ISSN:
1573-5036
Keywords:
ammonia volatilization
;
denitrification
;
grazed pasture
;
leaching
;
nitrogen
;
N2 fixation
Source:
Springer Online Journal Archives 1860-2000
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Notes:
Abstract Inputs and losses of nitrogen (N) were determined in dairy cow farmlets receiving 0, 225 or 360 kg N ha-1 (in split applications as urea) in the first year of a large grazing experiment near Hamilton, New Zealand. Cows grazed perennial ryegrass/white clover pastures all year round on a free-draining soil. N2 fixation was estimated (using 15N dilution) to be 212, 165 and 74 kg N ha-1 yr-1 in the 0, 225 and 360 N treatments, respectively. The intermediate N rate had little effect on clover growth during spring but favoured more total pasture cover in summer and autumn, thereby reducing overgrazing and resulting in 140% more clover growth during the latter period. Removal of N in milk was 76,89 and 92 kg N ha-1 in the 0, 225 and 360 N treatments, respectively. Denitrification losses were low (7–14 kg N ha-1 yr-1), increased with N application, and occurred predominantly during winter. Ammonia volatilization was estimated by micrometeorological mass balance at 15, 45 and 63 kg N ha-1 yr-1 in the 0, 225 and 360 N treatments, respectively. Most of the increase in ammonia loss was attributed to direct loss after application of the urea fertilizer. Leaching of nitrate was estimated (using ceramic cup samplers at 1 m soil depth, in conjunction with lysimeters) to be 13, 18 and 31 kg N ha-1 yr-1 in a year of relatively low rainfall (990 mm yr-1) and drainage (170–210 mm yr-1). Drainage was lower in the N fertilized treatments and this was attributed to enhanced evapotranspiration associated with increased grass growth. Nitrate-N concentrations in leachates increased gradually over time to 30 mg L-1 in the 360 N treatment whereas there was little temporal variation evident in the 0 (mean 6.4 mg L-1) and 225 (mean 10.1 mg L-1) N treatments. Thus, the 360 N treatment had a major effect by greatly reducing N2 fixation and increasing N losses, whereas the 225 N treatment had little effect on N2 fixation or on nitrate leaching. However, these results refer to the first year of the experiment and further measurements over time will determine the longer-term effects of these treatments on N inputs, transformations and losses.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00011293
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