A CRITICAL ASSESSMENT OF THE IMPORTANCE OF SEEDLING AGE IN THE SYSTEM OF RICE INTENSIFICATION (SRI) IN EASTERN INDIA

A survey of the system of rice intensification (SRI)-related literature indicates that different authors have drawn conflicting inferences about rice yield performances under the SRI, chiefly because the SRI methodology has been variously advocated, interpreted and implemented in the field using different rice varieties, seedling ages at transplantation, cultivation seasons and nutrient management regimes. In particular, the SRI method of single-seedling transplantation (SST) has potential economic advantage due to reduced seed costs, but it is not clear whether SST is an effective management strategy across a range of seedling ages, and whether there is any specific seedling age that is optimal for yield improvement of a given rice variety. This is an important consideration in rain-fed ecosystems where variable rainfall patterns and lack of controlled irrigation make it difficult to reliably transplant at a specific seedling age as recommended for the SRI. We conducted a five year-long experiment on a rain-fed organic farm using a short-duration upland and a medium-duration lowland landrace, following the SRI methodology. Rice seedlings of different ages (6, 10, 14, 18 and 28 days after establishment) were transplanted at 25 cm x 25 cm spacing in three replicated plots. The performance for each landrace was examined with respect to productive tillers, panicle density, total grain counts per hill and grain yield per unit area. Performances of seedlings of different ages were compared with that of control plots that employed all SRI practices with the exception that 28-day-old seedlings were transplanted with three seedlings per hill. The results indicate that (1) the SRI can improve mean panicle density if seedling age <= 18 days, but that responses differ between varieties; (2) the number of productive tillers per hill is significantly less in SST than that of multiple seedling transplants (MST) of 28-day-old seedlings of both upland and lowland varieties; (3) the total grain numbers per hill of the lowland variety is significantly greater for 14-day-old SST than 28-day-old MST; (4) the grain yield per unit area from young SRI transplants is significantly greater than that from 28-day-old MST for the lowland variety, although the magnitude of the improvement was small; (5) for the upland variety, grain yields declined with the oldest seedlings, but planting multiple seedlings per hill made the yield of the oldest transplants on par with that of younger seedlings planted singly. Our findings suggest that transplanting younger seedlings under the SRI management may not necessarily enhance grain yields.