Soil nutrient dynamics and rye cover crop efficacy to remediate

1. Soil nutrient dynamics and rye cover crop efficacy to remediate nutrient accumulation in broiler litter amended soils Annesly Netthisinghe, Becky Gilfillen, William Willian, and Naomi Rowland Department of Agriculture, Western Kentucky University, 1906 College Heights Blvd. 41066, Bowling Green, KY 42101. ABSTRACT Poultry litter has long been recognized as a good source of plant nutrients with greate potential for supporting many forage cropping systems. Farmers generally prefer disposing of larger volumes of poultry litter to their cropping lands. However, one major problem of soil amendment with high rates of poultry litter is accumulation of macro and micronutrients. This study was developed to examine how soil nutrient accumulation from poultry litter could be remediated through winter cover cropping. Sorghum-sudangrass fertilized with four different poultry litter application regimes were tested with rye cover cropping and winter fallow from 2005-2008. The four poultry litter application regimes used were, inorganic N, P, K fertilizer (I), poultry litter applied at recommended P rate (PLP), at recommended N rate (PLN), and at recommended P rate with supplemental inorganic N fertilizer (PLP+N). A randomized complete block design with split plot consisting of year as main plot and factorial combinations of broiler litter fertility regimes and cover crop treatments as sub-plot was utilized. Soil samples were analyzed for P, K, Mg, S, Cu, Zn, Fe, and Na contents. Results of this study indicate, that one year after sorghum-sudangrass establishment, there was P, K, Mg, S, Cu, Zn, and Na accumulation in high poultry litter amended PLN soils.However, after three cycles, rye cover cropping reduced Mg, Cu, and Na concentrations in high broiler litter amended PLN soils to levels similar in low poultry litter amendments. At this stage, there was no evidence for significant removal of P, K, S, and Zn by rye cover crop in the high poultry litter amended PLN soils. Phosphorus, K, S, and Zn contents in these soils were well below their fallow counterparts, but they were not as low as in other low poultry litter amended PLP and PLP+N soils. Indications are that the remediation process by a cover crop is fast and effective at lowering Mg, Cu, and Na concentrations when poultry litter application was based on crop N requirement, but P, K, S, and Zn contents are still at high levels. INTRODUCTION Poultry litter has long been recognized as a good source of plant nutrients with great potential to be used in production agriculture (Nyakatawa et al. 2001)). Poultry litter contains a relatively low N/P ratio (Sims and Wolf, 1994) that usually does not match with the high N/P ratio of forage crops (Robinson, 1996). When broiler litter is applied at higher rates, this incongruent N/P ratios can lead to accumulation of excess soil nutrients (Siatani et al., 2004; Han et al., 2000). Increased soil nutrient accumulation may enhance the potential for loss in surface runoff and leaching (Sharpley et al., 1993) causing environmental problems. However, with proper crop, manure and nutrient management practices, poultry litter can support plant nutrient requirements of many forage-cropping systems (Edwards, 1996) . Sorghum-sudangrass, is a high N responsive summer hay crop (Wanjari et al., 1996) that produce high biomass yields. With these agronomic properties, sorghum-sudangrass could become a good recipient for poultry litter application. However, repeated high poultry litter application rates to sorghum-sudangrass has shown elevated soil nutrient levels (Sleugh et al., 2006) . This study was developed to test the efficacy of cover cropping as a best management practice to remediate soil nutrient accumulation by poultry litter amendment. The objective of this study was to investigate if harvesting rye as a cover crop would reduce soil nutrient loading from broiler litter better than sorghum-sudangrass grown alone. MATERIALS AND METHODS A four-year study was conducted from 2005 through 2008 at the Western Kentucky University Agricultural Research and Education Complex in Bowling Green, Kentucky on a Pembroke silt soil. The experiment was laid out as a randomized complete block design with four replications. Four fertility regimes, broiler litter at recommended nitrogen rate (PLN), phosphorus rate (PLP), phosphorus rate supplemented with inorganic nitrogen (PLP+N), and inorganic fertilizer with no litter (I) and winter rye (C) vs. fallow (F) cropping were tested. All fertility regime treatments were imposed once before planting the sorghum-sudangrass in late spring. Beginning in fall 2005 through 2007, rye was planted on the residual fertility of sorghum-sudangrass growth. One composite soil sample composed of 15-20 sub samples was taken in spring 2005 to characterize initial soil nutrient status of the site. Subsequent soil sampling was performed after rye cover crop growing period in each year. Soil samples were analyzed for P, K, Mg, S, Cu, Fe, Zn and Na contents. RESULTS Initial and end of experiment soil fertility characteristics of treatments. Soil nutrient change in the PLN treatment with cover crop and fallow for 2006-2008. Average nutrient amounts from broiler litter and inorganic fertilizer applied to sorghum-sudangrass during 2005-2008. CONCLUSIONS Repeated application of high broiler litter rates to sorghum – sudangrass tends to accumulate P, K, Mg, S, Cu, Zn, and Na in soils. 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Digest. 16:25-27. † PLN - Poultry litter N rate I -Inorganic fertilizer PLP + N- Poultry litter P rate with inorganic N PLP - Poultry litter at P rate ‡ Broiler litter Authors wish to acknowledge the USDA-ARS for providing funding for this research.