Effects of liquid film on the quantity of microorganisms and activity of enzymes in a cotton field

Liquid film is a newly-developed organic macromolecular compound. A thin, solidified crust forms after the diluted compound was sprayed on the soil surface. It was widely reported that after the soil is treated, soil temperature, moisture and porosity increases, and bulk density does not increase. As a result, soil physical, chemical and biological properties differ when compared to non-treated soil. Soil microorganisms and enzymes are main components of soil biochemical properties. They play an important role in nutrient conversion, decomposition of organic matter, degradation of pollutants, and soil remediation. The objectives of this study were: (1) to quantify the effect of liquid film on soil microorganisms and soil enzymes, and (2) to evaluate effects on soil environmental factors. The experiment was completed on a sandy loam at Henan Agriculture University Experimental Station, Zhengzhou, Henan, China. Content of soil organic matter, total N, available P, and available K was 12.1 g/kg, 0.96 g/kg, 24.2 mg/kg, and 115.3 mg/kg, respectively. The product was produced by Henan Agriculture University. The treatments included: T1-75.0 kg/hm2, T2-112.5 kg/hm2, T3-150.0 kg/hm2, T4-187.5 kg/hm2, and CK (open field with no liquid film used). The material was applied at a dilution rate of 1 kg product per 20 kg of water and was sprayed on the interrow soil surface. Approximately 60% of the experimental field was treated. A randomized block design was employed with three replications. Each plot was 4×6 m2. One hundred and fifty kg/hm2 of N, 112.5 kg/hm2 of P_2O_5, and 112.5 kg/hm2 of K_2O were mixed and used as pre-planting fertilizers. Additional 34.5 and 138 kg/hm2 of N was top-dressed at seedling stage and boll stage, respectively. Soil samples in a depth of 0～20 cm for each treatment were taken at pre-sowing, young seedling, early budding, early flowering, and boll opening stage, respectively. Samples were fully mixed, put into sterile bags and transported to the lab as quickly as possible. Part of soil sample was sifted with a 1-mm sieve for analysis of microbial quantity, and part was air-dried for determination of activity of soil enzymes peroxidase, invertase, neutral phosphatase, urease, and polyphenoloxidase with potassium permanganate, sodium thiosulfate, disodium phenyl phosphate, sodium phenoxide, and pyrogallol, respectively. When recommended rates (112.5～150 kg product/hm2) were used, soil bacteria, actinomyces, and fungi significantly increased, and activity of soil peroxidase, invertase, neutral phosphatase, urease, and polyphenoloxidase was enhanced. The results also showed that soil microbial quantity and activity of soil enzymes varied with growing stages. Microorganisms and enhanced activity of soil enzymes was related to improved cotton growth and development, and in turn, status of cotton growth and development exerted influence on soil microorganism population and enzyme activity. Soil microbes were key factors for maintaining soil quality. Based upon above analyses, it could be concluded that the soil stabilizer was helpful for conversion and accumulation of soil organic matter, improvement in soil fertility, and had no negative influence on soil chemical properties.