Study on primary physicochemical characteristics and nutrient adsorption of four plant cultivation substrates

The primary physicochemical characteristics and the nutrient adsorption of different substrates were carried out, to select suitable cultivation substrates for plant cultivation in space. Four types of plant cultivation substrates (Profile substrate (P), black ceramsite (B), white ceramsite (W), and vermiculite (V)) were used to test and compare the primary physicochemical characteristics, such as micropore, bulk density, total porosity, specific surface area and available nutrient content, as well as the nutrients adsorption for NH₄⁺, NO₃^-, PO₄^3- and K⁺ with seven concentration gradients respectively. Substrate P contained more micropores, with higher parameter values of total porosity, cation exchange capacity, electrical conductivity, and specific surface area, moderate bulk density and pH, and more mineral nutrients such as potassium, magnesium, and sulfur; substrate B was porous, with smaller parameter values of total porosity, cation exchange capacity and specific surface area, minimum electrical conductivity, moderate bulk density, alkaline and smaller content of mineral elements (excepting for calcium); substrate W had smaller micropore size, the highest value of bulk density and contents of NO₃^- and PO₄^3-. Other physicochemical parameters were equivalent to those of substrate B; substrate V was flaky, with the smallest values of bulk density, and the highest values of total porosity and cation exchange capacity. The values of electrical conductivity and specific surface area were smaller than those of substrate P. It contained more mineral nutrients of calcium and sulfur. Substrate V had the highest adsorption capacity for NH₄⁺, NO₃^-, PO₄^3- and K⁺, followed by substrate P, while substrate B and substrate W had relatively weak adsorption capacity. The adsorption capacity of four substrates for cations (NH₄⁺ and K⁺) was significantly higher than that for anions (NO₃^- and PO₄^3-). The orders of average adsorption amount for NH₄⁺, NO₃^-, PO₄^3- and K⁺ by four substrates were respectively: V > P > B > W, P > V > W > B, V > P > B > W and V > P > W > B. In comparison, substrate P and substrate V had better physicochemical characteristics, and stronger adsorption capacity for NH₄⁺, NO₃^-, PO₄^3-, and K⁺.