| Cover crops are usually used in dryland small farmers orchards due to their good economic supply and ecosystem service adjustment capabilities.However,on the loess hilly areas where the groundwater depth is 10 m and agricultural development only depends on natural precipitation,whether a cover crop is suitable for green manure coverage in orchards in this area is highly dependent on its root water uptake profile,which is closely connected with water availability and whether there is a competitive relationship between fruit trees and crop.With the promotion of intercropping measures in orchards,the types of cover crops have become increasingly diversified.Leguminous and cruciferous crops are commonly used in loess hilly areas.However,it is still unclear whether their root distribution characteristics are different,whether root growth will aggravate soil water consumption,and whether they compete strongly with fruit trees.This will increase the resistance to select cover crops suitable for orchard intercropping,optimize the configuration of orchard intercropping system,and then realize the efficient use of limited water resources in the loess hilly area.In response to the above problems,this study focused on the three commonly used cover crops in loess hilly areas including soybeans(Glycine max Merr.),cabbage rape(Brassica campestris L.),and cabbage rape(Brassica napus L.)(The following articles were referred to as SYB,TTR,and CTR,respectively).A two-year field trial monitoring basic data was carried out in2019 and 2020.We systematic investigated the root water uptake distribution and its influencing factors of different crop by method of combining statistical analysis and numerical simulation,and got the main conclusions as follows:(1)The effects of different cover crops on the soil physical characteristics of the root zone are quantified.The average soil bulk density of each layer under the SYB was reduced by 5.6%compared with the bareland control.Compared with other treatments,SYB significantly improved the soil bulk density of the 45-60 cm soil layer;overall,the soil saturated hydraulic conductivity of nearly surface(0-20 cm)was increased while the deeper layer(30-60 cm)was decreased.Compared with the control treatment,except for the 30-45 cm soil layer,the growth of the three cover crops significantly increased the soil saturated hydraulic conductivity(p<0.05);althougth there was no significant difference in the perimeter of the macropores under each treatment,The SYB treatment obviously improved the parameters such as macroporosity and macropore area of each soil layer,and TTR is the smallest,especially SYB improved the distribution of macropores in the deeper soil(45-60cm).(2)The response of soil moisture dynamics to the growth of different cover crops was investigated.At the early stage of growth,the fine root length density(FRLD)of SYB was significantly greater than that of TTR and CTR(p<0.05),and the corresponding soil water content in the root zone of SYB was also the lowest during this period;soil moisture was supplied after the rainy season,the roots of CTR and SYB were significantly stretching deeper,but the soil water content under SYB has been improved,and the water content of the near surface soil(0-20 cm)and the deeper layer(45-60 cm)were higher,while that of the middle soil layer was low;in addition,although the soil water storage capacity under SYB was 0.21 mm lower than CTR,it had a more significant effect on improving the water storage capacity of the45-60 cm soil layer(p<0.05).(3)The applicability of the IM-SVD model to simulate the root water uptake rate of different crops was verified.Except for the seedling period in 2020,the IM-SVD and Hydrus-1D models simulated the soil water dynamics and root water uptake rate of the three cover crops,although they all were affected by rainfall,but R~2is between 0.7647-0.9562,and the RMSE is between 0.007-0.024 cm~3,the overall simulation effect was well.In addition,based on the same set of soil hydraulic parameters,the simulation accuracy of the IM-SVD model for soil moisture is higher than that of the Hydrus-1D model.The simulation results of the two models both showed that the daily root water uptake rate of SYB was higher than TTR and CTR except for the seedling stage in 2020.Moreover,the simulation results of the IM-SVD model on the daily root water uptake rate of different crops were consistent with those of FRLD,and showed a significant positive correlation,which indirectly verified the reliability of the simulation results.In summary,SYB absorbed and utilized water from the 0-30 cm soil layer more and faster than other cover crops,and its growth effectively improved the soil hydraulic properties,thus enhanced the infiltration of rainwater to the deeper soil layer(45-60 cm).At the same time,its root water uptake reduced the spatial heterogeneity of soil water to some extent.Therefore,it is the ideal cover crop type in the orchards in the Loess Hilly Region. |
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