Effects of super absorbent polymers on soil microbial properties and Chinese cabbage (Brassica chinensis) growth

Abstract

New water retention materials, super absorbent polymers (SAPs), have shown the potential to improve some soil physicochemical properties and promote growth of some crop species in arid and semi-arid areas. However, the impacts of SAPs on soil microbial properties are unclear. This study was conducted to clarify the effects of two SAPs on soil microbial properties and Chinese cabbage (Brassica chinensis) growth under different water conditions in the greenhouse. Experimental conditions included different irrigation conditions and different quantities of SAPs. Chinese cabbage was harvested after 1-month growth in the greenhouse. Meanwhile, soil samples were collected and sieved (<2-mm mesh). Some of the soils were kept at −4 °C for analysis of soil physicochemical properties, and some at −20 °C for analysis of soil microbial properties. Chinese cabbage samples were thoroughly washed with deionized water for the measurement of fresh weight, shoot length, and root length. The effects from SAPs were not obvious under water sufficient (WC1, watered every 2 days, and WC2, watered every 4 days) since plant properties were smaller in some SAP treatments than those in control. However, under water deficit (WC3, watered every 8 days), there were significant differences in plant shoot length and fresh weight between SAP treatments. There were also significant differences in relative soil water content between water condition (WC) or SAP treatments. The SAPs were beneficial for the formation of large aggregates. Under WC3, the soil organic matter (SOM) increased by 16.9 and 11.5 %, soil microbial biomass C (SMBC) by 32.5 and 19.3 %, and soil microbial respiration (SMR) by 52.1 and 37.2 % with Jaguar C (JC) and Jaguar S (JS), respectively. Under WC1 and WC2, significantly higher copy numbers of AOA in bulk treatment of JC were found compared with control treatment in this study. Under water deficit, the abundance of bacteria was significantly increased by application of SAPs. For almost every property of soil and plant, JC was showing better effects than JS. Our results showed that cabbage growth was restricted under water-deficit conditions and the application of SAPs could conserve soil water and be useful for increasing cabbage growth under water deficit, improving SOM, SMBC, and SMR under different WC, and stimulating amoA gene AOA copy numbers and bacterial gene copy numbers. Thus, there should be no adverse effects of SAP application on soil microbial environment and Chinese cabbage growth.