Growth patterns of high yielding rice (Oryza sativa L.) cultivars grown under different environments

The highest grain yield was 15.2 t/ha produced at Yunnan using Shanyou 63, a Chinese indica F1 hybrid, whereas maximum yield was 9.2 t/ha at IRRI [International Rice Research Inst., Los Banos, Laguna, Philippines] using troical indicate F1 hybrid IR68284 H. On average across cultivars, Yunnan produced 62 percent more yield than IRRI in 1996. Sink size (spikelets per sq m) was responsible for the yield differences. Large panicle (spikelets per panicle) was the major contributor to great sink size at Yunnan. Biomass production rather than harvest index was the cause of high yield at Yunnan. Yunnan had greater daily grain yield and radiation use efficiency than IRRI. Longer growth duration and greater daily biomass accumulation rate contributed almost equally to higher biomass production and grain yield at Yunnan compared with IRRI. Average crop growth rate (CGR) was 38 percent greater at Yunnan than at IRRI. The greatest and consistent differences in CGR between the two sites occurred during the period than midtillering to panicle initiation. Maximum leaf area index (LAI) averaged across cultivars was 9.3 at Yunnan and 7.2 at IRRI. Leaf area duration (LAD) was 46 percent greater at Yunnan than at IRRI. The difference became 29 percent after adjusting LAD for growth duration. Greater maximum LAI and LAD were mainly responsible for higher CGR at Yunnan than at IRRI. Greater yield at Yunnan was also due to higher CGR during ripening and greater contribution from dry matter accumulated before flowering compared with IRRI. Total plant N was greater at Yunnan than at IRRI during entire growing season. The difference was greatest at panicle initiation (PI) and declined gradually to 37 percent at flowering (FL) and 19 percent at physiological maturity (PM). Crop at Yunnan had greater N uptake than IRRI between midtillering (MT) and PI, similar to IRRI between PI and FL and less than IRRI between FL and PM. Leaf and plant N concentration at IRRI were significantly higher than Yunnan. Grain N concentration was lower and N translocation efficiency was higher at Yunnan than at IRRI. N harvest index and N utilization efficiency was greater at Yunnan than IRRI. Rice crop with yield of 13 to 15 t/ha produced nearly 60 kg grain for every kg of N uptake and about 250 kg/ha was required to produce such higher yield. The net income of rice crop was 514, 810, and 1099$/ha for low, moderate and high input farmers, respectively. The total income for the cropping patterns was increased from 1570 to 8090$/ha depending upon resource level. Adaptation of recommended technology are voluntary for all types of farmers. Therefore, the rice-based cropping system in Taoyuan Township are sustainable