Effect of crop rotation and fertilisation on wheat yields and yield stability in long-term experiments

In a long-term crop rotation experiment set up in 1961 the effect of five crop sequences and five fertiliser treatments on wheal yields and yield stability was studied. The soil of the experimental area was a humous loam of the chernozem type with forest residues, slightly acidic in the ploughed layer with weak supplies of available phosphorus and good supplies of potassium. The crop sequences included a wheat monoculture, a periodic wheat monoculture, dicultures, a triculture and a Norfolk crop rotation. The fertiliser treatments represented various fertilisation systems, including organic fertilisers (stable manure, or plant residues with NPK supplementation) and high levels of NPK fertilisation, together with a non-treated control. The yield results were evaluated by means of combined variance analysis, and with the variance and regression methods of stability analysis. Wheat yields in monoculture were lower in all cases than in crop rotation. The yield-increasing effect of crop rotation was inversely proportional to the ratio of wheat in the sequence. The yield-increasing effect (t/ha) was greatest in the Norfolk rotation (1.505), followed by the alfalfa-maize-wheat triculture (1.069), the wheal-maize diculture (0,692) and the wheat-alfalfa diculture (0.35). Compared to the wheat monoculture the yield increase was smaller in the alfalfa-wheat diculture than in the maize-wheat diculture. This is partly due to the fact that the favourable forecrop effect of alfalfa could only be demonstrated in the first two years. When evaluating the forecrop effect of alfalfa, its effect on the water management of the soil must also be taken into consideration. The yield-increasing effect of crop sequences compared to a wheat monoculture was not greatly influenced by fertilisation: the rotation effect was observed both in non-fertilised plots and in plots with good nutrient supplies. A comparison of the effect of the fertiliser treatments in various crop rotations indicated that the significantly highest yield was obtained al high NPK fertiliser levels. The experimental data suggest that the joint application of organic and artificial fertilisers creates better conditions for the manifestation of the crop rotation effect. Both the variance and regression methods of stability analysis contributed to the characterisation of the stability of the experimental treatments in different environments.