| China is the largest apple producer in the world,supplying approximately 40% of the global harvest.The Loess Plateau in the northwest China is one of the two largest apple growing regions in China.Water is a key factor for the sustainable development of rain-fed apple orchards on the Loess Plateau,and is also important for stable yields and the production of high quality fruit.Water scarcity is a critical problem for rain-fed agricultural production in the Loess Plateau,and this has greatly affected yield and quality of apples.Rainwater is the most valuable water resource in this area with a high potential for improved utilization.The exploitation and utilization of rainwater resources is an effective measure for alleviating water scarcity.The Rain Collection and Infiltration Systems(RWCI)is a new method suitable for rain-fed orchards in the Loess Plateau of China,and it has the advantage of saving water,preserving soil moisture,reducing drought stress and storing rainfall runoff.RWCI system is a composite technology including rainwater collection technology,drainage technology,anti-seep technology and water and fertilizer conservation.Six RWCI treatments(with 4replicates)were used in mature apple orchard with 3 design depth(pit depth of 40 cm,60 cm and 80 cm)and 2 watertight design(impervious barrier and non-impervious barrier),and fish-scale pit(CK)and Bare slope(BS)as the controlled trial.Under natural conditions(without irrigation all year round),this study was conducted to investigate the distribution characteristics of soil moisture and roots and the effect of RWCI system on fine roots and apple production.The main research and findings are as follows:(1)There was a low soil moisture zone appeared in the 60-80 cm soil profile under Fish-scale pit treatment(CK).In CK,the variability of soil moisture occurs mainly in the 0-80 cm soil layers and the soil moisture content declined linearly with the increment of the depth of soil layer.On the whole(0-300 cm soil layers),the mean soil moisture content under CK was significantly higher than that in BS.And the increment of the mean soil moisture content under CK was 13.69 % in the dry year(2015)relative to BS,and in the wet year it was0.98%.(2)RWCI system could significantly increase the soil moisture content in the rhizosphere soil of apple tree.All RWCI system(RWCI40,RWCI60 and RWCI80)clearly influence the soil moisture in the 20-100 cm soil layer,and in RWCI system,the increment of annual soil moisture content to CK in 2015(dry year)was obviously higher than that in 2016(wet year).In the 20-100 cm soil layers,the increment of annual soil moisture content in RWCI system(RWCI40,RWCI60 and RWCI80)with impervious barrier were 33.15%,37.40%and 37.40%,respectively,in 2015(dry year)and 45.22%,51.17% and 51.17%,respectively,in 2016(wet year).In the 20-100 cm soil layers,the increment of annual soil moisture content in RWCI system(RWCI40,RWCI60 and RWCI80)with non-impervious barrier were 33.21%,45.99% and 31.50%,respectively,in 2015(dry year)and 47.22%,55.69% and 44.64%,respectively,in 2016(wet year).It can be seen from the comparison of the difference of soil moisture between impervious and non-impervious barrier RWCI system that the shallower depth of RWCI system designed was,the greater the insignificant difference of soil moisture between impervious and non-impervious barrier RWCI system.The result showed clearly that it was not necessary to lay impervious barrier in the pit of RWCI system.The difference of soil moisture between impervious and non-impervious barrier RWCI system increase with design depth of RWCI system,and the annual soil moisture content in impervious barrier RWCI system was significantly higher than that in non-impervious barrier RWCI system,especially in the 80 cm design depth of RWCI system.(3)Under the typical rainfall condition(Daily rainfall: 80 mm),in short time the maximum depth of rain infiltration reached 40 cm under CK,however BS was 20 cm.In all RWCI system with impervious barrier(RWCI40,RWCI60 and RWCI80),the maximum depth of rain infiltration reached 80 cm,120 cm and 200 cm and the soil moisture in 0-80 cm,0-100 cm and 0-180 cm soil layers was obviously affected by RWCI system,respectively.And in all RWCI system with non-impervious barrier(RWCI40,RWCI60 and RWCI80),the maximum depth of rain infiltration was 200 cm,220 cm and more than 300 cm and the soil moisture in0-140 cm,0-160 cm and 0-220 cm soil layers was obviously affected by RWCI system,respectively.The comparison of soil moisture under RWCI system with between impervious and non-impervious barrier showed that the mainly difference of soil moisture was concentrated in the 0-140 cm(RWCI40),0-160 cm(RWCI60)and 0-220 cm(RWCI80)soil depth ranges.(4)The root system distribution proportion in 0-100 cm,100-200 cm and 200-300 cm soil profile was as follows,CK(67.24%,14.94% and 17.82%);impervious barrier design:73.75%,12.89% and 13.36%(RWCI40);66.88%,22.89% and 10.23%(RWCI60);56.96%,18.41% and 24.63%(RWCI80);non-impervious barrier design: 52.94%,27.70% and 19.36%(RWCI40);51.76%,21.40% and 26.86%(RWCI60);54.36%,24.13% and 21.51%(RWCI80),respectively.The result shows that the increasing design depth of RWCI system could increase roots and its activity of deep soil in apple tree.All the RWCI system significantly affects the fine roots of 0-0.1 mm root diameter,and the effects on coarser root is not remarkable.RWCI system could significantly increase weight of single fruit,fruit number per single plant and the yield per single plant,and the effects on fruit number and yield is remarkable.The fruit number under RWCI system(RWCI40,RWCI60 and RWCI80)with impervious barrier was 65.79%,125% and 43.42% higher than CK,respectively,and in RWCI system with non-impervious barrier it was 96.05%,100% and 14.47% higher than CK.Comparison of yield factors under RWCI system with between impervious and non-impervious barrier,the fruit number per single plant under RWCI system with impervious barrier was higher than RWCI system with non-impervious barrier.And the weight of single fruit under RWCI40 and RWCI60 of impervious barrier design reached the maximum value which was 245.5 g and 232.12 g.Overall,the fruit yield under RWCI system of impervious barrier design was highest.(5)The research on apple orchard works technical parameters of rainwater collection and infiltration system(RWCI)was conducted.It determines that the design specification of RWCI system is 80 cm×80 cm,the pit depth is 40-80 cm.And the bottom of the shallow RWCI system(RWCI40)does not need impermeable layer,however,RWCI60 and RWCI80 need. |
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