Thesis Abstract of AGS Students

Wang Guofa (1990)

Soybean (Glycine max (L.) Merrill) under saturated soil culture (SSC) can acclimate to the imposition of high water table which stimulates soybean growth, nodulation and increases yield. This study attempted to evaluate effects of saturated soil culture on soybean adaptation and nitrogen fixation in Chiang Mai, Northern Thailand.

Two soybean varieties, SJ 5 and NW 1, were cultivated under high water table and with conventional irrigation method in sandy loam soil during rainy season in 1989 in the experimental station, Multiple Cropping Centre. Meanwhile, effects of starter nitrogen fertilizer with two levels, nil and 50 kg/ha were observed. On 8 occasions during growth, plant dry matter, nitrogen status, nodulation and nitrogen fixation were measured and after harvest, yields and yield components were

recorded. SSC increased the amount of nitrogen fixed by 44% over the conventionally irrigated method. This effect was closely related to the depression of uptake of soil nitrogen, shoot nitrogen concentration and increases in nodulation. The crop in SSC derived more of its nitrogen from fixation throughout the growing season.

SSC treatment removed less soil nitrogen from the soil than CI. SJ 5 under SSC without starter nitrogen derived 74% of its nitrogen from the air compared with 54% when irrigated conven-tionally. With removal of 2 t/ha of soybean seed from the field, there was a positive balance of 25 kgN/ha after the SSC treatment compared with a depletion of -13 kgN/ha from the soil after a CI crop NW 1 responded in the same way.

The application of 50 kgN/ha depressed nodulation and nitrogen fixation at early stages, but the effects disappeared later. Plants under saturated soil and conventional irrigation method responded to starter nitrogen in the same way.

There was no significant dry matter and yield response to SSC for both soybean cultivars. However, as an alternative crop in water logging areas, SSC technique may produce soybean yield as high as that of well irrigated soybean.

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