Dothan Sandy Loam Research Articles

Nitrogen Storage with Cover Crops and Nitrogen Fertilization in Tilled and Nontilled Soils

Improved crop and N management practices are needed to increase soil N storage so that N fertilization rate and the potential for N leaching can be reduced in tilled and nontilled soils. We examined the influence of cover crops and N fertilization rates on N inputs from cover crops, cotton (Gossypium hirsutum L.) and sorghum [Sorghum bicolor (L.) Moench] and soil total N (STN) content at the 0‐ to 120‐cm depth in no‐tilled, strip‐tilled, and chisel‐tilled Dothan sandy loam (fine‐loamy, kaolinitic, thermic, Plinthic Kandiudults) from 2000 to 2002 in central Georgia. Cover crops were legume [hairy vetch (Vicia villosa Roth)], nonlegume [rye (Secale cereale L.)], biculture of legume and nonlegume (vetch + rye), and winter weeds and N fertilization rates were 0, 60 to 65, and 120 to 130 kg N ha−1. Nitrogen inputs in above‐ and belowground plant biomass varied with the season and were greater in vetch and vetch + rye with N rates than in rye and weeds with or without N in tilled and nontilled soils. The STN concentration varied with sampling times and decreased with depth. The STN content at 0 to 90 cm was greater in vetch and vetch + rye with N rates than in weeds with or without N in no‐tilled and chisel‐tilled soils. Similarly, STN content at 0 to 30 cm was greater with vetch and vetch + rye than with weeds in strip‐tilled soil. As a result, N storage at 0 to 30 cm gained at 71 to 108 kg N ha−1 yr−1 in vetch and vetch + rye with N fertilization compared with a loss at 110 kg N ha−1 yr−1 to a gain at 40 kg N ha−1 yr−1 in weeds with or without N fertilization in no‐tilled and chisel‐tilled soils. In strip‐tilled soil, N storage gained at 101 to 103 kg N ha−1 yr−1 with vetch and vetch + rye compared with a loss at 91 kg N ha−1 yr−1 with weeds. Nitrogen storage in tilled and nontilled soils can be increased by using legume or a biculture of legume and nonlegume cover crops compared with no cover crop with or without N fertilization. Because of similar levels of soil N storage and cotton and sorghum N uptake, legume can be replaced by biculture cover crop and N fertilization rate can be reduced to reduce the cost of N fertilization and the potential for N leaching.

Performance of Peanut and Cotton in a Bahiagrass Cropping System

Yields for peanut (Arachis hypogaea L.) and cotton (Gossypium hirsutum L.) have reached a plateau in the southeastern USA (SE). This, coupled with environmental concerns and increased production costs, prompt the need to find alternatives to the limited peanut/cotton rotation currently used. Bahiagrass (Paspalum notatum Fluegge) was introduced to the current peanut/cotton cropping system to evaluate its effect on peanut and cotton performance. Our objectives were to compare crop yields in a conventional rotation of cotton‐cotton‐peanut vs. a bahiagrass–bahiagrass–peanut–cotton rotation under irrigated and nonirrigated conditions. Field studies were conducted in Quincy, FL, on a Dothan sandy loam (fine, loamy siliceous, thermic Plinthic Kandiudults) from 2000 to 2004. During 2–3 yr of the study, peanut yields were 900 kg ha−1 greater (averaged across irrigation treatments) following 2 yr of bahiagrass compared with following 2 yr of cotton under both irrigated and nonirrigated conditions. Root biomass was greater for cotton in the bahiagrass rotation compared with cotton in the conventional rotation. The greater root biomass, however, resulted in rank growth and cotton in the bahiagrass rotation yielded the same as cotton in the conventional rotation. It appears potential exists for greater cotton yield in the bahiagrass rotation once effective management practices have been identified.

Cover crop effect on soil carbon fractions under conservation tillage cotton

Cover crops may influence soil carbon (C) sequestration and microbial biomass and activities by providing additional residue C to soil. We examined the influence of legume [crimson clover ( Trifolium incarnatum L.)], nonlegume [rye ( Secale cereale L.)], blend [a mixture of legumes containing balansa clover ( Trifolium michelianum Savi), hairy vetch ( Vicia villosa Roth), and crimson clover], and rye + blend mixture cover crops on soil C fractions at the 0–150 mm depth from 2001 to 2003. Active fractions of soil C included potential C mineralization (PCM) and microbial biomass C (MBC) and slow fraction as soil organic C (SOC). Experiments were conducted in Dothan sandy loam (fine-loamy, kaolinitic, thermic, Plinthic Kandiudults) under dryland cotton ( Gossypium hirsutum L.) in central Georgia and in Tifton loamy sand (fine-loamy, siliceous, thermic, Plinthic Kandiudults) under irrigated cotton in southern Georgia, USA. Both dryland and irrigated cotton were planted in strip tillage system where planting rows were tilled, thereby leaving the areas between rows untilled. Total aboveground cover crop and cotton C in dryland and irrigated conditions were 0.72–2.90 Mg C ha −1 greater in rye + blend than in other cover crops in 2001 but was 1.15–2.24 Mg C ha −1 greater in rye than in blend and rye + blend in 2002. In dryland cotton, PCM at 50–150 mm was greater in June 2001 and 2002 than in January 2003 but MBC at 0–150 mm was greater in January 2003 than in June 2001. In irrigated cotton, SOC at 0–150 mm was greater with rye + blend than with crimson clover and at 0–50 mm was greater in March than in December 2002. The PCM at 0–50 and 0–150 mm was greater with blend and crimson clover than with rye in April 2001 and was greater with crimson clover than with rye and rye + blend in March 2002. The MBC at 0–50 mm was greater with rye than with blend and crimson clover in April 2001 and was greater with rye, blend, and rye + blend than with crimson clover in March 2002. As a result, PCM decreased by 21–24 g CO 2–C ha −1 d −1 but MBC increased by 90–224 g CO 2–C ha −1 d −1 from June 2001 to January 2003 in dryland cotton. In irrigated cotton, SOC decreased by 0.1–1.1 kg C ha −1 d −1, and PCM decreased by 10 g CO 2–C ha −1 d −1 with rye to 79 g CO 2–C ha −1 d −1 with blend, but MBC increased by 13 g CO 2–C ha −1 d −1 with blend to 120 g CO 2–C ha −1 d −1 with crimson clover from April 2001 to December 2002. Soil active C fractions varied between seasons due to differences in temperature, water content, and substrate availability in dryland cotton, regardless of cover crops. In irrigated cotton, increase in crop C input with legume + nonlegume treatment increased soil C storage and microbial biomass but lower C/N ratio of legume cover crops increased C mineralization and microbial activities in the spring.

Nitrogen Contribution of Peanut Residue to Cotton in a Conservation Tillage System

ABSTRACT Leguminous crops, particularly winter annuals, have been utilized in conservation systems to partially meet nitrogen (N) requirements of succeeding summer cash crops. Previous research also highlights the benefits of utilizing summer annual legumes in rotation with non-leguminous crops. This study assessed the N contribution of peanut (Arachis hypogaea L.) residues to a subsequent cotton (Gossypium hirsitum L.) crop in a conservation system on a Dothan sandy loam (fine-loamy, kaolinitic, thermic Plinthic Kandiudults) at Headland, AL during the 2003–2005 growing seasons. Treatments were arranged in a split plot design, with main plots of peanut residue retained or removed from the soil surface, and subplots as N application rates (0, 34, 67, and 101 kg ha− 1) applied in fall and spring. Peanut residue did not influence seed cotton yields, leaf N concentrations, or plant N uptake for either growth stage or year of the experiment. There was a trend for peanut residue to increase whole plant biomass measured at the first square in two of three years. Seed cotton yields and plant parameters measured at the first square and mid-bloom responded favorably to spring N applications, but the recommended 101 kg N ha− 1 did not maximize yields. The results from this study indicate that peanut residue does not contribute significant amounts of N to a succeeding cotton crop, however, retaining residue on the soil surface provides other benefits to soils in the southeastern U.S.

Cotton Roots, Earthworms, and Infiltration Characteristics in Sod–Peanut–Cotton Cropping Systems

Diverse cropping systems offer many advantages to farmers. We evaluated root growth, soil water infiltration, and earthworm population densities in a conventional peanut (Arachis hypogaea L.)/cotton (Gossypium hirsutum L.) rotation using conservation tillage (CT), and a peanut/cotton/bahiagrass (Paspalum notatum Fluegge) farming system. The rotations were initiated in 2000 in Quincy, FL, and in 2001 in Headland, AL, in both cases on a Dothan sandy loam (fine, loamy siliceous, thermic Plinthic Kandiudults). In 2003, a year with more uniform rainfall, cotton in the sod‐based rotation had larger average crown root diameter per plant (22.6 vs. 16.3 mm), root area (87.2 vs. 57.4 cm2), root length (640 vs. 460 cm), and root biomass (18.59 vs. 10.45 g) as compared with cotton in the peanut/cotton rotation. Water infiltration rates were higher in both cotton and peanut after bahiagrass compared with the conventional peanut/cotton rotation in 2003. Earthworm population densities were greater in the sod rotation compared with the traditional peanut/cotton cropping system. Water infiltration was positively correlated to earthworm population densities. Despite the improvements in soil quality, cotton yield in the sod rotation was the same as the traditional cropping systems. Cotton developed excessive vegetative growth in the bahiagrass system at the expense of lint yield. Further research is needed to determine the N rate for the sod‐based rotation in comparison with the conventional cotton/peanut rotation.

Suitability of peanut residue as a nitrogen source for a rye cover crop

Leguminous winter cover crops have been utilized in conservation systems to partially meet nitrogen (N) requirements of succeeding summer cash crops, but the potential of summer legumes to reduce N requirements of a winter annual grass, used as a cover crop, has not been extensively examined. This study assessed the N contribution of peanut (Arachis hypogaea L.) residues to a subsequent rye (Secale cereale L.) cover crop grown in a conservation system on a Dothan sandy loam (fine-loamy, kaolinitic, thermic Plinthic Kandiudults) at Headland, AL USA during the 2003-2005 growing seasons. Treatments were arranged in a split plot design, with main plots of peanut residue retained or removed from the soil surface, and subplots as N application rates (0, 34, 67 and 101 kg ha-1) applied in the fall. Peanut residue had minimal to no effect on rye biomass yields, N content, carbon (C) /N ratio, or N, P, K, Ca and Zn uptake. Additional N increased rye biomass yield, and N, P, K, Ca, and Zn uptakes. Peanut residue does not contribute significant amounts of N to a rye cover crop grown as part of a conservation system, but retaining peanut residue on the soil surface could protect the soil from erosion early in the fall and winter before a rye cover crop grows sufficiently to protect the typically degraded southeastern USA soils.

Tillage, cover crops, and nitrogen fertilization effects on soil nitrogen and cotton and sorghum yields

Sustainable soil and crop management practices that reduce soil erosion and nitrogen (N) leaching, conserve soil organic matter, and optimize cotton and sorghum yields still remain a challenge. We examined the influence of three tillage practices (no-till, strip till and chisel till), four cover crops {legume [hairy vetch ( Vicia villosa Roth)], nonlegume [rye ( Secaele cereale L.)], vetch/rye biculture and winter weeds or no cover crop}, and three N fertilization rates (0, 60–65 and 120–130 kg N ha −1) on soil inorganic N content at the 0–30 cm depth and yields and N uptake of cotton ( Gossypium hirsutum L.) and sorghum [ Sorghum bicolor (L.) Moench]. A field experiment was conducted on Dothan sandy loam (fine-loamy, siliceous, thermic, Plinthic Paleudults) from 1999 to 2002 in Georgia, USA. Nitrogen supplied by cover crops was greater with vetch and vetch/rye biculture than with rye and weeds. Soil inorganic N at the 0–10 and 10–30 cm depths increased with increasing N rate and were greater with vetch than with rye and weeds in April 2000 and 2002. Inorganic N at 0–10 cm was also greater with vetch than with rye in no-till, greater with vetch/rye than with rye and weeds in strip till, and greater with vetch than with rye and weeds in chisel till. In 2000, cotton lint yield and N uptake were greater in no-till with rye or 60 kg N ha −1 than in other treatments, but biomass (stems + leaves) yield and N uptake were greater with vetch and vetch/rye than with rye or weeds, and greater with 60 and 120 than with 0 kg N ha −1. In 2001, sorghum grain yield, biomass yield, and N uptake were greater in strip till and chisel till than in no-till, and greater in vetch and vetch/rye with or without N than in rye and weeds with 0 or 65 kg N ha −1. In 2002, cotton lint yield and N uptake were greater in chisel till, rye and weeds with 0 or 60 kg N ha −1 than in other treatments, but biomass N uptake was greater in vetch/rye with 60 kg N ha −1 than in rye and weeds with 0 or 60 kg N ha −1. Increased N supplied by hairy vetch or 120–130 kg N ha −1 increased soil N availability, sorghum grain yield, cotton and sorghum biomass yields, and N uptake but decreased cotton lint yield and lint N uptake compared with rye, weeds or 0 kg N ha −1. Cotton and sorghum yields and N uptake can be optimized and potentials for soil erosion and N leaching can be reduced by using conservation tillage, such as no-till or strip till, with vetch/rye biculture cover crop and 60–65 kg N ha −1. The results can be applied in regions where cover crops can be grown in the winter to reduce soil erosion and N leaching and where tillage intensity and N fertilization rates can be minimized to reduce the costs of energy requirement for tillage and N fertilization while optimizing crop production.

Carbon Supply and Storage in Tilled and Nontilled Soils as Influenced by Cover Crops and Nitrogen Fertilization

Soil carbon (C) sequestration in tilled and nontilled areas can be influenced by crop management practices due to differences in plant C inputs and their rate of mineralization. We examined the influence of four cover crops {legume [hairy vetch (Vicia villosa Roth)], nonlegume [rye (Secale cereale L.)], biculture of legume and nonlegume (vetch and rye), and no cover crops (or winter weeds)} and three nitrogen (N) fertilization rates (0, 60 to 65, and 120 to 130 kg N ha(-1)) on C inputs from cover crops, cotton (Gossypium hirsutum L.), and sorghum [Sorghum bicolor (L.) Moench)], and soil organic carbon (SOC) at the 0- to 120-cm depth in tilled and nontilled areas. A field experiment was conducted on Dothan sandy loam (fine-loamy, siliceous, thermic Plinthic Paleudults) from 1999 to 2002 in central Georgia. Total C inputs to the soil from cover crops, cotton, and sorghum from 2000 to 2002 ranged from 6.8 to 22.8 Mg ha(-1). The SOC at 0 to 10 cm fluctuated with C input from October 1999 to November 2002 and was greater from cover crops than from weeds in no-tilled plots. In contrast, SOC values at 10 to 30 cm in no-tilled and at 0 to 60 cm in chisel-tilled plots were greater for biculture than for weeds. As a result, C at 0 to 30 cm was sequestered at rates of 267, 33, -133, and -967 kg C ha(-1) yr(-1) for biculture, rye, vetch, and weeds, respectively, in the no-tilled plot. In strip-tilled and chisel-tilled plots, SOC at 0 to 30 cm decreased at rates of 233 to 1233 kg C ha(-1) yr(-1). The SOC at 0 to 30 cm increased more in cover crops with 120 to 130 kg N ha(-1) yr(-1) than in weeds with 0 kg N ha(-1) yr(-1), regardless of tillage. In the subtropical humid region of the southeastern United States, cover crops and N fertilization can increase the amount of C input and storage in tilled and nontilled soils, and hairy vetch and rye biculture was more effective in sequestering C than monocultures or no cover crop.

The impact of tillage and residual nitrogen on wheat

Wheat ( Triticum aestivum L.) yield and quality is influenced by management of the previous crop but is highly dependent on current year management. The objective of this study was to evaluate the response of winter wheat seeded in two tillage systems [conventional tillage (CT) and no-till (NT)] to four N rates applied to a previous cotton ( Gossypium hirsutum L.) crop (0, 67, 134, and 202 kg ha −1). The experiment with wheat was conducted on a Dothan sandy loam (fine, loamy siliceous, thermic Plinthic Kandiudults) at the University of Florida North Florida Research and Education Center near Quincy, FL from 1995 to 1997. For most plant characteristics, there was a tillage x N x year interaction. Greater plant emergence (79.4 vs. 65.3%) and grain N (23.5 vs. 21.5 g kg −1), and lower grain moisture (139 vs. 142 g kg −1) were obtained under NT than CT, respectively, in one out of two years. Nitrogen applied to a previous cotton crop increased wheat grain yields, plant height and seed number under NT in 1995–1996 and CT in 1996–1997, head density under NT in both years, harvest index under CT in 1996–1997, and grain N concentration in 1995–1996 and 1996–1997 due to residual plant and soil N. With every 1 kg N applied to a previous cotton crop, wheat grain yields increased by 5.38 kg ha −1 under NT, whereas grain yield under CT was not influenced by N application to cotton in 1995–1996. In 1996–1997, grain yields increased by 4.96 and 4.23 kg ha −1 for wheat grown in NT and CT, respectively. Generally, wheat seeded in NT following cotton did not decrease stand or yields compared to CT and wheat grain yields and grain N content increased with N fertilization of the previous crop. However, we would have to apply about 134 kg N ha −1 to a previous cotton crop to maximize wheat production under NT and CT.

Biculture Legume–Cereal Cover Crops for Enhanced Biomass Yield and Carbon and Nitrogen

Biculture legume–cereal cover cropping may enhance above‐ and belowground biomass yields and C and N contents. The increase in C and N supply to the soil has the potential to improve soil quality and crop productivity compared with monoculture cover crop species. We examined above‐ and belowground (0‐ to 120‐cm soil depth) biomass yields and C and N contents of a legume [hairy vetch (Vicia villosa Roth)], nonlegume [rye (Secale cereale L.)], and biculture of legume and nonlegume (vetch and rye) cover crops planted without tillage in the fall of 1999 to 2001 in central Georgia. After cover crop kill in the spring, cotton (Gossypium hitsutum L.) and sorghum [Sorghum bicolor (L.) Moench)] were planted using three tillage practices (no‐till, strip till, and chisel till) with three N fertilization rates (0, 60 to 65, and 120 to 130 kg N ha−1). The field experiment was arranged in a split‐split plot treatment with three replications on a Dothan sandy loam (fine‐loamy, kaolinitic, thermic, Plinthic Kandiudults). Aboveground biomass yield of rye decreased from 6.1 to 2.3 Mg ha−1 from 2000 to 2002, but yield of hairy vetch varied (2.4 to 5.2 Mg ha−1). In contrast, biomass yield of vetch and rye biculture (5.6 to 8.2 Mg ha−1) was greater than that of rye and vetch planted alone in all years. Compared with winter weeds in no cover crop treatment, C content in rye (1729 to 2670 kg ha−1) was greater due to higher biomass yield, but N content in vetch (76 to 165 kg ha−1) was greater due to higher N concentration, except in 2002. As a result, C (2260 to 3512 kg ha−1) and N (84 to 310 kg ha−1) contents in biculture were greater than those from monocultures in all years. Similarly, belowground biomass yield and C and N contents were greater in biculture than in monocultures. In 2001, aboveground biomass yield and C and N contents in cover crops were also greater in strip till with biculture than in other treatments, except in chisel till with vetch and biculture, but belowground biomass yield and N content were greater in chisel till with biculture than in no‐till, strip till, and chisel till with weeds. Cotton lint yield was lower with biculture than with rye, but sorghum grain yield and cotton and sorghum biomass (stems + leaves) yields and N uptake were greater with biculture than with rye. Because of higher biomass yield and C and N contents, biculture of hairy vetch and rye cover crops may increase N supply, summer crop yields, and N uptake compared with rye and may increase potentials to improve soil organic matter and reduce N leaching compared with vetch.

Tillage, Cover Crops, and Nitrogen Fertilization Effects on Cotton and Sorghum Root Biomass, Carbon, and Nitrogen

Management practices may influence cotton (Gossypium hirsutum L.) and sorghum [Sorghum bicolor (L.) Moench)] root C and N inputs for improving soil quality. We examined the influence of three tillage practices [no‐till (NT), strip till (ST), and chisel till (CT)], four cover crops {legume [hairy vetch (Vicia villosa Roth)], nonlegume [rye (Secale cereale L.)], biculture of legume and nonlegume (vetch and rye), and no cover crops (winter weeds)}, and three N fertilization rates (0, 60–65, and 120–130 kg N ha−1) on cotton and sorghum root C and N from the 0‐ to 120‐cm soil depth. A field experiment was conducted in a Dothan sandy loam (fine‐loamy, kaolinitic, thermic, Plinthic Kandiudults) from 2000 to 2002 in central Georgia. Root C and N at 0 to 15 cm were greater in NT than in ST and CT in 2000 cotton and 2001 sorghum, but at 30 to 60 cm they were greater in ST than in NT and CT in 2000 cotton. Root C and N at 0 to 15 cm were also greater with vetch and rye biculture than with vetch and weeds in 2001 sorghum. Total root C and N at 0 to 120 cm were greater in ST with vetch than in ST with rye or in CT with weeds in 2000 cotton. In contrast, total root N was greater in NT with rye than in ST with rye or CT with vetch in 2001 sorghum and 2002 cotton. Total root N was also greater in CT with 60 kg N ha−1 than in NT or CT with 120 kg N ha−1 in 2000 cotton, but was greater in ST with 60 kg N ha−1 than in NT with 0 kg N ha−1 or CT with 120 kg N ha−1 in 2002 cotton. The NT or ST with vetch and rye cover crops and 60 kg N ha−1 may increase cotton and sorghum root C and N compared with CT with no cover crops and N fertilization, thereby helping to improve soil quality and productivity.

Carbon accumulation in cotton, sorghum, and underlying soil as influenced by tillage, cover crops, and nitrogen fertilization

Soil and crop management practices may influence biomass growth and yields of cotton (Gossypium hirsutum L.) and sorghum (Sorghum bicolorL.) and sequester significant amount of atmospheric CO2in plant biomass and underlying soil, thereby helping to mitigate the undesirable effects of global warming. This study examined the effects of three tillage practices [no-till (NT), strip till (ST), and chisel till (CT)], four cover crops [legume (hairy vetch) (Vicia villosa roth), nonlegume (rye) (Secale cerealeL), hairy vetch/rye mixture, and winter weeds orno covercrop], and three N fertilization rates (0, 60–65, and 120–130 kg N ha −1) on the amount of C sequestered in cotton lint (lint + seed), sorghum grain, their stalks (stems + leaves) and roots, and underlying soil from 2000 to 2002 in central Georgia, USA. A field experiment was conducted on a Dothan sandy loam (fine-loamy, kaolinitic, thermic, Plinthic Kandiudults). In 2000, C accumulation in cotton lint was greater in NT with rye or vetch/rye mixture but in stalks, it was greater in ST with vetch or vetch/rye mixture than in CT with or without cover crops. Similarly, C accumulation in lint was greater in NT with 60 kg N ha −1 but in stalks, it was greater in ST with 60 and 120 kg N ha −1 than in CT with 0 kg N ha −1. In 2001, C accumulation in sorghum grains and stalks was greater in vetch and vetch/rye mixture with or without N rate than in rye without N rate. In 2002, C accumulation in cotton lint was greater in CT with or without N rate but in stalks, it was greater in ST with 60 and 120 kg N ha −1 than in NT with or without N rate. Total C accumulation in the above- and belowground biomass in cotton ranged from 1.7 to 5.6 Mg ha −1 and in sorghum ranged from 3.4 to 7.2 Mg ha −1. Carbon accumulation in cotton and sorghum roots ranged from 1 to 14% of the total C accumulation in above- and belowground biomass. In NT, soil organic C at 0–10 cm depth was greater in vetch with 0 kg N ha −1 or in vetch/rye with 120–130 kg N ha −1 than in weeds with 0 and 60 kg N ha −1 but at 10–30 cm, it was greater in rye with 120–130 kg N ha −1 than in weeds with or without rate. In ST, soil organic C at 0–10 cm was greater in rye with 120–130 kg N ha −1 than in rye, vetch, vetch/rye and weeds with 0 and 60 kg N ha −1. Soil organic C at 0–10 and 10–30 cm was also greater in NT and ST than in CT. Since 5 to 24% of C accumulation in lint and grain were harvested, C sequestered in cotton and sorghum stalks and roots can be significant in the terrestrial ecosystem and can significantly increase C storage in the soil if these residues are left after lint or grain harvest, thereby helping to mitigate the effects of global warming. Conservation tillage, such as ST, with hairy vetch/rye mixture cover crops and 60–65 kg N ha −1 can sustain C accumulation in cotton lint and sorghum grain and increase C storage in the surface soil due to increased C input from crop residues and their reduced incorporation into the soil compared with conventional tillage, such as CT, with no cover crop and N fertilization, thereby maintaining crop yields, improving soil quality, and reducing erosion.

Tillage and Residual Nitrogen Impact on Wheat Forage

Wheat (Triticum aestivum L.) forage yield and quality can be affected by management of the previous crop. The objective of this study was to evaluate two tillage systems [no‐till (NT) and conventional (CT)] and residual response to four N rates (0, 67, 134, and 202 kg ha−1) applied to the previous cotton (Gossypium hirsutum L.) crop. The experiment was conducted on a Dothan sandy loam (fine, loamy siliceous, thermic Plinthic Kandiudults) in 1995–1996 and 1996–1997. Greater wheat dry matter yields were obtained from CT than NT in 1995–1996 (6.3 and 5.4 Mg ha−1, respectively), while tillage did not influence yields in 1996–1997 (7.5 and 8.0 Mg ha−1 for CT and NT, respectively). Wheat yields were not influenced by N application to the previous cotton crop. The in vitro organic matter digestion (IVOMD) was not influenced by tillage or N application to the previous cotton crop. With increasing N application to a previous cotton crop, neutral detergent fiber (NDFt) and neutral detergent ash‐free (NDFaf) increased in wheat forage under CT and decreased in NT. Nitrogen concentration of wheat increased with N application to the previous crop. Concentration of P was greater from CT than NT in 1995–1996, while tillage did not influence P concentration in 1996–1997 growing season. Increasing N application rates to the previous crop decreased NDFt and NDFaf in wheat grown in NT and increased N concentration in dry matter of wheat grown in both tillage systems. Generally, NT is a viable option for growing wheat forage following cotton.

Effect of Row Width and Nitrogen on Cotton Morphology and Canopy Microclimate

Canopy structure is a function of cultural practices, genetics, and environment; specifically, practices affecting plant row width and soil fertility can change canopy structure. Canopy structure affects canopy microclimate. Canopy microclimate determines the rate of fruit development, pest pressure, and crop response to ambient conditions. The rank growth associated with excess N in cotton (Gossypium hirsutum L.) is associated with delay in fruit development and increased boll rot. This study was conducted to determine the effect of ultra narrow row (UNR) planting on canopy microclimate in cotton. Canopy microclimate in UNR cotton (18‐ to 25‐cm row width) and conventional (76‐ to 91‐cm row width) plantings with low N (16.8 kg ha−1 at planting only) or high N (16.8 kg ha−1 at planting and 202 kg ha−1 3 wk after bloom) fertilizer was quantified by monitoring the plant canopy temperature, relative humidity (RH), and vapor pressure deficit (VPD) every 15 min during the growing season. The study was conducted at Quincy, FL, on a Dothan sandy loam soil (fine loamy siliceous, thermic Plinthic Kandiudult) in 2000 and 2001. Plant height and nodes per plant were determined 60, 90, and 120 d after planting (DAP). A split‐plot design was used with row width as the main effect and N rate as subplot. During the hours from 0700 to 1900, temperature was 1 to 2°C higher and RH 3 to 7% lower in the conventional vs. the UNR plantings. In general, N and row width effects did not have as great an impact on canopy microclimate as did plant height. In 2001, when correlations were significant, as plant height increased to 1 m, canopy temperature during the hours of 0700 to 1900 on average decreased from 33 to 25°C, RH increased from 55 to 85%, and VPD decreased from 0.16 kPa to less than 0.08 kPa. In 2002, plants grew much faster and correlations of microclimate and plant height were not observed. Plant height under typical production conditions had more of an effect on canopy microclimate than did plant density or N treatment.

Soil Organic Matter and Tomato Yield following Tillage, Cover Cropping, and Nitrogen Fertilization

Management practices can influence soil C and N and tomato (Lycopersicon esculentum Mill) yield. We examined the influence of tillage practices [no‐till (NT), chisel plowing (CP), and moldboard plowing (MP)], cover crops [hairy vetch (Vicia villosa Roth) vs. winter weeds], and N fertilization rates (0, 90, and 180 kg N ha−1) on soil organic C and N, potential C and N mineralization (PCM and PNM, respectively), inorganic N contents, and tomato yield and N uptake. A 3‐yr experiment was conducted on a Dothan sandy loam (fine‐loamy, siliceous, thermic, Plinthic Paleudults) in central Georgia. Soil organic C and N after 3 yr were greater in NT with vetch than in CP and MP with vetch or weeds at 0‐ to 20‐cm depth. The PCM, PNM, and inorganic N were greater in MP than in NT and CP at 7.5 to 20 cm in May 1996 but were greater in NT and CP than in MP at 0 to 7.5 cm in April 1997. At 0 to 20 cm, PNM and inorganic N were also greater with vetch than with weeds in April 1996 and 1997 and with 180 than with 0 kg N ha−1 in May 1996 and August 1997. Tomato yield and N uptake were greater in CP and MP than in NT and with 90 and 180 kg N ha−1 than with 0 kg N ha−1. Although NT with vetch can improve soil organic matter, CP can sustain tomato yield compared with MP, thereby reducing the potential for soil erosion. Hairy vetch can increase labile soil N pool and 90 compared with 180 kg N ha−1 can sustain tomato yield, thereby reducing the amount of N fertilizer and potential for N leaching.

Soil Organic Matter and Tomato Yield following Tillage, Cover Cropping, and Nitrogen Fertilization

Management practices can influence soil C and N and tomato (Lycopersicon esculentum Mill) yield. We examined the influence of tillage practices [no-till (NT), chisel plowing (CP), and moldboard plowing (MP)], cover crops [hairy vetch (Vicia villosa Roth) vs. winter weeds], and N fertilization rates (0, 90, and 180 kg N ha−1) on soil organic C and N, potential C and N mineralization (PCM and PNM, respectively), inorganic N contents, and tomato yield and N uptake. A 3-yr experiment was conducted on a Dothan sandy loam (fine-loamy, siliceous, thermic, Plinthic Paleudults) in central Georgia. Soil organic C and N after 3 yr were greater in NT with vetch than in CP and MP with vetch or weeds at 0- to 20-cm depth. The PCM, PNM, and inorganic N were greater in MP than in NT and CP at 7.5 to 20 cm in May 1996 but were greater in NT and CP than in MP at 0 to 7.5 cm in April 1997. At 0 to 20 cm, PNM and inorganic N were also greater with vetch than with weeds in April 1996 and 1997 and with 180 than with 0 kg N ha−1 in May 1996 and August 1997. Tomato yield and N uptake were greater in CP and MP than in NT and with 90 and 180 kg N ha−1 than with 0 kg N ha−1. Although NT with vetch can improve soil organic matter, CP can sustain tomato yield compared with MP, thereby reducing the potential for soil erosion. Hairy vetch can increase labile soil N pool and 90 compared with 180 kg N ha−1 can sustain tomato yield, thereby reducing the amount of N fertilizer and potential for N leaching.

Tillage, Cover Crop, and Kill‐Planting Date Effects on Corn Yield and Soil Nitrogen

Tillage and spring kill date may affect cover crop N accumulation and subsequent N release to the soil, thereby influencing corn (Zea mays L.) N uptake and yield. We examined the influence of three tillage practices [no till (NT), chisel plowing (CP), and moldboard plowing (MP)], two cover crop management systems [hairy vetch (Vicia villosa Roth) vs. winter weeds], and two cover crop kill–corn planting dates [early (early April cover crop kill and mid to late April corn planting) vs. late (mid to late April cover crop kill and late April to early May corn planting)] on cover crop N accumulation, soil inorganic N, and silage corn N uptake and yield. An experiment was conducted on a Dothan sandy loam (fine‐loamy, siliceous, thermic, Plinthic Paleudults) from 1997 to 1999 in central Georgia. Cover crop N accumulation was higher with late kill than with early kill (113 vs. 104 kg ha−1). Corn yield was higher with late planting in NT than in CP or MP (19.5 vs. 15.1–16.6 Mg ha−1) and higher in CP or MP with early planting than in MP with late planting (18.1–18.4 vs. 15.1 Mg ha−1). Similarly, corn N uptake was higher in NT with late planting than in CP or MP with early or late planting (217 vs. 133–171 kg ha−1). Soil inorganic N (0− to 30‐cm depth) at corn planting was higher in CP than in NT (18.4–30.2 vs. 9.9–20.5 mg kg−1). Corn yield and N uptake in NT and N concentration and uptake in CP and MP can be increased by delaying cover crop kill by 2 wk, but corn yield in CP and MP can be maintained by killing cover crop early in the spring.

Fiber Yield and Quality of Cotton Grown at Two Divergent Population Densities

Poor seed germination and early seedling damage often reduce plant populations in the north‐eastern cotton (Gossypium hirsutum L.) producing region of the USA. A field study was conducted at Clayton, NC, on a Dothan sandy loam (fine‐loamy, siliceous, thermic Plinthic Kandiudult) to investigate responses of cotton reproductive development to reduced plant population. All flowers on plants grown at 2 and 12 plants m−2 were tagged so that associations among boll and lint quantity and quality, flowering date, and fruiting position could be determined. On plants grown at 2 plants m−2, 33 and 65% of their fiber came from flowers initiated before 88 days after planting (DAP) in 1992 and 1993, respectively. Plants grown at 12 plants m−2 produced 63 and 88% of their fiber from flowers initiated before 88 DAP in 1992 and 1993, respectively. Plant population did not affect total lint yield, however. Because of favorable late‐season weather, plants grown at 2 plants m−2 produced more bolls on vegetative branches and at more distal sympodial positions than did plants grown at 12 plants m−2. Boll weight and micronaire were generally higher for earlier bolls at all positions for the lower population density. Later bolls exhibited poorer boll and fiber properties, indicating negative effects of reduced heat unit accumulation by later bolls. Our findings indicate that replanting, which might delay stand establishment by 3 to 4 wk, would be of little help toward improving fiber yield because it would rely more heavily on later produced bolls.

Tropical maize response to nitrogen and starter fertilizer under strip and conventional tillage systems in southern Alabama

Tropical maize ( Zea mays L.) is a promising new crop for the southeastern US, but optimum management practices have not been established for this alternative crop. Field studies were initiated in 1990 to evaluate its response to N and starter fertilizer under conventional and reduced tillage systems double cropped following wheat ( Triticum aestivum L.). The experiment was conducted on a Dothan sandy loam (fine–loamy, silicious, thermic Plinthic Paleudults) in Southern Alabama. Treatments included conventional (chisel plowing (25 cm depth), disking, and in-row subsoiling) and strip (in-row subsoiling) tillage systems; four N rates (0, 56, 112 and 168 kg ha −1); and five starter fertilizer combinations: (1) no starter; (2) 22.4 kg N ha −1; (3) 22.4 kg P ha −1; (4) 22.4 kg N and 22.4 kg P ha −1; (5) 22.4 kg N, 22.4 kg P and 11.2 kg S ha −1. The depth of subsoiling was 40 cm for both tillage systems. Tropical maize hybrids' Pioneer® Brand X304C (1990) and Pioneer® Brand 3072 (1991 and 1992) were utilized in the study. Maize silage yields (averaged over 1990 and 1991) under conventional tillage were 14% lower than with strip tillage, while grain yields in 1991 were 30% lower. Differences among tillage systems were not significant in 1992 except for the 0 and 168 kg N ha −1 rates where conventional tillage produced slightly higher yields as compared to strip tillage. Silage and grain yields increased with N rate with the largest response to N occurring in 1991 under strip tillage. For silage yields averaged over both tillage systems in 1990 and silage and grain yields in 1991 and 1992 under strip tillage there was a quadratic response to N rate. Silage and grain yields peaked at approximately 112 kg N ha −1. Under conventional tillage in 1991 and 1992, the response of silage and grain to N rate was linear. The best starter for silage was the N and P (NP) treatment. For grain, N alone gave the same yield as the NP starter in 1991, with the greatest response occurring under conventional tillage. In 1992, the NP treatment was the best starter for grain. This study demonstrated that double cropped tropical maize is a promising alternative crop for warm temperate/subtropical regions. High silage yields and reasonable grain yields can be obtained using conservation tillage systems and the addition of N in combination with a starter fertilizer containing N and P.

Dry Matter Allocation and Fruiting Patterns of Cotton Grown at Two Divergent Plant Populations

Reduced plant populations frequently occur in the northern Cotton Belt of the USA because of poor seed germination and early seedling damage. A field study was conducted at Clayton, NC, on a Dothan sandy loam (fine‐loamy, siliceous, thermic Plinthic Paleudult) to investigate the response of cotton (Gossypium hirsutum L.) vegetative and reproductive development to two plant populations. Cotton plants, grown at 2 and 12 plants m−2 in 1.0‐m rows had every flower tagged with week‐specific, color‐coded tags. Dry matter partitioning, flower development, flower retention, and boll development patterns were determined. Plants at the low population exhibited large increases in the vegetative dry weight of individual plants at maturity; however, all parameters of vegetative growth were reduced on a land area basis. Reproductive development of the 2 plants m−2 treatment was prolonged because of fewer early fruiting sites per unit land area and there was an average 16‐d delay in flowering maxima. No differences in total flowers per meter or flower retention occurred between treatments at final harvest. Slight differences in total bolls per meter occurred in 1993 (13% fewer bolls at 2 plants m−2); however, the low population plants had more bolls on monopodia, more late‐season flowers, and greater retention of these late bolls. Replanting low populations would not be advisable because the delay in maturity would probably be more injurious to boll production than the low population per se.