Nitrogen fertilization has a significant environmental impact in Europe due to the problems of wide-spread pollution. This paper deals with a series of field experiments conducted in a semiarid region of Southeast Spain. Irrigated maize was grown under different N fertilizer rates: control as in no nitrogen applied (C; 0 kg N ha^―1); conventional amount of nitrogen (Nc; 300 kg N ha^―1); and theoretical optimum (No; 130 kg N ha^―1) in a randomised block design with three replications.

In 1999 and 2000, when 175 and 150 kg N ha^―1 were respectively applied to No treatment, no significant differences were found. With the Nc treatment, a grain yield of 17.6 Mg ha^―1 was obtained in 2001, being significantly higher than the yield obtained with the No treatment (15.8 Mg ha^―1). This means that No rate was under the technical optimum, but both treatments were higher than C treatment (7.2 Mg ha^―1). A fertilizer rate of 130 kg N ha^―1 was lower than necessary to obtain maximum yields, although the rate of 150 kg N ha^―1 did not show significant differences with regard to Nc treatment (300 kg ha^―1) (2000).

Studies about crop response to different N rates could be very useful for farmers. Regional Technology Transfer Centres are incorporating the results of these studies in a Decision Support System (DSS).

由于普遍的污染问题，氮肥在欧洲对环境产生重大影响。本文涉及在西班牙东南部的半干旱地区进行的一系列现场试验。灌溉的玉米在不同的氮肥施用量下生长：控制为不施氮（C； 0 kg N ha ^-1）；常规氮含量（Nc; 300 kg N ha ^-1）; 且具有三个重复的随机区组设计中的理论最佳值（No； 130 kg N ha ^-1）。

在1999年和2000年，当分别对175和150 kg N ha ^-1进行No处理时，没有发现显着差异。通过Nc处理，2001年获得了17.6 Mg ha ^-1的谷物单产，大大高于不采用No处理的谷物单产（15.8 Mg ha ^-1）。这意味着没有速率低于技术最佳值，但是两种处理均高于C处理（7.2 Mg ha ^-1）。130 kg N ha ^-1的施肥量低于获得最大产量的必要肥料，尽管150 kg N ha ^-1的施肥量与Nc处理（300 kg ha ^-1）没有显着差异（2000年）。

关于农作物对不同氮含量的反应的研究可能对农民非常有用。区域技术转让中心正在将这些研究的结果纳入决策支持系统（DSS）。