| In order to investigate the effects of different water saving regulation on the plant physiology and growth characteristics,soil moisture dynamics,water consumption,yield,water use in a typical alley cropping system comprising apple(Malus pumila)-soybean(Glycine max),a field experiment combined mulching with regulated deficit irrigation was carried out in the Loess Plateau of west Shanxi Province in 2017—2018.Three levels of irrigation amounts based on soil moisture thresholds were set:namely 55%(low,W1),70%(medium,W2),and 85%(high,W3)of field capacity.Meanwhile,two kinds of mulching materials including straw mulching(M1)and plastic film mulching(M2)were also used.(1)The results indicated that:the maximum soil moisture content appeared in the straw mulching and the average soil water content in 0-60 cm soil depth increased by 6.55%compared with the CKO treatment.Factors of mulching,irrigation and interaction of the two have significant effects on soil water content,whereas mulching has the greatest impact of all.The soil moisture for all the treatments increased first then reduced and rose again as the distance from the tree row increased.The soil moisture in 0-30 cm soil layer was relatively higher than in 30-60 cm,in which the variation of soil moisture was small.The water-retaining effect of straw mulching was better than film mulching.The W1 and W3 irrigation treatments had better water retention effect than W2 when straw mulch was applied,while the W2 irrigation treatment had higher water-retaining effect as the film mulch was used.According to the indexes of water consumption during the whole growth period,the M2W2 treatment can reduce about 30-50 mm irrigation water compared with other treatments.(2)The water-saving regulation increased the total root length density of apple and soybean,and expanded the root length distribution of apple in horizontal and vertical directions as well.The apple root length density was negatively correlated with the distance from the tree row while the soybeans have positive correlation,and both the crops have negative correlation with the vertical depth.The distribution of soil moisture was first increased with the distance from trees to the crops then decreased at grain filling stage,and the minimum values occurred in the distance 1.5-2.0 m away from the tree line.The cluster analysis showed that the main competition area in soil moisture for the two plants was in the distance 0.5-1.5 m away from the tree row with soil depth of 0-40 cm.The apple fine roots in the M2W2 treatment were concentrated in 20-40 cm soil layer while the soybeans’ were mainly distributed in 0-20 cm soil layer,which alleviates water competition between the two species.(3)The effect of water-saving regulation on plant chlorophyll content(SPAD)was weak,and the maximum chlorophyll content of apple and soybean appeared in film mulching treatments.The water-saving regulation increased the net photosynthetic rate(Pn)and leaf water use efficiency(LWUE)for both apple and soybean,and the maximum value was observed in M2W2 treatment.In this treatment,Pn and LWUE values for both apple and soybean could be increased by 12.42%-22.51%,and 2.13%-35.13%,respectively,compared with other control measures.Although values of Pn and LWUE of soybean increased with the distance from the tree row,there was no significant relationship between the SPAD value and the distance from the tree row.The W2 and W3 irrigation groups combined with the film mulching can promote the growth of apple and soybean.(4)The M2W2 treatment has the highest yield and water use efficiency(WUE)during the two years.The yield was 19.38%-72.91%higher than in W1 and W3 groups,and 17.63%-86.48%for WUE respectively.When compared with CK1 and CK2 treatments,the yields were increased by 55.79%and 28.76%,respectively,and the WUEs were increased by 41.38%and 14.69%,respectively.Moreover,when compared with CKO treatment,the yield and WUE in M2W2 were increased by 52.93%and 38.79%,respectively.The maximum net income was obtained in M2W2 treatment,in which the total investment was reduced 30-650 yuan·hm-2 compared with W3 group,and the net income enhanced 845.7-3890.0 yuan·hm-2.The group of straw mulching was not conducive to improve net income,however the net benefit of M1 W3 treatment was minimal or even a loss occurs.This study showed that the film-mulching combined with medium-water deficit irrigation effectively promoted the physiology and growth of apple and soybean,improved the yield and water use efficiency,and achieved a water-saving,yield-increasing,high-efficiency and sustainable development of alley cropping system.The multi-index comprehensive evaluation and analysis showed that the optimum water saving regulation method was as follows:covering plastic film in young apple-soybean alley cropping system,combined with irrigation with the upper limit of soil moisture in 0-60 cm depth of 70%field capacity.The results of this study can provide a theoretical basis for the development of high-efficiency water resources utilization technology for alley cropping system in the loess region of western Shanxi province. |
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