Effect of crop rotation and fertilisation on maize and wheat yields and yield stability in a long-term experiment

Long-term experiments are leading indicators of sustainability and serve as an early warning system to detect problems that threaten future productivity. A non-decreasing trend in yield is necessary to call a system sustainable. The stability of yield is also an important characteristic to be considered when judging the value of a cropping system relative to others. In a long-term crop rotation experiment set up in 1961 the effects of seven crop sequences and five fertilisation treatments were studied on the yields of maize (Zea mays L.) and wheat (Triticum aestivum L.) and on yield stability. In the two-factorial split-plot experiment the main plots consisted of crop sequences, namely maize and wheat monocultures, three dicultures, one triculture and a Norfolk crop rotation (maize-spring barley-peas-wheat). Apart From the control the fertiliser treatments represented various fertilisation systems, namely organic manuring (farmyard manure or recycled crop residues supplemented with NPK) and high levels of NPK fertilisation. The long-term experiment was analysed by conventional analysis of variance procedures and stability analysis. The yields of maize and wheat were lower in all cases in a monoculture than in a crop rotation. Reductions in maize yield in a monoculture were chiefly recorded after a dry winter, particularly if the summer was also dry. The reduction in wheat yield in a monoculture could be attributed mainly to pathogenic factors stimulated by the weather. The yield-increasing effect of crop rotation was inversely proportional to the ratio of maize or wheat in the sequence and was greatest in the Norfolk rotation, followed by the alfalfa-maize-wheat triculture, the wheat-maize, the alfalfa-maize and the alfalfa-wheat rotation. Farmyard manure and the recycling of crop residues (maize stalks, wheat straw) with NPK supplementation are efficient ways of fertilising maize and wheat. Significantly higher yields were obtained at high levels of NPK fertilisation, especially in rotations where the proportion of maize or wheat was 50% or higher. The yield-increasing effect of crop sequences compared to the wheat monoculture was not affected by fertilisation. In maize crop sequences, however, fertilisation reduced the rotation effect by almost half. Further research will be required to determine the biological explanation of this phenomenon. The regression method of stability analysis shows that the stability of various crop sequences differed significantly from those of monoculture. The difference can be attributed mainly to the significant differences between the intercepts. The results show that stability analysis is a suitable method for the interpretation of the significant environment x treatment interactions observed in variance analysis models of long-term crop rotation experiments. Both the variance and regression methods of stability analysis contributed to the characterisation of the stability of the experimental treatments in various environments. (C) 2000 Elsevier Science B.V. All rights reserved.