FLOODING STRESS: The Effects of Planting Pattern and Water Regime on Root Morphology, Physiology and Grain Yield of Rice

Abstract

IntroductionRice production needs to be increased by 50 % or more above the current production level to meet the rising food demand. Much of the demand will be arising from Asia, which is the home of two-third of the world's population and where 90 % of total rice supply is grown in diverse environments (IRRI, 2008). Current challenges Keywords plant senescence; planting pattern; root oxidizing activity; single seedling; system of rice intensification; water regime Correspondence A. MishraAbstract Field experiments were conducted over two growing seasons to investigate the effects of variations in water regime and planting pattern on the growth of rice plant roots and shoots and on yield. Four water regimes were evaluated with split plot design: intermittent flooding during the vegetative stage only (IF-V); intermittent flooding extending into the reproductive stage (IF-R); not flooded (NF); and continuously flooded (CF), interacting with three different planting patterns: single seedling per hill with wider 30 · 30 cm spacing (P1); single seedling per hill with closer 20 · 20 cm spacing (P2); and three to four seedlings per hill with 20 · 20 cm spacing (P3). The treatment combination CF/P3 corresponds most closely with current conventional practice. The other combinations were evaluated to contribute to a better understanding of the effects of the two parameters studied, respectively and together. IF-V/P1 was considered as an approximation of System of Rice Intensification (SRI) practice. This study found that the combination of singly transplanted seedlings, both P1 and P2, with the IF-V water regime improved root length density, root physiological activity, and chlorophyll content of the upper and lower leaves, leading to higher grain yield compared with the other treatment combinations. With continuous flooding (CF), P2 gave 23 % more yield compared with the P3 planting pattern. Combining IF-V and P2 produced 32 % more grain yield compared with the CF/P3 treatment. These results showed a synergistic effect on grain yield from reduced intra-hill competition and IF-V water management. In these trials, there was no significant yield difference between the IF-V/ P1 and CF/P3 treatments. Wider spacing improved the performance of individual hills when grown under IF-V water regimes, but tiller number per unit area remained a dominant determinant of yield. The yield reduction observed for CF/P1 compared with CF/P3 indicated that in more hypoxic CF soils, denser plant populations can produce more than sparser ones, whereas the latter benefit from more aerobic soil conditions. Intermittent irrigation during the vegetative growth stage and transplanting single seedlings/hill are major elements of SRI methodology. These findings contribute to an understanding of why SRI methods can produce the higher yields reported. A consideration of the effects of interaction between planting pattern and water regime shows the need to establish empirically the optimum values for these treatments according to varietal, soil and climat...

Impact of Water Management on Rice Varieties, Yield, and Water Productivity under the System of Rice Intensification in Southern Taiwan

“…Plants grown under intermittent irrigation of three-day intervals were significantly taller compared to the others at both panicle initiation and heading stages, whereas comparable results were observed between CF and intermittent irrigation intervals of seven days at heading. This continues to support the findings of [12,42,43] among others, who detailed that rice does not need to be continuously submerged to produce high yields if adequate water is provided at critical growth stages. The SRI practices employed enhanced plant growth and tillering ability to improve plant/culm height and strengthen tillers.…”

“…Chlorophyll content were lowest under CF regimes, indicating that leaf senescence occurred faster compared to plants grown under intermittent irrigation. Such observations were also documented by [42], who confirmed that higher levels of chlorophyll are maintained in the leaves while fluorescence efficiency and photosynthetic rate can be increased under AWD-SRI compared with CF. Thakur et al [5] highlighted that SRI leaves had higher light utilization capacity and a greater photosynthetic rate which ensures sufficient supply of assimilates to the roots for their development and longevity.…”

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

“…Although chlorophyll content of the flag leaves and third leaves decreased with ripening, the rate of decrease is different among planting densities, and chlorophyll content was higher with wider spacing (30 by 30) compared to narrow spacing (20 by 20) (Mishra and Salokhe 2010). This high chlorophyll content with wider spacing was attributed to higher root-oxidizing activity of more widely-spaced rice plants (Mishra and Salokhe 2010). The SPAD value of the flag leaf of hybrid rice with lower plant density grown under SRI management was higher than with higher plant density at the flowering stage (Lin et al 2009).…”

“…Root length density of rice plants grown under SRI (intermittent flooding) was higher than under continuously flooded management, especially in the middle and late ripening growth stages of the rice plants (Mishra and Salokhe 2010). Significantly higher root dry weight per hill and per unit area with SRI compared to recommended management practices (RMP; kept flooded to maintain a ponded water of 5-8 cm depth during the entire vegetative stage of rice plant) was observed during the early ripening stage of the rice plants.…”

“…Thakur et al (2010a) reported that SRI practices through optimum spacing attempt to minimize competition among rice plants for the various growth factors. Although chlorophyll content of the flag leaves and third leaves decreased with ripening, the rate of decrease is different among planting densities, and chlorophyll content was higher with wider spacing (30 by 30) compared to narrow spacing (20 by 20) (Mishra and Salokhe 2010). This high chlorophyll content with wider spacing was attributed to higher root-oxidizing activity of more widely-spaced rice plants (Mishra and Salokhe 2010).…”