Effects Of Plastic-film Mulching On Maize Yields And Soil Quality In The Semi-arid Loess Plateau Of China

With increasing food demand worldwide, agriculture in semi-arid region becomes increasingly important. Cultivated area of semi-arid region in China is very large, abundant sunshine included. Then, latent potentialities for increasing grain yields are enormous in this region. In recent years, a rain harvested technology with plastic-film mulching method has been widely used in agriculture for its yield and income increasing effectively. In order to learn about the mechanism of grain yield increasing and evaluate the sustainability of agriculture production to plastic-film mulching method, a study was conducted with maize (Zea mays L.) at three different sites of Ningxian (35°29'N,107°45'E), Chongxin (35°21'N,106°53'E) and Yuzhong (35°54'N,104°05'E) on a semi-arid Loess Plateau of China from 2008 to 2010. Mean annual precipitation is about 565 mm,501 mm and 388 mm and mean annual temperature is about 8.7℃,9.7℃and 6.7℃for Ningxian, Chongxin and Yuzhong experimental sites respectively. Three treatments were tested, non-mulching (CK), half-mulching (HM) and full-mulching (FM). The plastic film was mulched at sowing and reserved in field till the next sowing time. Some main results were obtained.1. Soil daily average temperature increased in 0-20 cm top soil layer with plastic-film mulching in maize initial stage of growth. It increased by 4-6℃at sowing stage, maximally increasing range in maize growth period. With the passing of growth period, it declined gradually till tasseling stage. Compared with CK, FM increased soil moisture of 0-30 cm layer by a proportion of 5.3-39.6% in maize sowing and seedling stage in the following year and then soil moisture reached 15.2-21.5%. Moisture increasing effect for FM was greater than that of HM.2. Compared with no-mulching treatment, plastic-film mulching treatments increased grain yields and water use efficiency significantly. FM and HM increased grain yields by 25-126% and 6-84% respectively. Then grain yields reached 7768-10954 kg ha-1 and 6151-10991 kg ha-1 for FM and HM respectively. Grain yields increased by 43-126% with plastic-film mulching treatments at Yuzhong experimental site where the thermal and water-condition deficiency was more severe than that of Ningxian and Chongxin experimental sites. Increasing effect for grain yields with plastic-film mulching treatments by 6-50% was announced at Ningxian and Chongxin experimental sites. FM and HM increased water use efficiency by 21.3-125.0% and 5.5-75.8% respectively in contrast with CK. Then, water use efficiency was up to 13.7-28.8 kg ha-1 mm-1 and 12.7-23.2 kg ha-1 mm-1 for FM and HM treatments respectively. However, FM and HM decreased grain yields by 20.6% and 12.1% at Ningxian experimental site in 2009 due to serious drought in tasseling stage.3. Nutrients of total N and P content in seeds, stalk and leaf, corn cob and roots of maize were not affected with plastic-film mulching treatments in contrast with no-mulching treatment, but both amount of N and P output increased because biological yields increased. Compared with CK, FM and HM treatments increased amount of N output by 33-98% and 17-66%, P output by 29-108% and 15-69%, respectively. The amount of N output reached 159-228 kg ha-1 and 143-217 kg ha-1, P output reached 19-35 kg ha-1 and 17-33 kg ha-1, respectively. Then, nutrients utilization efficiency for N and P were improved.4. Total soil organic carbon (OC) pool was not affected by plastic-film mulching treatments, but soil labile OC pool decreased. Compared with no-mulching treatment, soil particulate OC, light OC and carbohydrate OC content decreased by 4.8-13.5%, 7.1-26.7% and 12.2-22.7% respectively with plastic-film mulching treatments after the first growth period. The dynamics of soil particulate OC, light OC and carbohydrate OC content was going upward gradually from the second growth period.5. Plastic-film mulching treatments increased soil mineral N content on soil ridges significantly compared with no-mulching treatment. At harvest, mineral N content for FM and HM was 5-208 times and 3-181 times of CK respectively. Then, it reached 70.7-435.9 mg kg-1 and 54.1-380.4 mg kg-1 for FM and HM respectively. The ratio of NH4+-N to total mineral N was less than 30% in soil by application of either plastic-film mulching or no-mulching treatments. Then, plastic-film mulching treatments couldn't make large quantity of NH4+-N accumulated in soil. The concentrations of NO3--N and NH4+-N in the top soil layer of 0-15 cm varied seasonally and reached peak value in maize tasseling period according to the analysis of maize growth stage.6. Soil microbial biomass and enzyme activities increased with plastic-film mulching treatments significantly compared with no-mulching treatment. Soil microbial biomass carbon content and soil alkaline phosphatase, P-glucosidase and urease activities increased with plastic-film mulching treatments. Soil enzyme activities and mineralized C and N content were accord with soil microbial biomass.In general, plastic-film mulching method improved soil temperature and moisture condition, increased soil microbial biomass and its activities, promoted soil organic matter decomposition and soil nutrients availability, accelerated crop growth and dry matter accumulation, increased nutrients and water use efficiency, and then grain yields increased. Simultaneously, plastic-film mulching method decreased soil labile OC pool, however, the dynamics of soil labile OC pool was going upward gradually from the second growth period. Then, whether the plastic-film mulching method was provided with sustainability to agriculture production should have a further research.