1a. Objectives (from AD-416):
1. Develop practices to enhance the beneficial use of manure nutrients and reduce offsite losses through management of the environmental fate and transport of organic carbon, nitrogen, and phosphorus derived from poultry, dairy, and beef cattle manures. 2. Develop integrated crop, soil, and dairy/beef/poultry manure management strategies to improve nutrient utilization and minimize leaching and runoff losses.
1b. Approach (from AD-416):
Real-time tools for rapid C, N, and P detection and multi-element analysis of manures, soils, and crops will be evaluated and adapted to develop precision nutrient management practices under changing soil microenvironment and weather conditions. Process knowledge affecting C, N, and P transformations and detection will be gained to establish databases and develop algorithms to assist in the management of bionutrient mineralization and availability in conservation cropping systems.
3. Progress Report:
Knowing nutrient contents of soil and crops, as close to real time as possible, allows timely management adjustments in response to changes in nutrient availability during the growing season. An X-ray fluorescence method was evaluated for its nutrient-specific ability to differentiate variations in phosphorus in crop seedlings. While irradiating a sample with incident X-rays, their intensity weaken as function of radiation energy and nutrient elements present in the sample. Light elements that include essential plant nutrients such as phosphorus, potassium, sulfur, etc… emit fluorescence radiation of long wavelength and low-energy. This resulted in low analytical sensitivity. In addition, these characteristic radiations were further attenuated by water content of fresh leaves. Calibrations for crop type and leaf characteristics were made to derive leaf nutrient composition, and for making comparison under varied field conditions. The adjustment and a high throughput screening of a crop canopy allowed a greater number of analyses under actual growing conditions across a large field. The ability of making on-the-spot analysis and the production of a spatial map of crop phosphorus status offer promise in managing phosphorus variability that are directly linked to actual crop phosphorus needs in order to reduce risks of environmental contamination from recycling manure nutrients on agricultural fields. Ammonia volatilization from surface-applied poultry litter can account for one-fourth to one-half of the litter’s ammonia nitrogen. A series of wind tunnel studies were completed that evaluated methods to reduce ammonia loss, yet retain high surface residue cover for erosion control. These studies were the basis for a manuscript that has been accepted for publication in a peer reviewed journal, but the paper has not been assigned an issue or pagination. The data showed that compared to surface-applied litter, ammonia volatilization decreased an average of 67% by light disking, and decreased 88% when litter was applied below the soil surface using the prototype applicator developed by ARS collaborators in Arkansas. These results show that subsurface injection of dry poultry litter can minimize ammonia loss, thus conserving nitrogen for row crops and reducing potential nitrogen losses to the environment. Cover crops can provide a valuable service by conserving residual nitrogen after corn. The recovery of isotope-labeled fertilizer was used to directly compare the ability of rye, wheat, and native weeds to recover residual N applied to a preceding corn-silage crop. The field phase of this study was completed, which involved collection of soil and crop samples in the early winter, early spring, and late spring. These samples are being analyzed for labeled N to follow changes in soil nitrate and the uptake of labeled N by the winter crops. This study will quantify the effectiveness of cover crop management strategies for capturing residual nitrate, which will reduce nitrate losses to ground water and the Chesapeake Bay.
1. Use-efficiency of phosphorus in agricultural fields is declining. Managing the decline is to know well the type and proportion of inorganic and organic phosphorus forms present in soil. An ARS scientist implemented a long-term study to determine whether a linkage exists between zones of phosphorus accumulation in a large field amended with dairy manure. Results showed that applying manure at a replacement rate equal to that removed by crops did not prevent overall accumulation of available and total phosphorus in these soils. Current comprehensive nutrient management plans involving efforts to control land application of animal manure by limiting phosphorus input rates to that removed by crops may be a pragmatic approach but an ineffective one, given weaknesses of current field management practices. The distribution of phosphorus forms in the soil is very uneven after 16 annual applications of dairy slurry. There are changes in the ratio of inorganic-to-organic forms and their uneven distribution across the field modified biological properties, microbial ecology, transformations between phosphorus forms in the root zone, and risks of losses at the soil surface. Knowing only water-soluble and total phosphorus content as currently required in management of total contaminant loading to nearby water bodies is inadequate for assessing phosphorus availability or for predicting losses and risk of contamination by edge-of-field runoff. Producers and land managers should be aware of inadequacies of manure nutrient application practices currently in use in conservation row crop production. The variability in the ratio of phosphorus forms persisted over the years and the phenomenon distorts the picture of phosphorus availability in the field, and the formulation of phosphorus recommendations for future growing seasons should an average value of field phosphorus status be used.
2. Opportunities to manage residual nitrate after drought are increasing. Residual nitrate following corn can readily be transported into water resources during the fall-spring water-recharge season in the Humid East. Residual nitrate is highly variable from site-to-site and year-to-year, which prompted a series of studies to evaluate crop monitoring techniques for forecasting sites likely to have high residual nitrate. Results showed that drought was a major factor linked to high residual nitrate. Measures of late-season crop water stress, such as canopy reflectance of visible and near infrared light that can be measured remotely, can provide early identification of drought sites. This early identification of high residual nitrate sites can provide opportunities for targeting cover crops to these sites, which can reduce nitrate losses to water resources during the subsequent water-recharge season in humid regions.
3. A new analytical method for ammonia can monitor ammonia emissions in real time. The development of a new method to measure ammonia losses can improve nitrogen recovery in agriculture and reduce nitrogen losses to the environment. The new ammonia method is based on monitoring the pH changes of an acid trapping solution. The method is accurate and precise, and can rapidly and non-destructively monitor ammonia accumulations in the trapping solution. The new method’s ability to continuously monitor ammonia emissions can provide insights for further developing management practices to reduce ammonia emissions from agriculture.Forrestal, P.J., Kratochvil, R.J., Meisinger, J.J. 2011. Late-season corn measurements to assess soil residual nitrate and nitrogen management. Agronomy Journal. 104:148-157.