Donald D. Tyler

Changes in soil quality and below-ground carbon storage with conversion of traditional agricultural crop lands to bioenergy crop production

Berm-isolated (0.5 ha) plots have been used since 1995 to quantify changes in soil and water quality with conversion from agricultural to bioenergy crops. Soil quality improvements, including increases in soil carbon storage, have occurred on sites planted to woody or herbaceous species, and no-till corn compared with tilled corn or cotton. Initial increases in soil carbon occurred within the upper 10 cm of the soil profile. Soil carbon on plantings of switchgrass, no-till corn, and sweetgum with a cover crop between the rows increased over the first 3 years. Soil carbon decreased by 6% on the sweetgum plantings without a cover crop and remained lower through the fifth growing season. Overall, the greatest increases in below ground carbon storage have occurred primarily within the upper 40 cm. Former land use, growth characteristics, management practices, and soil characteristics appear to be the primary factors determining the timing, depth. and extent of changes in soil carbon storage for bioenergy and no-till crops.

Assessing Indices for Predicting Potential Nitrogen Mineralization in Soils under Different Management Systems

A reliable laboratory index ofN availability would be useful for making N recommendations, but no single approach has received broad acceptance across a wide range of soils. We compared several indices over a range of soil conditions to test the possibility of combining indices for predicting potentially mineralizable N (N 0 ). Soils (0-5 and 5-15 cm) from nine tillage studies across the southern USA were used in the evaluations. Long-term incubation data were fit to a first-order exponential equation to determine N 0 , k (mineralization rate), and N 0 * (N 0 estimated with a fixed k equal to 0.054 wk -1 ). Out of 13 indices, five [total C (TC), total N (TN), N mineralized by hot KCI (Hot_N), anaerobic N (Ana_N), and N mineralized in 24 d (Nmin_24)] were strongly correlated to N 0 (r > 0.85) and had linear regressions with r 2 > 0.60. None of the indices were good predictors ofk. Correlations between indices and N 0 * improved compared with N 0 , ranging from r = 0.90 to 0.95. Total N and Hush of CO 2 determined after 3 d (Fl_CO2) produced the best multiple regression for predicting N 0 (R 2 = 0.85) while the best combination for predicting N 0 * (R 2 = 0.94) included TN, Fl_CO2 Cold_N, and NaOH_N. Combining indices appears promising for predicting potentially mineralizable N, and because TN and Fl_CO2 are rapid and simple, this approach could be easily adopted by soil testing laboratories.

Chemical and physical characteristics of four soil types under conventional and no-tillage systems

This study was conducted to determine how soils of different origin respond to no-till practices, with emphasis on organic C accumulation and its subsequent effect on soil properties. Tillage experiments which had been running for between 5 and 15 years on four southeastern USA soils with textures of sandy loam, loam, silt, and sandy clay loam were utilized. Soil samples were collected from conventional and no-tillage treatments at depths of 0–2.5, 2.5–7.6, and 7.6–15.2 cm. No-tillage plots had higher bulk density, aggregate stability, organic C, exchangeable cations and acidity, cation exchange capacity, and extractable P, K, and Mn, but most of these properties were not significantly different (P < 0.05) from those of conventional plots. Modulus of rupture and extractable Fe decreased in the no-till plots. Most of these changes, other than bulk density, occurred as a result of increases in organic C content, and the lack of more significant differences is attributed to inadequate residue production and/or its rapid decomposition in this relatively hot, moist climate.

Phosphorus distribution and availability in response to dairy manure applications

Abstract As livestock operations become larger and concerns about water quality become greater, attention must be paid to the composition of animal manure and its potential impact on the environment. One current concern involves the amount and forms of phosphorus (P) being added to land with manure. The objective of this experiment was to determine the forms and availability of P in soils receiving 4 years of continuous dairy manure applications. Soil samples were collected from lysimeter plots established in 1991 to study the impact of dairy manure applications on surface water and groundwater. Soil P was fractionated into available (NaHCO3), iron (Fe)‐ and aluminum (Al)‐bound (NaOH), and calcium (Ca)‐bound (HC1) forms. These data were related to manure application rates, soluble P concentrations, and anion exchange membrane (AEM) bound P. Results indicate that the potential to move P by leaching through these loessial soils is very low even at high manure application rates. Large manure additions resulted in increases in all P forms; however, the inorganic pools increased more than the organic pools. The AEM values were a good tool for predicting potential P movement by soil erosion or runoff with membrane bound P being strongly correlated with manure application rate (r2=0.82) and available P (NaHCO3). Best management practices for manure disposal need to consider the potential for P movement through erosion and runoff, and the AEM technique provides a means for evaluating this potential.

Stochastic Corn Yield Response Functions to Nitrogen for Corn after Corn, Corn after Cotton, and Corn after Soybeans

Deterministic and stochastic yield response plateau functions were estimated to determine the expected profit-maximizing nitrogen rates, yields, and net returns for corn grown after corn, cotton, and soybeans. The stochastic response functions were more appropriate than their deterministic counterparts, and the linear response stochastic plateau described the data the best. The profit-maximizing nitrogen rates were similar for corn after corn, cotton, and soybeans, but relative to corn after corn, the expected corn yield plateaus increased by 12% and 16% after cotton and soybeans, respectively. Expected net returns increased for corn after cotton and soybeans relative to corn after corn.

Variable Rate Nitrogen Application on Corn Fields: The Role of Spatial Variability and Weather

Meta-response functions for corn yields and nitrogen losses were estimated from EPIC-generated data for three soil types and three weather scenarios. These metamodels were used to evaluate variable rate (VRT) versus uniform rate (URT) nitrogen application technologies for alternative weather scenarios and policy option. Except under very dry conditions, returns per acre for VRT were higher than for URT and the economic advantage of VRT increased as realized rainfall decreased from expected average rainfall. Nitrogen losses to the environment from VRT were lower for all situation examined, except on fields with little spatial variability.

Fluometuron behavior in long-term tillage plots

Fluometuron (N, N-dimethyl-N′ -[3-(trifluoromethyl) phenyl] urea) is a preemergence herbicide used widely for weed control in cotton (Gossypium hirsutum L.). Field research results suggest that many herbicides, including fluometuron, may be subject to preferential transport and leaching through the soil profile. The objectives of this study were to evaluate the distribution and leaching of fluometuron in a Lexington silt loam (Typic Paleudalf) through 3 years of study by analyzing depth incremented soil samples and tension-free pan lysimeter leachates collected at a soil depth of 90 cm under no-till (NT) and conventional tillage (CT, disc 2× - roller harrowed) management. Fluometuron depth distribution following application and subsequent rainfall was related to soil organic carbon content, with tillage effects restricted to the surface 2-cm. The amount of herbicide remaining in the soil profile after application decreased with increasing rainfall amounts. On average, 11% of applied herbicide in NT and 6% in CT remained in the surface 15 cm after 1 year. Fluometuron was detected in all lysimeter leachates during the 3-year period. Peak herbicide leachate concentrations ranged from 68 mg L−1 to 1700 mg L−1, depending on herbicide application in relation to rainfall timing. Annual leaching losses ranged from 5 to 53% of applied fluometuron during the study. Of the amounts lost to leaching, 68 to 100% (averaging 87% of the total lost to leaching) were lost during the first two or three significant rainfall events after treatment. Rainfall timing in relation to herbicide application was the dominant effect in herbicide mobilization through the soil profile. Antecedent soil moisture content (predicted from rainfall amounts prior to fluometuron application) also influenced the appearance of leachate and herbicide in the lysimeters, with lower soil moisture conditions at application producing lower preferential flow. Depth-incremented soil sampling after initial rainfall events was a poor mechanism for detecting fluometuron mobility through the soil profile. The rapidity at which fluometuron was detected in the lysimeter leachates, the exceedingly high fluometuron concentrations, and the variability in leachate collection by the lysimeters, illustrated the significance of preferential flow. The influence of tillage practice on the volume of drainage collected by the lysimeters and on fluometuron leaching was of little significance when compared with the influence of natural infiltration heterogeneity.

On-Farm Tests Indicate Effects of Long-Term Tillage Systems on Soil Quality

ABSTRACT To sustain productivity and environmental quality, an awareness of the impacts our management systems are having on soil quality is needed. The soil quality test kit is an on-farm tool that has been developed for conservationists and farmers to track changes in soil quality. The use of the kit was demonstrated by comparing soil quality on long-term no-till versus conventional tillage systems on a silt loam soil in Tennessee. The no-till management system had significantly improved surface soil properties over the conventionally tilled management system at this site. The no-till management system had higher infiltration rates, more stable aggregates, a lower soil respiration rate, a greater resistance to slaking, greater earthworm numbers, and a greater water content in the 0–7.6 cm soil depth. The soil quality test kit was able to distinguish differences in soil properties on this long-term management comparison. The kit is a good on-farm tool for use in comparison of relative differences in surface soil properties.

Nitrogen-Fixing Winter Cover Crops and Production Risk: A Case Study for No-Tillage Corn

Winter legumes can substitute for applied nitrogen fertilization of corn. Stochastic dominance was used to order net revenues from legume and applied nitrogen alternatives. Stochastic dominance orderings indicate that systems combining vetch with low applied nitrogen fertilization (50 and 100 pounds/acre, respectively) were risk inefficient. By contrast, vetch and 150 pounds/acre applied nitrogen maximized expected net revenue and was risk efficient for a wide range of risk-averse and risk-seeking behavior. Farmers with these risk attitudes may not reduce applied nitrogen if they switch to a vetch cover. Extremely risk-averse or risk-seeking farmers would not prefer winter legumes.

Switchgrass yield and stand dynamics from legume intercropping based on seeding rate and harvest management

Intercropping legumes may reduce inputs and enhance sustainability of forage and feedstock production, especially on marginal soils. This approach is largely untested for switchgrass (Panicum virgatum L.) production, yet producer acceptance should be high given the traditional use of legumes in forage/agricultural systems. Our objectives were to evaluate three cool-season and two warm-season legumes and their required densities to influence yield and supply nitrogen (N) compared to three inorganic N levels (0, 33, and 66 kg N ha−1 [0, 30, and 60 lb N ac−1]) at three locations in Tennessee (Knoxville [Sequatchie Silt Loam], Crossville [Lilly Loam], and Milan [Loring B2 Series]). Fall of 2010 seeded, cool-season legumes (red clover [Trifolium pratense L.], hairy vetch [Vicia villosa L.], ladino clover [Trifolium repens L.]), arrowleaf clover (Trifolium vesiculosum L.), and a spring of 2011 seeded, warm-season legume (partridge pea [Chamaecrista fasciculate L.]) were interseeded into switchgrass at three (high, medium, and low) seeding rates each in two experiments. Harvest treatments were annual single, postdormancy biofuel (Experiment One) or integrated forage-biofuel (preanthesis and postdormancy; Experiment Two). Year one yield impacts were minimal. During the second harvest year, legumes increased yield versus Year 1; in general, yields for 33 and 67 kg N ha−1 did not differ from those for red clover, hairy vetch, ladino clover, or partridge pea (p < 0.05). Arrowleaf clover yields were not different from 0 kg N ha−1. Forage biomass yields were generally more responsive to legumes (p < 0.05) than the biomass regime. Legume persistence after three years was generally greatest for ladino clover and partridge pea. Forage quality (switchgrass only) in some cases was positively influenced by legume treatments, notably hairy vetch and partridge pea (p < 0.05). Intercropping selected legumes in switchgrass may enhance forage quality and yield while reducing nonrenewable inputs, fertilizer costs, and emissions/runoff to air and groundwater.