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Shaohua Wang, Weixing Cao, Dong Jiang, and Tingbo Dai
Key Laboratory of Crop Growth Regulation, Ministry of Agriculture, Nanjing Agricultural University, Nanjing 210095, China; Caow@public1.ptt.js.cn

A series of experiments were conducted at Nanjing and Jiangyin of Jiangsu Province from 1999 to 2001 to study growth and yield characteristics of paddy rice with different cultivation techniques under the SRI (system of rice intensification) management, in comparison with conventional management system. The cultivation techniques focused on cultivar, population density, nitrogen rate as well as density vs. nitrogen interaction under high yielding rice production systems.

Under the SRI, soil oxygen was enriched through a moderate water deficit without water layer appeared during irrigation. Compared with conventional management, the SRI enhanced rice root activity by 45%-100%, soluble sugar content in leaves by 50%-60%, protein-nitrogen by 23-25%, proline content by 30%-60% and malondialdehyde content by 10%-30%. The amount and percentage of dry matter, carbohydrate and nitrogen reserves remobilized from vegetative organs to panicle after heading were also increased by 50%-200% and 42%-180%, respectively. The plant population quality during rice growth was obviously improved by SRI.

The yield of japonica rice under SRI was lower than that of the conventional system because the initial population was reduced in single-seedling per hill transplanting. Moreover, the rate of population development slowed down under SRI due to the plants suffering from water deficit. With the japonica cultivar Wuxiangjing 9, the yields of SRI and conventional system were 7846 and 8300 kg/ha, respectively. The panicle number per hectare with SRI was decreased by 5.4%, resulting in the yield reduction of 5.5%.

With japonica rice under SRI, different planting configurations (row spacing×plant spacing=30cm×20cm, 25cm×25cm and 30cm×30cm) slightly complemented the shortage of panicle number per hectare. With the cultivar 9915, plant spacing configuration of 30cm×20cm, 25cm×25cm and 30cm×30cm produced the yields of 8535, 8205 and 8370 kg/ha, which were lower by 4.1%, 7.8% and 5.9% respectively than that of traditional system. The panicle number per hectare for the three spacing configurations under SRI were lower by 8.2%, 11.5% and 16.8% respectively than that of traditional system.

Compare to single-seedling transplanting, double-seedling per hill transplanting significantly increased the yield of japonica Wuxiangjing 9 under SRI in the experiment of plant density×nitrogen rate. The results also showed that the panicle number per hectare for double-seedling planting was increased by 23% to 36%, and dry matter production post heading increased by 6% to 11%. The plant population quality and dry matter partitioning were also improved. As a result, the yield of double-seedling transplanting under SRI was 9253 kg/ha in the nitrogen rate of 150kg/ha, which was 200 kg/ha higher than that of conventional system. Further results showed that under SRI, high nitrogen rate increased the rice population density, but decreased dry matter production post heading and inhibited dry matter redistribution, and therefore did not increase the rice yield.

With hybrid rice, SRI and conventional system produced rice yields of 11750 kg/ha and 11497 kg/ha, respectively, with similar panicle number per hectare. As compared to conventional rice, hybrid rice exhibited stronger root system and higher tillering ability, which insured sufficient panicle number under SRI. These results implied that hybrid rice was better adapted to the SRI with the benefits of water and nitrogen saving.