AgResearch Ltd, Ruakura Research Centre, Hamilton, New Zealand.
The New Zealand Institute for Plant & Food Research Ltd, Palmerston North, New Zealand.
J Sci Food Agric. 2018 Aug;98(10):3795-3805. doi: 10.1002/jsfa.8893. Epub 2018 Mar 1.
A combination of field experiment and modelling tested the hypothesis that dry summers increase the risk of nitrogen (N) leaching from pasture owing to a combination of: soil N accumulation in a dry summer; slow recovery of drought-affected pasture in the autumn; and the resultant inefficient use of fertiliser N by the pasture.
In the experiment, pasture response to urea and apparent N recovery in autumn after the drought was half that of irrigated pasture (7 vs 13 kg dry matter kg N; 28 vs 52% apparent recovery; P < 0.05). There was more soil mineral N at the start of drainage (P < 0.001) as a result of this inefficient fertiliser N use. Modelling of pasture growth in six different drought years demonstrated that subsequent N leaching risk after rewetting was inversely related to pasture N uptake during rewetting in the autumn.
When the period between post-drought pasture recovery and the onset of drainage is short, N leaching risk increases. Nitrogen leaching is determined by the type of autumn (slow or fast growing conditions before drainage) and the amount of fertiliser N applied. The latter can be managed by a farmer, but the former cannot. © 2018 Society of Chemical Industry.
田间试验和模型相结合检验了这样一个假设，即由于以下因素的综合作用，干旱夏季会增加氮（N）从牧场淋洗的风险：干旱夏季土壤中 N 的积累；秋季受干旱影响的牧场恢复缓慢；以及牧场对肥料 N 的利用效率低下。
在试验中，与灌溉牧场相比，牧场对尿素的反应和秋季干旱后的表观 N 恢复量只有一半（干物质 kg N 中的 7 公斤 vs 13 公斤；表观恢复率 28% vs 52%；P < 0.05）。由于这种肥料 N 利用效率低下，排水开始时土壤中的矿质 N 更多（P < 0.001）。在六个不同干旱年份的牧场生长模型中，表明重新湿润后随后的 N 淋洗风险与秋季重新湿润期间的牧场 N 吸收量成反比。
当秋季牧场恢复和排水开始之间的时间间隔较短时，N 淋洗风险增加。氮淋洗取决于秋季的类型（排水前的生长缓慢或快速）和施加的肥料 N 量。后者可以由农民管理，但前者不能。 © 2018 英国化学学会。
