Pollution Potential and Corn Yields from Selected Rates and Timing of Liquid Manure Applications

Abstract

ABSTRACT A6-year study was conducted to determine the effects of rate and time of liquid manure application, chemical fertilizer application, and no fertilizer, on the chemical composition of surface and subsurface water and on crop yield. Liquid manure was applied at three rates of 224, 560 and 897 kg/(ha-yr) of N in accordance with four application schedules (i.e. spring, fall, split rates in spring and fall, and winter). In all cases except winter application, manure was incorporated by plowing at time of application. During spring snow-melt, surface runoff concentra-tions of inorganic N, P, and K from winter-applied manure increased approximately in proportion to in-creased application rate. Also, they were much higher than concentrations from spring, fall, spring-fall, and chemical fertilizer treatments. In contrast to spring snowmelt surface runoff, tile drain effluent N03-N concentrations from the plots receiving manure at nearly 900 kg/(ha-yr) of N appeared to be little different from the plot chemically fertilized with 134 kg/(ha-yr) of N. However, at and above the 560 kg/(ha-yr) of N (140 kg/(ha-yr) of P) rates of manure the drain effluent P04-P concentrations tended to be higher than the concentration resulting from chemical fertilizer applications. Most of the nitrogen and phosphorus in surface runoff during June storms was associated with suspended sedi-ment that resulted from erosion. Neither the amounts of sediment nor their total N and total P contents were af-fected by manure or fertilizer applications. Although the concentrations of inorganic N and P04-P in the water portion of June storm runoff were small (<3 percent) compared to those in the sediment, plots with higher rate spring-applied manure tended to have higher concentra-tions of inorganic N, P04-P and K. No significant differences in silage corn yields were observed amongst any of the manure and the chemical fertilizer treatments. Based on trends in the water quality results, it is con-cluded that winter application of manure at any rate on areas that contribute runoff directly to bodies of surface water is not recommended. Non-winter applications of manure at and above rates of 560 kg/(ha-yr) of N may also lead to water quality impairment.