| Soil erosion and nutrient loss are very serious in China, and surface mulching is considered the most effective measurement for reducing these problems. Plastic film, crop residues are commonly used as mulching materials or cover vegetation is established for soil surface management. But these approaches may bring some adverse effects such as the pollution of plastic residues, cost of collecting crop residues and limiting crop growth by cover plants. Bio-degradable liquid film with its little contaminating risk and the convention of application has been concerned widely.In this study, liquid films were prepared with the bio-material contenting complex polysaccharide. The water retention capacity and degradable characteristics of prepared liquid films were observed. And the effects of liquid film mulching on preventing soil erosion, reducing nutrient loss and inhibiting weed germination and growth were investigated. The main results were as follows:1. The results of SEM observation showed that there were visible differences in the structure among the three prepared films. The film formed with kelp suspension only (Filmc) appeared stached particles while the films formed with mixed solution of kelp and polyvinyl alcohol appeared superimposed layering structure; The three prepared films all had pores and gaps on its surface, and the number of pores and gaps was reduced with the addition of polyvinyl alcohol. The results of water absorption indicated that the water absorption ratio of the film formed with kelp suspension only (Filmc) was 33.7%, the film formed with mixed solution of kelp and polyvinyl alcohol with the ratio of 1% kelp suspension to 5% polyvinyl alcohol solution as 9:1 (Film 1) was 57.6%, the film formed with mixed solution of kelp and polyvinyl alcohol with the ratio of 1% kelp suspension to 5% polyvinyl alcohol solution as 3:1 (Film 2) was 52.8%. Therefore, water absorption ratio of the films formed with the mixture of kelp and polyvinyl alcohol (Film 1 and Film 2) was significantly (P<0.05) larger than that of the film formed with kelp only (Filmc). Thus, mixing of kelp and polyvinyl alcohol in the preparation of liquid films could increase the water retention capacity of the films, and the films may be partially regarded as water retention agents. The results of film degradation experiments showed that the weight loss ratios of Filmc. Film 1 and Film 2 respectively were 100.0%,73.4% and 58.7%; The films formed with the mixture of kelp and polyvinyl alcohol (Film 1 and Film 2) were significantly (P<0.01) lower than that of the film formed with kelp only (Filmc). It was also found that the films of mixed kelp and polyvinyl alcohol prepared in this study were stable as well as degradable under field water conditions. With the comparison between Film 1 and Film 2, weight loss ratios of Film 2 was significantly (P<0.01) lower than that of Film 1. The result indicated that Film 2 with high ratio of polyvinyl alcohol was degraded more difficulty, and it maybe caused the adverse impacts of agricultural environments.2. The results of the simulative experiments showed that cumulative evaporation amounts of the treatments with liquid films (Filml and Film2) were significantly (P<0.01) lower than that of CK (no film) during the whole experimental period. Mulching with Film1 or Film2 could significantly reduce the evaporation of soil water. With the comparison between the treatment Film1 and treatment Film2, cumulative evaporation amount of treatment Film2 was significantly (P<0.05) lower than that of treatment Filml in the 15 days after treatment, implying that mulching with Film2 for reducing water evaporation from soil was more effective. The kinetic characteristics of cumulative evaporation in the simulative experiments with two soils could be illustrated with one-order kinetic equation, and the regression coefficients ranged 0.995-0.999** at the significant level of 1%(P<0.01). The kinetic parameters such as maximum evaporation and half life could be estimated by using the regression equations. The results of the estimation of kinetic parameters showed that mulching with the liquid films prepared not only lowered the maximum evaporation but also extended the half life, implying that the application of liquid films could increase the capacity of soil water retention.3. The results of the simulative experiment showed that mulching with the two liquid films prepared could significantly reduce soil erosion and nutrient losses through runoff. Nitrogen losses in erosion particles of gritty yellowish red soil were obviously less than that of silt-loamy soil, but phosphorus and potassium losses in erosion particles of gritty yellowish red soil were obviously larger than that of silt-loamy soil under 30 mm or 50 mm rainfall conditions. The differences of soil erosion and nutrient losses through runoff between the treatments with two prepared films were not significant.4. Napropamide could be adsorbed by Bentonite, kaolin and zeolite. The isothermal adsorption could well illustrated with Logistic equation, as the regression coefficients ranged 0.987-0.998** at the significant level of 1%(P<0.01). According to the regression equation, the maximum adsorption capacity of napropamide by bentonite, kaolin and zeolite were 265.83g/kg,71.85g/kg and 14.12g/kg, respectively. Bentonite may be used as a carrier of napropamide for preparing the liquid film with weed inhibitor.5. The results of pot experiment showed that mulching with liquid film only, liquid film mixed with napropamide and napropamide addition could inhibit weed germination and growth, with the comparison of the control treatment. Based on the observation of weed types, it was found that napropamide effectively inhibited the growth of Poa annua Linn, Alopecurus aequalis Sobol, Veronica didyma Tenore and Cerastium caespitosum Gilib, and the liquid film also effectively inhibited the growth of Veronica didyma Tenore and Cerastium caespitosum Gilib as well as inhibited the growth of Poa annua Linn and. Alopecurus aequalis Sobol. As seeds of the vegetable crop were sown directly on soil surface, napropamide also inhibited crop growth, but liquid films could alleviate the inhibition of napropamide on crop growth. |
