Decatur Silt Loam Research Articles

Agroeconomic differences among alternative cotton row spacings and row patterns

AbstractCrop growth and development is affected by intraspecies competition. This study was conducted to determine whether cotton productivity and profitability could be manipulated through planting geometry. The effects of row spacing, planting pattern, and variety on cotton fruit distribution, yield, and net returns were investigated near Bella Mina, AL, on a Decatur silt loam (fine, kaolinitic, thermic Rhodic Paleudults); Jackson, TN, on a Calhoun silt loam (fine‐silty, mixed, active, thermic Typic Glossaqualfs); Starkville, MS, on a Leeper silty clay loam (fine, smectitic, nonacid, thermic Vertic Epiaquepts); and Stoneville, MS, on a Bosket very fine sandy loam (fine‐loamy, mixed, active, thermic Mollic Hapludalfs). For both the 76‐ and 97‐cm row spacing, transitioning from a solid to a 2 × 1 skip row pattern reduced cotton lint yield by 19%. Reduced lint yield in the 2 × 1 skip row pattern was attributed primarily to a 7% decrease in the number of Zone 1 and first‐position bolls. Consequently, planting on a solid rather than skip row pattern increased net returns by 21%. Planting cotton in either 76‐ or 97‐cm rows using a solid rather than skip row pattern likely increases crop productivity and profitability across the US cotton belt.

Entomopathogenic nematode management of small hive beetles (Aethina tumida) in three native Alabama soils under low moisture conditions.

The goal was to determine the efficacy of entomopathogenic nematodes (EPNs) on Aethina tumida small hive beetle (SHB) in Alabama soils. The objectives were to (i) determine the pupation success of SHB wandering larvae; (ii) determine the efficacy of EPNs on SHB wandering larvae in natural and autoclaved soil; and (iii) determine the efficacy of EPNs on SHB wandering larvae in three Alabama soil types at typical low moisture levels. The Alabama soils were Kalmia loamy sand (KLS), Benndale fine sandy loam (BFSL), and Decatur silt loam (DSL). Heterorhabditis bacteriophora, H. indica, Steinernema carpocapsae, S. feltiae, S. kraussei, and S. riobrave were tested at population densities of 5, 10, 20, 40, and 80 third-stage infective EPN juveniles (IJ3) per 130 cm3 soil. Pupation success in SHB population densities of 5, 10, and 20 wandering larvae per Petri dish were similar. Of the six EPN species, S. carpocapsae achieved the highest efficacy across all EPN population densities in both natural and autoclaved soil. Steinernema riobrave and H. indica achieved the next highest efficacies; however, they were significantly less effective than S. carpocapsae. Steinernema carpocapsae parasitized 87% SHB wandering larvae across all population densities tested. Steinernema carpocapsae achieved the best efficacy colonizing 94% of the SHB in the KLS soil, 80% in the BFSL soil, and 47% in the DSL soil. In conclusions, S. carpocapsae is be a promising biological control EPN to implement into a management system on SHB.

Cultivar, irrigation, and soil contribution to the enhancement of Verticillium wilt disease in cotton

Verticillium wilt of cotton is incited by Verticillium dahliae Kleb., which colonizes the vascular cylinder of the plant resulting in defoliation, stunting, and yield loss. This project investigated cultivar selection and soil type predisposition for management of this disease to preserve cotton yields. All cotton cultivars planted in this study were susceptible to Verticillium wilt infection and all had some amount of vascular discoloration observed. However, there were varying ranges of tolerance found among different cultivars. ST 4747 GLB2 appeared to the consistently the most tolerant of the cultivars planted and exhibited the highest yields consistently over different seasons. Verticillium wilt disease incidence and severity were increased with irrigation in the controlled microplot test over six soil types. Verticillium wilt symptom severity was greater in the Decatur silt loam and Houston clay soils which have the highest clay and silt content.

Inorganic and Enzymatically Hydrolyzable Organic Phosphorus of Alabama Decatur Silt Loam Soils Cropped With Upland Cotton

Inorganic and Enzymatically Hydrolyzable Organic Phosphorus of Alabama Decatur Silt Loam Soils Cropped With Upland Cotton

Effects of Elevated CO2 and Agricultural Management on Flux of Greenhouse Gases From Soil

To evaluate the contribution of agriculture to climate change, the flux of greenhouse gases from different cropping systems must be assessed. Soil greenhouse gas flux (CO2, N2O, and CH4) was assessed during the final growing season in a long-term (10-year) study evaluating the effects of crop management (conservation and conventional) and atmospheric CO2 (ambient and twice ambient) on a Decatur silt loam (clayey, kaolinitic, thermic Rhodic Paleudults). Seasonal soil CO2 flux was significantly greater under elevated (4.39 Mg CO2-C ha−1) versus ambient CO2 (3.34 Mg CO2-C ha−1) and was generally greater in the conventional (4.19 Mg CO2-C ha−1) compared with the conservation (3.53 Mg CO2-C ha-1) system. Soil flux of both N2O (range, −1.5 to 53.4 g N2O-N ha−1 day−1) and CH4 (range, −7.9 to 24.4 g CH4-C ha−1 day−1) were low throughout the study and rarely exhibited differences caused by treatments. Global warming potential (calculated based on flux of individual gases) was increased by elevated CO2 (33.4%) and by conventional management (17.1%); these increases were driven primarily by soil CO2 flux. As atmospheric CO2 continues to rise, our results suggest adoption of conservation management systems represents a viable means of reducing agriculture's potential contribution to global climate change.

Poultry Litter Application Increases Nitrogen Cycling Compared with Inorganic Nitrogen Fertilization

Poultry litter, an inexpensive source of nutrients and available in abundant amounts in the southeastern USA, may increase N cycling and reduce N losses compared with inorganic N fertilization if applied for crop production. We evaluated the effect of long‐term application of poultry litter and inorganic N fertilizer on crop N uptake, soil N fractions, and N losses in conservation and conventional tillage with or without cover crop at the 0‐ to 20‐cm depth in a Decatur silt loam (clayey, kaolinitic, thermic, Typic Paleudults) in northern Alabama. Treatments were incomplete factorial combinations of three tillage practices [no‐till (NT), mulch till (MT), and conventional till (CT)], two cropping systems [cotton (Gossypium hirsutum L.)–cotton–corn (Zea mays L.) and rye (Secale cereale L.)/cotton–rye/cotton–corn], and two N fertilization sources and rates (0 and 100 kg N ha−1 from NH4NO3 and 100 and 200 kg N ha−1 from poultry litter). Nitrogen fractions were soil total N (STN), particulate organic N (PON), microbial biomass N (MBN), potential N mineralization (PNM), NH4–N, and NO3–N. Crop N uptake varied among treatments and years and total uptake from 1997 to 2005 was greater in rye/cotton–rye/cotton–corn than in cotton–cotton–corn and greater with NH4NO3 than with poultry litter at 100 kg N ha−1 After 10 yr, STN and PON contents at 0 to 20 cm were greater in NT with poultry litter than in other treatments, except in CT with poultry litter, resulting in N storage at 38 kg N ha−1 yr−1 with poultry litter compared with loss at 4 kg N ha−1 yr−1 with NH4NO3. The MBN, PNM, and NO3–N contents were greater with poultry litter than with NH4NO3, regardless of tillage. Calculation of estimated N balance showed that poultry litter conserved N at 191 to 556 kg N ha−1 compared with –75 to 201 kg N ha−1 with NH4NO3. Poultry litter application can increase soil N storage and mineralization and reduce the potential for N loss compared with inorganic N fertilization, thereby reducing the need for N fertilization and environmental N contamination.

Conservation tillage to effectively reduce interrill erodibility of highly-weathered Ultisols

Highly weathered Southeastern soils traditionally cropped under conventional tillage systems are drought-prone and susceptible to runoff and soil loss. We quantified differences in infiltration, runoff, soil loss, and interrill erodibilities (Ki) for three soils: Compass loamy sand, Decatur silt loam, and Tifton loamy sand managed under conventional- (CT), strip- (ST), and/or no-till (NT) systems with and without a residue cover (rye [Secale cerale L.]) (+C/-C) and with and without paratilling (+P/-P). Duplicate plots (1 m2 [~10 ft2]) on each tillage treatment received simulated rainfall (50 mm h-1 [2 in hr-1] for two hours). Runoff and sediment yields were continuously measured, and Ki values were calculated from measured data. The Water Erosion Prediction Project (WEPP) model was used to extend experimental data to long-term annual trends. For the Compass soil, NT-C plots increased runoff by as much as 43% and sediment yields by as much as 10-fold compared to NT+C plots. The NT+P+C plots decreased runoff by as much as 70% and sediment yields by 24-fold compared to CT-P-C. For the Decatur soil, NT+P plots decreased runoff by as much as 71% and sediment yields by as much as 2.7-fold compared to NT-P plots. The NT+P+C plots decreased runoff by as much as 73% and sediment yields by as much as 11.8-fold compared to CT-P-C. For the Tifton soil, ST+P+C plots decreased runoff by as much as 44% and sediment yields by as much as 2.7-fold compared to CT-P-C plots. Calculated Ki values for the Compass, Decatur, and Tifton soils were 0.37, 0.40, and 0.24, respectively. Residue cover decreased effective interrill erodibilities (Kieff) values by 11%, 2-fold, and 2.6-fold for the Decatur, Tifton, and Compass soils, respectively; Paratilling decreased Kieff values by 3-fold for the Compass and Decatur soils. The NT and/or ST systems had lower Kieff values than Ki values from corresponding CT-P-C treatments (Compass = 4- to 37-fold; Decatur = 4- to 13-fold; Tifton = 2-fold). Converting from a CT to a NT or ST system reduced predicted runoff (Compass = 1.7-fold; Decatur = 10% to 17%; Tifton = 1.6- to 2.3-fold) and sediment yields (Compass = 10- to 12-fold; Decatur = 6- to 33-fold; Tifton = 7.3- to 12.1-fold). The most benefit of NT or ST, as quantified by the maximum difference in 100-year predicted runoff and sediment yields, was for the Compass (78%) and Tifton (75%) soils for runoff and for the Compass (10.3-fold) and Decatur soils (9.7-fold) for sediment. Conservation tillage systems (NT, ST) coupled with surface residue cover and/or paratilling are effective in reducing runoff and sediment yields from highly-weathered soils by lowering effective Ki values.

Cotton Nitrogen Management in a High‐Residue Conservation System: Cover Crop Fertilization

Nitrogen is required for adequate residue production from cereal cover crops used in no‐till cotton (Gossypium hirsutum L.) production, but residues can immobilize N needed by cotton. We conducted a 3‐yr field study on a Decatur silt loam (clayey, kaolinitic, thermic Rhodic Paleudult) in northern Alabama to test N fertilizer practices for cotton grown with a rye (Secale cereale L.) cover crop and conservation tillage. Nitrogen rates applied to the rye cover crop were 0, 34, and 67 kg N ha−1 and cotton N rates were 0, 45, 90, and 135 kg N ha−1 Additionally, 15N microplots were established in cover crop N treatments of 34 kg N ha−1 and in cotton treatments of 90 kg N ha−1 Data collected included cover crop aerial biomass, cover crop C/N ratios, cotton leaf N at first flower, lint yield, lint quality, and 15N in plant and soil samples. Cotton grown in unfertilized rye treatments needed 57 to 60% (38–40 kg N ha−1) more N to maximize yields above median conventional tillage N recommendations (67 kg N ha−1). Cover crop N rates of 67 kg N ha−1 maximized cover crop biomass production for soil protection and soil organic matter aggradation. If the cover crop was fertilized, minimum cotton N applications of 70 and 76 kg N ha−1 were needed for economic optimum and maximum lint yield, respectively. We speculate that cotton N rates may be decreased in the future as new N and C pool equilibria are reached.

Cotton Nitrogen Management in a High‐Residue Conservation System: Source, Rate, Method, and Timing

More than 70% of cotton (Gossypium hirsutum L.) grown in the Tennessee Valley of northern Alabama is produced using conservation tillage systems with cereal cover crops. The resulting decreased N efficiency requires development of new N fertilizer recommendations. We conducted a replicated 3‐yr field study on a Decatur silt loam (fine, kaolinitic, thermic Rhodic Paleudult) to determine the effects of N source (NHNO3 [AN] and urea–NH4NO3 [320 g N kg−1, UAN]), N rates (0, 45, 90, 135, and 180 kg N ha−1), N application timing (all at‐planting or 50:50 split between planting and first match head square), and N application method (banded or broadcast) on cotton grown in high‐residue rye (Secale cereale L.) conservation systems. Generally, 67 to 80% more N was needed than average conventional N rate recommendations to reach optimal yields if N was split applied, while N applied at‐planting had yield responses with 169% of the recommended N rate. Urea–NH4NO3 applications resulted in greater yields when banded at‐planting (1045 kg lint ha−1), while AN was more effective when broadcast applied at‐planting or in split applications (1002 and 996 kg lint ha−1, respectively). Chlorophyll meter readings, petiole NO3, and leaf N were not useful predictors of cotton N deficiency or yield. The most efficient practice is to apply 88% more N (126 kg N ha−1 total) than the mean conventional N cotton recommendation as a broadcast split application using AN. We speculate that N requirements may be decreased with time as C and N pools reach a new equilibrium.

Effect of Five‐Year Continuous Poultry Litter Use in Cotton Production on Major Soil Nutrients

Repeated application of poultry (Gallus gallus) litter to crop lands may lead to nitrates leaching and build up of P and other elements in the soil profile, which are prone to loss from runoff and erosion. A study was conducted for 5 yr at Belle Mina, AL on a Decatur silt loam (fine, kaolinitic thermic Rhodic Paleudult) during 1994 to 1998 to determine the nitrate movement and quantify the build up of P, K, Ca, and Mg due to the application of nitrification inhibitor, carboxymethyl pyrazole (CP), treated fresh and composted poultry litter and urea in conventionally tilled cotton (Gossypium hirsutum L.). Poultry litter maintained soil pH (0–30 cm depth) where as application of urea resulted in a pH decline. The inhibitor, CP, significantly reduced the NO3−–N formation in all N sources for 41 d following application. However, over the longer period of time, very minimal changes in nitrate concentrations were observed due to change in rates or sources of N. Over the experimental period, P concentration increased significantly (by 74%) in composted litter applied plots (17.7 mg kg−1) but not in fresh litter plots (1.5 mg kg−1). Linear increase in P accumulation was observed with increase in rate of composted litter. Concentrations of K and Mg increased significantly both in fresh (93 and 25 mg kg−1, respectively) and composted litter (127 and 36 mg kg−1, respectively) applied plots by the end of 5 yr period. These results indicate that a well‐planned application of fresh poultry litter in soils that are not already overloaded with P is safe and treating litter with CP is advantageous from an environmental perspective.

Soil carbon and nitrogen sequestration as affected by long-term tillage, cropping systems, and nitrogen fertilizer sources

Disposal of poultry litter, a widely available organic manure in the southeastern USA because of a large-scale poultry industry, is a major concern because of its contamination in surface- and groundwater through N leaching and P runoff. Application of poultry litter in no-tilled intensive cropping system could increase soil C and N sequestration compared with the conventional-tilled system with inorganic N fertilization and reduce environmental contamination. We evaluated the 10-year effects of tillage, cropping systems, and N fertilizer sources on crop residue (stems + leaves) production and soil bulk density, organic C (SOC), and total N (STN) at the 0–20 cm depth in Decatur silt loam (clayey, kaolinitic, thermic, and Typic Paleudults) in northern AL, USA. Treatments were incomplete factorial combinations of three tillage practices [no-till (NT), mulch till (MT), and conventional till (CT)], two cropping systems [cotton ( Gossypium hirsutum L.)–cotton–corn ( Zea mays L.) and rye ( Secale cereale L.)/cotton–rye/cotton–corn], and two N fertilization sources and rates (0 and 100 kg N ha −1 from NH 4NO 3, and 100 and 200 kg N ha −1 from poultry litter) in randomized complete block with three replications. Rye was grown as winter cover crop and corn as residual crop without tillage and fertilization. Mean crop residue returned to the soil from 1997 to 2005 was greater in rye/cotton–rye/cotton–corn than in cotton–cotton–corn and greater with NH 4NO 3 than with poultry litter at 100 kg N ha −1. While SOC and STN concentrations at 10–20 cm after 10 years were not influenced by treatments, SOC and STN contents at 0–20 cm were greater with poultry litter than with NH 4NO 3 in NT and CT. These resulted in a C sequestration rate of 510 kg C ha −1 year −1 and N sequestration rates of 41–49 kg N ha −1 year −1 with poultry litter compared with −120 to 147 kg C ha −1 year −1 and −23 to −3 kg N ha −1 year −1, respectively, with NH 4NO 3. Cropping and fertilization sequestered C at 730 kg C ha −1 year −1 and N at 67 kg N ha −1 year −1 compared with fallow and no-fertilization in NT. Tillage and cropping system did not influence SOC and STN. Long-term poultry litter application or continuous cropping can sequester C and N in the soil compared with inorganic N fertilization or fallow, thereby increasing soil quality and productivity and reducing the potentials for N leaching and greenhouse gas emission.

Tillage, Cropping Systems, and Nitrogen Fertilizer Source Effects on Soil Carbon Sequestration and Fractions

Quantification of soil carbon (C) cycling as influenced by management practices is needed for C sequestration and soil quality improvement. We evaluated the 10-yr effects of tillage, cropping system, and N source on crop residue and soil C fractions at 0- to 20-cm depth in Decatur silt loam (clayey, kaolinitic, thermic, Typic Paleudults) in northern Alabama, USA. Treatments were incomplete factorial combinations of three tillage practices (no-till [NT], mulch till [MT], and conventional till [CT]), two cropping systems (cotton [Gossypium hirsutum L.]-cotton-corn [Zea mays L.] and rye [Secale cereale L.]/cotton-rye/cotton-corn), and two N fertilization sources and rates (0 and 100 kg N ha(-1) from NH(4)NO(3) and 100 and 200 kg N ha(-1) from poultry litter). Carbon fractions were soil organic C (SOC), particulate organic C (POC), microbial biomass C (MBC), and potential C mineralization (PCM). Crop residue varied among treatments and years and total residue from 1997 to 2005 was greater in rye/cotton-rye/cotton-corn than in cotton-cotton-corn and greater with NH(4)NO(3) than with poultry litter at 100 kg N ha(-1). The SOC content at 0 to 20 cm after 10 yr was greater with poultry litter than with NH(4)NO(3) in NT and CT, resulting in a C sequestration rate of 510 kg C ha(-1) yr(-1) with poultry litter compared with -120 to 147 kg C ha(-1) yr(-1) with NH(4)NO(3). Poultry litter also increased PCM and MBC compared with NH(4)NO(3). Cropping increased SOC, POC, and PCM compared with fallow in NT. Long-term poultry litter application or continuous cropping increased soil C storage and microbial biomass and activity compared with inorganic N fertilization or fallow, indicating that these management practices can sequester C, offset atmospheric CO(2) levels, and improve soil and environmental quality.

Carbon Dioxide Efflux from Soil with Poultry Litter Applications in Conventional and Conservation Tillage Systems in Northern Alabama

Increased CO2 release from soils resulting from agricultural practices such as tillage has generated concerns about contributions to global warming. Maintaining current levels of soil C and/or sequestering additional C in soils are important mechanisms to reduce CO2 in the atmosphere through production agriculture. We conducted a study in northern Alabama from 2003 to 2006 to measure CO2 efflux and C storage in long-term tilled and non-tilled cotton (Gossypium hirsutum L.) plots receiving poultry litter or ammonium nitrate (AN). Treatments were established in 1996 on a Decatur silt loam (clayey, kaolinitic thermic, Typic Paleudults) and consisted of conventional-tillage (CT), mulch-tillage (MT), and no-tillage (NT) systems with winter rye [Secale cereale (L.)] cover cropping and AN and poultry litter (PL) as nitrogen sources. Cotton was planted in 2003, 2004, and 2006. Corn was planted in 2005 as a rotation crop using a no-till planter in all plots, and no fertilizer was applied. Poultry litter application resulted in higher CO2 emission from soil compared with AN application regardless of tillage system. In 2003 and 2006, CT (4.39 and 3.40 micromol m(-2) s(-1), respectively) and MT (4.17 and 3.39 micromol m(-2) s(-1), respectively) with PL at 100 kg N ha(-1) (100 PLN) recorded significantly higher CO2 efflux compared with NT with 100 PLN (2.84 and 2.47 micromol m(-2) s(-1), respectively). Total soil C at 0- to 15-cm depth was not affected by tillage but significantly increased with PL application and winter rye cover cropping. In general, cotton produced with NT conservation tillage in conjunction with PL and winter rye cover cropping reduced CO2 emissions and sequestered more soil C compared with control treatments.

Cotton Yield and Fiber Quality from Irrigated Tillage Systems in the Tennessee Valley

Cotton (Gossypium hirsutum L.) yield and quality responses to irrigation have not been described for conservation management systems that growers are rapidly adopting. We conducted a field experiment from 2001–2003 in the Tennessee Valley near Belle Mina, AL on a Decatur silt loam (fine, kaolinitic, thermic Rhodic Paleudults) to examine how irrigation regimes and tillage systems affect ginning percentage, lint yield, and fiber quality (length, micronaire, strength, and fiber length uniformity). Treatments were arranged with a split‐plot structure in a randomized complete block design with three replications. Main plots were a factorial combination of conventional tillage (CT) with and without a fall paratill operation and no surface tillage (NST) following a rye (Secale cereale L.) cover crop with and without a fall paratill operation. Subplots were irrigation regimes (0, 2.7, 5.4, and 8.1 mm d−1). Ginning percentage increased 2% following CT in 1 of 3 yr (2002) while irrigation improved ginning percentage in 2 of 3 yr (2002 and 2003). The NST systems increased lint yields 13% in 2003 compared with CT systems while irrigation increased yields 46 and 32% over nonirrigated yields in 2002 and 2003, respectively. Fiber properties were affected by tillage systems, primarily in 2002. Irrigation regimes affected length, micronaire, and fiber length uniformity in 2002 and 2003. Fall paratilling had no effect on any measured variable, except for an inconsistent difference between tillage systems for fiber length uniformity. An irrigated conservation system, utilizing a cover crop, can improve cotton yields and positively influence fiber characteristics in the Tennessee Valley.

Elevated atmospheric CO2 effects on biomass production and soil carbon in conventional and conservation cropping systems

AbstractIncreasing atmospheric CO2 concentration has led to concerns about potential effects on production agriculture as well as agriculture's role in sequestering C. In the fall of 1997, a study was initiated to compare the response of two crop management systems (conventional and conservation) to elevated CO2. The study used a split‐plot design replicated three times with two management systems as main plots and two CO2 levels (ambient=375 μL L−1 and elevated CO2=683 μL L−1) as split‐plots using open‐top chambers on a Decatur silt loam (clayey, kaolinitic, thermic Rhodic Paleudults). The conventional system was a grain sorghum (Sorghum bicolor (L.) Moench.) and soybean (Glycine max (L.) Merr.) rotation with winter fallow and spring tillage practices. In the conservation system, sorghum and soybean were rotated and three cover crops were used (crimson clover (Trifolium incarnatum L.), sunn hemp (Crotalaria juncea L.), and wheat (Triticum aestivum L.)) under no‐tillage practices. The effect of management on soil C and biomass responses over two cropping cycles (4 years) were evaluated. In the conservation system, cover crop residue (clover, sunn hemp, and wheat) was increased by elevated CO2, but CO2 effects on weed residue were variable in the conventional system. Elevated CO2 had a greater effect on increasing soybean residue as compared with sorghum, and grain yield increases were greater for soybean followed by wheat and sorghum. Differences in sorghum and soybean residue production within the different management systems were small and variable. Cumulative residue inputs were increased by elevated CO2 and conservation management. Greater inputs resulted in a substantial increase in soil C concentration at the 0–5 cm depth increment in the conservation system under CO2‐enriched conditions. Smaller shifts in soil C were noted at greater depths (5–10 and 15–30 cm) because of management or CO2 level. Results suggest that with conservation management in an elevated CO2 environment, greater residue amounts could increase soil C storage as well as increase ground cover.

Variation of Soil Dielectric Constant, Moisture Holding Capacity, and Nitrate-Nitrogen as Influenced by Application of Fresh and Compost Poultry Litter on a Decatur Silt Loam Soil

ABSTRACT Currently, there are major concerns about potential environmental impacts of poultry litter application as a nutrient source for agricultural crops. Composting of poultry litter is reported to have less groundwater pollution effects as compared to fresh litter. A field study was conducted to evaluate the effect of poultry litter applications at three different rates on variations of soil dielectric constant, moisture holding capacity, and soil NO3 −-N distribution on a Decatur slit loam soil. The results were compared with effects of urea (inorganic fertilizer) and composted poultry litter applications. The addition of fresh and composted poultry litter increased the soil dielectric constant and water holding capacity due to the increase in soil organic matter. The study indicates that there is a potential of groundwater contamination by application of urea, fresh poultry litter or composted poultry litter at the rates investigated. Urea and fresh poultry litter applications have comparable effects on surface and groundwater contaminations, whereas composting of litter reduced the potential risk for groundwater contamination.

Conservation Tillage Systems for Cotton in the Tennessee Valley

Yield reductions from no‐tillage cotton (Gossypium hirsutum L.) jeopardized adoption of conservation systems in the Tennessee Valley region of north Alabama in the early 1990s. We conducted a study from 1995 to 1999 on a Decatur silt loam (fine, kaolinitic, thermic Rhodic Paleudults) to develop a practical conservation tillage system with competitive yields for the region. Treatments included a factorial combination of fall ridging (ridged and nonridged) and fall non‐inversion deep tillage (none, in‐row subsoiling, paratilling), along with spring strip tillage and conventional tillage (fall chisel‐spring disk). All treatments, except conventional tillage, were established with a rye (Secale cereale L.) cover crop. Tillage systems were evaluated for soil temperature, penetration resistance, a soil compaction index, soil water, plant population, and seed cotton yield. Paratilling reduced soil compaction index 29 and 31% compared with conventional tillage and no‐tillage, respectively. Subsoiling reduced the compaction index 12 and 15% compared with conventional tillage and no‐tillage, respectively. Soil water content was decreased with the fall paratilled and subsoiled conservation tillage systems, compared with conventional tillage and no‐tillage, suggesting increased rooting. Fall non‐inversion deep tillage, either paratilling or in‐row subsoiling with a narrow‐shanked subsoiler, resulted in the highest seed cotton yields; 16% greater than conventional tillage (2660 kg ha−1), and 10% greater than strict no‐tillage (2810 kg ha−1) across a 4‐yr duration. In this region, non‐inversion deep tillage under the row in fall, coupled with a rye cover crop to produce adequate residue for moisture conservation and erosion control, is a highly competitive and practical conservation tillage system.

Conservation Tillage Systems for Cotton in the Tennessee Valley

Yield reductions from no-tillage cotton (Gossypium hirsutum L.) jeopardized adoption of conservation systems in the Tennessee Valley region of north Alabama in the early 1990s. We conducted a study from 1995 to 1999 on a Decatur silt loam (fine, kaolinitic, thermic Rhodic Paleudults) to develop a practical conservation tillage system with competitive yields for the region. Treatments included a factorial combination of fall ridging (ridged and nonridged) and fall non-inversion deep tillage (none, in-row subsoiling, paratilling), along with spring strip tillage and conventional tillage (fall chisel-spring disk). All treatments, except conventional tillage, were established with a rye (Secale cereale L.) cover crop. Tillage systems were evaluated for soil temperature, penetration resistance, a soil compaction index, soil water, plant population, and seed cotton yield. Paratilling reduced soil compaction index 29 and 31% compared with conventional tillage and no-tillage, respectively. Subsoiling reduced the compaction index 12 and 15% compared with conventional tillage and no-tillage, respectively. Soil water content was decreased with the fall paratilled and subsoiled conservation tillage systems, compared with conventional tillage and no-tillage, suggesting increased rooting. Fall non-inversion deep tillage, either paratilling or in-row subsoiling with a narrow-shanked subsoiler, resulted in the highest seed cotton yields; 16% greater than conventional tillage (2660 kg ha−1), and 10% greater than strict no-tillage (2810 kg ha−1) across a 4-yr duration. In this region, non-inversion deep tillage under the row in fall, coupled with a rye cover crop to produce adequate residue for moisture conservation and erosion control, is a highly competitive and practical conservation tillage system.

Tillage, cover cropping, and poultry litter effects on selected soil chemical properties

Conservation tillage systems such as no-till with winter rye cover cropping change soil chemical properties, which affect crop growth and the environment. The objectives of this study were to investigate the effect of no-till and mulch-till systems, surface application of poultry litter, and winter rye ( Secale cereale L.) cover crop on soil pH, soil organic matter (SOM), and N and P concentrations in cotton ( Gossypium hirsutum L.) plots. The study was done on a Decatur silt loam in north Alabama from 1996 to 1998. SOM under no-till and mulch-till systems in the 0–15 cm soil depth in November 1998 was 22 g kg −1 ( P<0.05) compared with 15 g kg −1 in November 1996. A similar result was obtained with winter rye cover cropping compared with cotton–winter fallow system. Surface application of poultry litter at 100 or 200 kg N ha −1 increased SOM by 55–80%. In the 200 kg N ha −1 poultry litter treatment, NH 4 in the 30–90 cm soil depth in November 1998 was 22% higher than that in November 1996. Compared with the ammonium nitrate, the poultry litter treatment plots had up to 40% more NO 3 in the 0–30 cm soil depth after the first year of study. Extractable P and soil pH at the end of the study were similar to those at the beginning. This study shows that no-till and mulch-till, winter rye cover cropping, and surface application of poultry litter in cotton production systems can rapidly increase surface SOM. The increase in SOM was attributed to less biological oxidation of crop residues and from soil C contributed by poultry litter. Crop uptake of N and P prevented a significant build up of these nutrients. These results are important to production systems in the US cotton belt where soil productivity is threatened by erosion because of low SOM levels and the safe disposal of poultry litter is becoming a major environmental problem.

Starter fertilizer and the method and rate of potassium fertilizer effects on cotton grown on soils with and without winter grazing by cattle1

A three‐year field study was conducted on a Decatur silt loam (clayey, kaolinitic, thermic Rhodic Paleudult) in North Alabama. The objective of the study was to evaluate the effects of winter grazing by cattle on the potassium (K) and starter fertilizer needs of cotton (Gossypium hirsutum L.) the following season. Grazed and non‐grazed treatments were established by planting a wheat (Triticum aestivum L.) cover crop in the fall and allowing cattle to graze half of the treatment area for 35 to 65 days in late winter‐early spring. After grazing, the grazed and non‐grazed wheat was killed and cotton was planted using a strip‐tillage system. Test areas had medium to high soil test ratings for K. Fertility treatments consisted of three rates of K (0, 37, and 74 kg K ha‐1), three methods of K application (surface broadcast; in‐row, band application at a depth of 30.5 cm; and surface banding using a spacing of 50.8 cm) and two rates of starter fertilizer (no starter and 168 kg#lbha‐l of a liquid 15–15–0). Seed cotton yields were affected by grazing of the winter cover crop prior to planting, but not by the method of K fertilizer application. During the two years that a yield reduction was observed, winter grazing reduced seed cotton yields by an average of 14%. Cotton responded to K rate only under the ungrazed system. During the first and second year of the test, an application of 37 kg K ha‐1 increased seed cotton yields by an average of 351 kg#lbha‐1. Starter fertilizer consistently gave slightly higher yields with a significant response occurring in two out of the three years.