| Water resources scarcity, lower water use efficiency (WUE) and soil desertification are the main factors restricting the sustainable development of agriculture in irrigated oasis of Hexi corridor. It is proved by practice that conservation tillage is an effective system for the reduction of soil wind and water erosion. In order to investigation the probability of popularizing conservation tillage in Hexi region, the thoroughgoing study on soil nutrient conditions, physical properties and biological traits are significant. Thus, two different height of stubble left (20cm and 40cm stubble left), two different stubble retaining styles (stubble pressed and standing after harvest), and two different straw mulching treatment (mulching 6750kg/hm~2 and 3750kg/hm~2) were designed using conventional tillage as control to study the effects on topsoil ecological properties of no-tillage with straw cover in irrigated oasis in this region, through field experiment in Zhangye, China. The results are summed up as below.A. The significant effects of increasing yield and WUENPS20 (leaving 20cm high stubble at harvest, then press) had not only the highest yield and water useefficiency (WUE), but the most efficient water-saving effects. The yields of NPS20, NPS40 (leaving 40cm high stubble at harvest, then press) and NS40 (leaving 40cm high stubble at harvest) which improved greatly were improved 53.08%, 46.59% and 40.81% respectively compared to conventional tillage (CT), and the yields of NS20 (leaving 20cm high stubble at harvest), NSB40 (covering 6750kg/hm~2 straw) and NSB20 (covering 3750kg/hm~2 straw) which had little changes were increased 19.93%, 17.33% and 4.34%. WUE of NPS20, NS40, NPS40, NS20, NSB40 and NSB20 improved 58.02%,43.40%,47.27%,23.78%,20.69% and 8.56% respectively.B. Water-saving effect of conservation tillagea. The effect of straw cover on water maintaining mainly presented at the early stage of spring wheat growth, and it became evident with the increase of mulched straw quantities. At the conditions of same straw quantity, the capability of water maintaining of standing stubble mulch was stronger than that of pressed stubble after harvest. For an instance, the sequence of water content in 0~10cm soil depth was NSB20(15.89%)>NSB40(14.03%)> NS40(12.04%)>NPS40(11.19%)>NS20(10.46%)>NPS20(10.18%)>CT(9.93%).b. Soil water evaporation could be decreased by conservation tillage. Compared to CT, the evaporation of NPS20, NS40, NPS40, NS20, NSB20, NSB40 decreased 5.38%, 40.02%, 48.06%, 51.43%, 39.34% and 46.22%. All though straw mulch has significant water maintaining effects at certain time, It is not the fact that the capability of water maintaining intensified with the increase of mulched stubble quantity. For an instance, the evaporation of NPS20 decreased 114.53% while NSB40 and NSB20 decreased 80.36% and 120.40% respectively compared with CT at winter fallow stage.c. Water reservation in fallow stage could be increased through using conservation tillage, and greater straw mulched treatment had more efficient in reducing soil water evaporation and was benefit to soil water reservation. Soil water reservation of NSB20 and NSB40 that had the most straw was maximal, and increased 27.58mm and 26.44mm compared to CT.d. Soil water content of conservation and CT all had evident seasonal changes. Soil water contents of different soil depth at sowing stage were significantly higher than that of maturing stage and before winter irrigation, while the soil content of latter two stage had no different except that of before irrigation was higher than that at maturing stage.e. Conservation tillage had significant water saving effects that increased irrigation quantum 1950 m3/hm2, which saved water 1950 m3/hm2 on winter irrigation and 800m3/hm2 in growth duration.C. The effects of conservation tillage on soil microbial biomass (SMB)a. Conservation tillage accelerated the activity of soil microbial biomass carbon (SMB-C), which created an-active nutrient storeroom for the favorable growth of crop. After conservation tillage treatment, SMB-C content in 0~20cm soil depth of fallow stage, sowing stage and maturing stage increased 55.67%, 22.67% and 13.14% respectively compared to that of CT. The varieties of SMB-C under different straw and tillage management in different stage had significant different.b. Although some differences lie in the behaviors of soil microbial biomass nitrogen (SMB-N) and SMB-C, parallels also could be found. For an instance, NSB40 and NSB20, which had the maximal straw, had the highest SMB-N content at fallow and maturing stage (increased 435.42% and 66.65% respectively compared to CT), while SMB-N contents of NS40 and NPS40 which had the medium straw were maximum (increased 227.84% and 261.49% respectively compared to CT) at sewing stage in 0~5cm soil depth.c. Not like that of SNB-C and SMB-N that the content in spring was significantly higher than that after harvesting, the tendency of soil microbial biomass phosphorus (SMB-P) changed less with the variety of temperature. As a whole, the SMB-P content in 10~20cm soil layer declined and that in 0~5cm and 5-10cm soil layer ascent with the increase of temperature.d. Soil water has severe influences on soil microbial biomass (SMB) that are not always positive. In some certain conditions, immoderate soil water content could directly restrain the activities of SMB or do that indirectly by leading to unsuitable lower soil temperature in cool season.D. The effects of conservation tillage on soil physical propertiesa. Soil bulk density (BD) of different treatment in different stage had the same tendency. With the increase of soil depth, BD increased or presented the tendency as "increase—decrease". The larger mulched strew quantity had the smaller BD and had the effects of reducing the difference between different soil layer. With the increase of soil depth, BD behaves of CT in seedling stage were similar to that in conservation tillage, but that appeared differences as the time prolongation (with the increase of soil depth, BD decreased at first, then increased, presented the evident tendency as "decrease—increase"). Not only in 0~5cm soil layer but in all tilled one during the whole period, NSB20 had the smallest BD, and BD of NS20 after harvesting was also blower.b. Temperate quantity of mulched straw could decrease BD and increase soil stability. Under the conditions of same quantity of mulched straw, different straw treatment (stubble standing and stubble pressed after harvesting)had no significant effects on BD. BD of 0~5cm soil layer in different treatment presented the tendency of "increase—decrease".c. The profile distribution (0~40cm) of soil strength presented as "increase-*decrease-*increase—decrease"with the increase of soil depth, and the treatment on straw had no significant effects on soil strength. Soil strengthincreased with the increase of soil depth in 0~6cm soil layer and reached maximum in 10~14cm soil layer andincrease to the second maximum in 220~240cm soil layer after decreased to minimum in 16~18cm soil layer, thendecreased in 24~40cm soil layer.E. The effects of conservation tillage on soil organic matter (SOM) and quick-acting nutrienta. After one year's of conservation tillage, the content of SOM in 0~5cm soil layer increased, while that in 5~10cm and 10~20cm were lower compared to the beginning of the trial, and that under CT in different soil layer were all lower than that at the beginning of the trial.b. The SOM content in 0~5cm soil layer of conservation tillage treatment was higher than that of CT, while the difference of the content in 5-1 Ocm and 10~20cm under CT and no-tillage was not evident.c. Through the influences of conservation tillage on alkaline-N, the results showed that the content of alkaline-N in different soil layer under conservation tillage was higher than that under CTd. Olson-P contents in different soil depth under conservation tillage were lower than that of CT, while no difference was found between different treatments.
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