Abstract/Summary

Agricultural management practices that increase soil organic matter (SOM), such as no-tillage (NT) with crop residue retention, together with crop varieties best able to source nutrients from SOM may help reverse soil degradation and improve soil nutrient supply and uptake by plants in low-input environments of tropical and sub-tropical areas. Here, we screened germplasm representing genetic diversity within tropical maize breeding programs in relation to shaping SOM mineralisation. Then we assessed effects of contrasting genotypes on nitrification rates, and genotype by management history interactions on these rates. SOM-C mineralisation and gross nitrification rates varied under different maize genotypes. Cumulative SOM-C mineralisation increased with root diameter but decreased with increasing root length. Strong influences of management history and interaction of maize genotype by management history on nitrification were observed. Overall, nitrification rates were higher in NT soil with residue retention. We propose that there is potential to exploit genotypic variation in traits associated with SOM mineralisation and nitrification within breeding programs. Root diameter and length could be used as proxies for root-soil interactions driving these processes. Development of maize varieties with enhanced ability to mineralize SOM combined with NT and residue retention to build/replenish SOM could be key to sustainable production.