Interactive effects of species composition and soil conditioners on soil functions and plant responses

Soil conditioners are important for modifying soil degradation and optimizing the management of cultivated grasslands. Soil conditioners may improve soil properties, which directly and/or indirectly affect plant growth and biomass. However, different responses of plant monocultures and mixtures to soil conditioners are still poorly understood. Here, joint effects of soil conditioners and species composition on soil properties, plant growth and biomass accumulation were evaluated in a manipulation experiment. Species compositions were created by growing two typical forages, Onobrychis viciifolia and Elymus sibiricus, either in monocultures or in a mixture, to which five popular commercial soil conditioners (Genbao, Shuijiejumalaisuangan, Hekang, Jinmianshengeng and Tujingpiyoujisuan) were applied. Traits for soil properties (pH, electrical conductivity, soil organic carbon, nitrate nitrogen and ammonium nitrogen) and plant growth (plant height and chlorophyll content) were measured twice after adding soil conditioners, whereas plant biomass was estimated at the end of the experiment. Results showed that species composition and soil conditioners significantly affected the soil and plant properties, and such effects had decreased with the time after adding soil conditioners. Specifically, soil conditioners decreased the soil pH (2.3%) 1 month after their additions, while the soil pH slightly increased after 3 months. On the other hand, plant growth traits and biomass were not significantly impacted by soil conditioners 1 month after their additions, while soil conditioners increased chlorophyll content (4.2%) 3 months after their additions. However, soil conditioners decreased plant biomasses at community (7.5%) and individual (8.9%) scales. Moreover, the improvements in soil properties by soil conditioners were related to plant growth. Tujingpiyoujisuan was identified as the best among the five soil conditioners in terms of its impact on decreasing the soil pH. Its use is recommended for saline-alkali soils in order to improve soil properties to support cultivation of grass mixture at an early growing stage. However, further studies are needed to validate these findings under field conditions in long-term experiments.