Dynamics of Soil Moisture, pH, Organic Carbon, and Nitrogen Under Switchgrass Cropping in a Semiarid Sandy Wasteland

Switchgrass (Panicum virgatum L.) is a perennial biofuel crop with a high production potential and suitable for growth on marginal land. This study investigates the long-term planting effect of switchgrass on the dynamics of soil moisture, pH, organic carbon (SOC), total nitrogen (TN), nitrate nitrogen (NO₃–-N) and ammonium nitrogen (NH₄⁺-N) for soils to a depth of 90-cm in a sandy wasteland, Inner Mongolia, China. After crop harvesting in 2015, soil samples were collected from under switchgrass stands established in 2006, 2008, and 2009, native mixture, and a control that was virgin sand. Averaged across six layers, soil moisture and pH was significantly higher under the native mixture than switchgrass or virgin sand. However, SOC and TN were significantly higher under the 2006 switchgrass stand when compared with all other vegetation treatments and the control. The SOC and TN increased from 2.37 and 0.26 g kg⁻¹, respectively, for 2009 switchgrass stand, and to 3.21 and 0.42 g kg⁻¹, respectively, for 2006 switchgrass stand. Meanwhile, SOC and TN contents were 2.51 and 0.27 g kg⁻¹, respectively, under the native mixture. The soil beneath switchgrass and native mixture showed the highest NO₃–-N and NH₄⁺-N, respectively. The soil moisture increased with depth while SOC, TN, and NO₃–-N decreased. An obvious trend of increasing moisture, SOC, TN, and mineral N was observed with increasing switchgrass stand age. Thus, growing switchgrass on sandy soils can enhance SOC and TN, improve the availability of mineral N, and generate more appropriate pH conditions for this energy cropping system.