Zeolite as a Tool to Recycle Nitrogen and Phosphorus in Paddy Fields under Straw Returning Conditions

Abstract

Excess nitrogen (N) caused by straw returning to paddy fields undergoing flooding irrigation deteriorates the water quality. The purpose of this research was to use both simulated field and pot experiments to explore a new approach using zeolite to recycle this excess N. The results from simulated field experiments in stagnant water showed N adsorption with different zeolite applications (25, 50, 75, 100, 125, and 150 g L−1). Pot experiments revealed how straw and reused zeolite applications affected the concentrations of ammonia N (NH4+-N), nitrate N (NO3−-N), total N (TN), and total phosphorus (TP) in the surface water and soil layers of the paddy field. Zeolite showed a strong ability to adsorb NH4+-N in wastewater, even in a simulated drainage ditch (100 g L−1 zeolite adsorbed 74% NH4+-N). The zeolite recycled from the drainage ditch was still able to reduce N concentration caused by straw decomposition in the surface water. Zeolite adsorption reduced the peak values of NH4+-N, TN, and TP by 30%, 19%, and 5%, respectively. Based on these findings and conventional field designs, the use of 20 t ha−1 zeolite in the field is effective for recycling N and P. This research provides a sustainable development method to mitigate the water quality deterioration caused by straw returning to the field.