Effects Of Alternate Partial Rootzone Drying Irrigation On Crops Growth And Soil Microorganism

The conventional surface irrigation is very popular in northwest of China for field irrigation, a large amount of water is wasted and the agricultural water use efficiency is only about 0.46. Such low water use efficiency created enormous room for improving of water-saving irrigation technique. Agriculture developing should give priority to enhancing water use efficiency through improving irrigation technique. Controlled alternate partial rootzone drying irrigation (APRI) is a new irrigation technique which requires that approximately half of the root system is always exposed to drying soil and prevent from water consumption. Moreover, the dried and wetted sides may be shifted periodically. Part of the root system in drying soil can produce large amount of abscisic acid (ABA) and regulate stomatal opening while the rest of the root system in wet soil may function normally to keep the plant hydrated.Thus, APRI is the main line of this thesis. Pot experiment and field experiments of maize were designed, including distinct water patterns (conventional irrigation, alternate irrigation and fixed irrigation), distinct watering levels (sufficient, moderate water deficit and severe water deficit), distinct fertilizer levels (no fertilizer, 120 kgNhm-2 and 240 kgNhm-2) and fertilizer placement treatments. The number, distribution of soil microorganism in rootzone of maize, the growth and yield of maize were investigated. Other two experiments about oilseed rape were carried out under near-field rain shelter, one of them was conducted in big size of container (50×50×70cm), water patterns and groundwater condition were involved. The growth and distribution of oilseed rape roots were monitored and the data of morphological parameter and yield were recorded. The main results of this thesis are as follows:(1)Maize roots distributed evenly in both sides of rootzone and plants grew well under alternate irrigation. Meanwhile, roots were asymmetry under fixed irrigation because of extremely severe water deficit on one side of root system, resulting in restraining growth of aboveground and dry biomass accumulation. Although vigorous maize plants and preponderance yield were gained under conventional irrigation, water use efficiency was lower than that of alternate irrigation. The dry biomass of plant under full irrigation outperformed other water levels in pot experiment, but the highest yield was gained under moderate water deficit treatment, especially with low nitrogen application in field experiments. Moreover, water and nitrogen were provided in distinct furrows, which could avoid environment pollution and enhanced nutrition absorption and yield of plants.(2)Water patterns had little effect on oilseed rape growth and yield components (number of branches, branch lengths, number of pods, etc.). The results suggest that partial root-zone drying doesn't work well with oilseed rape. More researches on indeterminate growth habit plants under APRI should be conducted to determine the limits of this irrigation technique.(3)In pot experiment of maize, soil microorganism distributed evenly in both sides of rootzone under APRI. But under fixed irrigation, the bacteria and actinomyces were less in dry rootzone than that of wet rootzone. However, the fungi preferred drying soil to wet part. In field experiments, the distribution of soil microorganism was more complex because of the treatment factors and their interaction. In general, special wet-dry cycling condition under alternate irrigation created an appropriate micro environment for soil microorganism, especially for bacteria and fungi.(4)A quadratic parabola relationship between the number of soil microorganisms and soil water content was found, indicating the number of soil microorganisms reached a peak at the moderate soil water deficit condition, possibly due to better soil aeration. In terms of nitrogen condition in soil, bacteria multiplied very well in high nitrogen level rootzone; on the contrary, lower nitrogen level in soil provide an appropriate soil environment for fungi and actinomyces. Moreover, the total number of soil microorganism grows with the growth period of maize going on and reached the peak during dough stage and decreased in harvesting period.Our results suggest that APRI could enhance soil microorganism reproduction, resulting flourishing plants and high yield. But APRI is not the most ideal water pattern for all of plants. APRI has its limit in agriculture, restricted by plant species, climate, geographic condition and so on. Moreover, the main goal of agricultural production is not only the greatest economic interest, but also water-nitrogen-saving and sustainable development of agricultural environment.