| Based on a long-term conservation tillage project at Lijiabu Village, Dingxi, Gansu Province, six treatments with two tillage systems and three ground covers, namely conventional tillage (T), no-till without stubble retention (NT), conventional tillage with stubble incorporated (TS), no-till with stubble retention (NTS), conventional tillage with plastic film mulch (TP) and no-till with plastic film mulch (NTP) had been studied. The experiment was fully-phased with two rotation sequences. The objectives of this thesis are to explore soil water characteristics, crop water property, soil water balance and soil water transfer in different interfaces of SPAC system by studying soil water retention curves, soil saturated conductivity, soil organic matter, soil temperature, crop leaf water potential, air water potential, crop leaf relative water content and water saturation deficient under different tillage measures.The key results from the study are summarized as follows:1)With the soil suctions variation, the effect of conservation tillage on soil water retention curves varied in both rotation sequences. Soil water retention curves under different tillage measures coincided in spatial variation with high suctions, being 5bar and 15bar, but it was diversity in spatial variation with low suctions, being 0.5bar, 1bar and 3bar.2) Soil bulk density in 0-5cm was lower under NTS and TS than under T and TP in both rotation sequences. As a result, soil total porosity in surface soil and subsurface soil was greatly improved by two stubble retention treatments.3) Effects of tillage measures on mechanical-stable aggregates, water-stable aggregates, stability coefficient at 0-30 cm was determined. Results showed that the macro- aggregate was dominant in mechanism -stable aggregates measured by dry sieve method. Soil water stable aggregates, especially the macro- aggregates, and aggregates stability could be improved by the 5 conservation tillage measures.4) Saturated hydraulic conductivity was significantly difference in different tillage measures. Saturated hydraulic conductivity under NTS was highest, being higher than that under T, TS TP and NTP, while lowest under NTP, being lower than that under T, TS and NT.5) Soil total organic carbon content in 0-30cm was higher under NTS and TS than under T in both rotation sequences. Soil microbial biomass carbon content, especially in surface soil, was higher under NTS, NT and TS than under T in both rotation sequences. Two stubble retention treatments can improve carbon pool management index in 0-30cm. NT can improve carbon pool management index in 0-5cm rather than in 5-30cm. These showed that not no-tillage but stubble retention that could help improve carbon pool management index, indicating NTS is a sustainable measure for soil organic carbon pool management.6) The effect of conservation tillage on soil temperature varied in different environments and different mulch. NTS decreased soil temperature, while NT and TS increased soil temperature. TP and NTP could keep stable temperature arose from buffering the soil temperature changing on the night7) During the whole growing stages, spring wheat and field pea had similar diurnal variation trend of leaf water potential, i. e., the highest in early morning, followed by a descent, and a gradual ascent after the descent. Compared with T, TS, NT and NTS could improve the leaf water potential and relative water content of spring wheat and field pea, while the water saturation deficient was just in adverse. The order of leaf relative water content of spring wheat from high to low was heading stage, jointing, flowering stages and filling stage. The order of leaf water potential of field pea from high to low was squaring stage, branching stage, flowering stage and podding stage.8) For both spring wheat and field pea, grain yield, evapotranspiration (ET) and water use efficiency (WUE) were significantly higher under NTS, NTP and TP than under T, NT and TS . The result in 2008 showed that the order of evaporation from high to low was: TS, T, NTS and NT in spring wheat while T, TS NT and NTS in field pea. For both spring wheat and field pea, NTS increased total amount of evaporation and transpiration significantly. Order of evapotranspiration from high to low was: NTS, T, NT and TS. To sum up, with the crops growth, evapotranspiration of spring wheat and field pea raised and then declined regardless till or not, cover or not, and covered by stubble or plastic film mulch.9) Since the soil water storage was affected by different factors at different stages, such as precipitation, crop growth and evaporation, the difference between treatments were various at different times. There was no big difference between different conservation tillage practices'soil water storage at 0-200cm profiles. But, there was huge difference over years and seasons, and the soil profile had never been full to drainage upper limit (DUL) during research period. From these soil water storage dynamics over 8 years, annual regime for total soil water storage in the whole soil profile (0-200cm) can be divided into three periods: Soil moisture decreasing rapid with crop growth from late spring to early summer (mid of May-mid of July), soil water profile recharging during the rainy season in summer and autumn (mid of July-end of October) and soil moisture keeping relatively constant in winter and early spring (November-early May).10) Path analysis showed that air water potential is the dominant factor for spring wheat to affect diurnal variation of leaf water potential, followed by relative air humidity, soil water suction and air temperature. Relative air humidity is the dominant factor for field pea to affect daily dynamics of leaf water potential, followed by air water potential, soil water suction ,air temperature and solar radiation.
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