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, M150, 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°C. The N 0 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 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.