Interspecific Root Interactions, Nitrogen Acquisition And Utilization In Fruit Trees/Crops Intercropping In Southern Xinjiang

Fruit trees/crops intercropping play an important role in agricultural production in Hetian old oasis, Southern Xinjiang Uygur Autonomous Region, northwest China because of its high economic value from edible fruit and significant food crop yields. Furthermore, the intercropping also plays a key role for resolving the conflicts between fruit trees and food crops in the region charactered with shortage of arable lands and enhaned population. However, the limited understanding on interspecific interactions and nutrient utilization in the main agroforestry systems inhibit their further healthy development in the area. Field experiments were conducted in Hetian in2011and2012to investigate jujube tree (Zizyphus jujuba Mill.)/wheat (Triticum aestivum L.) intercropping, young walnut tree (Juglans regia L.)/wheat intercropping and corresponding monocropping included jujube trees, walnut trees and wheat. The nitrogen acquisition and utilization and root distributions were determined by various methods, such as roots collection by auger sampling, nitrogen competition and acquisition by1N stable isotope labeling. Our objectives were to understand grain and fruit advantages for jujube/wheat and young walnut/wheat intercropping in terms of root distributions, nitrogen acquisition, fertilizer-use efficiency.The main results were as follows:(1) Experiment parameters suggesting that the two fruit trees/crops intercropping systems had an advantage in land use. Average land equivalent ratio (LER) of yield and above-ground biomass were1.44,1.45,1.24and1.38,1.67,1.51for wheat/2,4,6-year-old jujube tree intercropping, respectively. LER of yield and above-ground biomass were1.29,1.38,1.20and1.23,1.32,1.30for wheat/3,5,7-year-old jujube tree intercropping, respectively. In addtion, LER of above-ground biomass were1.44,1.45for wheat/1,2-year-old walnut tree intercropping, respectively, over the two-year study period.(2) The yield and above-ground biomass were lower in the two fruit trees/food crops intercropping systems than in the corresponding monocrops. The above-ground biomass and yields of intercropped wheat did not decreased significantly in wheat/2,3-year-old jujube tree intercropping, but decreased mostly in wheat/6,7-year-old jujube tree intercropping systems, compared to corresponding monocropped wheat. In contrast, the above-ground biomass and yields of intercropped jujube were reduced to some extent at2or3years of age of jujube, but did not reduce significantly at6or7years of age of jujube, compared to corresponding ages of monocropped jujube. For wheat/young walnut tree intercropping systems, there was significant decreases in the above-ground biomass of intercropped tree and wheat, and grain yield of intercropped wheat in2012, although there was no significant decreases in2011, compare to corresponding monocropped wheat and walnut tree, respectively.(3) The RLDs of both intercropped species decreased to some extent compared to monocropping because of belowground interspecific competition in wheat/jujube tree intercropping systems. The interspecific competitive intensity of jujube tree was stronger than that of wheat. In addition, the roots of intercropped jujube trees spread into the root zone under wheat and tend to have a more shallow distribution in the soil profile compared to monocropped jujube trees. The roots of walnut trees spread under the crop and there were consequently relatively lower RLDs at all soil depths than in monocropped walnut trees especially in the second year (2012). The roots of wheat intercropped with walnut trended to have more shallow distribution in the soil profile and had smaller RLD than monocropped wheat. The closer to the tree row, the more intense the interspecific competition.(4) Nitrogen acquisition, nitroen derived from fertilizer (%NDFF) and total fertilizer N use efficiency (%UFN) were higher in the fruit trees/wheat intercroppings than in the weighted means of corresponding monocropped trees and wheat in both years. This indicated an advantage of intercropping in terms of efficient N utilization for both the soil available N and the fertilizer N through complementary effects in time and space. In addition,%UFN of intercropped tree was lower than intercropped wheat. Moreover, the lowest%UFN of every system mentioned above was observed at the15N imbedding depth of120and200cm. This is because there was less crop root in the deep soil layer.