Precision-Placed Separated Slurry Sludge Provides P and N For Silage Corn.

Fertilizer containing P and N is commonly added as a ‘starter’ for corn even on high-P testing fields to improve early growth, yield and maturity in coastal BC, Canada. Separated dairy solids have relatively high concentrations of P which can replace mineral P if placed near corn rows at planting. The current study was designed to assess the multi-year effect of separated (settled) dairy sludge precision-placed pre-plant as a replacement for starter commercial fertilizer. The sludge was injected (12 cm deep) with offset disks at 75 cm spacing to match corn rows. The corn was planted within 10 cm of sludge furrows a few days later. Treatments included 3 sludge rates, with and without starter commercial fertilizer and additional broadcast N. The trial was repeated on the same plots in 2010-2012. Results show that yield of corn with sludge injected at 32.5 kg P ha^-1 and supplemented with broadcast mineral N  was similar to corn receiving equivalent rates of mineral fertilizer (18 t DM ha^-1). When sludge was injected at 16 kg P ha^-1 with additional broadcast mineral N fertilizer, 89% of applied manure P was recovered by the crop. At this application rate, corn yield was 1.8 t ha^-1 below the maximum achieved with mineral fertilizer. Application of sludge at 32.5 kg ha^-1 reduced P recovery to only 50% of applied but yield was increased to within 0.5 t ha^-1 of maximum. Only ~40% of applied manure N was recovered by the corn and there was little recovery of N from manure applied in the previous year. Results show that precision applied sludge can provide adequate P and some N for corn and this would be a sustainable practice for utilizing manure P. Long term effects of applied N are being assessed.