Phycoremediated N-fertilization approaches on reducing environmental impacts of agricultural nitrate leaching

Abstract

Nitrate leaching is one of the prominent problems of extensive agriculture in attaining maximum yield. Excessive use of nitrogenous fertilizers leads to nitrate (NO3−) pollution in the groundwater and detrimental effects on the environment. In this study, we have phycoremediated the sewage wastewater and evaluated the impact of remediated wastewater on the extent of nitrate leaching in the field condition on the spinach crop. The experiment was set up in polyvinyl chloride (PVC) pipes of dimension 100 cm in length and 30 cm in diameter. The leachates were collected from the depth of 15, 30, 45, 60, and 90 cm to measure the nitrate leaching. The application of microalgal manure significantly reduced NO3− leaching compared to chemically fertilized treatment. The NO3− content in the collected leachate in the treatment T1 at the depth of 0–15 cm (5.03 mg/L), 15–30 cm (5.80 mg/L) and 30–45 cm (4.98 mg/L) was significantly lower than the treatment T5 at the depth of 0–15 cm (8.57 mg/L), 15–30 cm (7.97 mg/L) and 30–45 cm (8.16 mg/L). The reason behind less leaching of nitrate in the algae manure applied treatment was due to the fact, as most of the N fixed by the microalgae present in the form of complex compounds. The leaching could only occur after the mineralization of these compounds. In addition, ammonium content in spinach after harvest was also analysed. Similar to nitrate, the ammonium content was also lesser in phycoremediated manure treatment than chemical fertilizers. The cumulative ammonium content at the depth of 0–15, 15–30 and 30–45 cm in the treatment T1 (121.70 mg/kg) was significantly lower that the treatment T5 (136.43 mg/kg). Optimization methodology of sewage wastewater phycoremediation and its use as adapted N-fertilization presented in this study can be applicable as a policy guideline for sewage wastewater use for irrigation which reduce nitrate leaching and reduce the dependency on the environmentally harmful chemical fertilizers.