Nitrogen Availability of Sewage Effluent to Maize Compared to Synthetic Fertilizers under Surface Drip Irrigation

Abstract

Abstract. Field experiments on maize ( L.) under surface drip irrigation were carried out during two consecutive growing seasons to examine the influence of water quality (groundwater and secondary sewage effluent) and nitrogen (N) application rate on growth and yield, N agronomic efficiency, and N availability of effluent. Pot experiments were conducted using the 15N isotope tracer method and the fertilizer equivalence (FE) approach to provide direct evidence of the effluent N availability derived from the field experiments. Four N application rates ranging from 0 to 180 kg ha-1 for field experiments and from 0 to 2.64 g pot-1 (0 to 210 kg ha-1 equivalent) for pot experiments were investigated with secondary sewage effluent (SW) and groundwater (GW). Results showed that either irrigation with sewage effluent or increasing N application rates from 0 to 120 kg ha-1 were conducive to increasing maize productivity. Nonetheless, SW irrigation reduced the agronomic efficiency of applied N compared to GW irrigation supplemented with fertilizers, suggesting greater potential N losses under SW irrigation. Effluent N that was absorbed by maize was negatively correlated to increasing N application rates. On average, the N contained in effluent was only 51% to 69% as available as an equivalent application rate of urea N in improving maize production. The organic N fraction of effluent (20%) and higher potential N losses from SW irrigation primarily explained the lower effluent N availability in comparison to fertilizer urea. Overall results recommended an economic and ecological N application rate of 107 kg ha-1 for maize under drip irrigation when applying SW, with an approximate 14% urea N reduction to attain a satisfactory yield in comparison to GW irrigation. Keywords: Agronomic efficiency, Fertilizer equivalence approach, Isotope tracer method, Secondary treated wastewater.