ISSN:
1365-2494
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Notes:
The pool of nitrate-N (NO3–-N) in the soil is more prone to losses than that of ammonium-N (NH4+-N) so any shift towards NO3–-N dominance in the soil pools, caused by management intensity, could have environmental implications. The change in the balance of soil NH4+-N and NO3–-N content with time was studied using grazed grass swards receiving different fertilizer N inputs. In addition, the effect of past management on net nitrification of 400 μg NH4+-N g–1 was investigated in a soil incubation study. Mineral N was determined at frequent intervals (at least every 2 weeks) throughout the year in the top 5 or 7·5 cm of a sandy clay-loam soil at the Agricultural Research Institute of Northern Ireland at Hillsborough, County Down, for a 7-year period (1989–90 to 1995–96). The treatments were a perennial ryegrass–white clover sward receiving no fertilizer N, together with perennial ryegrass swards receiving 100, 200, 300, 400 or 500 kg N ha–1 year–1 as calcium ammonium nitrate. The plots were continuously grazed by beef steers from April to October to maintain a constant sward height of 7 cm. There was little or no change in average soil NO3–-N and NH4+-N content from 1989–90 to 1995–96 on the grass–clover sward and plots receiving 100 and 200 kg N ha–1 year–1. However, with the plots receiving 300, 400 and 500 kg N ha–1 year–1 NO3–-N became progressively more dominant with time. The incubation study confirmed that this was due to an increase in net nitrification rate. There was evidence that rapid microbial assimilation of NO3–-N occurred during the soil incubations. Past management history can play an important role in determining soil NO3–-N content and hence potential losses of N to the environment.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1046/j.1365-2494.1999.00177.x
