| With the implementation of “Green for Grain” project in Chinese Loess Plateau since 1999, the ecological develoed with great achievement, the cultivation area of jujube trees went up quickly, and became the dominant industry to response decreased farmland area and farmers’ income in this region. While, the water shortage and uneven distribution of rainfall induced to seasonal drought for the key growth stage of jujube trees, and finally affected the yield. Meanwhile, majority of the jujube orchards were managed in a traditional way-clean cultivation that means most of the slope surface was naked, which will raise the risk of potential soil erosion, induece poor water retention of surface soil as well as fertility degradation. It has been problem for agriculture and ecological development in this region, that how to efficiently use the limited rainfall resource to meet the requirement, ensuring jujube production, and reduce soil water erosion.As a part of conservation farming, mulching and tillage will improve the soil structure, conserve more rainfall as soil water, increase soil fertility, reduce slope runoff and efficiently control soil erosion, and has been become the popular topic in academic research. By using an artificial rainfall device to simulate the precipitation of loess hilly region, this study discussed the effects of different mulching and tillage system on soil physical properties, dynamics of water content and available nutrients as well as jujube growth characteristics based on 5 mulch and tillage systems(MTSs), as whole ground jujube mulch(WJBM), stripe tillage(ST), whole ground white clover mulch(WCC), jujube branches mulch beneath the jujube tree + strip tillage(JBM+ST), jujube branches mulch beneath the jujube tree + strip white clover mulch(JBM+SWC), the clean cultivation(CC) was chosen as the control. Following conclusions were obtained:(1) The soil physical propersities were improved under MTSs. The bulk density under all treatments fluctuated during the study period, it increased compared to the initial value in March 2011, and slightly decreasing during the test period. In the end of study(Augus, 2013), the bulk density under MTSs was smaller than CC. The soil-water retention curve showed that the soil water content tended to increase at high soil suction(>0.25 bar) under MTSs. The residual water content, saturated water content under all treatments decreased. The filed water capacity, capillary and available water content increased under MTSs. Soil hydraulic conductivity fluctuated to increase under MTSs, and unsaturated hydraulic conductivity varied to decrease with water head pressure decrease.(2) There is high rainfall interception, obverious runoff and sediment reduction as well as high rainfall infiltration under MTSs during individual rainfall event. The rainfall interception was the highest under WJBM with 13.2%. There is a linear relation between rainfall interception and rainfall amount. Compared to CC, mulch and tillage significantly postponed time to runoff, and controlled the slope runoff and sediment(P < 0.05), in which WJBM, WCC and JBM+SWC are the efficient treatments. The runoff and sediment development under CC and MTSs can be fitted by exponential function and polynomial function, respectively. The fitting result indicates that R-squared was over 0.8. A linear equation was used to fit the accumulated runoff and sediment process, the R-squared was over 0.85. The rank of average soil infiltration rate during the studying period were WCC>WJBM>JBM+SWC>JBM+ST>ST>CC. The Horton and Kostiakov equation were used to fit the infiltration under all treatments, the results indicates that Horton equation was more reasonable and reliable at this scale.(3) The soil water content and distribution under MTSs were better, and the daily water consumption was lowest udner WJBM. The soil water content was the highest under WJBM during the whole study period. The rank of 3-year average soil water content were WJBM>JBM+SWC>JBM+ST>ST>CC>WCC. The soil water content continue to decrease from flowering period and fruit enlarging period and not rise back until fruit ripen period and leaf falling period. With the depth increase, soil water content increased and its CV decreased. The soil water content under CC was lower and more stable. The soil water increment under MTSs was significantly higher that CC in all of the year(P < 0.05), in which WCC was the highest with average value of 58.3±14.3 mm,followed by WJBM, there is no significant difference between MTSs. The daily water consumption under WCC was significantly high than the other treatments, it was least under WJBM, the rank of 3- year average value was WCC>JBM+SWC>CC>JBM+ST>ST>WJBM.(4)There is no significant difference in available nitrogen(AN), available phosphorus(AP) and soil water soluble carbon(WSOC) concentration between all treatments, there is a slight accumulation of AN and WSOC under MTSs during un-growing season. The AN concentration under JBM+SWC and CC are significantly higher than that under WCC in 2011 and higher than WJBM and JBM+ST in 2012(P < 0.05). The rank of AN concentration of 2-year average was JBM+SWC>ST>CC>WJBM>JBM+ST>WCC. The AN and WSOC concentration fluctuated as “decrease-increase-decrease” during the studying period with different range, while AP concentration increased in the beginning and then continually decreased. During non-growing period, the soil nutrients under WJBM and JBM+SWC showed an excellent recovery. The AN and WSOC were consumed during growth season of jujube tree and while clover, and recovered during the non-growing season. While, AP showed a continue consumption. During 2011, AN was consumed most under JBM+SWC and CC, AP was consumed most under ST. Besides, the nutrients loss with sediment was significantly most under CC(P < 0.05). The rank of AN concentration in sediment was ST>CC>WCC>WJBM>JBM+ST>JBM+SWC.(5) There is no significant difference between each treatment. The branches mulch and tillage are good for jujube growth, while WCC showed a slight limitation on jujube tree’s growth. The leaf area index(LAI) showed a similar tendency in jujube tree and white clover, both of them reached a peak in August, of which is the fruit enlarging period, and then decreasing until the next growing season. The LAI under MTSs were higher than that under CC in 2011-2012, LAI was higher under ST in earlier study period and higher under JBM+ST latterly. The chlorophyll content(CHC) variation of jujube tree was similar to LAI during the growth season. The rank of CHC was WCC>ST>CC>WJBM>JBM+ST>JBM+SWC during the whole studying period. The indicators showed that photosynthesis is more intensive under WCC and WJBM. According to the hourly data, the peak of net photosynthetic rate Pn, stomatal conductance Cond appeared at 11:00, the peak of transpiration rate Tr appeared during 11:00-13:00 and the peak of water use efficiency WUE appeared at 9:00, the beginning of measurement.(6) Based on above results, whole ground jujube branches mulch(WJBM) was considered to be the best mulch and tillage mode in loess hilly region after comprehensive evaluation. Consider about the efficient utilization of soil water resource and conservation, 6 representative indicators(soil water increment, runoff reduction, sediment reduction, AN, AP, WSOC) were selected to evaluate the mulch and tillage systems by using the relative difference sum evaluation and the gray multidimensional comprehensive feudatory degree evaluation. The results of relative difference evaluation showed WJBM to be the best mode with a difference sum of 0.01296 with ideal mode. The results of gray multidimensional comprehensive feudatory degree evaluation also showed WJBM to be the best. |
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