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

Abstract

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 (N0), 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, M150, and M300, respectively) from 1995 to 2004. Soil samples collected in fall 2004 were used to estimate N0 using a 44‐wk aerobic incubation at 25°C. The N0 values were 62 and 49% higher in the M300 treatment (324 and 480 kg N ha−l) 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 N0 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.