Using Cesium-137 to investigate soil quality under conservation tillage on steep lands

Abstract

Few studies have demonstrated the long-term effects of different tillage practices on changes of soil quality; however, understanding such effects is vital for the selection and establishment of appropriate soil conservation measures on steep hillslopes. This study was conducted at two adjacent sites in the Sichuan Basin, China, with one cultivated by traditional tillage (TT; i.e., hoeing starts at the bottom position and soil is moved downslope because of gravity and drag) and the other cultivated by conservation tillage (CT; i.e., hoeing is performed from hilltop to bottom, but soil is moved uphill because of drag). We used the Cesium-137 (¹³⁷Cs) tracer technique to identify the pattern of soil constituent distribution and soil quality differences between the two tillage practices. The ¹³⁷Cs residual rate for the CT practice ranged from −29.44% to 34.16% with an average of −8.56%, and the TT practice ranged from −57.12% to 4.63% with an average of −29.49%. A greater increase (ranging from 18.43% to 50.69%) in soil constituents (i.e., soil organic matter, total nitrogen [N], phosphorus [P], and potassium [K], available N, and extractable P and K) was found in the CT soils than in the TT soils. The CT treatment site exhibited markedly higher concentrations of soil constituents in each soil depth profile (0 to 40 cm [0 to 15.7 in] and each 5 cm [2 in] in length increment). The soil degradation index (SDI) for the CT practice significantly increased compared to the TT practice in the 0 to 15 cm (0 to 5.9 in) and 15 to 40 cm (5.9 to 15.7 in) depth of the profiles (p < 0.05). The greatest difference in SDI induced by these two tillage practices occurred at the summit and toeslope positions, with an increase in SDI of 28.07% and 15.76% in the 0 to 15 cm (0 to 5.9 in) depth and of 49.16% and 31% in the 15 to 40 cm (5.9 to 15.7 in) depth, respectively. The ¹³⁷Cs residual rate showed a corresponding relationship with the SDI changing trend, which implied that the ¹³⁷Cs residual rate may be considered an indicator for appraising soil quality for eroding hillslopes. It is suggested that the long-term practice of CT largely diminishes soil degradation because of upslope soil translocation; therefore, it would also significantly improve soil quality in steeply sloping fields.