Thesis Abstract of AGS Students

Delayed of sowing rice bean into upland rice

Elena R. Pantollana (1992)

With intensive cropping systems in the upland areas, cereal-legume intercropping system is considered as one way to increase productivity of the land. Upland rice (Oryza sativa L.), the staple crop of the hilltribe households, is often intercropped on small scale with vegetables and legumes and is commonly grown without nitrogen fertilizer. Yields are low and unstable.

This study was designed to evaluate the effects of intercropping on the yield and yield components, dry matter and nitrogen accumulation of the component crops; to calculate a simple nitrogen balance in the system; to assess effects of time of rice bean introduction into upland rice; and to determine residual effects of the bean treatments on a subsequent crop.

Rice was intercropped with rice bean (Vigna umbellata (Thunb.) Ohwi and Ohashi) in three sowing schedules: simultaneous with rice, intermediate (2 weeks after rice sowing), and late sowing (4 weeks after rice sowing). The additive series design was used to quantify the effects of competition. Residual effects of the bean treatments were examined by a subsequent corn crop.

Results indicated that grain and dry matter yields of intercropped rice in both simultaneous and intermediate sowing were very much depressed. The depression in yield of intercropped rice resulted from the strong competitiveness of rice bean, when the bean was sown late into rice, the depression was lessened. Nevertheless, rice intercropped with late bean sowing yielded only 1,668 kg/ha compared with 2,750 kg/ha in monoculture rice. Estimates of N2 fixation determined from ureide analysis indicated the enhancement of N2 fixation in intercropped rice bean, sown late into rice. Rice sown four weeks before rice bean may have taken up greater portion of soil N that induced rice bean to be more dependent on N2 fixation. Land equivalent ratios (LER) for grain (1.49 SE ± 0.20), dry matter (1.66 SE ± 0.09), and nitrogen (1.51 SE ± 0.40) indicated an advantage of inter-cropping over sole cropping.

Corn yield did not differ significantly (P < 0.05) among the sole and intercropped bean treatments. The average grain yield of corn grown in sequence was 7.7 t/ha after bean treatments and 5.4 t/ha after sole rice. This suggests the effect of some yield-enhancing mechanisms in addition to nitrogen contribution of rice bean.

Nitrogen input into the system was represented by fixation from the air by the rice bean; and nitrogen was removed in the harvested grains of rice, rice bean, and corn. In all intercropping treatments, nitrogen removal in harvested grain exceeded the amount fixed by rice bean. The negative balance was highest in the upland rice monoculture followed by corn, since there was no legume nitrogen fixation. The largest amount of nitrogen fixed by the rice bean intercropped with upland rice resulted in the smallest negative balance of nitrogen in the system of upland rice/ rice bean intercrop followed by corn.

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