have had different land conditions and variations in rotational stocking approaches, surface residue N content suggested more ungrazed forage and/or manure deposition covering the soil surface than with continuous grazing and/or haying.
Several surface soil properties (0-to-10-cm depth) were greater with improved than conventional forage utilization strategies (Table 4). Particulate organic C and N were most notably greater by ∼40% with improved than conventional forage utilization. Particulate organic C and N reflect recent organic matter inputs from surface residues and roots because this is an intermediately decomposed fraction of organic matter (Cambardella & Elliott, 1992; Wander, 2004). Soil organic C was also significantly greater with improved than conventional forage utilization, a result that is consistent with a previous observation in Texas (Teague et al., 2011). Total soil N was greater with improved than conventional forage utilization without other variables in the analysis but was not significant when pasture age, elevation, and soil texture index were included. Greater soil organic C and N fractions with improved forage utilization were also associated with lower sieved density. Bulk density in the field was not affected by forage utilization strategy (1.17 ± 0.11 Mg m−3). Both sieved density and bulk density in the field were negatively associated with soil organic C (Figure 1). The negative association between bulk density and soil organic C has been observed before in soils of the southeastern United States (Franzluebbers, 2010), and the negative association between sieved density and soil organic C has been reported across a diversity of soils in the eastern United States (Franzluebbers, 2020b). Extractable Cu was also greater with improved than conventional forage utilization strategies, and this may have been a consequence of those farmers choosing to use poultry litter as fertilizer. Poultry litter often contains significant Cu as a consequence of feed additive to control animal disease (Adeli, Sistani, Tewolde, & Rowe, 2007). The cause of greater net nitrification with improved than conventional forage utilization is likely from a soil microbial community shift, but the consequences of this change are not clear and might be dependent on overall soil N availability along with input of N fertilizers.
|Property||Conventionala||Improvedb||Pr > F|
|Sieved density, Mg m−3||1.00||0.94||.01|
|Cation exchange capacity, molc m−3||95||113||.03|
|Extractable Mg, g m−3||214||273||.009|
|Extractable Mn, g m−3||87||60||.05|
|Extractable Cu, g m−3||2.5||4.4||.05|
|Total organic C, g kg−1||22.9||28.8||.01|
|Particulate organic C, g kg−1||4.2||5.7||.002|
|Particulate organic N, g kg−1||0.24||0.34||.005|
|Net nitrification, %||72||82||.005|
|Crude protein, g kg−1 DM||120||131||.05|
|DM × N fertilizer, g DM kg−1 N||2.3||1.3||.05|
|Moisture × N fertilizer, g kg−1 kg−1 N||0.39||0.26||.01|
- Note. Several surface residue and soil variables were not significantly affected by forage utilization, including surface residue C (2.23 ± 1.13 Mg ha−1), field bulk density (1.17 ± 0.11 Mg m−3), sand concentration (461 ± 158 g kg−1), clay concentration (220 ± 73 g kg−1), humic matter (5 ± 4 kg m−3), acidity (13 ± 5 molc m−3), pH (6.2 ± 0.5), soil-test P (110 ± 84 g m−3), soil-test K (161 ± 104 g m−3), extractable Ca (1376 ± 635 g m−3), extractable Zn (10.5 ± 8.6 g m−3), extractable Cu (3.8 ± 4.2 g m−3), cumulative C mineralization (1002 ± 316 mg kg−1 24 d−1), basal soil respiration (23.5 ± 7.5 mg kg−1 d−1), residual soil ammonium-N (13 ± 9 mg kg−1), and residual inorganic N (20 ± 12 mg kg−1). DM, dry matter.
- aConventional was with haying and/or continuous grazing.
- bImproved was with rotational stocking.
Perhaps equally important, there was a large cadre of soil properties that were not affected by forage utilization strategy, including many routine soil chemical properties. This may have been (a) a result of historical fertilization strategies that are routinely agricultural advisors and adopted by many farmers, (b) from generous application rates of fertilizer nutrients in excess of immediate need to accumulate mineral reserves in soil, and (c) from inadequate differentiation of nutrient recommendations based on differences in management style. Curiously, extractable Mn was lower with improved than conventional forage utilization. Extractable Mn was most strongly correlated with clay concentration (r = .46; P < .001), so mineralogy differences among fields may have been the causal factor.
Only a few forage nutritive value characteristics were affected by forage utilization strategy in this regional analysis (Table 4). Improved pasture management with rotational stocking appears to have improved soil organic C and N fractions enough to have affected supply of N to stockpiled forage, resulting in greater CP than with conventional pasture management through either continuous grazing or haying of available forage. Combined with reduced forage yield response to N fertilizer, this result illustrated how improved grazing management can significantly improve internal cycling of nutrients from soil. Reduced forage moisture response to N fertilizer also supported this interpretation. Accumulation of soil organic C and N fractions, therefore, provides strong evidence that soil N supply from mineralization of organic matter affects nutrient uptake potential of forage. These results show that improved pasture soil fertility through soil organic matter improvement can add value to production and potentially reduce N fertilizer requirements, as described before (Franzluebbers & Poore, 2020; Franzluebbers et al., 2018).
Literature comparing forage nutritive value of pastures managed with different grazing methods is available but is complicated by seasonal changes in sward composition with long rest periods and over years with sustained management. In Florida on ‘Callie’ bermudagrass (Cynodon dactylon var. aridus), in vitro digestible organic matter was typically greater in rotational than with continuously grazed pastures, but CP was rarely affected by grazing method (Mathews, Sollenberger, & Staples, 1994). In this 2-yr study, dairy heifers gained as much with continuous as with rotational stocking. In Arkansas on ‘Midland’ bermudagrass overseeded with annual cool-season forages, in vitro DM digestibility and CP were not affected by grazing method during 2 yr of evaluation, but higher stocking rate (2.2 vs. 1.6 Mg body weight [BW] ha−1) was achieved with rotational than continuous stocking during the cool season, which resulted in greater live-weight gain (Aiken, 1998). The study also found that more intensive rotational stocking with 11 paddocks compared with three paddocks was more productive. Comparing six dairy farms in Wisconsin, available forage offered to grazing animals and CP were greater and NDF was lower with rotational than with continuous stocking (Paine, Undersander, & Casler, 1999). Differences in nutritive value could have been due to pastures managed with rotational stocking having regular frost-seeding of red clover (Trifolium pratense L.), whereas continuously grazed pastures did not. In a 3-yr investigation of continuous (0.77 Mg BW ha−1), rotational (6.36 Mg BW ha−1), and mob (49.49 Mg BW ha−1) stocking density with the same stocking rate per year (0.44 Mg BW ha−1), nutritive value of cool-season forages (tall fescue, orchardgrass [Dactylis glomerata L.], Kentucky bluegrass [Poa pratensis L.], white clover [Trifolium repens L.], and red clover mixture) varied seasonally but rarely was affected by grazing method (Tracy & Bauer, 2019).
Overall, small differences in forage nutritive value between conventional and improved forage utilization were consistent with most studies on grazing method effects conducted in different regions. However, there could be significant differences in animal performance and production between methods, as well as on environmental quality, economic performance of farming system, and/or cultural and family well-being issues. Greater total organic C and cation exchange capacity with improved than conventional forage utilization were consistent with an on-farm study in Texas (Teague et al., 2011), but greater particulate organic C and N, greater CP of forage, and less sensitivity of forage to N fertilizer input with improved than with conventional management are unique results. Chan et al. (2010) noted high variability of soil properties with on-farm surveys. Other studies that have not found soil and forage differences between rotational and continuous stocking attributed the lack of difference to management-specific gradients of grazing methods and small expected changes in soil properties due to climatic conditions (Sanderman, Reseigh, Wurst, Young, & Austin, 2015) and limited time of exposure to management (Manley, Schuman, Reeder, & Hart, 1995). Compared with haying, grazed pastures have been shown to accumulate greater soil organic C and N fractions due to return of fouled forage and feces directly to the pasture (Franzluebbers, Stuedemann, & Wilkinson, 2001; Franzluebbers et al., 2012).
3.2 Pasture age
Surface residue C and N prior to stockpiling were not affected by stand age of pastures (data not shown). Older pastures had greater residual forage mass prior to stockpiling (Table 5), suggesting that a greater abundance of forage proliferated during the summer or that simply some older fields may not have been grazed as intensively during the pre-stockpile period. Pasture age was the most broadly influential of the four factors in this analysis, significantly affecting 20 soil properties and three forage properties (Table 5). Most soil properties were greater with older than younger pastures, except for sieved density, bulk density, and sand concentration. Declines in soil bulk density and sieved density were logical based on accumulation of surface soil organic matter in more mature pastures (Franzluebbers et al., 2001). Data in Figure 1 support this interpretation. The negative association of sand concentration with pasture age appears to be a spurious result that can occur with random surveys of farm management characteristics. Translocation of clay from surface soil to deeper layers can occur over centuries, but this was opposite to the effect observed. High variability of soil properties with on-farm surveys has been noted before (Chan et al., 2010), and results from on-farm surveys should be assessed with caution because of this random variation and potential for spurious results.
|Response variable||Linear regression component|
|Intercept||Age, yr−1||Elevation, m−1||Soil texture index, unit−1|
|Field bulk density, Mg m−3||1.31||−0.0022***||−0.00014**||−0.074**|
|Sieved density, Mg m−3||1.16||−0.0017***||−0.00015***||−0.142***|
|Sand, g kg−1||0.682||−0.0011*||NSa||−0.326***|
|Clay, g kg−1||0.448||NS||NS||0.121***|
|Base saturation, %||83||0.1**||NS||NS|
|Acidity, molc m−3||11||NS||0.01**||NS|
|Cation exchange capacity, molc m−3||66||0.4*||NS||33***|
|Soil-test P, g m−3||110||NS||NS||NS|
|Soil-test K, g m−3||95||1.4*||0.11*||NS|
|Extractable Ca, g m−3||904||7.3*||NS||478**|
|Extractable Mg, g m−3||176||NS||NS||59*|
|Extractable S, g m−3||16||NS||0.01**||3**|
|Extractable Mn, g m−3||54||NS||NS||52***|
|Extractable Zn, g m−3||10.5||NS||NS||NS|
|Extractable Cu, g m−3||3.8||NS||NS||NS|
|Residual soil ammonium-N, mg kg−1||9.0||0.14**||NS||NS|
|Residual soil nitrate-N, mg kg−1||2.2||0.09**||0.008**||NS|
|Residual inorganic N, mg kg−1||10.1||0.23***||0.012*||NS|
|Total organic C, g kg−1||12.6||0.15***||0.013***||6.2**|
|Total soil N, g kg−1||1.06||0.020***||0.0012***||0.61***|
|Particulate organic C, g kg−1||3.6||0.03***||NS||NS|
|Particulate organic N, g kg−1||0.19||0.003***||NS||NS|
|Soil microbial biomass C, mg kg−1||749||4.7**||0.55***||272**|
|Carbon mineralization, mg kg−1 24 d−1||542||6.7***||0.56***||208***|
|Net N mineralization, mg kg−1 24 d−1||44.2||1.18***||0.092***||35.2***|
|Net nitrification, %||78||NS||-0.02**||NS|
|Basal soil respiration, mg kg−1 d−1||14.0||0.11**||0.013***||4.7**|
|Soil-test biological activity, mg kg−1 3 d−1||183||3.0***||0.20***||85***|
|Residual forage mass at stockpile, Mg DM ha−1||1.85||0.012*||NS||NS|
|Dry matter yield, Mg DM ha−1||1.40||NS||−0.0006*||NS|
|Forage moisture, kg kg−1||0.611||NS||NS||NS|
|Forage moisture × N fertilizer, g kg−1 kg−1 N||0.44||−0.002*||NS||NS|
|Crude protein, g kg−1 DM||114||NS||0.02*||NS|
|Neutral detergent fiber, g kg−1 DM||595||NS||−0.05**||NS|
|Acid detergent fiber, g kg−1 DM||355||NS||−0.05**||NS|
|Lignin, g kg−1 DM||57||NS||−0.01*||NS|
|Ca, g kg−1 DM||6.4||NS||NS||0.6*|
|K, g kg−1 DM||17.8||0.04*||NS||NS|
|P, g kg−1 DM||2.7||NS||0.001**||NS|
|Relative feed value||96||NS||0.02**||NS|
- *Significant at the .05 probability level. **Significant at the .01 probability level. ***Significant at the .001 probability level.
- a Not significant at P > .05.
Older pastures led to enrichment of soil organic C and N fractions compared than younger pastures (Table 5). This enrichment was likely due to more years of forage growth, decay, and fecal deposition on the soil. Although the statistical analysis of various factors with the stepwise procedure used linear associations, accumulation of soil organic C content (Mg C ha−1) with time was better fitted to a nonlinear relationship (Figure 2). Large random variation could be expected from a survey of pastures having a wide diversity of soils in a large geographic region. Based on regression parameters, an additional 19.3 Mg C ha−1 was sequestered with maturation of pastures. This sequestration was more than double the soil organic C content in the surface 10 cm at pasture initiation (11.1 Mg C ha−1). Rate of change in soil organic C was calculated as 1.9 Mg C ha−1 yr−1 during the first 5 yr of management, 1.4 Mg C ha−1 yr−1 during the first 10 yr of management, 0.9 Mg C ha−1yr−1 during the first 20 yr of management, and 0.4 Mg C ha−1 yr−1 during the first 50 yr of management. Total soil N accumulation was fitted to a mixed nonlinear plus linear model. Rate of soil N accumulation was 158 kg N ha−1 yr−1 during the first 5 yr of management, 127 kg N ha−1 yr−1 during the first 10 yr of management, 87 kg N ha−1 yr−1 during the first 20 yr of management, and 43 kg N ha−1 yr−1 during the first 50 yr of management. Rates of soil organic C and N accumulation during the first 10 yr of management were 40–70% greater than those reported previously for grazed tall fescue pastures in a chronosequence study in Georgia (Franzluebbers et al., 2000). However, rates in the current study were only 20–30% greater than this earlier study when comparing sequestration from 0 to 50 yr of management. Regression of total soil N with pasture age had a small linear component that suggests sustained accumulation of 7 kg N ha−1 yr−1 was occurring over decades and not just the first 20 yr, in which the nonlinear component essentially became exhausted.
Rates of soil organic C and N accumulation in these pastures illustrate how N fertilization could be ecologically managed in pastures over time. Greater rates of N fertilization would likely be necessary in younger pastures to stimulate forage growth but also to cycle N from urine and dung return to soil to be sequestered in organic matter. With maturation of the pasture toward a steady-state level of organic matter accumulation, mineralization of organic N can be used to supply forage with N. Defining minimum levels of exogenous N fertilizer in specific seasons and holistically over time on different soils and in different climates to balance productivity with environmental quality remains an underexplored aspect of sustainable pasture management. Data from this study suggest that an inflection point of ∼10 yr from establishment may be needed to shift from dominance of net N immobilization to net N mineralization on a yearly basis.
Other more biologically active fractions of C and N increased with pasture age too, including particulate organic C and N, soil microbial biomass C, cumulative C mineralization, net N mineralization, basal soil respiration, and soil-test biological activity (Table 5). Linear changes in these C and N fractions over the 70-yr chronosequence period were 1.3 ± 0.7% yr−1. These values were much lower than the 40 ± 22% yr−1 changes in the surface 6 cm of soil, as reported during the first 5 yr of bermudagrass pasture development (Franzluebbers & Stuedemann, 2003). Active fractions of C and N are more concentrated near the surface and, as shown for total organic C and N, are more rapidly affected during the first decade of pasture development compared with several decades of management. When fitted to a nonlinear regression equation, the change in soil-test biological activity was 41% yr−1 (data not shown) during the first 5 yr of management, a value considerably greater than the linear association over 70 yr. Other active fractions of organic C and N also had greater responses early in pasture development than later.
Some small changes occurred in a few soil chemical properties with pasture age, but there were also several chemical properties not significantly affected by pasture age (Table 5). A possibility is that poultry litter fertilization of some of the fields may have contributed to greater soil chemical properties with repeated applications over time. Records of manure application were not available, other than recent history during the past few years prior to on-farm trials. Greater extractable Ca, K, and cation exchange capacity would have supported this interpretation, but lack of difference in extractable P and Cu did not. Many of these soil chemical properties are particularly affected by poultry litter application (Adeli et al., 2007).
A few forage properties were weakly related to pasture age (Table 5). Forage K concentration during the stockpile period was associated with increasing pasture age, suggesting that K cycling from soil to forage was greater in older stands. This may have been a consequence of historical fertilization, either with inorganic or organic sources. Significance of this result is not readily apparent without greater details on pasture management. Reduced forage moisture response to N fertilization in the fall was likely due to reduced need for N in older pastures with satiation of N demand in older pastures. Therefore, most data indicated that nutritive value was not greatly affected by pasture age. These results suggest that well-maintained older pastures can be productive and with adequate nutritive value, partly due to accumulation of recycled and readily mineralizable organic substrates in surface soil (Franzluebbers & Poore, 2020; Franzluebbers et al., 2018).
3.3 Elevation gradient
Elevation was the second-most influential factor, affecting 15 soil properties and seven forage properties (Table 5). Residual forage mass prior to the fall-stockpile period and surface residue C and N were not different along the elevation gradient. A broad suite of soil organic C and N fractions increased with increasing elevation. Figure 3 shows the linear association of net N mineralization and soil-test biological activity as a function of elevation.
Other indices of N availability also increased with increasing elevation, including residual soil nitrate and net nitrification (Table 5). Minor increases also occurred in soil acidity and extractable K and S. These differences may have been more from inherent soil geochemical properties because many other soil chemical properties were not affected along the elevation gradient. Reduced soil bulk density and sieved density with increasing elevation were likely due to greater soil organic C and N (Figure 1) and greater soil clay concentration that enhanced aggregation and formation of pores.
Elevation gradient was inversely associated with mean annual temperature as well as with soil clay concentration (r = .25; P = .02). Mean annual temperature and precipitation (1961–1990) at nearby weather stations were 15.3 ± .7 °C and 1,155 ± 39 mm in the Coastal Plain, 14.4 ± 1.0 °C and 1,151 ± 69 mm in the Piedmont, and 11.6 ± .8 °C and 1,103 ± 164 mm in the Appalachian region. The Coastal Plain typically has sandy soils, but both sandy and clayey soils can be found throughout the Piedmont and Appalachian regions. Therefore, the long-term temperature gradient and source of soil parent material would have played roles in soil and forage responses.
Effects of elevation on soil properties in agro-ecosystems have not been extensively studied. In Switzerland, soil organic C of grasslands increased with elevation (Leifeld, Bassin, & Fuhrer, 2005). The associated effect of lower mean annual temperature with increasing elevation leads to greater total soil N (Jenny, 1929). In a shrub-steppe ecosystem in Washington state with a 500-m elevation gradient, total organic C and N and nitrification potential increased with increasing elevation (Smith, Halvorson, & Bolton, 2002). However, in a natural grassland ecosystem in China with 1,000-m elevation gradient, in situ N mineralization and nitrification potential declined with increasing elevation (Zhang et al., 2011).
Increasing elevation was associated with lower DM yield of stockpiled forage, but with greater nutritive value (Table 5). Decline in DM yield with elevation was proportionally greater (40% difference in yield with 1,000 m elevation difference) than most of the changes in forage nutritive value. With a 1,000-m elevation difference, P concentration increased 37%, CP increased 18%, lignin decreased 18%, acid-detergent fiber decreased 14%, NDF decreased 8%, and relative feed value increased 21%. A slower growth rate likely occurred with lower fall temperature in the Appalachian region, thereby affecting forage mass and nutritive value. Nutritive value may have also increased with more moderate temperatures and/or less evaporative demand during a greater portion of the year.
Reports of differences in forage nutritive value along elevation gradients are not common, partly due to a focus on more in-depth analyses of individual studies at a particular location. The current study had an alternative approach of numerous, relatively simple field trials across a diversity of locations. This allowed an assessment of variations due to farm management and environmental conditions.
3.4 Soil textural gradient
Soil texture index significantly affected 16 soil properties and one forage property (Table 5). By definition of the soil texture index, clay concentration was positively associated, and sand concentration was negatively associated. Soil bulk density and sieved density were also negatively associated with the soil texture index, likely due to greater clay concentration leading to greater soil structural development (Hassink, 1992). Along with the relatively large effects of soil texture on soil density (6–12% per unit change in soil texture index), there were even greater changes in soil chemical properties (50 ± 24% per unit change in soil texture index as affected by cation exchange capacity and extractable Ca, Mg, S, and Mn) and soil organic C and N fractions (49 ± 15% per unit change in soil texture index as affected total organic C and N, soil microbial biomass C, cumulative C mineralization, net N mineralization, basal soil respiration, and soil-test biological activity). The diversity of soil properties affected and the magnitude of their change point to the important role of soil texture on soil properties, some of which are strongly linked to soil health condition (Lehman et al., 2015).
Soil textural effects on organic C and N fractions would have likely affected soil structural development from microbial decomposition of C substrates returned to soil with pasture management. Cumulative C mineralization and basal soil respiration were positively associated with soil texture index (Figure 4). Differences between coarse- and medium-textured soils appeared to have been most important in differentiating these indicators of soil biological activity, whereas differences between medium- and fine-textured soils had minimal effect.
Clay mineralogy can have a large impact on protection of soil organic C and N associated with clay surfaces and within aggregates (Merckx, den Hartog, & van Veen, 1985). Clay mineralogy was not determined, but soil series names suggested varying mineralogy (e.g., active, kaolinitic, mixed, semiactive, and subactive) among fields. Although 2:1 clay lattices often have a strong positive effect on soil organic C accumulation (Nichols, 1984), the association between clay and organic C concentrations in soils dominated by 1:1 clay lattices (e.g., kaolinite) is not as obvious (Franzluebbers, 1999). Mineralogy of the clay fraction was often mixed and therefore was likely influenced by Fe oxides and silicate clays interacting with different forms of organic matter (Kahle, Kleber, Torn, & Jahn, 2003).
The lack of difference in soil pH, base saturation, and soil-test P along the soil texture gradient, as well as among other management and environmental categories, suggests that perhaps liming and fertilization strategies over decades of management may have neutralized any inherent differences in these chemical features among soils.
The only effect of soil texture index on forage properties was Ca concentration (Table 5). This was likely a consequence of greater extractable Ca concentration with greater soil texture index, leading to greater plant-available Ca. It can be reasonably concluded based on the large number of fields evaluated over 3 yr and the relatively equal distribution among fine- (n = 35), medium- (n = 35), and coarse-textured (n = 22) soils that soil texture index had little direct impact on the capability of fall-stockpiled tall fescue stands to supply plant nutrients, besides Ca, for forage digestibility by ruminant livestock.
In a series of on-farm tall fescue stockpile trials across 92 fields over 3 yr, surface residue C and N contents were not significantly affected by forage utilization strategy, pasture age, elevation gradient, or soil textural gradient. Soil organic C and N fractions (i.e., total, particulate, and mineralizable C and N) were more sensitive to management effects of forage utilization strategy and pasture age than routine soil testing (i.e., chemical properties). Significant differences in both organic and inorganic soil properties were evident in elevation and soil textural gradients. Mean soil organic C and N sequestration rates across a 20-yr period for these 92 tall fescue fields of the southeastern United States were 0.90 Mg C ha−1 yr−1 and 87 kg N ha−1 yr−1, respectively. This apparent sequestration was substantially reduced over a 50-yr period to 0.38 Mg C ha−1 yr−1 and 43 kg N ha−1 yr−1, respectively. Total and particulate organic C and N fractions and cation exchange capacity were greater with improved (i.e., rotational stocking) than conventional (i.e. haying and/or continuous grazing) forage utilization.
Although older pastures were able to maintain equally high forage nutritive value as younger pastures, they did not respond as much to additional N fertilizer due to the accumulation of soil organic C and N. Younger pastures were more responsive in nutritive value to increasing N fertilization. Soil organic C and N fractions and forage nutritive value increased along an elevation gradient, although forage mass showed an opposite trend. Soil texture had a large influence on a broad suite of organic and inorganic soil properties but had little influence on forage nutritive value. Overall, this study contributed several unique findings on management and environmental influences on soil, surface residue, and forage nutritive value on farms throughout North Carolina and surrounding states. Tall fescue pastures in the southeastern United States can be improved with rotational stocking, and these pastures can lead to improved soil health conditions with high levels of soil organic C and N fractions.
Hannah Frank, Ellen Leonard, Ashton Mizelle, Smriti Pehim-Limbu, Erin Silva, and Ashley Turner provided sound technical support in the laboratory and field. Becky Barlow, Jonathan Black, Philip Brown, Rick Brown, Ben Chase, Mark Clements, J. B. Daniel, Brad Graham, Brad Hardison, Ethan Henderson, Lee Holcomb, Danny Hyatt, Sheryl Jarvis, Jay Marshall, Tim Mize, Gabe Pent, John Michael Phillips, Ed Rayburn, H. R. Scott, Robert Shoemaker, Carl Stafford, Lorie Townsend, Jason Wheatley, Abigail Whitaker, and Kimberly Woods provided key logistical support at field locations. Sincere appreciation is extended to all research station managers, including Dean Askew, Eric Elsner, David Fiske, Joe French, Joe Hampton, Teresa Herman, Cathy Herring, Johnnie Howard, Rick Kern, Jeremy Martin, Andy Meier, Kaleb Rathbone, Greg Shaeffer, and Tracy Taylor. Collaborating farmers deserve special mention for their dedication, insights, and trust: thanks to Kent Beck, Norman Bower, Brandon and Allison Brown, David Brown, Jason Byrd, Ronnie Carver, Terry Chandler, Ryan Clark, Donnie Clayton, John Cothren, Oscho and Eric Deal, Tim Eaton, Joe French, Michael Hall, Adam Hilton, Ross Holcomb, Calvin Honeycutt, Buck Harrison, Ted Hughes, Bass and Sandra Hyatt, Mike and Jean Jones, Tim and Jamie Kelley, William King, Buron and Sara Lanier, Bette and Doan Laursen, Franklin Lee, Carl Lindgren, Nathan Lowder, Vance Mattox, Brad Moore, Ronnie Nuckols, Matt Poore, Roger Pritchard, Johnny Rogers, Blair Sanders, Steve and Josh Sorrells, Brad Storie, Mark Strauss, Herman Wheatley, Werter Willis, Chad and Kim Woods, and Don York. Financial support was provided by USDA-ARS and USDA Natural Resources Conservation Innovation Grant 69-3A75-14-251.
CONFLICT OF INTEREST
The authors declare no conflicts of interest.
- 2007). Broiler litter application effects on selected trace elements under conventional and no-till systems. Soil Science, 172, 349–365. https://doi.org/10.1097/ss.0b013e318032ab7d
- 1998). Steer performance and nutritive values for continuously and rotationally stocked bermudagrass sod-seeded with wheat and ryegrass. Journal of Production Agriculture, 11, 185–190. https://doi.org/10.2134/jpa1998.0185
- 1977). Effects of N, P, and K fertilization on yield and quality of tall fescue forage in winter. Agronomy Journal, 69, 425–428. https://doi.org/10.2134/agronj1977.00021962006900030023x
- 2019). The wonder grass – the story of tall fescue in the United States. Salem, OR: Oregon Tall Fescue Commission.
- 1995). Tall fescue development in response to Acremonium coenophialum and soil acidity. Crop Science, 35, 529–533. https://doi.org/10.2135/cropsci1995.0011183X003500020041x
- 1979). Conservation. In R. C. Buckner & L. P. Bush (Eds.), Tall fescue (pp. 319–340). Madison, WI: ASA, CSSA, SSSA.
- 2002). Reinfection of tall fescue cultivars with non-ergot alkaloid-producing endophytes. Agronomy Journal, 94, 567–574.
- 1994). Nitrogen availability indices. In R. W. Weaver, J. S. Angle, & P. S. Bottomley (Eds.), Methods of soil analysis. Part 2. Microbiological and biochemical properties (pp. 951–984). Madison, WI: SSSA.
- 2006). Grazing influences on mass, nutritive value, and persistence of stockpiled Jesup tall fescue without and with novel and wild-type fungal endophytes. Crop Science, 46, 1898–1912. https://doi.org/10.2135/cropsci2005.09-0327
- 1992). Particulate organic-matter changes across a grassland cultivation sequence. Soil Science Society of America Journal, 56, 777–783. https://doi.org/10.2136/sssaj1992.03615995005600030017x
- 2010). Soil carbon stocks under different pasture management in the higher rainfall areas of southeastern Australia. Australian Journal of Soil Research, 48, 7–15. https://doi.org/10.1071/SR09092
- 2009). Growth and reproductive performance of beef heifers grazing endophyte-free, endophyte-infected and novel endophyte-infected tall fescue. Livestock Science, 125, 254–260. https://doi.org/10.1016/j.livsci.2009.05.003
- 1999). Microbial activity in response to water-filled pore space of variably eroded southern Piedmont soils. Applied Soil Ecology, 11, 91–101. https://doi.org/10.1016/S0929-1393(98)00128-0
- 2010). Achieving soil organic carbon sequestration with conservation agricultural systems in the southeastern United States. Soil Science Society of America Journal, 74, 347–357. https://doi.org/10.2136/sssaj2009.0079
- 2020a). Carbon concentration predicts soil contamination of plant residues. Agricultural & Environmental Letters, 5(1), e20037. https://doi.org/10.1002/ael2.20037
- 2020b). Holding water with capacity to target porosity. Agricultural & Environmental Letters, 5(1), e20029. https://doi.org/10.1002/ael2.20029
- 2012). Tall fescue management in the Piedmont: Sequestration of soil organic carbon and total nitrogen. Soil Science Society of America Journal, 76, 1016–1026. https://doi.org/10.2136/sssaj2011.0347
- 1999). Soil carbon and nitrogen pools under low- and high-endophyte-infected tall fescue. Soil Science Society of America Journal, 63, 1687–1694. https://doi.org/10.2136/sssaj1999.6361687x
- 2018). Soil-test biological activity with the flush of CO2: IV. Fall-stockpiled tall fescue yield response to applied nitrogen. Agronomy Journal, 110, 2033–2049. https://doi.org/10.2134/agronj2018.03.0146
- 2020). Soil-test biological activity with the flush of CO2: VII. Validating nitrogen needs for fall-stockpiled forage. Agronomy Journal, 112, 2240–2255. https://doi.org/10.1002/agj2.20153
- 2021). Nutritive value of fall-stockpiled tall fescue pastures on southeastern US farms. Agronomy Journal, 113, 610–622. https://doi.org/10.1002/agj2.20517.
- 2003). Bermudagrass management in the Southern Piedmont USA: III. Particulate and biologically active soil carbon. Soil Science Society of America Journal, 67, 132–138. https://doi.org/10.2136/sssaj2003.1320
- 2000). Soil organic C and N pools under long-term pasture management in the Southern Piedmont USA. Soil Biology & Biochemistry, 32, 469–478.
- 2001). Bermudagrass management in the Southern Piedmont USA: I. Soil and surface residue carbon and sulfur. Soil Science Society of America Journal, 65, 834–841. https://doi.org/10.2136/sssaj2001.653834x
- 2019). Enhancing the adoption of stockpiling tall fescue and managed grazing. Translational Animal Science, 3, 1099–1105. https://doi.org/10.1093/tas/txz086
- 1971). Nitrogen accumulation in fescuegrass sod. Agronomy Journal, 63, 451–454. https://doi.org/10.2134/agronj1971.00021962006300030031x
- 2011). Soil organic carbon fractions differ in two contrasting tall fescue systems. Plant and Soil, 338, 43–50. https://doi.org/10.1007/s11104-010-0352-z
- 1992). Effects of soil texture and structure on carbon and nitrogen mineralization in grassland soils. Biology and Fertility of Soils, 14, 126–134. https://doi.org/10.1007/BF00336262
- 1929). Relation of temperature to the amount of nitrogen in soils. Soil Science, 27, 169–188. https://doi.org/10.1097/00010694-192903000-00001
- 2003). Carbon storage in coarse and fine clay fractions of illitic soils. Soil Science Society of America Journal, 67, 1732–1739. https://doi.org/10.2136/sssaj2003.1732
- 2003). Herbage mass, nutritive value, and ergovaline concentration of stockpiled tall fescue. Crop Science, 43, 1001–1005. https://doi.org/10.2135/cropsci2003.1001
- 2015). Soil biology for resilient, healthy soil. Journal of Soil and Water Conservation, 70, 12A–18A. https://doi.org/10.2489/jswc.70.1.12A
- 2005). Carbon stocks in Swiss agricultural soils predicted by land-use, soil characteristics, and altitude. Agriculture, Ecosystems & Environment, 105, 255–266.
- 1995). Rangeland soil carbon and nitrogen responses to grazing. Journal of Soil and Water Conservation, 50, 294–298.
- 1994). Dairy heifer and bermudagrass pasture responses to rotational and continuous stocking. Journal of Dairy Science, 77, 244–252. https://doi.org/10.3168/jds.S0022-0302(94)76947-2
- 1984a). Mehlich-3 soil test extractant: A modification of Mehlich-2 extractant. Communications in Soil Science & Plant Analysis, 15, 1409–1416.
- 1984b). Photometric determination of humic matter in soils, a proposed method. Communications in Soil Science & Plant Analysis, 15, 1417–1422.
- 1985). Turnover of root-derived material and related microbial biomass formation in soils of different texture. Soil Biology & Biochemistry, 17, 565–569.
- 2016). Nitrogen rate and initiation date effects on stockpiled tall fescue during fall grazing in Tennessee. Crop, Forage & Turfgrass Management, 2(1), 1–8. https://doi.org/10.2134/cftm2015.0174
- 1984). Relations of organic carbon to soil properties and climate in the Southern Great Plains. Soil Science Society of America Journal, 48, 1382–1384. https://doi.org/10.2136/sssaj1984.03615995004800060037x
- 1999). Pasture growth, production, and quality under rotational and continuous grazing management. Journal of Production Agriculture, 12, 569–577. https://doi.org/10.2134/jpa1999.0569
- 2000). Production and use of stockpiled fescue to reduce beef cattle production costs. Journal of Animal Science, 79, 1–11. https://doi.org/10.2527/jas.00.079ES1001i
- 1979). Winter tall fescue yield and quality with different accumulation periods and N rates. Agronomy Journal, 71, 959–963. https://doi.org/10.2134/agronj1979.00021962007100060017x
- 2020). Management strategies for sustainable cattle production in southern pastures. San Diego, CA: Academic Press.
- 2015). Impacts of rotational grazing on soil carbon in native grass-based pastures in southern Australia. PLOS ONE, 10, e0136157. https://doi.org/10.1371/journal.pone.0136157
- 2000). Spatial distribution of extractable phosphorus, potassium, and magnesium as influenced by fertilizer and tall fescue endophyte status. Agronomy Journal, 92, 981–986. https://doi.org/10.2134/agronj2000.925981x
- 2002). Soil properties and microbial activity across a 500 m elevation gradient in a semi-arid environment. Soil Biology and Biochemistry, 34, 1749–1757. https://doi.org/10.1016/S0038-0717(02)00162-1
- 1988). Fescue endophyte: History and impact on animal agriculture. Journal of Production Agriculture, 1, 39–44. https://doi.org/10.2134/jpa1988.0039
- 2011). Grazing management impacts on vegetation, soil biota and soil chemical, physical and hydrological properties in tall grass prairie. Agriculture, Ecosystems and Environment, 141, 310–322. https://doi.org/10.1016/j.agee.2011.03.009
- 2019). Evaluating mob stocking for beef cattle in a temperate grassland. Plos ONE, 14, e0226360. https://doi.org/10.1371/journal.pone.0226360
- 2004). Soil organic matter fractions and their relevance to soil function. In F. Magdoff & R. R. Weil (Eds.), Soil organic matter in sustainable agriculture (pp. 67–102). Boca Raton, FL: CRC Press.
- 2004). Productivity of cow-calf pairs grazing tall fescue pastures infected with either the wild-type endophyte or a nonergot alkaloid-producing endophyte strain, AR542. Journal of Animal Science, 82, 3388–3393. https://doi.org/10.2527/2004.82113388x
- 1989). Spatial variability of soil chemical properties in grazed pastures. Soil Science Society of America Journal, 53, 784–789. https://doi.org/10.2136/sssaj1989.03615995005300030026x
- 2011). Impacts of altitude and position on the rates of soil nitrogen mineralization and nitrification in alpine meadows on the eastern Qinghai-Tibetan Plateau, China. Biology and Fertility of Soils, 48, 393–400. https://doi.org/10.1007/s00374-011-0634-5