Aluminum sulfate [Al2(SO4)3·14H2O] applications to poultry litter can greatly reduce P concentrations in runoff from fields fertilized with poultry litter, as well as decrease NH3 volatilization. The objective of this study was to evaluate metal runoff from plots fertilized with varying rates of alum‐treated and untreated (normal) poultry litter. Alum‐treated (10% alum by weight) and untreated litter was broadcast applied to small plots in tall fescue (Festuca arundinacea Schreb.). Litter application rates were 0, 2.24, 4.49, 6.73, and 8.98 Mg ha−1 (0, 1, 2, 3, and 4 tons acre−1). Rainfall simulators were used to produce two runoff events, immediately after litter application and 7 d later. Both concentrations and loads of water‐soluble metals increased linearly with litter application rates, regardless of litter type. Alum treatment reduced concentrations of As, Cu, Fe, and Zn, relative to untreated litter, whereas it increased Ca and Mg. Copper concentrations in runoff water from untreated litter were extremely high (up to 1 mg Cu L−1), indicating a potential water quality problem. Soluble Al, K, and Na concentrations were not significantly affected by the type of litter. Reductions in trace metal runoff due to alum appeared to be related to the concentration of soluble organic C (SOC), as well as the affinity of SOC for trace metals. Metal runoff from alum‐treated litter is less likely to cause environmental problems than untreated litter, since threats to the aquatic environment by Ca and Mg are far less than those posed by As, Cu, and Zn.

In recent years an expansion of rice (Oryza sativa L.) acreage in Arkansas has resulted in rice being produced on soils with a history of cotton production. Most of these cotton soils have had repeated applications of monosodium methanearsonate (MSMA) as a herbicide. There is some evidence that arsenical residues in the soil can lead to sterility in rice. In an effort to answer this question, we conducted a field experiment on a Crowley silt loam soil (Typic Albaqualf) in 1975 to evaluate the influence of MSMA on plant growth and yield of rice. Treatments included two water management regimes (continuous flood vs. one drain and dry), three levels of MSMA [0, 1.1, and 11.2 kg/ha of arsenic (As)] and 15 rice cultivars and experimental strains differing in susceptibility to straighthead disease (abnormally developed or sterile flowers resulting in reduced grain yields). Soil samples taken 65 days after arsenic application showed that As remained in the rice root zone. Vegetative growth prior to panicle initiation was not affected by any of the treatments; however, visual observations made near maturity showed that where MSMA had induced sterility, the plants were dark green suggestive of straighthead. Reproductive growth as shown by panicle weights and sterility ratings was affected most by high MSMA rates and continuous flooding. Under continuous flood, panicle weights were reduced and sterility ratings increased as MSMA rate increased. This effect was more pronounced in cultivars most susceptible to straighthead and was minimized by draining the flood and drying the soil. This data suggests that the MSMA residues induced straighthead. A significant and similar relationship was found between panicle weights and sterility ratings at maturity for both water management regimes.

A kinetic description of crop residue decomposition makes assessment of the global C cycle and nutrient cycling possible for a wide variety of crop production systems. It was the objective of this study to compare decomposition kinetics of soybean [Glycine max (L.) Merr.], rice (Oryza sativa L.) and grain sorghum [Sorghum bicolor (L.) Moench.] residues for 3 yr to determine if variability among years was similar to that among crops. Crop residues were incorporated into a Crowley silt loam (fine, montmorillonitic, thermic Typic Albaqualf) soil and incubated at 25°C under optimum soil moisture for 54 to 66 d. Initial (0–2‐wk) decomposition was related to crop residue organic N and C/N ratio, while subsequent decomposition was not related to these factors. Decomposition data were evaluated using first‐order kinetics and sequential and simultaneous decomposition models. As a result of the variability among crops and years, which was not related to residue characteristics (organic N or C/N ratio), it was concluded that mean estimates of rate constants and the rapid fraction would provide a reasonable estimate of crop residue decomposition for a variety of crops using either decomposition model. For the sequential model, mean rapid‐ and slow‐fraction rate constants were 0.025 and 0.0091 d−1, respectively, while the rapid fraction was 31%. Parallel values for the simultaneous model were 0.21 and 0.0080 d−1 and 20%.

The ability to estimate net N mineralization from C decomposition data has the potential to improve our understanding of N dynamics in soil systems. It was the objective of this study to study this relationship using substrates with varying decomposition rates and C/N ratios. Five substrates including sewage sludge, alfalfa (Medicago sativa L.), clover (Trifolium sp.), bermudagrass [Cynodon dactylon (L.) Pers.] and ryegrass (Lolium multiflorum Lam.) were incubated in Crowley silt loam (Typic Albaqualfs) or Captina silt loam (Typic Fragiudults) soil at known soil temperatures and moistures. Concurrent CO2 evolution and soil inorganic N concentrations were measured periodically. A significant linear relationship between N mineralization and CO2 evolution was found experimentally for each substrate. A computer simulation model was developed which used first order kinetics for conversion of substrate C to CO2. Substrate C mineralization rate constants, substrate C/N ratios and microbial efficiency were primary inputs, while substrate, biomass, and soil organic matter were the major compartments of the model. Microbial efficiency was defined for any C pool undergoing decomposition as the ratio of assimilated C to assimilated C plus dissimilated C. An important feature of the approach was the introduction of a fraction with a C/N ratio of protein that decomposed very rapidly for those substrates where initial N mineralization was large while CO2 evolution was small. Model predictions of both CO2 evolution and net N mineralization were in good agreement with experimental results.

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