Nutrient Release from Weathering of Purplish Rocks in the Sichuan Basin, China
Purplish soils having high fertility with mineral nutrients inherited from the parent rock are widely distributed in the hills along the Yangtze River, especially in the Sichuan Basin. Pot and field weathering experiments were conducted to mimic rock weathering and nutrient release processes in order to better understand soil fertility and nutrient compensation. Three types of purplish rock formations formed in the Jurassic period, Shaximiao (J2s), Suining (J3s), and Penglaizhen (J3p), as well as one type formed in the Cretaceous period, the Chengqiangyan group (K1c), were used in this study. Results showed that the soil formation rate was in the range from 11.2 to 19.6 mm every year, and rock weathering was in the order of J3s > J3p > J2s > K1c. Because more rock surface was exposed to sunlight and rainfall in field conditions, pot weathering was slower than field weathering. Nutrient release rates increased with rock weathering and was in the order similar to that of rock weathering: J3p > J3s > J2s > K1c. Potassium release was the most important in all rocks; after 2 years of weathering, 19.4% to 46.9% of K was released from the initial parent rocks, which suggested that K release from weathering could meet most of the crop K requirement in purplish soils. Thus, rapid release of nutrients from weathering of purplish rocks was key to nutrient replenishment and fertility of purplish soils.