Effects of super-absorbent polymers on a soil–wheat (Triticum aestivum L.) system in the field
Introduction
Eighty percent of available water resources in the world are currently used to support irrigated agriculture (Wallace, 2000). As a result of the water resource crisis, water-saving agriculture is essential for the sustainable development of human societies. Furthermore, droughts are predicted to be increasingly severe due to climate change (Gornall et al., 2010). China is the world's most populous country and one of the most impoverished countries in terms of water resources per capita, which suggests that people may be more concerned with water shortages, especially in North and Northwest China. Therefore, new effective water-saving measures are urgently needed. Super-absorbent polymers (SAPs) may help ameliorate this crisis.
SAPs are hydrophilic networks that can absorb and retain 1000 times more water or aqueous solutions than their original size and weight (Sojka and Entry, 2000). Thus, the application of SAPs to soil may increase water-holding capacities and nutrient utilization efficiency (Lentz and Sojka, 1994, Lentz et al., 1998) and reduce water loss (Al-Omran and Al-Harbi, 1997). Previous studies on SAPs have been focused on their effects on particular soil physical and chemical properties (Nadler et al., 1996, Zhang and Miller, 1996), such as pH, electrical conductivity (EC) and soil water content (Bai et al., 2010), for soil erosion control and irrigation management (Sojka et al., 1998) and to study the effects on plant growth and production (Busscher et al., 2009, Islam et al., 2011a). However, few studies have investigated the effects of SAPs on soil microorganisms and plant available water in the natural environment.
In this study, we examined the changes in the soil physical properties, soil microbial activity and biomass that occurred after SAPs were applied in the field during wheat growth. The aim of this study was to provide fundamental information about the impacts of SAPs on the natural environment and the establishment of a framework for environmental safety assessment for soil additives.
Section snippets
Field experimental setup and sampling
The field experiments were conducted in Linfen City, Shanxi Province, China. The site is located at the eastern edge of the Loess Plateau and has a typical semi-arid continental monsoon climate. The soil was a loam with an organic matter carbon of 0.8%, pH of 7.6 and CEC of 13.2 cmol kg and is classified as cinnamon soil (Luvisols) in Chinese soil taxonomy or Alfisols in USA soil taxonomy.
The experimental field was divided into five plots. One plot was set as the control (without SAPs), and
Plant properties
The plants grew quickly from the jointing to the booting stage and more slowly from the booting to the filling stage (Fig. 1). The shoot lengths of the plants showed significant differences between the three stages, but the effect of SAPs was minimal. Only JC-B significantly increased the total grain dry weight (56%; P < 0.05).
Soil water-stable aggregates
Table 2 shows the variation of soil water-stable aggregates throughout wheat growth and among treatments. There were significant differences in the soil particle sizes
Effect of SAPs on the soil water and the growth of wheat
The results of the current study clearly showed that the addition of SAPs could improve the soil water-holding capacity and allowed the soil to hold much more water. Meanwhile, SAPs also had significant impacts on SMHM, while SMHM was fixed by soil particles and could not be used by plants. The fact that SAPs increased soil water content but not soil available water content suggested that the benefit of SAPs to plant growth might be limited. This phenomenon was consistent with the results that
Conclusions
Based on a field experiment using winter wheat, our results indicate that the application of SAPs would be beneficial to the improvement of soil physical properties, which might assist in the control of water loss. At a concentration of 200 kg ha−1, the SAPs strongly increased the absorption of water and the presence of water-stable aggregates. The SAPs did not lead to detectable adverse effects on the soil microbial community and might even enhance it. The influences of SAPs also depended on the
Acknowledgments
This study was supported by the National Science Foundation of China (41071163, 41025004) and the Youth Innovation Promotion Association, Chinese Academy of Sciences.
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