Phosphorus Losses as Affected by Tillage and Manure Application

Abstract

AbstractThere is a lack of data on conservation tillage under field conditions characteristic of a dairy operation. Thus, simulated rainfall was used to compare total P (TP), algal‐available P (AAP), and dissolved molybdate‐reactive P (DMRP) losses from the conventional, chisel, and no‐till systems for corn both with and without surface‐applied manure prior to tillage. Rainfall was applied at several times during the growing season of 1978 and 1979. A portion of the previous year's residue was removed in 1978 and all the residue was left in 1979. Concentrations and losses of TP and AAP among unmanured tillage treatments were similar to trends observed for sediment concentrations and losses. In 1978, the chisel and no‐till systems were ineffective in reducing TP and AAP losses relative to the conventional system. In contrast in 1979, lower TP and AAP losses occurred from unmanured chisel and no‐till sites relative to unmanured conventional sites. In both years of the experiment, surface spread manure increased DMRP concentrations where the manure was not completely incorporated by tillage. In contrast, little difference was observed in DMRP concentrations among unmanured treatments. Manure also increased AAP concentrations for no‐till but had only a slight effect and no effect for the chisel and conventional systems, respectively. AAP concentrations from manured sites followed the order no‐till > conventional = chisel. Differences in runoff volumes among treatments influenced P losses. Runoff losses were relatively high for no‐till, particularly after planting, and losses of DMRP and AAP were very high where manure was surface applied. Often, runoff was reduced for the chisel system relative to other tillage systems, and consequently these reductions increased the effectiveness of this system in reducing P losses.