Miguel L. Cabrera

Nitrogen mineralization in soils amended with composted and uncomposted poultry litter

Abstract When applied to land, poultry litter can be a valuable source of plant macro‐ and micro‐nutrients. However, if poultry litter is overapplied, then its mineralized nitrogen (N) can contaminate ground and surface waters. Composting poultry litter may slow down the rate of N mineralization thereby reducing the risk of environmental pollution. The objective of this work was to determine if N mineralization from composted poultry litter is slower than that from uncomposted poultry litter when these materials are mixed with soil. Two composted broiler litters, one composted hen manure, and two uncomposted broiler litters were mixed with Dothan loamy sand (pH 4.3) and Hiwassee fine sandy loam (pH 5.5), and incubated at 25°C for 56 d. Subsamples for inorganic N determinations were taken at 1, 2, 4, 7, 14, 21, 28, and 56 d. After 56 d, the proportion of organic N mineralized ranged from 0.4 to 5.8% for the composted materials, and from 25.4 to 39.8% for uncomposted broiler litters. These results indicate ...

Assessing Indices for Predicting Potential Nitrogen Mineralization in Soils under Different Management Systems

A reliable laboratory index ofN 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 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 0 , k (mineralization rate), and N 0 * (N 0 estimated with a fixed k equal to 0.054 wk -1 ). Out of 13 indices, five [total C (TC), total N (TN), N mineralized by hot KCI (Hot_N), anaerobic N (Ana_N), and N mineralized in 24 d (Nmin_24)] were strongly correlated to N 0 (r > 0.85) and had linear regressions with r 2 > 0.60. None of the indices were good predictors ofk. Correlations between indices and N 0 * improved compared with N 0 , ranging from r = 0.90 to 0.95. Total N and Hush of CO 2 determined after 3 d (Fl_CO2) produced the best multiple regression for predicting N 0 (R 2 = 0.85) while the best combination for predicting N 0 * (R 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.

Temperature and moisture effects on C and N mineralization from surface applied clover residue

A better understanding of the effect of temperature (T) and moisture on soil microbial activity should improve our ability to predict N mineralization from soil organic matter and crop residues. The objective of this study was to evaluate the effects of water potential (ψ) and T on C and N mineralization from unamended Cecil loamy sand soil (clayey, kaolinitic, thermic Typic Kanhapludult) and from crimson clover (Trifolium incarnatum L.) residues applied on the soil surface. Cecil soil was packed into acrylic plastic cylinders, adjusted to -5.0, -1.5, -0.03, or -0.003 MPa, treated with clover residues on the surface or left unamended, and incubated at 10, 20, 28, or 35°C for 21 d. Headspace gas samples for CO2 and N2O determinations were taken periodically and NH3 evolved was trapped. Inorganic N in soil and residue extracts was analyzed after 21 d. When ψ increased from -5.0 to -0.003 MPa, total CO2 evolved from unamended soil increased linearly with ln(-ψ), whereas total CO2 evolved from clover residue increased exponentially with ψ. In both cases the effect of ψ was enhanced as T increased. Two-dimensional (T, ψ) equations were developed to describe these effects. Apparent net mineralized N from the clover residue increased with ψ until it reached a maximum between -0.5 and -0.03 Mpa.

Effects of drying and rewetting on carbon and nitrogen mineralization in soils and incorporated residues

An understanding of nitrogen mineralization from residues and soil organic matter is important to understand the quantity of N available from the soil for crop production. The objective of this study was to determine effects of repeated wetting and drying of soils on rates of N mineralization. The study compared mineralization rates in three kaolinitic, low organic matter soils, utilizing cotton leaves or compost as residues. One set of treatments was subjected to repeated drying and rewetting, whereas the other was kept at constant moisture content. Mineralized N was measured by leaching with 0.01 M CaCl2 periodically, for 185 days. Rates of C mineralization were measured in the treatment containers by periodic measurement of CO2 respiration rates. In constant moisture conditions, soils with cotton leaf residue mineralized between 25% and 40% of N applied as residue, whereas soils with compost mineralized between 3.8% and 9.3%. In fluctuating moisture conditions, soils with cotton leaf residue mineralized between −1.3% and 6.9%, whereas soils with compost mineralized from 1.6% to 3.3%. Moisture effect was not significant in soils without residue, with soils mineralizing between 16 and 47 mg N kg–1. Carbon mineralization rates were not significantly affected by moisture. Both residue and soil type affected rates of C mineralization.

Nutrient losses in surface and subsurface flow from pasture applied poultry litter and composted poultry litter

Over application of poultry litter may cause pollution of surface and ground water. Spatial variability in soil characteristics makes predictions difficult. Composting poultry litter could reduce the risk of pollution by creating more stable organic components. Three rates of poultry litter and compost (10 Mg ha-1 litter, 20 Mg ha-1 litter and 10 Mg ha-1 litter combined with 50 Mg ha-1 compost) to three watersheds under pasture. The watersheds were monitored for surface and subsurface flow. Nitrate-N concentrations in subsurface flow did not exceed the U.S. Environmental Protection Agency drinking water standard of 10 mg L-1. Soluble phosphorus concentrations in runoff were high, reaching a maximum of 8.5 mg L-1 under the compost treatment. These concentrations are generally lower than reported on smaller scale studies, which shows the need of studies at the correct scale.

Ligninase-mediated removal of natural and synthetic estrogens from water: II. Reactions of 17β-estradiol.

We have demonstrated in our earlier work that a few natural and synthetic estrogens can be effectively transformed through reactions mediated by lignin peroxidase (LiP). The behaviors of such reactions are variously influenced by the presence of natural organic matter (NOM) and/or veratryl alcohol (VA). Certain white rot fungi, e.g. Phanerochaete chrysosporium, produce VA as a secondary metabolite along with LiP in nature where NOM is ubiquitously present. Herein, we report a study on the products resulting from LiP-mediated oxidative coupling reactions of a representative estrogen, 17beta-estradiol (E2), and how the presence of NOM and/or VA impacts the formation and distribution of the products. A total of six products were found, and the major products appeared to be oligomers resulting from E2 coupling. Our experiments revealed that these products likely formed colloidal solids in water that can be removed via ultrafiltration or settled during ultracentrifugation. Such a colloidal nature of the products could have important implications in their treatability and environmental transport. In the presence of VA, the products tended to shift toward higher-degree of oligomers. When NOM was included in the reaction system, cross-coupling between E2 and NOM appeared to occur. Data obtained from E-SCREEN test confirmed that the estrogenicity of E2 can be effectively eliminated following sequential reactions mediated by LiP.

Anoxia-induced release of colloid- and nanoparticle-bound phosphorus in grassland soils.

Particle-facilitated transport is a key mechanism of phosphorus (P) loss in agroecosystems. We assessed contributions of colloid- and nanoparticle-bound P (nPP; 1-415 nm) to total P released from grassland soils receiving biannual poultry litter applications since 1995. In laboratory incubations, soils were subjected to 7 days of anoxic conditions or equilibrated at pH 6 and 8 under oxic conditions and then the extract was size fractionated by differential centrifugation/ultrafiltration for analysis of P, Al, Fe, Si, Ti, and Ca. Selected samples were characterized by transmission electron microscopy-energy dispersive spectroscopy (TEM-EDS) and field flow fractionation (FFF-ICP-MS). Particles released were present as nanoaggregates with a mean diameter of 200-250 nm, composed of ~50-nm aluminosilicate flakes studded with Fe and Ti-rich clusters (<10 nm) that contained most of the P detected by EDS. Anoxic incubation of stimulated nPP release with seasonally saturated soils released more nPP and Fe(2+)(aq) than well-drained soils; whereas, nonreductive particle dispersion, accomplished by raising the pH, yielded no increase in nPP release. This suggests Fe acts as a cementing agent, binding to the bulk soil P-bearing colloids that can be released during reducing conditions. Furthermore, it suggests prior periodic exposure to anoxic conditions increases susceptibility to redox-induced P mobilization.

Land Application of Manure for Beneficial Reuse

The concentration of animal production systems has increased efficiency and improved overall economic return for animal producers. This concentration, along with the advent of commercial fertilizers, has led to a change in the way animal producers view manure. Manure, once valued as a resource by farmers, is now treated as a waste. Air and water quality concerns that arise primarily from the under-utilization or inefficient use of manure contribute to these changing views. However, when properly used, manure is a resource and should be regulated as such. In the United States, the USDA/EPA Unified National Strategy for Animal Feeding Operations outlines how animal feeding operations should be regulated and acknowledges that land application at proper agronomic rates is the preferred use for manures. However, many limitations such as water quality concerns, uncertainty in manure nutrient availability, high transportation costs, and odor concerns cause some to question land application. This paper documents the benefits of land application of manure, discusses limitations that hinder greater manure utilization, and outlines research and extension needs for improving manure utilization.

Influence of cover crops on potential nitrogen availability to succeeding crops in a Southern Piedmont soil

Winter cover crops are essential in conservation tillage systems to protect soils from erosion and for improving soil productivity. Black oat (Avena strigosa Schreb) and oilseed radish (Raphanus sativus L.) could be useful cover crops in the southeastern USA, but successful adoption requires understanding their influence on N availability in conservation tillage systems. Black oat and oilseed radish were compared to crimson clover (Trifolium incarnatum L.) and rye (Secale cereale L.) for biomass production and effects on N mineralization during the summer crop growing season from fall 1998 through summer 2002 near Watkinsville, GA. Rye produced 40 to 60% more biomass, although N contents were less than the other cover crops. Oilseed radish and black oat N contents were similar to crimson clover. Black oat, oilseed radish, and crimson clover C/N ratios were less than 30, whereas rye averaged 39. Amount of N mineralized in 90 days (Nmin90) measured with in situ soil cores was 1.3 to 2.2 times greater following black oat, crimson clover, and oilseed radish than following rye. No differences in Nmin90 were found between black oats, crimson clover, and oilseed radish in 1999 and 2000. The amount of potentially mineralizable N (N0) was not different due to cover crop, but was 1.5 times greater in 2000 and 2002 than in 1999. The rate of N mineralization (k) was 20 to 50% slower following rye than the other three cover crops. Black oat and oilseed radish biomass production and soil N mineralization dynamics were more similar to crimson clover than to rye, which indicates that they could be used as cover crops in the southeast without significant changes in N recommendations for most crops.

Modeling Phosphorus in the Environment

Basic Approaches Modeling Phosphorus Movement from Agriculture to Surface Waters, A. Sharpley Modeling Runoff and Erosion in Phosphorus Models, M.L. Wolfe Modeling Phosphorus in Runoff: Basic Approaches, M.L. Cabrera Basic Approaches to Modeling Phosphorus Leaching, N.O. Nelson and J.E. Parsons Phosphorus Transport in Streams: Processes and Modeling Considerations, B.E. Haggard and A.N. Sharpley Uncertainty Estimation in Phosphorus Models, K. Beven, T. Page, and M. McGechan Models Phosphorus Modeling in Soil and Water Assessment Tool (SWAT) Model, I. Chaubey, K.W. Migliaccio, C.H. Green, J.G. Arnold, and R. Srinivasan Modeling Phosphorus with Hydrologic Simulation Program-Fortran, D.E. Radcliffe and Z. Lin Phosphorus Modeling in the Annualized Agricultural Nonpoint Source Pollution (AnnAGNPS) Model, Y. Yuan, R.L. Bingner, and I. Chaubey Answers-2000: A Nonpoint Source Pollution Model for Water, Sediment, and Phosphorus Losses, F. Bouraoui and T.A. Dillaha Watershed Ecosystem Nutrient Dynamics - Phosphorus (WEND-P) Models, R.L. Kort, E.A. Cassell, and S.G. Aschmann Modeling Phosphorus with the Generalized Watershed Loading Functions (GWLF) Model, E.M. Schneiderman Phosphorus Indices, Best Management Practices, and Calibration Data Phosphorus Indices, J. Weld and A. Sharpley Challenges to Using and Implementing Phosphorus Indices in Nutrient Management Planning: an MMP Perspective, P. Hess, B. Eisenhauer, and B. Joern Quantifying the Effects of Phosphorus Control Best Management Practices, M.W. Gitau and T.L. Veith Small Watershed Data Collection to Support Phosphorus Modeling, D. Harmel and B. Haggard Modeling in the Future Suggestions to Improve Modeling of Phosphorus, D.E. Radcliffe and M.L. Cabrera Index