Data from: Effects of fertilizer on inorganic soil N in East Africa maize systems: vertical distributions and temporal dynamics

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−3-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（SSA）的化肥施用量有望增加，但添加的氮素（N）的去向在很大程度上仍不明确。我们在两个土壤类型迥异的玉米（Zea mays L.）种植区，测定了化肥施用后土壤无机氮的垂直分布和时间变化特征。在肯尼亚Yala的粘质土壤和坦桑尼亚Tumbi的砂质土壤上建立了化肥试验，施肥量为0–200千克氮/公顷/年。每年采集0–400厘米深度的土壤剖面（Yala采集3年，Tumbi采集2年），以分析无机氮库的变化。每3–6周采集表层土壤（0–15厘米），以探究降水和施肥管理对植物可利用土壤氮的影响。施肥管理改变了土壤无机氮含量，且不同地点间存在显著差异，这与土壤质地的不同一致。Yala的初始土壤氮库大于Tumbi（240 vs. 79千克/公顷）。Yala的无机氮库未发生变化（277千克/公顷），但Tumbi在耕作和施肥后无机氮库增加了四倍（371千克/公顷）。Tumbi表层土壤中硝态氮浓度的年内变异性（3–33微克/克）强烈表明，砂质土壤更易发生高淋失损失。关于土壤无机氮库及其在土壤剖面中迁移的信息，可帮助评估SSA农田氮素损失的脆弱性，并在氮素施用量增加时确定最佳施肥管理措施。更好地理解土壤氮库的垂直和时间分布模式，有助于提升我们预测非洲农田集约化过程中施肥量大幅增加所带来的潜在环境影响的能力。