Nitrate leaching from the critical root zone of maize in two tropical highlands of Tanzania: Effects of fertilizer-nitrogen rate and straw incorporation
Nitrate leaching from the critical root zone of maize in two tropical highlands of Tanzania: Effects of fertilizer-nitrogen rate and straw incorporation
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DOI：
10.1016/j.still.2019.104295
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发表时间：
2019-11
影响因子：
6.5
通讯作者：
Jinsen Zheng;Ying Qu;M. Kilasara;W. N. Mmari;Shinya Funakawa
中科院分区：
文献类型：
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作者：
Jinsen Zheng;Ying Qu;M. Kilasara;W. N. Mmari;Shinya Funakawa
农业中的硝酸盐（NO3-）浸出是一个日益严重的环境问题，但撒哈拉以南非洲的种植系统却很少受到关注，那里正在努力增加肥料（特别是氮）的使用，以确保粮食生产。在2015-2017年期间，我们使用重新包装的土壤整体蒸渗仪监测了坦桑尼亚热带高地玉米关键根区的NO3−淋溶。在两种土壤类型（桑迪淋溶土和粘质灰岩土）中，对四种尿素氮水平（0-150 kg N ha−1）和与玉米秸秆（102 Mg C ha−1; C：N ≥ 60）的组合进行了评价。土壤再湿润过程，特别是在雨季开始和施氮后，是NO3−通量的关键驱动因素。硝态氮淋失随施氮量的增加呈指数增加，但年际变化。在增加施氮量的条件下，累积NO3-通量与玉米产量的关系揭示了一个临界点，即产量增加伴随着大量NO3-淋失。第二季，在桑迪和粘土质土壤中，这种临界点分别出现在施氮量为62和50 kg N ha− 1时。秸秆还田在生长季节早期诱导了净氮固定，并使NO3−淋失减少了3.3-6.3 kg N ha−1，但对累积NO3−通量或玉米产量没有影响。NO3−淋溶减少量（相当于1.2-2.7 kg N Mg−1C）远低于掺入秸秆的净N固定潜力（18.0-38.1 kg N Mg−1C; C：N比为60-206）。这可能是由于在田间使用的大片秸秆（约0.15米），减少了暴露于土壤和微生物的表面积，因此，只有有限的N在分解微位点可以固定。研究结果表明，在坦桑尼亚热带高原地区，采用适宜的施氮量可以在不引起大量氮素淋失的情况下提高玉米产量，同时强调了在田间使用大秸秆暂时固定可淋失氮对提高氮素同步性和产量效益的效果不佳。
Nitrate (NO3−) leaching from agriculture is a growing environmental concern, but little attention has been given to the cropping systems in sub-Saharan Africa, where efforts are underway to increase fertilizer (especially nitrogen, N) use to secure food production. During 2015–2017, we monitored NO3−leaching from the critical root zone of maize in the tropical highlands of Tanzania using repacked soil monolith lysimeters. Four urea-N rates (0–150 kg N ha−1) and in combination with maize straw (∼2 Mg C ha−1; C:N ≥ 60) were evaluated in two soil types (sandy Alfisols and clayey Andisols). The soil rewetting process, particularly at the onset of the rainy season and following N applications, was a critical driver of NO3−flux. Nitrate leaching increased exponentially with increasing N rates, yet inter-annual variation was observed. Relating cumulative NO3−flux to maize yield under increasing N rates revealed a tipping point—occurrence depending on season—above which yield increments were accompanied by substantial NO3−leaching. Such a tipping point occurred at the N rate of 62 and 50 kg N ha−1at the sandy and clayey site, respectively, in the second season. Straw incorporation induced net N immobilization in the early growing season, and reduced NO3−leaching by 3.3–6.3 kg N ha−1, but no effect was observed on the cumulative NO3−fluxes or maize yields. The NO3−leaching reductions (equivalent to 1.2–2.7 kg N Mg−1C) were far below the net N immobilization potential of the incorporated straw (18.0–38.1 kg N Mg−1C; for C:N ratios of 60–206). This was likely caused by large pieces of straw (∼0.15 m) used in the field, which reduced the surface area exposed to soil and microbes; consequently, only limited N in the decomposition microsites could be immobilized. Our results showed the potential to enhance maize yield without inducing substantial N leaching by adopting the proper N rate in the tropical highlands of Tanzania, and highlighted that temporary immobilization of leachable N by using large pieces of straw in the field was inefficient for the improvement of N synchrony and benefits to yield.