Effects of across- and along-slope ploughs on soil aggregate stability

Soil aggregate is an key soil fertility identification index which determines the quality and erosion resistance of soils. Soil organic carbon content somehow influences soil stability and soil water-stable aggregate forms. It is a critical driving factor of soil fertility and soil cushioning property. Farming measures also influence changes in soil organic carbon pool and different farming measures have different effects on soil physical and chemical property. To find proper tillage measures on slope croplands in purple soils, the effects of across- and along-slope ploughs on soil aggregate stability in purple soils were studied. Through plot runoff experiments, the characteristics of water-stable aggregates and organic carbon contents in top soils (0~20 cm) were studied. On the slope-land of South China, peasants preferred doing along-slope plough than across-slope plough because ease of along-slope plough. However, rill erosion easily occurred in along-slope plough conditions, especially in big rainfall events. This worsened the degree of soil erosion in the region. On the other hand, research on soil nutrient loss in across-slope plough conditions has sown that due to high risks and inputs, across-slope plough farming was unacceptable to most peasants. Studies have shown that soil aggregate organic carbon content accounts for 90% of surface soil nutrients and agricultural production activities occurred mostly in surface soils. This research studied the effects of across- and along-slope ploughs on water-stable aggregates and organic carbon in surface purple soils. The study offered some theoretical bases for effective utilization of soil management measures in slope-land conditions. Results showed that compared with along-slope plough, across-slope plough increased aggregate water stability index by 38.99%. Aggregate dispersion index in along-slope plough was 1.64 times that in across-slope plough. This suggested that erosion resistance in across-slope plough was stronger than in along-slope plough conditions. Compared with along-slope plough, the average content of >0.25 mm water-stable aggregate in across-slope plough increased by 3.62%. Meanwhile, the average contents of water stable aggregate in >5 mm, 5~3 mm and 3~2 mm sizes in across-slope plough were higher than in along-slope plough. This suggested that across-slope plough significantly improved the >2 mm water-stable aggregate content. Percent destruction of soil aggregates in across-slope plough decreased by 3.05%, compared with along-slope plough. Also mean weight diameter (MWD) in across-slope plough was 1.39 times that in along-slope plough conditions. Organic carbon contents in 0.5~2 mm aggregates of the two tillage types were the highest. Under the two tillage measures, percent organic carbon contents in >0.25 mm aggregates decreased with decreasing diameter, reaching the lowest value in 0.5~0.25 mm aggregates. There was no significant difference between the two tillage measures in organic carbon contents in 2~1 mm aggregates, but significant differences existed in the other sizes aggregates. Across-slope plough significantly improved water-stable aggregate contents. It also had a better effect on soil retention capacity of organic carbon and better improved soil structure.