| Two years' field experimentation for spring wheat has been carried out in the semi-arid areas on the loess plateau where there is 415mm average precipitation per year. The purpose of this paper is to deal with the impact of plastic film mulch course, pre-sowing irrigation and fertilize nitrogen on soil moisture, soil temperature, nitrogen validity, crop physiological and ecological, yield and nitrogen efficiency. The plastic film mulch course includes no-tectorial, mulching 30 days after sowing, mulching 60 days and mulching the whole growth period. The main result and new opinion are as follows:There are coherence of plastic film mulching effect soil moisture, soil temperature and nutrient validity during different years. The results of two years' experimentation demonstrate that film mulching can increase soil moisture and temperature. The extent of increared temperature appears "U" in the whole growth period. Plastic film mulching can increase soil water content about 1~ 4% in till layer, which is favorable to germinating, seedling and the upgrowth of overground and root. And it can accelerate absorbing nutrient.The improvement of soil moisture and temperature condition induce increase of organic nitrogen mineralization rate and decrease of active nitrogen mass (for instance soil microbial biomass nitrogen). The impact of plastic film mulching course on accumulation of NO3-N in soil profile mainly depends on accumulation and using of crop to nitrogen, and fertilization and other factors. The results of different years are variance.Plastic film mulching affects physiological and ecological of spring wheat. The degree of affection relates with pre-sowing irrigation,crop growth period and precipitation and so on.There is not only the coherent aspect between results of the two years, but the conflicting conclusion. The former lies in elementary coherence of diurnal change rule among various physiological and ecological items. Whereas the latter mostly exists in the large variability of different results in different periods.The proper mulching period effects not only the growth course of spring wheat, but the distribution of photosynthesis production, and accelerates growth and yield formation. The conclusion are drawn from the results that mulching treatment come out earlier 1～9 days than no mulching treatment (mostly earlier 3~6 days). The mulch treatment can accelerate dry matter accumulation and root development; increase underlayer root proportion, which favor to absorb deep soil water. Yield of mulched wheat can exceed unmulched treatment largely, due to high water use efficiency. But the negative impact of mulching lies in the transportation of photosynthesis production to stalk and leaf (shoot).The effect of mulching course on yield and nitrogen efficiency relates with not only pre-sowing irrigation and fertilization, but also precipitation during growth stage. The impact of mulching on yield are different accordance with pre-sowing irrigation condition, fertilize nitrogen and mulching course. The statistical analysis to each yield inscape during two years demonstrates that the number of spike and the number of valid spike are main factors, which affect yield. Nitrogen using efficiency mainly relates with precipitation during crop growth stage. Diversified nitrogen efficiency is lower in 2000 than in 1999, which show that nitrogen effectiveness is not manifest, even with negative effectiveness.As for the whole, mulching during the whole growth stage don't increase yield, uptake nitrogen mass and nitrogen efficiency with high degree. To maintain soil fertility and good soil ecological condition, and to maintain the maintainable development of agriculture, it should be advocated mulching 30~60 days after sowing. |
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