An Assessment of Physiological Effects of System of Rice Intensification (Sri) Practices Compared With Recommended Rice Cultivation Practices in India

Abstract

SUMMARYAn evaluation was conducted in eastern India over three years, 2005–2007, to compare the performance of certain System of Rice Intensification (SRI) practices: transplanting single, young (10-day-old) seedlings in a square pattern; no continuous flooding; and use of a mechanical weeder – with those currently endorsed by the Central Rice Research Institute of India, referred to here as recommended management practices (RMP). All plots received the same fertilization, a combination of organic and inorganic nutrients, and the SRI spacing used was 20% less than usually recommended. Accordingly, the results reported here are designated as a modification of SRI recommendations (SRIm). The objective of this research was to understand the benefits in terms of yield and other physiological parameters, if any, from using most if not all recommended SRI practices compared to RMP. These selected SRI practices out-yielded RMP by 42%, with the higher yield associated with various phenotypical alterations, which are reported here. Significant measurable changes were observed in physiological processes and plant characteristics, such as longer panicles, more grains panicle−1 and higher % of grain-filling. The decreased plant density with SRIm management was compensated for by increased per-plant productivity. SRIm hills with single plants were found to have deeper and better-distributed root systems, higher xylem exudation rates, more open plant architecture with more erect and larger leaves, and more tillers than did RMP hills having multiple plants. Due to the reduction in number of hills m−2 in SRIm plots compared to RMP, no significant difference was found in root dry weight or leaf number, tillers or panicle number on an area basis. Nevertheless, in spite of SRIm having fewer hills and fewer tillers per unit area, the leaf area index (LAI) with SRIm practice was greater due to larger leaves. These together with altered plant architecture, contributed to more light interception by SRIm plants. The higher leaf chlorophyll content at ripening stage reflected delayed senescence and the greater fluorescence efficiency (Fv/Fm and ФPS II) associated with SRIm practices contributed to more efficient utilization of light and a higher rate of photosynthesis, which was probably responsible for the observed increase in grain filling and heavier grains compared to RMP plants. The higher photosynthesis rate coupled with lower transpiration in SRIm plants indicated that they were using water more efficiently than did RMP plants. The latter produced 1.6 μ mol CO2 fixed per m mol water transpired, compared to 3.6 μ mol CO2 in SRIm plants.

Towards an understanding of the high productivity of rice with System of Rice Intensification (SRI) management from the perspectives of soil and plant physiological processes

“…Normally, HI of highyield varieties grown in irrigated fields range between 0.4 and 0.5 (Chang and Li 1991). Therefore, the HIs of Zhao et al (2009) and Thakur et al (2010b) obtained in conventionally flooded practices were a little bit lower than the normal value. There is no consistent result for biomass production and HI compared between SRI and conventional practices.…”

“…The harvest index (HI) of rice plants under SRI (0.44-0.51) was higher than under traditional flooding (0.38-0.45) (Zhao et al 2009). Thakur et al (2010b) reported that biomass production of SRI was the same as that with RMP, but the grain yield of SRI was significantly higher than RMP. This difference was attributed to the difference in HI.…”

“…The management practices of system of rice intensification (SRI) include the following points: (1) the age of seedlings at transplantation is less than 15 days (two-tothree-leaf stage); (2) seedlings are transplanted with wide spacing, and one seedling per hill; (3) water management is undertaken to maintain paddy soils in mostly aerobic condition, e.g., by small daily applications of water with no flooding, AWD, shallow water management from PI to harvest, and also active soil aeration through mechanical weeding, and application of organic matter for improving soil structure and function as well as nutrient availability (Dobermann 2004;Tsujimoto et al 2009;Thakur 2010;Thakur et al 2010b). Although these practices might affect the synergistic effects on the growth and yield of the rice plant, each factor should be verified by scientific methods.…”

“…Few reports were available about the effect of N application rate on the growth and yield of rice under SRI (Lin et al 2009;Zhao et al 2009), because N fertilizer was not widely referred to SRI practices (Thakur et al 2010b) and more organic matter was commonly applied to SRI fields than to conventional practice fields (e.g., Tsujimoto et al 2009). The application of N at the rate of greater than 180 kg ha À1 (which included compost as an N source) recorded a maximum yield of 9.5 t ha À1 for hybrid rice grown under SRI, while the yield of hybrid rice grown conventionally with the same N dose by chemical N fertilizer, was 7.7 t ha À1 and yield increased with more N (Lin et al 2009).…”

“…The SRI fields in Madagascar have been continuously plowed to a depth of 25 to 30 cm by double-digging since the adoption of organic matter application in the early 1990s, while conventional fields were plowed 10 to 20 cm (Tsujimoto et al 2009). The depth of the plowed layer was not reported in other references, but the management practices of SRI often include application of compost or other organic amendments (Thakur et al 2010b). Tsujimoto et al (2009) reported that average mineralizable N (at depths of 0-30 cm) was linearly related to rice grain yield irrespective of management practices.…”