| The Loess Plateau is a typical rain-fed agricultural region where precipitation is scarce.Water scarcity is the main factor limiting agricultural development in this region.Rational agricultural management measures is an important approach to promote agricultural development in the Loess Plateau area.In order to alleviate food shortages and the crisis of global climate change,it is crucial to understand crop water use in semi-arid ecosystems and improve water resource management.Therefore,this study was conducted from 2018 to 2022.Through field experiments,stable isotope analysis was used to investigate the impact of maize-soybean intercropping,soybean-apple tree intercropping,maize densification,and organic fertilizer application on crop water uptake strategies,as well as the changes in crop yield and water use efficiency.This study aims to provide a theoretical basis and guidance for determining suitable cropping systems and agricultural practices to improve crop water use efficiency,regional productivity,and production efficiency.The main conclusions are as follows:1.The study of five different treatments of maize and soybean(monocropped maize,M,monocropped soybean,S,2 rows of maize intercropped with 2 rows of soybean,M2S2,2 rows of maize intercropped with 4 rows of soybean,M2S4,and 4 rows of maize intercropped with 2 rows of soybean,M4S2)revealed the following findings:the land equivalent ratio(LER)values for different intercropping patterns were all higher than 1,and the water use efficiency of intercropping systems is improved by 5.1%to 26.1%compared to monoculture,indicating that intercropping significantly improved crop productivity and water use efficiency.Maize and soybean have different water uptake strategies.For monocropped maize,the main depths of water uptake during the jointing stage,silking stage,and maturity stage are 0-20 cm,150-200 cm,and 20-70 cm,respectively.For intercropped maize,the main depths of water uptake during the jointing stage,silking stage,and maturity stage are 0-20 cm,70-150 cm,and 150-200 cm,respectively.For soybeans,the main depth of water uptake was consistently 0-20 cm for both intercropped and monocropped.In the later stages of crop growth,intercropped maize absorbs water from deeper soil layers compared to soybeans,indicating a niche differentiation in water utilization.Maize in the M4S2 intercropping pattern had shallower water uptake depths and higher water use efficiency compared to the M2S2 and M2S4 patterns.2.Delaying sowing in maize-soybean intercropping systems has an impact on intercropping efficiency,with the greatest yield advantage observed in delayed-sown soybean.Delayed sowing of soybeans and maize in intercropping had no effect on the water uptake depth of soybeans,but it significantly affected the water uptake depth of maize.Compared to conventional sowing time,in the delayed sowing intercropping pattern for soybean(M2s4),the main depth of water uptake for maize during the jointing stage(0-20 cm)remained unchanged,deepened during the silking stage(20-150 cm to 70-200 cm),and became shallower during the maturity stage(70-200 cm to 20-150 cm).In the delayed sowing intercropping pattern for maize(m2S4),the main water uptake depth of maize in the jointing stage(0-20 cm)and silking stage(20-150 cm)did not change,but became shallower during the maturity stage(70-200 cm changing to 20-150 cm).Different sowing dates can lead to temporal and spatial niche differentiation in water utilization,reducing interspecific competition and promoting crop growth and yield improvement.The land and water equivalent ratios indicate differences in the impact of intercropping sowing dates on yield and water use efficiency,with the M2s4 intercropping pattern having the highest land equivalent ratio(1.01-1.34)and water equivalent ratio(0.93-1.33).3.The application of organic fertilizers and increased planting density are important measures to increase maize yield in the Loess Plateau region,and they also affect maize root water uptake.During the jointing stage,maize primarily absorbs water from the 0-20 cm soil layer,which is not influenced by planting density and organic fertilizer.During the silking stage,compared to low-density maize,high-density maize absorbs water from deeper soil layers(from 20-150 cm to 70-200 cm).Compared to the sole application of chemical fertilizers,maize with the combined application of organic fertilizers and chemical fertilizers absorbs water from deeper soil layers(from 20-200 cm to 70-200 cm).During the maturity stage,the interaction between high planting density and organic fertilizer results in maize absorbing water from deeper soil layers(from 0-20 cm to 20-70 cm).The yield and water utilization efficiency of crops with higher planting density increased by 7.2%-14.4%and 7.6%-15.8%respectively,compared to crops with lower planting density under the same fertilizer level.Similarly,under the same planting density,the application of organic fertilizer resulted in a yield and water utilization efficiency increased by 15.4%-23.2%and 17.2-26.1%respectively.By increasing planting density and applying organic fertilizer,maize absorbs water from deeper soil layers,improving yields and water use efficiency.4.As the age of apple trees increases,they tend to absorb water from deeper soil layers.The main water uptake depths for 3-year-old,5-year-old,10-year-old,and 15-year-old apple trees were 0-100 cm,0-300 cm,20-300 cm,and 20-500 cm,respectively.In comparison,soybeans mainly absorbed water from the top 0-20 cm layer.As the age of apple trees increases,their root systems become more developed.The moisture content in the deeper layers of the soil decreases as apple trees age,leading to an increased proportion of water absorption from the shallow soil layers.This intensifies the competition between apple trees and soybeans,thereby affecting the growth and yield of soybeans.Consequently,the output-input ratio is highest in the treatment with 5-year-old apple trees.Therefore,it is not recommended to intercrop soybeans with apple trees that are 5 years or older. |
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