| The effects under conservation tillage system on topsoil infiltration characteristics of Huangmian soil have been determined through the field trial conducted in Dingxi Experiment Station of Dry Land Farming of Gansu Agriculture University. The results are as following: 1. Effects of soil management on sorptivity, macroscopic capillary length as well as mean pore size radius can be summed up effects of soil management on saturated hydraulic conductivity and unsaturated hydraulic conductivity 。In Wheat →Pea→Wheat rotation sequence (field plot with spring wheat), saturated hydraulic conductivity in conventional tillage treatment (T) is 41.71 mmh-1,65.68 mmh-1 and 35.70 mmh-1 respectively at before sowing, after harvesting and fallow stage; Saturated hydraulic conductivity is 40.57 mmh-1,64.17 mmh-1 and 58.21 mmh-1 respectively in No-till without stubble retention (NT); Saturated hydraulic conductivity is 46.46mmh-1, 69.54 mmh-1 and 50.76mmh-1 respectively in conventional tillage incorporated with straw treatment (TS), and 70.4mmh-1,98.7mmh-1 and 116.2 mmh-1 respectively in No-till with stubble retention treatment (NTS). Statistics show that saturated hydraulic conductivity in NTS is significantly higher than that in T, NT and TS at three stages. In Pea→Wheat→Pea rotation sequence(field plot with field pea), saturated hydraulic conductivity saturated hydraulic conductivity in T is37.13 mm h-1,76.55 mm h-1,47.52 mm h-1 respectively at before sowing, after harvesting and fallow stage; Saturated hydraulic conductivity is 59.00 mmh-1, 69.06 mmh-1, 65.37 mmh-1 respectively in NT; Saturated hydraulic conductivity is 38.12mmh-1, 73.73mmh-1 and 50.0 lmmh-1 respectively in TS, and 108.4 mmh-1, 81.1mmh-1 and 103.7 mmh-1 respectively in NTS. Statistics show that saturated hydraulic conductivity in NTS was significantly higher than that in T, NT and TS treatment at the first and third stage. These results showed that NTS treatment can significantly increase saturated hydraulic conductivity. As result, soil water infiltration can be improved in NTS treatment. Both in P→W and W→P rotation sequence, unsaturated hydraulic conductivity was significantly lower in NTS treatment than T, NT and TS treatments. These results showed that NTS treatment can significantly improve soil water infiltration. As result, soil water infiltration can be improved in NTS treatment. Both in Wheat→Pea→Wheat and Pea→Wheat→Pea rotation sequence, unsaturated hydraulic conductivity in NTS treatment is 5.15 mm h-1and 4.82 mm h-1,which is significantly lower than that in T, NT and TS treatments. 2. Both in two rotation sequence, soil bulk density of surface soil can be increased at beginning stage in no-till treatment. But maintained at special level after 2-3 years, which showed that there is modify ability in soil by itself. Soil total porosity in Wheat→Pea→Wheat is 57.994%, 58.295%, 58.732% and 55.832% respectively in T, NT, TS and NTS treatment, and 59.684, 59.088%, 61.680% and 56.212% respectively in Pea→Wheat→Pea rotation sequence. Both in two rotation sequence, soil total porosity is lowest in NTS treatment, which showed that no-tillage can increase soil bulk density as well as reduce total pores. >30um pores content was significantly higher in NTS treatment than that in other treatments. Water stable macro-aggregates(>0.25mm) was higher significantly in NTS treatment than that in T and TS treatments, but not than that in NT treatment. These results show that NTS treatment can improve topsoil structure, which is mechanism that NTS treatment can improve water infiltration. 3. In Wheat→Pea→Wheat rotation sequence, soil total organic carbon is 8.182 gKg, 8.528 gKg"', 8.658 gKg'1 and 9.227 gKg-1 respectively in T, NT , TS and NTS treatment,. And in Pea→Wheat→Pea rotation sequence, that is 8.395gKg-1, 8.497gKg-1, 8.755 gKg-1 and 9.227 gKg-1respectively. Both in two rotation sequence, total organic carbon was significantly higher in NTS treatment than that in T and NT treatments, but not in T and NT treatment. As for T and TS treatment, there exist significant difference only in Pea→Wheat→Pea rotation sequence. These results indicate that No-till with stubble retention can led to increasing of topsoil total organic carbon, which is responsible for improvement of soil water infiltration, but only no -till or straw retention has no effect. 4. Simple correlation analysis showed that there existed significant liner relationships between these characters. Partial correlation analysis showed that onlypartial correlation between saturated hydraulic conductivity (Y) and soil macro-pores content(X3) reached significant level. Multiple step regression analysis showed that there were significant partial regression coefficient between Y and X3, and between Y and total organic carbon(X5). Multiple step regression equation obtained was, Y=1.332X3+0.056X5-0.747. Path coefficient analysis showed that soil macro-pores content and total organic carbon are primary factor of effecting saturated hydraulic conductivity. There existed other characters, such as soil bulk density, total porosity and water stable macro-aggregates, which may effectsaturated hydraulic conductivity, but these effects are minor.
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