Submitted to: Applied Engineering in Agriculture
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/9/2004
Publication Date: 11/2/2004
Citation: Karlen, D.L. 2004. Liquid swine manure management challenges on tile-drained soils. Applied Engineering in Agriculture. 20(5):693-699. Interpretive Summary: This northeast Iowa field study was conducted to develop a better understanding of the problems that farmers encounter when using liquid swine manure as their primary nutrient source for crop production. It demonstrated that manure can be a valuable resource for soil management and it should not be considered a "waste" but it is not a uniform material and its use for crop production is not a simple task. Crop yield, soil-test, and nitrate nitrogen loss through subsurface drainage measurements quantified many of the challenges farmers encounter. To manage manure variability, we recommend that producers establish a manure nutrient database that reflects on-site management conditions. This database should be updated continuously to account for variation in diet, animal numbers, types, and other factors to ensure nutrient application rates are consistent with crop requirements. Our study also suggests that the manure nutrient management practices should be based on phosphorus application rates rather than nitrogen. Additional studies are needed to determine if accurate application rates can be achieved by using a quick measure of the percent solids in the liquid manure mixture. The primary impact of this research, however, is that it clearly documents how difficult it is to manage liquid swine manure and thus demonstrates why no assumptions should be made on "villainy" for improper management of animal manures.
Technical Abstract: Managing liquid swine manure is more difficult than policy makers and the general public often assume. Achieving target rates of 134 or 157 kg N/ha for rotated or continuous corn, was nearly impossible, because variability in manure composition resulted in N rates ranging from 68 to 286 kg N/ha. Furthermore, the low rates resulted in N deficiencies in the corn while high rates increased N leaching loss through subsurface drainage tile. Total P, total K, and percent solids in the liquid swine manure also varied significantly, but there was good correlation between total P and the percent solids. This suggests that P-based manure application could be implemented by developing and installing sensors to measure percent solids on the applicators. Establishing an on-farm database enabled us to predict manure composition more accurately and significantly improved predictability of N rates during the last three years of this 6-year study. Grain removal accounted for 150, 65, and 122 percent of the N, P, and K, respectively, applied through the swine manure to rotated plots, but with continuous corn it accounted for only 39, 21, and 22% of that applied. Bray P and exchangeable K soil-test values were quite variable but showed an average increase of 20 and 82 mg/kg for continuous corn but decreased 24 and 10 mg/kg, respectively, with rotation. Our results suggest that maintaining on-farm manure composition records, following a corn-soybean rotation rather than continuous corn, and using periodic soil-testing to monitor nutrient changes are among the most important practices needed for improved management of liquid swine manure.