| Subtropical red soil area is mainly located in region of sub-humid areas, in the traditional concept where it is rich in water and heat, where drought has not been given much attention. In fact, the sustainable agriculture in red soil area of China is restricted severely by seasonal drought and poor physical properties of red soil. Seasonal drought is a very important stress factor to plant growth and development. Straw mulches retard the loss of soil moisture and coordinate water and nutrient, which is extensively used in the southern red soil region. But the effects on crop growth and yield by straw mulches are different because of the different environment. The objectives of this study were to investigate the effects of straw mulch on soil temperature, moisture, nutrients, crop growth and yield, to quantity the relationship between straw mulch and water use efficiency,nitrogen use efficiency. From the results, some scientific basis were provided for defending the seasonal drought through straw mulch coordinating soil water and fertilizer.An experiment with summer maize as a tested material had been conducted in field. The experiment consisted of 3 levels of straw mulch (0,5000,10000 kg/hm2) and 3 nitrogen treatments (0,140,280 kg/hm2). All the treatments were replicated twice in a complete randomized block design. There were 24 plots, each of which was 3.24 m2. The summer maize was sowed in June 1,2010, and harvested September 15. Rice straw was applied at the soil surface in July 10,2010. The soil moisture was explored by FDR; monthly field NH4+-N and NO3--N in 0-20 cm,20～40 cm soil layers were estimated; summer maize morphological changes, including plant height, leaf blade length, leaf blade width and stem diameter were observed from July 10; soil temperature was observed by the thermometer. In the end, the biomass and total N uptake of summer maize were measured after havest. The main finding were obtained as follows:The range of soil surface temperature was narrowed and soil moisture was increased by straw mulch. With the amount of straw mulch increasing, the effect of straw mulch suppressing the soil surface temperature is more significant. Under different weather conditions straw mulch had different effects on soil surface temperature. In sunny day, straw mulch had no obvious effect on soil temperature between 0 to 7 o'clock, and in other time straw mulch depress the soil temperature; In the rainy day, straw mulch mainly played the role of increasing soil temperature. Straw mulch provided a more moderate and adequate moisture for root growth of summer maize as it increased soil water content and narrowed the range of soil temperature, so that the increased number and length of roots expand the scope of plants absorbing water and nutrients and then drought resistance crops was improved. Under the application of nitrogen, straw mulch increased the water use efficiency of summer maize. Under the improved soil moisture status, water use efficiency of summer maize increased with the amount of N fertilizer applied and then the drought resistance of summer maize was improved. Without application of nitrogen fertilizer, the nitrogen deficiency inhibited the growth of roots and reduced water use efficiency and yield of summer maize.Crop production is one of the reflection of whether the crop can resist the drought.When no nitrogen was applied,the yield and biomass of summer maize with 5000 kg/hm2 was higher than nonmulch and mulch 10000 kg/hm2.The yield of summer maize increased with the amount of straw increasing in the 280 kg/hm2 N fertilizer treatment. Rainfall during the test is 80.4% more than the average annual rainfall, so in N fertilizer treatments, morphological characters of summer maize was no significant difference, but the straw mulch had a significant impact on the dry matter accumulation and yield. It is proved that when the soil moisture is sufficient, fertilization can increased crop yield and improve crop resistance to drought.The results obtained from incubation showed that straw mulch slowed the rate of nitrogen mineralization in the soil. When the temperature was raised, the difference was narrowed and even disappeared. When the soil moisture was 0.20 cm3/cm3 or 0.25 cm3/cm3, the difference between the mulch treatment and non-mulch treatment was more remarkable than at 0.15 cm3/cm3. In field maize experiment, the content of NH4+-N and NO3--N was higer in non-mulch than in mulch treatment during the early stage of summer maize and in the later stage it was contrary. This showed that N fertilization in the field stimulated nitrogen mineralization in the soil, then there were more nitrogen for the maize in the later growth period. The results showed that maize N uptake was significantly higer in the mulch treatment than nonmulch. With the increased amount of straw mulch, nitrogen use efficiency of summer maize was increased in no N fertilizer treatment; straw mulch reduced the nitrogen use efficiency in N fertilizer treatment. |
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