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/（m2？a） in a semi-arid steppe in Inner Mongolia of China,aiming to clarify the relationships of base cations with soil p H,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 p H.The increases of SOC and soil p H would be the dominant factors that contribute to the increase of cations in soil.On a comparison with the initial soil p H before the experiment,we deduced that sheep manure application could partly buffer soil p H 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.

Sensitivity of soils to acid rain in South China

This paper deals with the sensitivity of soils to acid rain in 5 provinces, South China. Based on field work and literature, and taking soil pH, CEC, and the types of residua into account, the authors classified the sensitivity into 4 categories: highly sensitive, sensitive, slightly sensitive, and non-sensitive. By overlapping the maps of soil pH, CEC, and types of residua, the map of soil sensitivity in South China has finally resulted.The authors try to summarize the regularity of soil sensitivity to acid rain in this area. The sensitivity of different soil types in the studied area has also discussed.The seriousness and its prospects of acid rain in this area have been pointed out in order to draw the attention of relevant authorities.

Mitigation strategies for soil acidification based on optimal nitrogen management

Soil acidification is a serious constraint to food production worldwide.This review explores its primary causes,with a focus on the role of nitrogen fertilizer,and suggests mitigation strategies based on optimal N management.Natural acidification is determined by the leaching of weak acid mainly caused by climate and soil conditions,whereas the use of ammonium-based fertilizers,nitrate leaching and removal of base cations(BCs)by crop harvesting mostly accounts for anthropogenic acidification.In addition,low soil acid buffering capacity,mainly determined by soil parent materials and soil organic matter content,also accelerates acidification.This study proposes targeted mitigation strategies for different stages of soil acidification,which include monitoring soil carbonate content and p H of soils with p H>6.5(e.g.,calcareous soil),use of alkaline amendments for strongly acidic soils(p H<5.5)with aluminum toxicity risk to p H between 5.5 and 6.5,and decreasing acidification rates and supplementing BCs to maintain this optimal p H range,especially for soils with low acid buffering capacity.Effective mitigation involves optimizing the rate and form of N fertilizers used,regulating N transformation processes,and establishing an integrated soil–crop management system that balances acid production and soil buffering capacity.