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Effect of Different Fertilizer Management on Water Quality in the Paddy Field

Agricultural intensification is one of the major causes of water pollution. In recent decades, agricultural water quality degradation has become more severe, which in turn emphasizes the importance of improving and implementing sustainable agricultural practices. Precision agriculture variable rate fertilizer application technology is seen as a strategy to reduce environmental pollution caused by excessive fertilizer usage. Fertilizer input rate is altered within the field in response to factors affecting the optimal application rate. The objective of this study was to investigate the effects of uniform rate and variable–rate (N) fertilizer management on surface water quality. Various physical and chemical water quality parameters at the water inlet, paddy field, irrigation canal, and drainage canals were also examined to evaluate seasonal water quality trends. Water sampling was carried out twelve times between September 2018 and July 2019, involving two cultivation seasons within a total of 60 hectares of paddy field in FELCRA Seberang Perak, Malaysia. All water quality measures fall within classes II to IV of the Malaysian National Water Quality Standards (NWQS) with the exception of P, Al, and Fe. In season one, 64% of P, 46% of Al, and 18% of Fe concentrations were found to exceed NWQS Class IV. However, the percentages were lower compared to season two. During the monitoring period, the average concentration of nitrate and ammonia in variable-rate plots was lower than uniform rate plots in both seasons. Furthermore, temperature, Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), pH, Cu, Fe, K, and Mn were significantly different between the two seasons of cultivation.