Sub-Saharan Africa is facing food security challenges due, in part, to decades of soil nitrogen (N) depletion. Applying N fertilizer could increase crop yields and replenish soil N pools. From 2010 to 2015, field experiments conducted in Embu and Kiboko, Kenya and Harare, Zimbabwe investigated yield and N uptake response of six maize (Zea mays L.) hybrids to four N fertilizer rates (0 to 160 kg N ha⁻¹) in continuous maize production systems. The N recovery efficiency (NRE), cumulative N balance, and soil N content in the upper 0.9 m of soil following the final harvest were determined at each N rate. Plant and soil responses to N fertilizer applications did not differ amongst hybrids. Across locations and N rates, NRE ranged from 0.4 to 1.8 kg kg⁻¹. Higher NRE values in Kiboko and Harare occurred at lower post-harvest soil inorganic N levels. The excessively high NRE value of 1.8 kg kg⁻¹ at 40 kg N ha⁻¹ in Harare suggested that maize hybrids deplete soil inorganic N most at low N rates. Still, negative cumulative N balances indicated that inorganic soil N depletion occurred at all N rates in Embu and Harare (up to − 193 and − 167 kg N ha⁻¹, respectively) and at the 40 kg N ha⁻¹ rate in Kiboko (− 72 kg N ha⁻¹). Overall, maize N uptake exceeded fertilizer N applied and so, while yields increased, soil N pools were not replenished, especially at low total soil N levels (< 10,000 kg N ha⁻¹ in top 0.9 m).

中文翻译：

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氮含量对非洲东部和南部热带玉米的氮利用效率和土壤氮耗竭的影响。

撒哈拉以南非洲正面临粮食安全挑战，部分原因是数十年来土壤氮（N）的消耗。施用氮肥可以增加作物产量并补充土壤氮库。从2010年到2015年，在肯尼亚的恩布和基博科和津巴布韦的哈拉雷进行了田间试验，调查了六个玉米（Zea mays L.）杂交种对4种氮肥用量（0至160 kg N ha ^-1）的产量和氮素吸收响应。玉米连续生产系统。在每个氮含量下，确定最终收获后上部0.9 m土壤中的N回收效率（NRE），累积的N平衡和土壤N含量。杂种间，植物和土壤对氮肥的反应无差异。在各个地点和N比率下，NRE的范围从0.4到1.8 kg kg ^-1。在Kiboko和Harare地区，较高的NRE值发生在收获后土壤无机N含量较低的情况下。在哈拉雷，在40 kg N ha ^-1时NRE值过高，为1.8 kg kg ^-1，这表明玉米杂交种以低N率消耗最多的土壤无机氮。尽管如此，负累积Ñ余额表明无机土壤氮耗尽发生在在Embu和哈拉雷所有N个速率（高达- 193和- 167千克Ñ公顷^-1分别），并在40千克氮公顷^-1率在Kiboko（ -72 kg N ha ^-1）。总体而言，玉米吸收的氮超过施用的肥料氮，因此，尽管单产增加，但土壤氮库并未得到补充，特别是在土壤总氮水平较低（最高0.9 m时<10,000 kg N ha ^-1）的情况下。