Paddy rice can be cultivated in upland conditions by film mulching to create anaerobic soil conditions

Many people are adapted to the taste of paddy rice and therefore upland cultivation of paddy rice has been tried in water resource limited areas. However, the aerobic soil conditions make paddy rice susceptible to blast disease. The present study aimed at examining responses of grain yield, plant growth and physiology to the relatively anerobic soil conditions created by film mulching for the upland-cultivated paddy rice crop. In Experiment 1, upland and paddy varieties of rice grown in upland conditions were compared with the same paddy variety grown in lowland conditions and the grain filling dynamics, leaf photosynthesis, leaf blast incidence and the final grain yield were examined. In Experiment 2, film mulch was adopted to create relatively anaerobic soil conditions for the paddy variety grown in upland fields and the grain filling dynamics, plant water relations, plant soil nitrogen nutrition and leaf blast incidence as well as the grain quality were compared between upland-grown paddy varieties with and without film mulch and to the same variety grown in lowland conditions. In Experiment 1, grain yield of upland cultivated paddy rice reached a level close to lowland cultivated paddy rice although lower than that of an excellent upland variety. In Experiment 2, the paddy variety grown upland with film mulch showed a higher grain yield than that in non-mulch plots and reached a close level to that in lowland conditions. Film mulch created a relatively anaerobic soil conditions, decreased soil NO 3 -N and increased NH 4 -N, and consequently reduced risk of blast incidence. Compared to those in lowland conditions, paddy rice plants grown upland showed clear osmotic adjustment and improvement in leaf turgor and consequently maintained photosynthetic activities, which would rather be inhibited in dryland conditions. Moreover, the upland cultivated paddy rice contained more proteins and nitrogen and the higher nutritional quality could not be denied although it might not fit the Japanese diet taste. It was possible to produce paddy rice with a reasonable grain yield in upland conditions if film mulching was adopted to create relatively anaerobic soil conditions in the upland field to generate more N in NH 4 + instead in NO 3 status for avoidance of leaf blast incidence.