Effect of Manure Application Timing, Crop, and Soil Type on Nitrate Leaching

Timing of manure application affects N leaching. This 3‐yr study quantified N losses from liquid manure application on two soils, a Muskellunge clay loam and a Stafford loamy sand, as affected by cropping system and timing of application. Dairy manure was applied at an annual rate of 93 800 L ha −1 on replicated drained plots under continuous maize ( Zea mays L.) in early fall, late fall, early spring, and as a split application in early and late spring. Variable rates of supplemental sidedress N fertilizer were applied as needed. Manure was applied on orchardgrass ( Dactylis glomerata L.) in split applications in early fall and late spring, and early and late spring, with supplemental N fertilizer topdressed as NH 4 NO 3 in early spring at 75 kg N ha −1 Drain water was sampled at least weekly when lines were flowing. Three‐year FWM (flow‐weighted mean) NO 3 –N concentrations on loamy sand soil averaged 2.5 times higher (12.7 mg L −1 ) than those on clay loam plots (5.2 mg L −1 ), and those for fall applications on maize‐cropped land averaged >10 mg L −1 on the clay loam and >20 mg L −1 on the loamy sand. Nitrate–N concentrations among application seasons followed the pattern early fall > late fall > early spring = early + late spring. For grass, average NO 3 –N concentrations from manure application remained well below 10 mg L −1 Fall manure applications on maize show high NO 3 –N leaching risks, especially on sandy soils, and manure applications on grass pose minimal leaching concern.