Soil Macro- and Micro-Nutrient Pools' Role in Yield and Nitrogen Use Efficiency Responses of Maize Hybrids to N in Africa.

Continuous cropping of maize in Sub-Saharan Africa with minimal inputs over the last 50 years has depleted the soil of essential macro- and micro-nutrients, widening the yield gap and damaging the potential of future harvests. It is crucial to look at how improved maize hybrids and the application of N fertilizer interacts with soil nutrients in different environments to understand the yield limiting factors and, therefore, to develop future management approaches for soil fertility remediation. This study was conducted in 3 low N environments in Kenya and Zimbabwe which have been under continuous maize cultivation for 5-9 seasons starting in spring 2010 at different N rates ranging from 0 to 160 kg N/ha as part of CIMMYT’s Improved Maize for African Soils project. At each site, 6 maize hybrids with varying N use efficiencies were planted to see how different hybrids impact on soil fertility at a range of fertilizer N rates. The soil was sampled to a depth 90 cm at 5 depth increments and analyzed for all plant essential nutrients as well as Fe oxides, pH, %OM, and texture. Results showed that while N and P were low at all sites, soil Zn was also low at one site resulting in plant Zn deficiency. Meanwhile, there were toxic levels of soil Mn at all three sites and resultant high Mn accumulation in the stover, thus limiting potential grain yield. The low pH (<6) at two of the three sites coupled with high Al and Fe oxide concentrations limited the availability of P for plant uptake. The higher pH (~7) at the third site increased P availability and subsequent uptake. Targeted nutrient replenishment and pH adjustment approaches are necessary improve soil fertility and optimize grain yield in Africa’s depleted soil.