Soil restoration amendments are of great importance to maintain soil health. However, the effects of joint application of multiple (more than two) restoration amendments are rarely addressed. We selected nine restoration amendments allocated to three functional groups: organic amendments, inorganic amendments and microbial inoculation. We investigated effects of amendment functional dissimilarity, i.e. if amendments from diverse groups can perform better than amendments from the same group. By maintaining a balanced selection across three groups, we increased the number of amendments to 3, 6 and 9 to unravel its impacts. We further tested if such combinations enhanced resistance against drought by comparing plant biomass, soil enzyme activities, and soil physiochemical properties under drought (30 % water holding capacity) and well-watered conditions (60 % water holding capacity). Increasing the number of restoration amendments increased soil pH toward neutrality, driven primarily by inorganic amendments such as bentonite and vermiculite, irrespective of watering conditions, while improvements in aggregate stability and plant growth occurred only under well-watered conditions. Three amendments from diverse functional groups maximized plant growth and soil multifunctionality under well-watered conditions. On the other hand, under drought conditions, individual amendments- such as straw and vermiculite- showed the strongest positive effects on the overall soil functional performance and plant biomass, exceeding those of combined treatments. Our work highlights the importance of applying restoration amendments from diverse functional groups under well-watered conditions and applying single restoration amendments facing drought stress.
Li et al. (Thu,) studied this question.