MECHANICAL AERATION AND LIQUID DAIRY MANURE APPLICATION IMPACTS ON GRASSLAND RUNOFF WATER QUALITY AND YIELD

Abstract

The runoff water quality and agronomic impacts of mechanical aeration and liquid dairy manure (LDM) applicationto grassland (orchard grass with 10% to 20% alfalfa) were evaluated in two blocks. Simulated rainfall-generated runoffwas collected six times from block A, and natural runoff was collected from block B once. Runoff samples were analyzed fornitrate-nitrogen (NO3--N), ammoniacal-N, total Kjeldahl N (TKN), dissolved reactive phosphorus (DRP), total P, and totalsuspended solids (TSS). The four treatments applied to the plots were control (CTL, no aeration and no LDM), aeration (AER),LDM application but no aeration (MAN), and aeration plus LDM application (AER+MAN). The plots were harvested threetimes, and crop yields and crop nutrient (N-P-K) contents were determined. Aeration impact on soil impedance was evaluatedwith a penetrometer. In one simulated event, AER+MAN significantly reduced runoff, while the other treatments werecomparable. Nutrient concentrations in simulated runoff increased with LDM application but were unaffected by aeration.Aeration reduced nutrient loadings of three or more species (not TKN) from manured plots in two of six simulated runoff eventsbut not from non-manured plots. Aeration of manured plots was more effective in reducing DRP losses than other nutrientspecies. Mean total loadings of all nutrient species in simulated runoff were reduced >26% by AER+MAN vs. MAN. Whileaeration significantly increased TSS concentrations in simulated runoff, LDM application did not. In one of six simulatedevents, AER had the highest TSS loadings, while AER+MAN had the lowest, with the two other treatments in between. Notreatment effects were observed with natural runoff for any constituent. The MAN treatment significantly increased forageyield in two harvests vs. CTL and AER and in one harvest vs. AER+MAN. Compared with MAN, total forage yields with CTL,AER, and AER+MAN were 78%, 67%, and 81%, respectively. Aeration reduced soil impedance and could improve rootpenetration in compacted soils.