Soil Properties Change after Eight Years Under Biofuel Cropping Systems.

Biofuel crops can be important complements to fossil fuels. To investigate the impact of annual and perennial crops grown specifically for biofuel conversion on soil properties, Iowa State University established in 2008 a randomized complete block design experiment with four large-scale, replicated plots for each of four cropping systems: continuous corn (CC), continuous corn with rye cover crop (CCW), unfertilized reconstructed prairie (P), and fertilized reconstructed prairie (PF). All of the experimental plots are tile drained, and they have been managed without tillage. In fall of 2008 and 2015 and after harvest, four soil cores were collected from each plot at two depths of 0-15 and 15-30 cm. We determined soil bulk density (SBD), pH, soil organic carbon (SOC), and soil total nitrogen (STN) for all of the collected samples. Compared to 2008, SBD in 2015 increased in CC and CCW in the surface depth (0-15 cm). In CC, SBD significantly increased from 1.41 to 1.49 Mg m^-3 in 2008 and 2015, respectively. In contrast, because of their dense root system, the prairie cropping systems (P and PF) conserved SBD and kept it lower in 2015 than it was in 2008. Soil pH significantly increased from 2008 to 2015 in all of the treatments because of lime application. After eight years, SOC stock increased in all of the cropping systems in the following order: P > CCW > PF > CC of 9.7, 8.2, 5.2, and 1.0 Mg ha^-1 30cm^-1, respectively. In plots of CC and CCW, STN concentration slightly increased; however, it slightly declined in P and PF.