Abstract
An accurate estimation of crop evapotranspiration (ETc) in intercropping is critical for a theoretical basis for formulating an intercropping irrigation system of fruit trees and improving the soil moisture condition of orchards in arid regions of Southern Xinjiang. Herein, observational data such as soil moisture and plant physiological indicators were measured in jujube/cotton intercropping in the Aksu region from 2015 to 2017. The evapotranspiration of single-crop jujube and cotton was estimated using the modified dual crop coefficient method. Then, based on the proportion of intercropping crops, the soil water stress coefficient was introduced to estimate the evapotranspiration of the jujube/cotton intercropping. The results show that the model has good applicability to simulate single-crop jujube and cotton, and jujube/cotton intercropping. However, compared with single cropping, the accuracy of simulated daily evapotranspiration was decreased. In addition, adjusting the cotton irrigation amount caused the simulation accuracy to further decrease. From the perspective of interspecies complementarity and competition, cotton dominated the intercropping system and had better tolerance to external environmental changes than jujube trees. Intercropping had negative effects on jujube trees in general, and very obvious positive effects on cotton. Based on the 3-year crop yield, 5-year-old jujube trees are recommended for intercropping. During this time, the yield of cotton under the effect of interspecific complementation increased by 26.47%, and the yield of intercropping jujube was similar to that of single crop. As the jujube tree age increases, the effect of increasing cotton production gradually diminishes. The jujube trees also had a significant reduction in yield due to interspecific competition. Our research supports the dual crop coefficient method as appropriate to estimate crop ETc in intercropping and may be further used to improve irrigation scheduling for jujube/cotton intercropping.
Highlights
With the rapid development of the forest and fruit industries in Xinjiang province, China, jujube trees are becoming a new pillar of the local economy
The results showed that both agroforestry systems clearly improved soil water at depths of 0–20 cm and 20–60 cm under jujube trees
The results showed that evapotranspiration calculated by the dual crop coefficient method had a positive correlation with those values obtained by water balance methods, and the root mean square error was about 10 mm
Summary
With the rapid development of the forest and fruit industries in Xinjiang province, China, jujube trees are becoming a new pillar of the local economy. Large areas of orchards have been established by farmers. Young jujube trees produce little fruit, and their economic benefits are often negative, so some farmers use intercropping to relieve economic pressure. Due to the lack of scientific guidance on irrigation systems, fruit trees are vulnerable to great impacts of climate and low agricultural output [1], leading to low enthusiasm for planting new trees among farmers. It is important to establish a scientifically informed irrigation system and achieve higher water use efficiency in order to develop the forest and fruit industry in Xinjiang, China. Intercropping is an efficient way to utilize land for farmers. Due to its comprehensive use of land nutrients, water, light, thermal energy, and other agricultural resources [2,3], it has attracted more and Agriculture 2020, 10, 65; doi:10.3390/agriculture10030065 www.mdpi.com/journal/agriculture
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