Maintaining green leaf area in grain sorghum increases nitrogen uptake under post-anthesis drought

Abstract

To improve yield under water-limited conditions, Australian breeders have been selecting for the stay-green drought resistance trait. A study was conducted in Queensland during summer 1995 to determine whether more nitrogen will need to be applied to stay-green hybrids than to senescent hybrids if the yield advantage of stay-green types is to be realized under drought conditions. Nitrogen uptake was determined in 9 hybrids varying in rate of leaf senescence. Results showed that grain yield was highly correlated (r2 = 0.69) with above-ground nitrogen uptake at maturity. When water was limiting during grain filling, stay-green hybrids A35 × QL36 and AQL41 × QL12 extracted more nitrogen from the soil (∼280 kg N/ha) than senescent hybrids AQL41 × 69264 and AQL39 × QL36 (∼185 kg N/ha). Green leaf area at maturity explained over 70% of the variation in grain yield, and the relationship between nitrogen uptake and green leaf area at maturity was highly significant (r2 = 0.47). Differences in leaf and root uptake of nitrogen between stay-green and senescent genotypes are discussed. It is concluded that stay-green genotypes will require more nitrogen if they are to realize their yield potential under drought conditions.