Studies on the Rotation of Upland Crops : XI. Yield trends of crops in continuous cropping and several rotation systems over the 42-year experiments

To establish the suitable cropping systems in the northern part of the Tohoku district, the experiments have been conducted at Fujisaka Branch, Aomori Agricultural Experiment Station since 1936. In the present study the yields of crops during the period 1936 to 1977 were analyzed and cropping systems were evaluated by the yields of crops and their trends. The experiments were consisted of the continuous cropping of six crops, four types of 2-year rotation (2R), four types of 3-year rotation (3R), and one type of 6-year rotation (6R). To survey the trend of crop yields over the period the original data were transferred to ratios to the mean yield of all rotation plots of the crop in each year. The yield ratios were also averaged over the period of each rotation cycle and in the case of the continuous cropping system 3-year averages were adopted to reduce the effects of seasonal conditions. Yield trends were evaluated by fitting the regression model of an intersecting line. The relationship between the yield trends of each crop and several types of combination of crops was discussed and the following results were obtained. 1. Injuries by continuous cropping were observed in all crops studied and the order of the injuries was barnyard millet > rape > soybeans > wheat > potatoes, corn. A stable yield at a certain lower level of yield was obtained in most of the crops after several cycles of continuous cropping, which was considered the general pattern of the injury by continuous cropping resulting from the balance of input and output of nutrients. 2. As for the rotation period, the longer the period, the higher the yield on the average, i.e. 6R > 3R > 2R. 3. The stable and relatively high performance of all rotation crops was obtained in 6R, 2R-3, 3R-3 and 3R-4. In these systems the soil fertility was also expected to be preserved. 4. Among 2-year rotations, the 2R-3 was considered the most favourable combination. While potatoes, rape and buckwheat in 2R-4 were all expected to promote the soil fertility for succeeding crops, wheat in 2R-3 was considered to keep the nitrogen balance sheet minus for the succeeding crop (buckwheat) and thus to results in the higher yield of the crop by preventing its spindly growth. 5. Favourable systems among 3-year rotations were ones in which higher amount of organic fertilizer was applied per annum through green manure such as soybeans and red clover and also crops of high ability of nutrient uptake were not included or few if any. 6. Unfavourable rotation systems were ones in which total amount of fertilizer application during the period was less and also crops of high ability of nutrient uptake were included.