Field leveling and direct seeding methods for rice in Portugal.
1991
Luzes D.
In Portugal, irrigated rice is grown on 34,000 ha, with the 140,000 t annual production supplying approximately 2/3 of national consumption. The rice crop is grown exclusively by direct seeding under flooded conditions. Land leveling and seeding are two important operations in this system. Three treatments resulting from the combination of two leveling methods and two seeding methods were tested in the Sado valley in 1988 and 1989 dry seasons: broadcast seeding by airplane onto a flooded field that had been conventionally leveled, and drill seeding and broadcast seeding onto dry fields leveled by airplane using laser equipment. Grain yield, dry matter production, relative growth rate, leaf area index, and plant population were compared. Yields with drill seeding and broadcast seeding onto dry fields were similar; yields with conventional leveling were 30% lower. Plant population seemed to account for the yield differences. Poor germination and emergence had a strong influence on development of the productive population. The main factors responsible for the population reduction were difficult oxygen diffusion caused by a high water level (20 cm.), strong wind velocities (4.5 m/s at 1800 h), and a decrease in available light intensity due to water turbidity with conventional leveling. Dry matter production per plant and relative growth rate were similar in all three treatments. Leaf area index was closely correlated with yield in a parabolic relationship. The data indicate that, at near optimal growing conditions, an asymptotic yield response to population density occurs.
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