Charles C. Mitchell

Influence of management practices on soil organic matter, microbial biomass and cotton yield in Alabama's “Old Rotation”

The “Old Rotation” cotton experiment was designed to aid farm managers in implementing rotation schemes that not only increase yield, but also improve soil quality. Six different crop rotation treatments were imposed since 1896. Rotations were: IA, cotton (Gossypium hirsutum L.) grown every year without a winter legume and without N fertilization; IB, cotton grown every year with a winter legume and without N fertilization; IC, cotton grown every year without a winter legume and with 134 kg N as NH4NO3 ha-1 year-1; IIA, 2-year cotton-corn (Zea mays L.) rotation with a winter legume and without N fertilization; IIB, 2-year cotton-corn rotation with a winter legume and with 134 kg N ha-1 year-1 as NH4NO3; and III, 3-year cotton-corn- alternating soybean [Glycine max (L.) Merr.] or rye (Secale cereale L.) rotation with a winter legume and with 134 g N as NH4NO3 ha-1 year-1. Crimson clover (Trifolium incarnatum L.) was the winter legume cover crop. The 2-year cotton-corn rotation with a winter legume and with 134 kg N ha-1 year-1 (IIB) and the 3-year cotton-corn soybean/rye rotation with a winter legume and with 134 kg N ha-1 year-1 (III) had higher amounts of soil organic matter, soil microbial biomass C and crop yield than the other four treatments. The cotton grown every year without a winter legume or N fertilizer (IA) had a lower amount of soil organic matter, soil microbial biomass C and N and cotton seed yield than all other rotations. In 1988 and 1992 cotton seed and legume yield were correlated in positive, curvilinear relationships with soil organic matter (r2 ranged from 0.72 to 0.87). In most months, soil microbial biomass C and N was lower in the cotton grown every year without winter legumes or fertilizer (IA) than the other five rotations. In 1994, microbial biomass C and the Cmic:Corg ratio correlated in positive, curvilinear relationships with seed cotton yield (r2=0.87 and 0.98, respectively). After 99 years of management the “Old Rotation” cotton experiment indicates that winter legumes increase amounts of both C and N in soil, which ultimately contribute to higher cotton yields. Microbial biomass C and the Cmic:Corg ratio are poor predictors of annual crop yield but may be an accurate indicator of soil health and a good predictor of long-term crop yield.

Soil C, N and crop yields in Alabama's long-term `Old Rotation' cotton experiment

The Old Rotation cotton experiment at Auburn, Alabama, is the oldest, continuous cotton experiment in the world (cf. 1896). Long-term cropping systems provide a unique opportunity to observe the effects of 100 years of cropping on soil organic carbon (SOC). The objective of this paper was to summarize limited data on SOC and N cycling in this historic experiment. Soil organic C has been measured on the 13 plots (6 cropping systems) in 1988, 1992 and 1994. Long-term planting of winter legumes with no other source of N applied resulted in higher SOC (9.5 g C kg -1 ) in the plow layer (0-20 cm depth) compared to continuous cotton with no winter cover crops (4.2 g C kg -1 ). A 3-year rotation of cotton-winter legumes-corn-small grain-soybean resulted in 12.1 g C kg -1 . There was a significant (P<0.05), quadratic cotton yield response (R 2 =0.54) to increasing SOC. Winter legume cover crops supplied between 90 and 170 kg N ha -1 . Where no N has been applied in fertilizer or from a legume crop, annual N removal in the cotton crop is around 13 kg ha -1 , about the same as that fixed in precipitation.

Comparing phosphorus indices from twelve southern U.S. states against monitored phosphorus loads from six prior southern studies.

Forty-eight states in the United States use phosphorus (P) indices to meet the requirements of their Natural Resources Conservation Service (NRCS) Code 590 Standard, which provides national guidance for nutrient management of agricultural lands. The majority of states developed these indices without consultation or coordination with neighboring states to meet specific local conditions and policy needs. Using water quality and land treatment data from six previously published articles, we compared P loads with P-Index values and ratings using the 12 southern P indices. When total measured P loads were regressed with P-Index rating values, moderate to very strong relationships (0.50 to 0.97) existed for five indices (Arkansas, Florida, Georgia, North Carolina, and South Carolina) and all but one index was directionally correct. Regressions with dissolved P were also moderate to very strong ( of 0.55 to 0.95) for the same five state P indices (Arkansas, Florida, Georgia, North Carolina, and South Carolina); directionality of the Alabama Index was negative. When total measured P loads were transformed to current NRCS 590 Standard ratings (Low [<2.2 kg P ha], Moderate, [2.2-5.5 kg P ha], and High [>5.5 kg P ha]) and these ratings were then compared to the southern-Index ratings, many of the P indices correctly identified Low losses (77%), but most did not correctly identify Moderate or High loss situations (14 and 31%, respectively). This study demonstrates that while many of the P indices were directionally correct relative to the measured water quality data, there is a large variability among southern P indices that may result in different P management strategies being employed under similar conditions.

Effects of swine lagoon effluent application on chemical properties of a loamy sand

Abstract In order to determine the effects of lagoon effluent application on soil chemical properties, swine lagoon effluent was applied to land with a 10% slope by an overland flow irrigation system on hybrid bermudagrass ( Cynodon dactylon L. Pers.) and annual ryegrass ( Lolium multiform Lan). Treatments included a control with no nutrient additions, ammonium nitrate at 560 kg N ha −1 yr −1 , and swine lagoon effluent at 560, 1120, and 2240 kg N ha −1 yr −1 . Soil on the research site is a Marvyn loamy sand (fine-loamy, siliceous, thermic, Typic Kanphapludults). At the termination of the experiment, soil core samples were taken to 120 cm, and depth-incremental samples were analyzed for total C, NH 4 -N, NO 3 -N, Mehlich-I extractable P, K, Ca, Mg, Cu, Zn, and Mn, soil pH and electrical conductivity. Treatment had no significant effects on soil NH 4 -N and extractable soil Cu, Zn, and Mn concentrations. Lagoon effluent application did not increase soil total C. Lagoon effluent and ammonium nitrate applications supplying the N loading resulted in a buildup of NO 3 -N, especially for the high N loading rate. Soil NO 3 -N in the lower depths throughout soil profiles reached approximately 30 mg kg −1 . Application of lagoon effluent resulted in significant P buildup to a depth of 40 cm. Mehlich-I extractable P accumulated to as high as 115 mg kg −1 on the upper portion and 40 mg kg −1 on the lower portion of the sloping land in the surface 0–20 cm soil layer. Extractable soil K concentration increased with increasing rates of lagoon effluent application. The application of swine lagoon effluent resulted in a decrease in soil pH and an increase in soluble salt accumulation.

Southern Phosphorus Indices, Water Quality Data, and Modeling (APEX, APLE, and TBET) Results: A Comparison

Phosphorus (P) Indices in the southern United States frequently produce different recommendations for similar conditions. We compared risk ratings from 12 southern states (Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, and Texas) using data collected from benchmark sites in the South (Arkansas, Georgia, Mississippi, North Carolina, Oklahoma, and Texas). Phosphorus Index ratings were developed using both measured erosion losses from each benchmark site and Revised Universal Soil Loss Equation 2 predictions; mostly, there was no difference in P Index outcome. The derived loss ratings were then compared with measured P loads at the benchmark sites by using equivalent USDA-NRCS P Index ratings and three water quality models (Annual P Loss Estimator [APLE], Agricultural Policy Environmental eXtender [APEX], and Texas Best Management Practice Evaluation Tool [TBET]). Phosphorus indices were finally compared against each other using USDA-NRCS loss ratings model estimate correspondence with USDA-NRCS loss ratings. Correspondence was 61% for APEX, 48% for APLE, and 52% for TBET, with overall P index correspondence at 55%. Additive P Indices (Alabama and Texas) had the lowest USDA-NRCS loss rating correspondence (31%), while the multiplicative (Arkansas, Florida, Louisiana, Mississippi, South Carolina, and Tennessee) and component (Georgia, Kentucky, and North Carolina) indices had similar USDA-NRCS loss rating correspondence-60 and 64%, respectively. Analysis using Kendalls modified Tau suggested that correlations between measured and calculated P-loss ratings were similar or better for most P Indices than the models.

World's oldest cotton experiment : Relationships between soil chemical and physical properties and apparent electrical conductivity

Abstract Measuring and mapping apparent soil electrical conductivity (ECa) is a potentially useful tool for delineating soil variability. The “Old Rotation,” the worlds oldest continuous cotton (Gossypium hirsutum L.) experiment (ca. 1896), provides a valuable resource for evaluating soil spatial variability. The objectives of this study were to determine the relationship between soil chemical and physical properties and ECa in the Old Rotation, to determine spatial differences in these properties, and to relate differences in these properties to long‐term management effects. Soils at the site classified as fine, kaolinitic, thermic Typic Kanhapludults. Soil ECa was measured at 0–30‐ and 0–90‐cm depths (ECa‐30 and ECa‐90) using a Veris® 3100 direct contact sensor with georeferencing. Soils were grid sampled (288 points) at close intervals (1.5×3.0 m) for chemical properties and grid sampled (65 cells, 7.5×6.9 m) for soil texture. Soil organic carbon (SOC) and total nitrogen (N), extractable phosphorus (P), potassium (K), calcium (Ca), pH, buffer pH, and estimated cation exchange capacity (CECest) were measured at two depths (0–5‐ and 5–15‐cm). Soil ECa was highly spatially correlated. The ECa‐30 was more highly correlated with clay content (r=0.58, P≤0.01) and P(r=0.43, P≤0.01) than other soil properties. Total nitrogen and SOC had little or no relationship with ECa‐30. Cropping systems affected chemical properties in the Old Rotation, indicating crop rotation and cover crops are beneficial for soil productivity. The relatively poor relationship between soil chemical parameters and ECa suggest that mapping plant nutrients and SOC using ECa is problematic because of strong dependence on clay content.

Evaluation of a liquid potassium bicarbonate/amino acid co‐product as a source of potassium, nitrogen, and sulfur

Abstract Potassium bicarbonate (KHCO3), methionine, alanine, and other organic sulfur (S) compounds are present in a liquid co‐product (DPF for Degussas Potassium Fertilizer) resulting from the manufacture of methionine as a poultry feed supplement. DPF contains approximately 20, 97, and up to 30 g/kg of nitrogen (N), potassium (K), and S, respectively. Field, greenhouse, and incubation studies were conducted to evaluate crop response to N and K in DPF as compared to ammonium nitrate (NH4NO3) and potassium chloride (KCl), to determine mineralization of N and S in DPF and to determine any potentially phytotoxic effects of high rates of DPF in sandy soils of the Gulf Coastal Plain. In both field and greenhouse studies using four different crops, plant dry matter, grain yield, and N and K uptake with DPF were equivalent to comparable rates of N and K as NH4NO3 and KCl. Nitrogen and S in DPF, methionine, and ground cotton (Gossypium hirsutum L.) leaves were mineralized by soil microorganisms at similar rates...

Laboratory and Greenhouse Evaluation of Quicklime Sources for Suitability as Agricultural Liming Materials

Abstract Quicklime or burnt lime (CaO), is a highly soluble liming material recognized as an acceptable means for neutralization of acid soils in the United States. Blending CaO and MgO with agricultural lime (CaCO3) may prove an alternative to ground agricultural limestone for raising soil pH and providing fertilizer Ca and Mg for crop growth. The objectives of this study were to determine the chemical properties of several CaO, MgO, and CaCO3 liming blends compared to carbonate limestones, and analyze their respective effects on soil solution chemistry and shoot yield of a sorghum-sudangrass hybrid grown under greenhouse conditions. Three formulations of oxide liming materials (CaO, CaO + CaCO3, and CaO + MgO + CaCO3) were evaluated in the laboratory to determine their respective effectiveness as soil amendments compared to two dolomitic limestones (ground and pelletized) and reagent-grade calcium hydroxide [Ca(OH)2]. A 150-day incubation study was conducted to determine the effects of liming materials on soil pH and extractable nutrients, and a greenhouse study was completed to observe the effects of liming materials and rates on the herbage yield of a sorghum-sudangrass hybrid. Oxide liming materials averaged higher calcium carbonate equivalence (CCE) than ground and pelletized dolomitic limestones. An incubation study found CaO, CaO + CaCO3, and CaO + MgO + CaCO3 resulted in rapid pH adjustments (from pH 4.1 and 4.4 to 6.0 +) at one day after test initiation for two soil types and gave higher mean pH values than carbonate limes when applied at equivalent rates based upon CCE. Oxide liming materials also resulted in higher concentrations of soil extractable calcium (Ca) and magnesium (Mg), and the use of all liming materials, regardless of chemical form, alleviated Al toxicity. In a nine week greenhouse bioassay, all oxide liming materials and reagent-grade Ca(OH)2 were applied at 1/2X, 1X, and 2X the recommended application rate of ground dolomitic limestone based on CCE, resulting in similar or higher shoot yields comparatively at conclusion of this study. Because oxide liming materials have higher CCE values and provide more water-soluble sources of fertilizer Ca and Mg compared to ground and pelletized limestone, producers have potential for obtaining a more complete neutralization of acid soil conditions and shoot yields similar to or higher than those obtained with dolomitic limestone, using less material in the process. This study did not determine if changes in current liming practices would result in reductions of total fertilizer costs per year using oxide limes in place of carbonate forms.

EFFECT OF LIMING MATERIALS ON SOIL AVAILABLE NUTRIENTS, YIELD, AND GRADE DISTRIBUTION OF DOUBLE-CROPPED TOMATO AND CUCUMBER GROWN WITH PLASTICULTURE

For economical reasons, cucumber (Cucumis sativus L.) may be grown as a double crop after tomato (Lycopersicon esculentum Mill.). In this production system, plant nutrition may be limited for the second crop due to pH change or insufficient levels of calcium or magnesium. The objective of this 2-year field study was to compare the effects of selected liming materials on yield and grade distribution, and soil available nutrients of a tomato/cucumber double crop produced with plasticulture. Liming materials were compared to a control and a CaSO4 treatment based on the same neutralizing value as standard agricultural limestone. Supplemental N fertilization was provided by weekly injections at a rate of 7 kg/ha/week from ammonium nitrate (NH4NO3) or calcium nitrate [Ca(NO3)2]. Each year, soil samples were collected at the beginning of the study and after each crop to determine nutrient availability. All liming materials raised soil pH in 1998 and 1999 over the unlimed control, though not to the target level for tomato and cucumber production (pH 6.5). Throughout the study, agricultural limestone, a high CaO-containing blend (calcitic blend) and a CaO/MgO (dolomitic blend), resulted in greater fruit weights compared to the control and CaSO4. These materials, along with quick lime (CaO), provided higher levels of soil Ca and Mg available for plant growth. However, it was found that current recommendations for potassium (K), regardless of liming source, were not adequate for optimal soil reserves and yields in this tomato/cucumber cropping system. Ammonium nitrate as a source of N for fertilization was as effective as Ca(NO3)2.

Wheat varietal response to sulfur1

A nutrient solution-sand culture study was conducted in a greenhouse to evaluate the response of 35 soft red winter wheat varieties to S. Wheat seedlings were grown for 35 days in sand that was leached every other day with complete nutrient solution containing 0, 1 or 5 mg SO 4 -S L −1 . (…)