IRRIGATION OF SECONDARY SEWAGE EFFLUENT - SALINITY AND NITROGEN EFFECTS ON GROWTH AND NITROGEN-FIXATION OF NODULATED AND NONNODULATED SOYBEANS

Salinity and nitrogenous components are tile most critical water quali ties in secondary sewage effluent (SSE) when used as an alternative re source for agricultural irrigation water. In this study a pot experime nt was conducted to investigate tile effects of salinity and inorganic nitrogen in the irrigation water on the growth and nitrogen fixation of soybean (Glycine max (L.) Merrill) isoline T201 and T202. Nitrogen in the irrigation water as the plant nutrient contributed slightly to dry matter production because the total amount of nitrogen applied int o a pot was small compared to the plant's demand for nitrogen or to th e dosage of applied fertilizer nitrogen. Nitrogen in the irrigation wa ter, however, alleviated the toxic effect of salinity on nitrogen fixa tion of soybean. Moderate salinity that is similar to the salinity of SSE from the city sewage disposal plant slightly affected nitrogen fix ation and reduced dry matter production. Sever salinity water with ele ctroconductivity of 270 mS/m greatly reduced both growth and nitrogen fixation. We should pay more attention to salinity as the water qualit y of SSE rather than nitrogen components when SSE is reclaimed and use d as irrigation water in upland fields.