Crop rotational effects on irrigated winter and summer grain crops at Vaalharts

Abstract

The beneficial effect of crop rotation on yield is well known on annual dryland cropping while knowledge is lacking on the rotational effect in short cycle cropping with two annual irrigated crops. Canola, barley and wheat were rotated with groundnut, maize and soybean in 10 different rotation systems of one and two year cycle lengths over four years in a field trial at Vaalharts. Maize crown and root rot intensity and associated pathogens were identified during the fourth year of the trial. Compared to barley and wheat, canola as preceding crop suppressed yields of maize and groundnut by 10% and 13%, respectively. Groundnut, canola and wheat yields were affected by a season x crop system interaction. Barley yields were unaffected by crop rotation. Contrary to expectation, summer crop yields in some one-year systems were not different from those of the two-year systems, indicating that one-year crop systems can be sustainable, provided that two matching crops namely maize and barley in rotation, and wheat and groundnuts in rotation are grown. Maize root rot ratings correlated well (r =−0.80) with maize grain yield. Fungi most frequently isolated from maize crowns were Fusarium oxysporum and Trichoderma spp. and from roots were F. equiseti, F. oxysporum, F. solani, Pyrenochaeta terrestris and Trichoderma spp.