NejadiJ., and RaoufatM. H. “Field Performance of a Pneumatic Row Crop Planter Equipped With Active Toothed Coulter for Direct Planting of Corn in Wheat Residue”. Spanish Journal of Agricultural Research, Vol. 11, no. 2, Apr. 2013, pp. 327-34, doi:10.5424/sjar/2013112-2632.