Evaluation of Growth, Yield, Water and Nitrogen Balance in Rice –Maize Rotation Grown Under Aerobic and Flooded Irrigation Conditions in Semi-Arid Tropics.

Rice (Oryza sativa L.) is the world's most important food crop and a major source of food for more than one third of the world's population. Irrigated rice is typically grown in submerged conditions under 5-10 cm depth of water. However, most of the water is lost through percolation, seepage and evaporation. The availability of water to agriculture and increasing costs of water threaten the traditional way of irrigated rice production requiring development of water-saving rice production technologies.

A field experiment was conducted at the Agricultural University research farm in Hyderabad, India, to compare traditional transplanted rice-maize system with water saving aerobic rice-maize system, with the overall objective of studying water and nitrogen (N) balance in the both systems, using δN15 through field experimentation and simulation modeling. Results from the field experiments showed that irrigating aerobic rice at soil moisture tension of 20 kpa (upper 10 cm depth) throughout the crop growth saved 589 mm of water compared to traditional flooded rice system but with 39% yield reduction. The reduction in the yield in aerobic rice was attributed to reduction in spikelet number and in grain weight. Increased dosages of N application up to 180 kg/ha resulted in increased rice yields by 12% in aerobic systems and by 6% in the flooding systems compared to the standard recommended dose of N application (120 kg/ha). The rice plants have shown positive response to additional N application. The average fertilizer N recovery in aerobic rice was 25.6% in main field and 21% in micro plot, while it was 41% in main field and 32.2% in micro plot in flooded conditions. The fraction of δN15 that was found in soil after the harvest of rice crop was 22.4% in aerobic rice and 25% in flooded rice. Average recoveries of δN15 fertilizer in maize after first growing season was 3.6% and the corresponding recoveries in soil was 16.7%. There was an additional 1.6% of the fertilizer was recovered by the crops during subsequent two seasons. Significantly higher yields were obtained with no till maize grown after aerobic rice than the no-till maize after transplanted rice, possibly due to residual soil N and enhanced soil physical conditions.