|Powell, J mark|
Submitted to: Journal of Environmental Quality
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/15/2005
Publication Date: 12/15/2005
Citation: Grande, J.D., Karthikeyan, K.G., Miller, P.S., Powell, J.M. 2005. Corn residue level and manure application timing effects on phosphorus losses in runoff. Journal of Environmental Quality. 34:1620-1631. Interpretive Summary: Many dairy farmers are expanding herd size and devoting more of their cropland to corn silage production. This shift to corn silage, which removes more plant material from fields than corn grown for grain, leaves soil surfaces exposed and could increase erosion. This study examined the effects of residue cover and manure application on phosphorus (P) losses in runoff from no-till corn plots. Treatments included corn grown for grain, silage, and high-cut (60-65 cm) silage. Three manure treatments were also included in the study: no manure, manure applied in the fall, and manure applied in the spring. Simulated rainfall was applied in the spring and fall for 2 years and runoff from experimental plots was collected and analyzed for total phosphorus (TP) and dissolved reactive phosphorus (DRP). TP losses from grain plots were 94% less than silage plots. High-cut silage had lower amounts of TP in fall runoff than conventional silage. Manure application in conjunction with high-cut silage lowered P losses even more. Manure applied in spring increased DRP concentrations in spring runoff by 2-5 times but did not affect the actual amount of DRP in runoff. Manure applied in spring reduced the amount of TP in spring runoff by 77-90% compared to no manure plots. Reductions were greatest in silage plots that received manure. This study showed that dairy farmers could reduce most negative erosive effects of corn silage harvest by applying manure in the spring and by leaving more crop residue in the field by increasing silage cut height.
Technical Abstract: Increasing interest in corn silage utilization has implications for nutrient losses from agricultural lands. High cut silage (SH) that provides greater nutritional value of feed may provide an alternative that, by producing more residue cover after harvest, may minimize nutrient losses and surface water impacts compared to harvesting conventional corn silage (SL). We examined the effects of residue level and manure application timing on phosphorus (P) losses in runoff from no-till corn. Treatments included conventional corn grain (G) and silage and non-conventional, high-cut (60-65 cm) silage. Treatments also received one of three manure treatments: no manure (N), application in fall (F) or spring (S). Manure P was added at the rate of 59-62 kg P/ha. Simulated rainfall (76 mm/hr; 1 h) was applied in spring and fall for 2 years (2002-03), runoff from 2.0 m x 1.5 m plots collected, and runoff sub-samples analyzed for dissolved reactive P (DRP) and total P (TP). TP of sediments in four particle size classes was determined and P enrichment ratios calculated. Runoff and sediment losses were previously reported. DRP loads and residue cover were inversely related but DRP concentrations were not affected by residue level. Manure application increased DRP concentrations in spring runoff by 2-5 times but did not significantly affect DRP loads. Higher DRP concentrations were compensated for by lower runoff volumes resulting from manure addition. TP concentrations were similar to sediment concentrations but were little affected by either manure or residue level. Spring manure reduced TP loads in spring runoff by 77-90% compared to no manure plots; reductions were greatest at the lowest residue levels (<40%). Higher residue levels lowered TP loads in fall runoff: TP losses from G plots were 94% less than SL plots. Sediment TP concentrations increased as the particle size decreased. In addition, manure application increased the TP concentration of the 0-2 µm fraction by 79-125% but elevated the 2-10 and 10-50 µm fractions to a lesser extent. P enrichment ratios were most influenced by recent manure additions. Increases in residue cover alone were often insufficient to reduce nutrient losses in runoff; however, manure application in conjunction with higher residue levels can significantly lower phosphorus losses.