Data from: Effects of fertilizer on inorganic soil N in East African 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-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-1 yr-1. Soil profiles were collected (0-400 cm) annually 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-1). Inorganic N pools did not change in Yala (132 kg ha-1), but increased four-fold after two years of cultivation and fertilization in Tumbi (371 kg ha-1). Intra-annual variability in Tumbi topsoil NO3--N concentrations (3-33 μg g-1) strongly suggested that the sandier soils were prone to high leaching losses. Information on soil inorganic N pools and movement through soil profiles can be an important way of assessing vulnerability of different SSA croplands to N losses and managing N fertilizer to reduce losses as fertilizer application rates increase. Better soil biophysical data will be important when projecting potential environmental effects of a dramatic change to the N cycle in intensifying African croplands.