The Effects of Polyaspartic Acid Amendment on Nitrogen Dynamics in Soil Irrigated with Piggery Wastewater

【Objective】 Polyaspartic acid (PASP) is widely used in agricultural production as a fertilizer synergist, and the aim of this paper is to investigate its impact on mineral nitrogen, pH and EC of soil irrigated with piggery wastewater. 【Method】 The pot experiment was conducted in laboratory. It consisted of four treatments with the PASP concentration being: 0% (P0), 2.5% (P1), 5% (P2) and 7.5% (P3), respectively. Each pot was irrigated by either clean water (W0), or diluted piggery wastewater at volumetric ratio of 1∶10 (W1) or 1∶5 (W2). For each treatment, without fertilization and PASP application was taken as the control. 【Result】 Addition of PASP reduced inorganic nitrogen at the early stage and increased it at the late stage during the time course of the experiment. P3 was more effective in treating the piggery wastewater. Under W0, P2 and P3 reduced NO3- by 21.63 mg/kg and 10.46 mg/kg, and NH4+ by 7.39% to 49.37% in the early stage, respectively, while at the late stage they increased NO3- and NH4+ by 1.41 to 48.07 times, respectively, compared to P0. Under W1, adding PASP reduced NO3- from 5.11 to 25.52 mg/kg, compared with P0, while under W2, it increased NO3- by 5.91 mg/kg to 22.70 mg/kg, compared to P0. From Day 8 to Day 36 after commencement of the experiment, adding PASP increased NO3- by 14.6%~16.10%, compared with P0. Under W1 and W2, adding PASP increased NH4+ at the late stage, and the difference between P2 and P3 was significant. Compared with CK, nitrogen application reduced soil pH, as opposed to other treatments where the pH remained unchanged. Irrigating with the diluted piggery wastewater increased soil EC by 60.15% to 69.76%, compared to the clean water irrigation. 【Conclusion】 Compared with isonitrogenous clean water treatment, adding 7.5% of PASP with the diluted piggery wastewater reduced mineral nitrogen in soil in the early stage while increasing it in the late stage. This is beneficial to nitrogen use efficiency as it reduces nitrogen loss, especially when irrigating with the less-diluted piggery wastewater.