| Agroforestry is one of the important approaches in turning the farmland into forestryprogramme. Tree and medical plant intercropping, as one of the agroforestry sytles, has beenwidely applied in the development of industry restructuring in this area. Seasonal drought,barren soil, and bad irrigation condition result in shortage of water resources in this area, andresultantly water deficit restrict sustainable development of foresty and agriculture. Thus, studyon water ecology of walnut-woad/cassia agroforestry system based on interspecific waterrelation can instruct forestry construction, improve farmer’s income, and promote thesustainable development of ecology and economy. In this paper, indices including stable waterand carbon isotope information, sap flow, and group tranpiration has been used to studyinterspecific water relation in walnut-woad/cassia agroforestry system of planting spacing3m×8m at low hilly area of north China in Jiyuan, Henan province during the year2011to2013.The above research aimed to provide thearetical basis for developing efficient and stableagroforestry system in this area, the results are as follows:（1）Soil water of each plantation pattern all showed obvious spatial and temporal variation.Vertically, soil water content increased with the increase of soil depth; The soil water content atsurface layer of0-10cm varied greatly; horizontally, soil water content in both walnut-woadand walnut-cassia intercropping systems were highest at the distance of0.5m to tree trunck,and lowest in the middle of two tree row. Shade effect of walnut trees decreased soil waterevaporation, which may explain why soil water content in the walnut-woad intercroppingsystem was36.5%and8.78%higher than, and in the walnut-cassia intercropping21.05%and16.1%higher than that in the sole woad or cassia crop system, respectively in the year2012and2013.（2）The spatial distribution of root in different systems was also studied. Vertically, walnutroot was mainly distributed at the10-50cm soil profile, accounting for more than60%. Whilemore than70%of woad and cassia roots (root lenth density) distributed at0-30cm soil profile; horizontally, woad and cassia roots increased with the increase of their distance to tree rows inthe intercropping system. Crop had more roots in the middle of two tree row. Intercroppingalso influence the distribution of tree roots. The root lenth density and root specific area ofintercropping walnut was less than that in the sole walnut system at0-40cm soil profile, butmore than that in the sole system below40cm soil layer. The above results indicated thatwalnut root in the intercropping system shift to a deeper soil layer as a result of the competitionof intercroped crops. In the intercropping system, both tree and crop roots distributed roots atthe range of150~250cm to tree row in10~30cm soil layer, thus, this area may be the mainsoil water and fertilizer competition area.（3）Rainfall was rare during the growth of woad, and it was dry season of a year. Walnutin the walnut/woad intercropping mainly use water from deep soil layer (30-80cm), accoutingfor59.7%of its total water use; cassia mainly grown during July to September, and it rained alot in this peroid, and walnut in the walnut/cassia intercropping mainly use water from shallowsoil layer (0-30cm), accouting for69.9%of its total water use. Both woad and cassia weremainly use shallow layer soil water. During seedling peroid of woad,5.7%and9.7%of theirwater were from the deep soil layer of the intercropping system, but no woad roots were foundin the deep soil profile, which indicated that walnut root had hydraulic lift effect.（4）Water use efficiency (WUE) of potted cassia/woad were researched through theweighing method and stable carbon isotope method simutaneously. The results showed thatWUE calculated by the two methods were positively related (P<0.01), which indicated thatmeasurement of cassia/woad WUE with stable carbon isotope technique is feasible.（5）In the walnut-woad intercropping, the ratio of water used by walnut and woad was0.7:1, accounting for41.25%and58.75%in the year2012; the growth of woad mainly absorbshallow soil water was affected because of spring drought, but a litter influence to walnut relyon deep soil water, while the ratio was2.06:1in the following year in2013, and walnut andwoad accounted for67.4%and32.6%, respectively. In the walnut-cassia intercropping, theratio of water used by walnut and cassia was1.79:1, accounting for64.2%and35.8%in the year2012; and the ratio was1.42in the following year in2013, and walnut and woadaccounted for58.73%and41.27%, respectively. Woad intercropping with walnut reduced45.29%and49.63%of water use respectively in2012and2013, comparing to sole indigowoad.Cassla intercropping with walnut reduced55.84%and61.83%of water use respectively in2012and2013, comparing to sole cassia. And water use of walnut trees form walnut-Woad/cassia intercropping reduced9.83%and6.86%respectively in2012and2013, comparing tosole walnut. Peak water use period of walnut appeared during Jun-Aug, accounted for52%ofthe total water consumption of the growing season. While, woad and cassia consumed watermainly during April to May, and August to September, respectively, they avoid main water useperiod.（6）Although yield of each compoment in the intercropping system was less than the solesystem, the total income of the agroforestry was higher than that of the sole systems, for walnut,the yield in the intercropping system were1.47and1.24times of that in the sole walnut systemin2012and2013, respectively, and for woad and cassia in the intercropping system were1.24and1.49times of that in the sole crop system in2012and2013.According to the above research, deep-rooted trees and shallow-rooted medicine plant inthe walnut-woad/cassia intercropping used water in a complementary manner to use differentlevels of soil moisture. Shade of walnut trees improved water status of crops underneath,reduced their water use and increased their water use efficiency and income. Trees and cropsavoid main water use period. Therefore, it’s feasible to develop walnut-woad/cassiaintercropping in the low hilly area of north China. The above research can instruct structureconfigration and management of agroforestry system in the turning crop to forest program. |
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