Soil health evaluation of rehabilitation lands based on Cornell Soil Health Assessment

Objective: Returning farmland to forests is an important ecological construction project in China. Establishing a soil health evaluation system to evaluate the soil health of returning farmland to forests under different vegetation restoration in the black soil region of Northeast China can provide data support for scientific evaluation of the ecological benefits of returning farmland to forests. Methods: Taking the surface soil of two major vegetation types (pure birch forest and elm-lonicera mixed forest) in the black soil region of Northeast China as the object of study, and using the soil of cultivated land as the control. Combination of field sampling and indoor experiments was used to investigate the characteristics and differences of physical, chemical and biological properties of the soil under the conditions of different vegetation restoration. Based on the Cornell Soil Health Assessment, the soil health evaluation of different vegetation was carried out. Results: i) In the 0~10cm soil layer, the soil bulk density of pure forest and mixed forest decreased significantly by 15.14%~19.18%, and the saturated water holding capacity increased significantly by 33.35%~58.53% compared with the control. In the 10~20cm soil layer, the soil bulk density of pure forest and mixed forest decreased significantly by 6.71%~9.04% compared with the control, and the difference of saturated water holding capacity was insignificant compared with the control.(ii) In the 0-10cm soil layer, the soil carbon, nitrogen and available potassium contents of pure forest and mixed forest increased significantly by 21.75%-29.15%, 35.05%-47.71% and 35.12%-121.63% respectively compared with the control. In the 10-20cm soil layer, the soil carbon, nitrogen and available potassium contents of pure forest and mixed forest increased significantly by 53.57%-54.78%, 93.29%-120.34% and 60.71%-183.28%. iii) In the 0-10cm soil layer, the soil microbial carbon and nitrogen content of pure and mixed forests significantly increased by 97.46%-183.43% and 60.54%-142.54%, respectively compared with the control and in the 10-20cm layer, the soil microbial carbon and nitrogen content of pure and mixed forests significantly increased by 18.63% - 82.55% and 59.00% - 101.34% compared with the control. iv) In the 0-10cm soil layer, the results of soil health scores were mixed forests (11.80 points) > pure forests (8.80 points) > CK (5.47 points). In the 10-20cm soil layer, the results of soil health scores were mixed forests (8.41 points) > pure forests (7.03 points) > CK (4.03 points). Conclusion: The soil health scores of pure and mixed forests were significantly higher than those of the control, and the soil health scores of mixed forests were the highest.The effect of vegetation on the restoration of top soil was more significant after the return of farmland to forest.Vegetation mainly improved soil health by increasing the stability of soil structure.It is suggested that plant species can be enriched in the restoration of degraded soils, and the plant configuration method of mixed tree-irrigation can be used to better restore soil health.