Effect of roots of two mixed sowing herbaceous plants on soil shear strength
LIU Yufei1, ZHAO Yike2, YANG Yuanjun1, ZHANG Liyun3, LIU Wujiang4, XIONG Shoude4, DUAN Qingsong3
1. College of Water Resources, Yunnan Agricultural University, 650201, Kunming, China; 2. Kunming Land Development and Consolidation Center, 650100, Kunming, China; 3. College of Mechanical and Electrical Engineering, Yunnan Agricultural University, 650201, Kunming, China; 4. College of Resources and Environment, Yunnan Agricultural University, 650201, Kunming, China
Abstract：[Background] Plant roots have a positive effect on improving slope stability and reducing soil erosion. Herbaceous sowing methods include single sowing and mixed sowing. Previous studies demonstrate that, compared with single sowing, mixed sowing is more beneficial to increasing the total coverage and the height of the grass belt,which in turn enhances the soil and water conservation effect. Therefore, the aim of this study is to explore effects and mechanism of mixed sowing herb roots in natural state improving shear strength of soil, so as to select a reasonable sowing method to strengthen the soil-fixing effect of herbaceous plants, and provide a scientific basis for ecological environment construction.[Methods] The experiment was carried out at the experimental farm of the Yunnan Agricultural University, China. In July 2017, a total of 40 PVC tubes, 51 cm in length, 110 mm in diameter and 3.2 mm in thickness, were all cut in half, and then the halves were bound together by pair with rubber bands. Upland red soil <5 mm in particle size was packed into the rubber-band-fixed tubes with the bottom sealed with plastic film up to 50 cm. The experiment was conducted with 4 treatments(10 samples for each):pure soil, Medicago sativa, Setariaanceps stapf ex massey, and mixture of M. sativa and S. stapf ex massey (1:1). Six seeds were put in each tube, separately. In October 2018, out of each group, 9 tubes were picked randomly, placed in water for 24 h until being fully saturated. Soil columns were taken out from the tubes. Shoots of the plants were cut off. The soil columns were cut into two, 25 cm for each. From each half of the soil columns, a section of 20 cm in the middle was taken as test samples and the section was 10.36 cm in diameter. The saturation density of the samples were tested. Unconfined shear strength was tested on a SJ-1A type strain controlling triaxial apparatus.[Results] :1) ΔC (cohesion increment) in the upper layer of root-soil composite of single M. sativa, single S. stapf ex massey and the mixed sowing were 10.85, 15.587 and 20.284 kPa, respectively; the cohesion of the respective root-soil composite was 125.93%, 180.90% and 235.42% of pure soil cohesion(8.616 kPa).ΔC of the lower layer were 5.134, 11.356 and 14.950 kPa, respectively; the cohesion of the respective root-soil composite was 62.82%, 139.04% and 183.04% of pure soil cohesion(8.168 kPa). 2) The results showed that 85.80% of M. sativa roots were >1 mm in diameter, thinner roots were larger than 0.2 mm; roots of S. stapf ex massey were <0.6 mm in diameter; roots of mixed sowing were in all observed diameter classes. 3) The relationship of ΔC with Rd (root density), Rar (root area ratio) and Q (root content in a column) was significant or extremely significant, and the correlation between ΔC and Q was the strongest.[Conclusions] The soil shear strength increment in the mixed sowing is higher than that in single sowing, which indicates that mixed sowing has better effect on soil and water conservation. The soil shear strength increment of the mixed sowing has fine correlation with Rd, Rar and Q, and the correlation with Q is the best. Thus, Q can be used to predict the soil shear strength increment of mixed herbaceous roots.
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2021, Vol. 19 
