Tully Katherine L, Hickman Jonathan, McKenna Madeline, Neill Christopher, Palm Cheryl A
Department of Plant Science and Landscape Architecture, University of Maryland, College Park, Maryland, 20742, USA.
Agriculture and Food Security Center, The Earth Institute, Columbia University, New York, New York, 10025, USA.
Ecol Appl. 2016 Sep;26(6):1907-1919. doi: 10.1890/15-1518.1.
Fertilizer applications are poised to increase across sub-Saharan Africa (SSA), but the fate of added nitrogen (N) is largely unknown. We measured vertical distributions and temporal variations of soil inorganic N following fertilizer application in two maize (Zea mays L.)-growing regions of contrasting soil type. Fertilizer trials were established on a clayey soil in Yala, Kenya, and on a sandy soil in Tumbi, Tanzania, with application rates of 0-200 kg N/ha/yr. Soil profiles were collected (0-400 cm) annually (for three years in Yala and two years in Tumbi) to examine changes in inorganic N pools. Topsoils (0-15 cm) were collected every 3-6 weeks to determine how precipitation and fertilizer management influenced plant-available soil N. Fertilizer management altered soil inorganic N, and there were large differences between sites that were consistent with differences in soil texture. Initial soil N pools were larger in Yala than Tumbi (240 vs. 79 kg/ha). Inorganic N pools did not change in Yala (277 kg/ha), but increased fourfold after cultivation and fertilization in Tumbi (371 kg/ha). Intra-annual variability in NO -N concentrations (3-33 μg/g) in Tumbi topsoils strongly suggested that the sandier soils were prone to high leaching losses. Information on soil inorganic N pools and movement through soil profiles can h vulnerability of SSA croplands to N losses and determine best fertilizer management practices as N application rates increase. A better understanding of the vertical and temporal patterns of soil N pools improves our ability to predict the potential environmental effects of a dramatic increase in fertilizer application rates that will accompany the intensification of African croplands.
撒哈拉以南非洲地区（SSA）的肥料施用量有望增加，但添加氮（N）的去向在很大程度上尚不清楚。我们在两个土壤类型不同的玉米（Zea mays L.）种植区测量了施肥后土壤无机氮的垂直分布和时间变化。在肯尼亚亚拉的黏土土壤和坦桑尼亚通比的沙质土壤上开展了肥料试验，施氮量为0 - 200千克氮/公顷/年。每年（亚拉为三年，通比为两年）采集土壤剖面（0 - 400厘米），以研究无机氮库的变化。每3 - 6周采集一次表土（0 - 15厘米），以确定降水和肥料管理如何影响植物可利用的土壤氮。肥料管理改变了土壤无机氮，不同地点之间存在很大差异，这与土壤质地的差异一致。亚拉的初始土壤氮库比通比大（240对79千克/公顷）。亚拉的无机氮库没有变化（277千克/公顷），但通比在耕种和施肥后增加了四倍（371千克/公顷）。通比表土中NO₃⁻-N浓度的年内变化（3 - 33微克/克）强烈表明，沙质土壤更容易发生高淋失损失。关于土壤无机氮库以及通过土壤剖面的移动信息，可以帮助了解SSA农田氮损失的脆弱性，并在氮肥施用量增加时确定最佳肥料管理措施。更好地了解土壤氮库的垂直和时间模式，有助于我们预测随着非洲农田集约化，肥料施用量大幅增加可能产生的潜在环境影响。
