Effects of a cover crop on deep soil water and root characteristics in a dryland apple orchard on the Loess Plateau

doi:10.11686/cyxb2022009

Abstract

Abstract:

To clarify the interaction between soil water content and root distribution and provide information for orchard cover crop management in the Loess Plateau， the distribution of apple tree root systems and deep soil moisture contents in the presence or absence of a cover crop were investigated. The experiment was conducted in the apple orchard of Qingyang National Field Station of Grassland Agroecosystems. Two planting patterns were set up， namely， orchard with cover crop （Dactylis glomerata， planted in 2014） and orchard with clean tillage， with annual crop farmland as control. Soil moisture and fine root length density in 0-500 cm soil layer were measured at four locations in the tree rows and between the tree rows for two consecutive years in summer and the effects of cover crop on soil moisture deficit and fine root length density were determined. Soil moisture levels in 0-300 cm soil horizon of orchard with clean tillage decreased by 6.7%-8.3% （P<0.01） compared to the control farmland， while soil moisture in 300-500 cm soil layer was not significantly changed （P>0.05）； soil moisture levels in the whole profile of 0-500 cm of the cover crop treatment were on average 11.5%-12.3% lower than those of the clean tillage treatment. The water deficit in the 0-500 cm soil horizon of the control farmland was 163.9-172.1 mm after 6-7 years of cover crop planting， which was 3.2-4.2 times of that in the clean tillage orchard. In addition， the fine root length density of apple tree roots in the 0-100 cm soil layer was higher than that in deeper layers， and averaged 0.187 cm·cm^-3 in density. Cover crop promoted root length density in the 0-100 cm soil layer. The soil moisture content in the various soil horizons from 0-500 cm decreased with increase in fine root length density and the correlation coefficient was increased by the presence of a cover crop， and was higher in the dry season.In summary， long-term cover crop planting in apple orchards in the dryland area on the Loess Plateau promoted the growth of apple tree roots， reduced deep soil moisture and aggravated deep soil drying， which would have a negative effect on the production of apple trees and water cycling in the local agricultural ecosystem. Cover crop management in apple orchard should be reviewed to ensure sustainable water use.

Key words: Loess Plateau dryland, tree-grass system, soil water deficit, fine root length density, deep soil desiccation

Wei-jie LI, Li WANG, Jing-yong MA, Zi-kui WANG. Effects of a cover crop on deep soil water and root characteristics in a dryland apple orchard on the Loess Plateau[J]. Acta Prataculturae Sinica, 2023, 32(1): 63-74.

Figures/Tables 12

Fig.1 Dynamics of precipitation and air temperature at Qingyang experimental station in 2020 and 2021 and comparison with the long-term average

Table 1 Soil bulk density and field water capacity in the 0-500 cm soil profiles in apple orchard

土层深度 Soil depth （cm）	土壤容重 Soil bulk density （g·cm^-3）	田间持水量 Field water capacity （cm³·cm^-3）
0~10	1.43	28.0
10~20	1.38	27.8
20~30	1.36	28.4
30~40	1.35	29.0
40~60	1.43	30.0
60~80	1.39	31.6
80~100	1.43	28.8
100~150	1.40	29.8
150~200	1.38	28.7
200~250	1.39	29.4
250~300	1.40	29.3
300~350	1.39	28.5
350~400	1.39	27.8
400~450	1.37	28.6
450~500	1.36	28.2

Fig.2 Diagram of apple tree-cover crop system and soil sampling points in cover crop （a） and clean tillage （b） treatments

Fig.3 Soil water content distribution of 0-500 cm profiles in apple orchards and the reference crop field

Fig.4 Soil water content distribution of 0-500 cm profiles at different places on the tree row and inter row in apple orchards with and without cover crop in 2020

Fig.5 Soil water content distribution of 0-500 cm profiles at different places on the tree row and inter row in apple orchards with and without cover crop in 2021

Fig.6 Soil water storage in 0-500 cm soil profiles at different sampling points in apple orchards with and without cover crop in 2020 and 2021

Fig.7 Soil water deficit in 0-100 cm， 100-300 cm， 300-500 cm and 0-500 cm soil layers in apple orchards as compared with reference crop field in 2020 and 2021

Fig.8 Distribution of fine root length density in 0-500 cm in apple orchards with and without cover crop

Table 2 Fine root length density and statistical analysis of 0-100 cm shallow soil in apple orchards

土壤深度 Soil depth （cm）	细根长密度 Fine root length density （cm·cm^-3）	年际 Year （Y）	覆盖模式 Mulching pattern （MP）	年际×覆盖模式 Y×MP
0~10	0.121	NS	NS	NS
10~20	0.125	NS	NS	NS
20~30	0.197	NS	NS	NS
30~40	0.197	**	*	NS
40~60	0.150	**	NS	NS
60~80	0.121	*	NS	NS
80~100	0.059	NS	NS	NS

Fig.9 Fine root length density in 30-40 cm in apple orchards with and without cover crop

Fig.10 Correlation between soil water content and fine root length density of apple trees in apple orchards with and without cover crop

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