Soil Responses To Corn Residue Removal, Tillage, and Fertilizer Application.

Corn stover is considered a major candidate feedstock for cellulosic ethanol refineries, but the long-term effects of residue removal on soil fertility need to be better understood before harvesting residue could be regarded as a viable option. Several recent studies have investigated how the complete removal of stover would lead to changes in soil carbon and nitrogen pools. However, there are little current data on changes in available phosphorus (P) and exchangeable potassium (K) under a residue removal scheme. The interaction of farm management practices, such as tillage and fertilizer application, with the removal of potassium-rich residue could further complicate how soil fertility is altered. This study examined the effect of residue removal on available P and K in soils under continuous corn at four sites in Illinois, USA, five years after establishment. Each site had three levels of residue removal (full, partial, and no removal), two levels of tillage (till and no-till), and four levels of nitrogen fertilizer application rates (67, 134, 201, and 268 kg N ha^-1). Residue removal decreased levels of exchangeable K at two of the four sites, with full-removal values of 82.6 mg kg^-1 and 73.0 mg kg^-1 compared to no-removal values of 94.0 mg kg^-1 and 99.49 mg kg^-1.  At two sites, exchangeable K decreased with higher rates of N application; a third site had its highest level of K, 88.7 mg kg^-1, under the lowest rate of N application. Unlike the observed fluctuations in K levels, P levels showed little significant response, with plant-available P only reduced under the highest rate of N application at one site. These results, and the finding that K levels differed significantly across tillage treatments from site to site, suggest that producers under a residue removal scheme will need to adjust their management practices and possibly apply more potash to ensure that the soil has sufficient K to preserve the system's yields.