Long-Term Effects of Semisolid Beef Manure Application to Forage Grass on Soil Mineralizable Nitrogen

Livestock manure is an important source of N for forage grass production. The long-term effects of semisolid beef manure application to forage grass on potentially mineralizable N (N-0), mineralizable N pools, and field estimates of soil N supply were evaluated in dike-land (heavy textured, poorly drained) and upland (medium-textured) soils in Nova Scotia, Canada. Treatments included an unfertilized control, annual spring application of 100 kg N ha(-1) mineral fertilizer or annual applications of 75, 150, or 300 kg total Kjeldhal N ha(-1) as manure (M75, M 150, and M300, respectively) from 1995 to 2004. Soil samples collected in fall 2004 were used to estimate N-0 using a 44-wk aerobic incubation at 25 degrees C. The N-0 values were 62 and 4996 higher in the M300 treatment (324 and 480 kg N ha(-1)) than the other manure treatments (199 and 323 kg N ha(-1)) for the upland and dike-land soils, respectively. The mineralization rate coefficient ranged from 0.045 to 0.082 wk(-1). Manure application increased the readily mineralizable N pool (Pool I); higher rates of application resulted in higher values in both soils. The intermediate and stable mineralizable N pools were increased only by the M300 treatment in the upland soil but not in the dike-land soil. Long-term manure application of the M300 treatment resulted in high N-0 with no yield benefits, which can increase the risk of N losses to the environment in both soils, whereas Pool I was responsive to all manure application rates.