AGRONOMIC AND NITROGEN RECOVERY EFFICIENCY OF RICE UNDER TROPICAL CONDITIONS AS AFFECTED BY NITROGEN FERTILIZER AND LEGUME CROP ROTATION

Nitrogen is one of the most limiting factors for crop growth and productivity. However excessive application can lead to low N efficiency, higher production costs and environmental pollution. Winged bean, bush bean and rice crop plants were grown in a greenhouse with different rates of N fertilizer to estimate nitrogen agronomic efficiency (NAE), nitrogen recovery efficiency (NRE) and N uptake of rice when tropical two vegetable legume plants were grown in rotation with rice crop. Bush bean and winged bean were grown with N fertilizer at rates of 0, 2, 4 and 6 g m-2 preceding rice planting while rice was grown with N fertilizer at rates of 0, 4, 8 and 12 g m-2. Rice after winged bean grown with N at the rate of 4 g N m-2 achieved significantly higher NRE (30-33%) and NAE (24-27 g g-1) during both years. This prevailing effect of rice after winged bean is likely associated with higher biomass and N uptake during both years. Data from two growing seasons showed that rice after winged bean at the rate of 4 g m-2 can produce higher biomass and N accumulation of rice along with superior NRE and NAE values, which indicated a positive response for rice production without deteriorating soil fertility.