Managing swine manure in double-crop soybean
Animal production, especially swine (Sus scrofa domesticus) and poultry, has increased in the United States prompting the need to manage the larger volume of manure beyond land applications to supply nitrogen (N) for corn (Zea mays) production. Applying swine manure to soybean (Glycine max) has been shown to increase grain yield due to N supply. The goal of this research was to determine if swine manure applications to double-crop soybean following wheat can limit manure N loading to the soil by extending management options, increase soybean biomass and grain production, and increase N removal rates. Manure N availability to soybean and potential manure N loss were also to be determined. Four field-scale trials were initiated in 2012 near Russiaville, IN and Farmland, IN and in 2013 near Farmersburg, IN and Fort Branch, IN. Three rates of swine manure were applied that ranged from 116 to 599 kg N ha-1 depending on location. Fertilizer UAN was also applied at 168, 336, and 504 kg N ha -1, and an untreated control (UTC) was included to total seven treatments. Biomass and nutrient accumulations were determined with plant samples at full bloom (R2) and full seed (R6), and grain subsamples at harvest. Soil N was determined for the 0 to 30 and 30 to 60 cm depths at R2 and post-harvest, and soils were incubated at 25¢ªC and -0.33 bar water content for zero, four, eight, and sixteen (2012 only) weeks. Swine manure application increased soybean grain yield in conjunction with increased application rates in 2012 at Russiaville. This increase of yield was preceded by increased biomass accumulation at R2, but N application generally did not affect biomass accumulation at R6. All treatments supplied more N in the top 60 cm of soil after harvest compared to the UTC. In 2013, effects of swine manure application to soybean were negligible to negative. At Farmersburg, grain yield was negatively affected by manure application, and significant amounts of soil N were present after harvest in the manure-amended plots. At Fort Branch, biomass, grain yield, grain N removal, and post-harvest soil N were not affected by swine manure application suggesting less benefit from swine manure in a high yield environment with adequate moisture. Manure and UAN increased soil N levels compared to the UTC at sampling times (wk 0), but generally did not affect N release. Differences in N levels among treatments stayed constant throughout incubation indicating that mineralization rates were similar across treatments. Additional N from swine manure application was present throughout the growing season, including post-harvest if conditions were dry or the yield environment was low. This presented a potential for N loss through nitrate leaching during the winter if N was not accumulated in the soybean crop, removed by grain, or lost during the season. Overall, manure application to double-crop soybean can be a sound manure management option if it can be executed with minimal soil disturbance, and it is especially beneficial for those producers that need to free up manure storage space.
Casteel, Purdue University.
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