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A reliable laboratory index of N 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.sub.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.sub.0], k (mineralization rate), and [N.sub.0.sup.*] ([N.sub.0] estimated with a fixed k equal to 0.054 [wk.sup.-1]). Out of 13 indices, five [total C (TC), total N (TN), N mineralized by hot KC1 (Hot_N), anaerobic N (Ana_N), and N mineralized in 24 d (Nmin_24)] were strongly correlated to NO (r > 0.85) and had linear regressions with [r.sup.2] > 0.60. None of the indices were good predictors of k. Correlations between indices and [N.sub.0.sup.*] improved compared with [N.sub.0], ranging from r = 0.90 to 0.95. Total N and flush of C[O.sub.2] determined after 3 d (Fl_C[O.sub.2]) produced the best multiple regression for predicting [N.sub.0] ([R.sup.2] = 0.85) while the best combination for predicting [N.sub.0.sup.*] ([R.sup.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. Abbreviations: Ana_N, anaerobic N mineralization; TC, total carbon; Ca_hypcl, calcium hypochlorite; Cold_N, KCl extractable N[O.sub.3]--N; CT, conventional tillage; Fl_CO2, flush of C[O.sub.2] during 3 d; Hot_N, hot KCl extractable N[H.sub.4]- -N; Hyd_N, hydrolyzable N; k, mineralization rate constant; TN, total nitrogen; NaOH_N, sodium hydroxide distillable N; [N.sub.0], potentially mineralizable N; [N.sub.0.sup.*], value of [N.sub.0] determined using a fixed value for k, Nmin_24, N mineralization during 24 d; NP, not plowed (prairie soil); NT, no-Tillage; NT+SS, no-tillage with non-inversion subsurface deep tillage; PB_N, phosphate- berate distillable N; POMC, particulate organic matter C; POMN, particulate organic matter N; SM, stubble mulch tillage (sweeps to undercut weeds); ST, strip tillage (in-row subsoil for disruption of subsurface pan and coulters for preparation of narrow strip of tilled soil).

Quantification of the impact of long-term agricultural land use on soil organic C (SOC) is important to farmers and policymakers, but few studies have characterized land use and management effects on SOC across physiographic regions. We measured the distribution and total stock of SOC to a depth of 20 cm under conventional tillage (CvT), conservation tillage (CsT), and pasture in 87 production fields from the Southern Piedmont and Coastal Plain Major Land Resource Areas. Across locations, SOC at a depth of 0 to 20 cm was: pasture (38.9 Mg [ha.sup.-1]) > CsT (27.9 Mg [ha.sup.-1]) > CvT (22.2 Mg [ha.sup.-1]) (P [less than or equal to] 0.02). Variation in SOC was explained by management (41.6%), surface horizon clay content (5.2%), and mean annual temperature (1.0%). Higher day content and cooler temperature contributed to higher SOC. Management affected SOC primarily at the soil surface (0-5 cm). All SOC fractions (i.e., total SOC, particulate organic C, soil microbial biomass C, and potential C mineralization) were strongly correlated across a diversity of soils and management systems (r = 0.85-0.96). The stratification ratio (concentration at the soil surface/concentration at a lower depth) of SOC fractions differed among management systems (P < 0.0001), and was 4.2 to 6.1 under pastures, 2.6 to 4.7 under CsT, and 1.4 to 2.4 under CvT; these results agree with a threshold value of 2 to distinguish historically degraded soils with improved soil conditions from degraded soils. This on-farm survey of SOC complements experimental data and shows that pastures and conservation tillage will lead to significant SOC sequestration throughout the region, resulting in improved soil quality and potential to mitigate C[O.sub.2] emissions. Abbreviations: CMIN, potential C mineralization; CsT, conservation tillage row cropping; CvT, conventional tillage row cropping; MLRA, Major Land Resource Area; MWD, mean-weight diameter; POC, particulate organic carbon; SMBC, soil microbial biomass carbon; SOC, soil organic C; SOM, soil organic matter.

Simulation models integrate our knowledge of soil organic C (SOC) dynamics and are useful tools for evaluating impacts of crop management on soil C sequestration; yet, they require local calibration. Our objectives were to calibrate the Environmental Policy Integrated Climate (EPIC) model, and evaluate its performance for simulating SOC fractions as affected by soil landscape and management. An automated parameter optimization procedure was used to calibrate the model for a site-specific experiment in the Coastal Plain of central Alabama. The ability of EPIC to predict corn (Zea mays L.) and cotton (Gossypium hirsutum L.) yields and SOC dynamics on different soil landscape positions (summit, sideslope, and drainageway) during the initial period of conservation tillage adoption (5 yr) was evaluated using regression and mean squared deviations. Simulated yield explained 88% of measured yield variation, with the greatest disagreement on the sideslope position and the greatest agreement in the drainageway. Simulations explained approximately 1, 34, and 40% of the total variation in microbial biomass C (MBC), particulate organic C (POC), and total organic C (TOC), respectively. The lowest errors in TOC simulations (0-20 cm) were found on the sideslope and summit. We conclude that the automated parameterization was generally successful, although further work is needed to refine the MBC and POC fractions, and to improve EPIC predictions of SOC dynamics with depth. Overall, EPIC was sensitive to spatial differences in C fractions that resulted from differing soil landscape positions. The model needs additional refinement for accurate simulations of field-scale SOC dynamics affected by short-term management decisions. Abbreviations: CT, conventional tillage; CTm, conventional tillage plus manure; EPIC, Environmental Policy Integrated Climate; FHP, fraction of humus in the passive pool; HI, harvest index; MBC, microbial biomass carbon; MSD, mean squared deviation; NT, no-till; NTm, no-till plus manure; PARM 20, microbial decay rate; PARM 51, microbial activity in the top layer; POC, particulate organic carbon; SOC, soil organic carbon; SOM, soil organic matter; TOC, total organic carbon; WA, biomass/energy ratio.

Integrating livestock with cotton (Gossypium hirsutum L.) offers profitable alternatives for producers in the southeastern USA, but could result in soil water depletion and soil compaction. We conducted a 3-yr field study on a Dothan loamy sand (fine-loamy, kaolinitic, thermic Plinthic Kandiudult) in southern Alabama to develop a conservation tillage system for integrating cotton with winter-annual grazing of stocker cattle under rainfed conditions. Winter annual forages and tillage systems were evaluated in a strip-plot design where winter forages were oat (Avena sativa L.) and annual ryegrass (Lolium mutiflorum L.). Tillage systems included moldboard and chisel plowing and combinations of noninversion deep tillage (none, in-row subsoil, or paratill) with or without disking. We evaluated forage dry matter, N concentration, average daily gain, net returns from grazing, soil water content, and cotton leaf stomatal conductance, plant populations, and yield. Net returns from winter-annual grazing were between US$185 to US$200 [ha.sup.-1] [yr.sup.-1]. Soil water content was reduced by 15% with conventional tillage or deep tillage, suggesting that cotton rooting was increased by these systems. Oat increased cotton stands by 25% and seed-cotton yields by 7% compared with ryegrass. Strict no-till resulted in the lowest yields--30% less than the overall mean (3.69 Mg [ha.sup.-1]). Noninversion deep tillage in no-fill (especially paratill) following oat was the best tillage system combination (3.97 Mg [ha.sup.-1]) but deep tillage did not increase cotton yields with conventional tillage. Integrating winter-annual grazing can be achieved using noninversion deep tillage following oat in a conservation tillage system, providing producers extra income while protecting the soil resource. Abbreviations: AAES, Alabama Agricultural Experiment Station; ACES, Alabama Cooperative Extension System; DOY, day of year.

In August of 1995, six researchers from the United States were invited to observe conservation farming systems in the mountains and rolling hills of Rio Grande do Sul, in the [...]

Winter cereals are often used as cover crops before planting cotton (Gossypium hirsutum L.). Black oat (Avena strigosa Schreb.) is the predominate cereal cover crop for cash crops in southern Brazil and Paraguay, but limited information is available on the suitability of black oat as a cover crop in the southeastern USA. The objectives of this study were to compare black oat with adapted winter cereals for this region and to determine the effect of cereal residue species and amount on cotton growth, N status, and lint yield, in a greenhouse study in which black oat and rye (Secale cereale L.) residues were mixed with soil, tap root elongation of both cotton and radish (Raphanus sativa L.) was inhibited more by black oat residue than by rye residue. In a field experiment on a Goidsboro loamy sand (fine-loamy, siliceous, thermic Aquic Kandiudult), cotton was grown in 1995 and 1996 following black oat, oat (Avena sativa L.), rye, and wheat (Triticum aestivum L.) that were planted at three different times (October, November, and December). All four winter cereals had similar biomass production at each planting date in 1995. In 1996, rye was the only species not visibly damaged by a low temperature of -12.2 ° C that occurred during the winter. Black oat biomass was comparable to wheat in all planting dates but averaged 60% less than rye over all three planting dates and was 37% less than oat in the October planting date in that year. Black oat tended to have a higher N concentration than the other cereal species. Cotton plant density was lowest following black oat and rye. Cotton growth, leaf blade N, and petiole [NO.sub.3]-N were more dependent on residue amount than on residue species. Cotton lint yield following black oat was 120 kg [ha.sup.-1] higher than lint yield of cotton following rye. Cotton following black oat, wheat, and oat had similar lint yield. Black oat may be a promising cover crop for the southeastern USA, but evaluations of other cultivars and/or improvement programs to improve cold hardiness are needed to improve the utility of this species., WINTER CEREALS are often used for as cover crops for cotton because they grow rapidly in the fall and provide ground cover throughout the winter. Several winter cereal species, including [...]

The impact of conservation tillage, crop rotation, and cover cropping on soil-quality indicators was evaluated in a long-term experiment for cotton. Compared to conventional-tillage cotton, other treatments had 3.4 to 7.7 Mg ha-1 more carbon (C) over all soil depths. The particulate organic matter C (POMc) accounts for 29 to 48 and 16 to 22% of soil organic C (SOC) for the 0- to 3-and 3- to 6-cm depths, respectively. Tillage had a strongth influence on POMc within the 0- to 3-cm depth, but cropping intensity and cover crop did not affect POMc. A large stratification for microbial biomass was observed varing from 221 to 434 and 63 to 110 mg kg-1 within depth of 0-3 and 12-24 cm respectively. The microbial biomass is a more sensitive indicator (compared to SOC) of management impacts, showing clear effect of tillage, rotation, and cropping intensity. The no-tillage cotton double-cropped wheat/soybean system that combined high cropping intensity and crop rotation provided the best soil quality. [ABSTRACT FROM AUTHOR]

Cotton (Gossypium hirsutum L.) growers have adopted no-tillage systems with a cover crop in the Tennessee Valley under non-irrigated conditions, but a comparison of plant and soil parameters across irrigated tillage systems has not been investigated in this region of Alabama. This study was conducted to compare seed cotton yields, whole plant biomass, leaf nitrogen (N) concentrations at mid-bloom, soil moisture contents at two depths, and leaf stomatal conductance on a Decatur silt loam across different tillage systems and irrigation regimes during the 2001 to 2003 growing seasons. Treatments were arranged as a split-plot in a randomized complete block design with three replications. Tillage systems (conventional tillage; no cover crop and no surface tillage with a cover crop both with and without fall paratillage) were the main plots, and irrigation regimes (0, 2.7, 5.4, 8.1 mm day-1) were the subplots. Tillage system and irrigation regime increased seed cotton yields two out of three years, and leaf stomatal conductance during a drought year. No surface tillage, regardless of fall paratillage, produced 15% more whole plant biomass than conventional tillage treatments one of three years, while an irrigation rate of 5.4 mm day-1 maximized plant biomass two of three years. Leaf N concentrations at mid-bloom were approximately 7% lower in the no surface tillage systems compared with the conventional tillage systems when averaged across all three years. Differences in soil water contents were only observed in 2001 with soil water contents 15% lower in the 0 to 20-cm depth following fall paratillage compared with no fall paratillage. Higher soil moisture contents were observed in the conventional tillage system following paratillage, while soil moisture contents following no fall paratillage were higher in the no surface tillage system in the 20- to 40-cm depth. Results of these plant and soil measurements suggest that cotton growers in the Tennessee Valley using irrigation should not change from the recommended conservation tillage system with a cover crop. [ABSTRACT FROM AUTHOR]

Focuses on the findings of the Agricultural Research Service (ARS) that the Tropic Sunn, a United States Department of Agriculture (USDA) developed variety of sunn hemp for the South, grows to its full 6-foot height in ten weeks. Time that the sunn hemp, Crotalaria juncea can be planted; Benefit from the tropic sun; Investigation of the ARS on the sunn hemp fibers.