Effect of crop rotation on the yield of maize at various nutrient supply levels in long-term field experiments

Crop rotation is a classical element in sustainable, low input agriculture. A wise choice of the proportion and order of crops grown means that the water and nutrient reserves of the soil can be preserved or increased, while the utilisation of the nutrients in the mineral and organic fertilisers applied can be regulated. In addition plant protection costs can also be reduced. The long-term experiments on the effect of crop sequence which have been underway on chernozem brown forest soil in Kompolt since 1962 provide answers to questions of present and future interest in line with the international trend towards drawing practical conclusions from the results of long-term experiments (Workshop 1996). The effect of crop sequence on soil fertility was determined using maize as indicator plant. A maize monoculture and a crop rotation involving four crops were examined with 2x9 fertiliser treatments (for nutrient rates see Figures 1 and 2) on the basis of the following agronomic factors: -type and quantity of nutrient, method of application; -crop sequence. These factors contribute jointly to the fertility of the soil. The individual factors are in synergistic relationship with the soil and with each other. In Table 2 the effects of crop sequence, mineral fertilisation and stable manuring are analysed by means of variance analysis for the full factorial design on the basis of the maize yields obtained over 7 experimental cycles. Figure 1 illustrates correlations between the nutrient levels applied in the experiment and the maize yields in the monoculture and in the 4-crop sequence. Of the nine treatments included in the figure, M-1/2d, M-1d, M-3/2d and M-2d represent periodically applied nutrient rates (4 years with and 4 years without fertilisation) equivalent to the M-1, M-2, M-3 and M-4 rates. It can be seen from the established trend that the nutrient application system caused no significant yield difference in either crop sequence. According to marginal analysis the optimum points exhibited considerable differences for the two crop sequences. In the maize monoculture the upper limit of the nutrient rate can be determined in the 1 1/2-2 times interval (175.5-234 kg/ha mixed NPK active agents, with an optimum value of 218 kg/ha) based on the analysis of the nutrient - yield function. For the 4-crop sequence the marginal optimum (Fig. 1) was 30 kg/ha mixed active agents. Figure 2 illustrates the correlation between crop sequence and nutrient rate as the difference between the two functions plotted in Figure 1. The effect of crop sequence was greatest in the non-fertilised treatment and smallest in the treatment with the highest rate of fertiliser. It is thus clear why crop rotation has regained its popularity in farms using a low rare of fertilisation, while in production systems which can afford a plentiful supply of fertilisers it is of little or no importance. It is also worth noting that different yield levels can be achieved with the same fertiliser rates as a function purely of the crop sequence. However, nutrients applied to compensate for unfavourable crop sequences are not incorporated into the plants and have been proved to pollute the environment (Gefer 1997). The processing and analysis of the data obtained in long-term experiments in Kompolt is designed not only to broaden our knowledge, but also to serve as a basis for the elaboration of models for practical decisions adapted to the changed economic environment. The present paper emphasises the economic advantages of crop rotation, which are proved by statistical analysis.