Effect of different super absorbent polymers on soil moisture and soil nitrogen holding capacity

Application of super absorbent polymer (SAP) is important for improving water and fertilizer use efficiency. In the present study, a soil column experiment was simulated to determine the effects of three SAPs polyacrylate (SAP-A), organic-inorganic multiple agent (SAP-B) and humic acid (SAP-C) on soil moisture and urea/ammonium nitrate nitrogen conservation under eight rounds of watering. Soil nitrogen application without SAP was used as the control treatment. The analyses show that all the three SAPs enhance soil moisture and nitrogen holding capacity, but at different degrees. For soil moisture conservation, SAP-A and SAP-B exhibit similar and better effect, while SAP-C shows relatively less effect. With increasing rounds of watering, the conservation effect of the three SAPs on soil moisture decreases. For soil nitrogen holding capacity, the effect of SAP-C on the two sources of fertilizer is sig-nificantly higher than that of the control, while the effect for ammonium nitrate is higher than for urea. Though SAP-A has significant holding capacity for urea, its holding capacity for ammonium nitrate is lower, and it even shows increasing nitrogen lose effect after 8 rounds watering. The nitrogen holding capacity of SAP-B is similar to that of SAP-C after 8 rounds watering for urea, but it is moderate for ammonium nitrate. The SAPs have some form of influence on soil urease activity, which correlates with soil nitrogen transformation. The order of the effects of the three SAPs on urease activity is SAP-B > SAP-C > SAP-A with urea application, and is SAP-A > SAP-B > SAP-C with ammonium nitrate application.