Sheep manure application increases soil exchangeable base cations in a semi-arid steppe of Inner Mongolia

The long-term productivity of a soil is greatly influenced by cation exchange capacity (CEC). Moreover, interactions between dominant base cations and other nutrients are important for the health and stability of grassland ecosystems. Soil exchangeable base cations and cation ratios were examined in a 11-year experiment with sheep manure application rates 0-1,500 g/(m(2)center dot a) in a semi-arid steppe in Inner Mongolia of China, aiming to clarify the relationships of base cations with soil pH, buffer capacity and fertility. Results showed that CEC and contents of exchangeable calcium (Ca2+), magnesium (Mg2+), potassium (K+) and sodium (Na+) were significantly increased, and Ca2+ saturation tended to decrease, while K+ saturation tended to increase with the increases of sheep manure application rates. The Ca2+/Mg2+ and Ca2+/K+ ratios decreased, while Mg2+, K+ and Na+ saturations increased with increasing manure application rates. Both base cations and CEC were significantly and positively correlated with soil organic carbon (SOC) and soil pH. The increases of SOC and soil pH would be the dominant factors that contribute to the increase of cations in soil. On a comparison with the initial soil pH before the experiment, we deduced that sheep manure application could partly buffer soil pH decrease potentially induced by atmospheric deposition of nitrogen and sulfur. Our results indicate that sheep manure application is beneficial to the maintenance of base cations and the buffering of soil acidification, and therefore can improve soil fertility in the semi-arid steppes of northeastern China