Nitrogen use and crop performance of rice under aerobic conditions in a semiarid subtropical environment

Aerobic rice (Oryza sativa L.) is gaining in popularity across South Asia, mainly because it saves water and labor. Under warm (sub) tropical conditions of this region, this unconventional system aimed at improved resource use efficiency is still in the development phase. We tested crop performance and N uptake of three local genotypes in relation to di¬fferent water and N supply rates under aerobic conditions at the research station of the University of Agriculture, Faisalabad, Pakistan. In field experiments during 2009 to 2010, covering two rice seasons, three irrigation levels (high, moderate, and low), three N rates (0, 170, and 220 kg N ha–1), and three genotypes (KSK133, IR6, and RSP1), crop performance and total N uptake (TNU) were strongly influenced by irrigation and di¬ffered among genotypes. At the highest level of irrigation, genotype KSK133 performed better than RSP1 and IR6, resulting in an accumulated aboveground biomass of 13 Mg ha–1 and a grain yield of 5 Mg ha–1. The TNU ranged from 34 to 126 kg ha–1 in 2009 and from 52 to 123 kg ha–1 in 2010. For all genotypes, we observed a strong positive correlation between TNU and grain yield. Surprisingly, the N application rate did not influence TNU, but the high irrigation regime increased TNU. The limited response to N application suggests significant losses of the applied N. This highlights the need for careful N management in aerobic rice systems; N application should match periods of sufficient soil moisture availability and the greatest crop N demand