| This experiment was used to compare the differences in yield and dry matter accumulation,plant nitrogen,phosphorus and potassium absorption law and the change of the soil bacterial community of maize which was released in different years in continuous cropping of soybeans-maize,soybeans-soybean-maize under three planting systems.Agronomic trait and nutrient absorption of the maize hybrids was discussed based on the planting systems released in different years.The experiment was conducted in 2017 and 2018 at liaozhong pilot base of shenyang agricultural university.The experimental pattern adopted was completely random design.Ten hybrids were selected as test materials.Some samples were taken from three maize plants for testing at jointing stage,tasseling stage,milk-ripening stage and wax-ripening stage with their dry matter for yield quality,nitrogen,phosphorus and potassium contents in each organ.Meanwhile,the diversity of the soil bacterial community has been analyzed.The main research results are as follows:1.Under the three planting systems,the plant height and stem diameter of maize were significantly different.In the whole stage of growth and development,plant height of maize was higher than that of continuous cropping under soybean-soybean-maize rotation and soybean-maize rotation.In the early stage of growth and development,the stem diameter of maize was lower than that of continuous cropping under soy-soy-maize rotation and soy-maize stubble,and higher than that of continuous cropping at the later stage of growth and development.The results showed that the plant height and stem diameter of the newly developed maize hybrids were higher than those of the earlier hybrids.The plant height and stem diameter of maize hybrids increased gradually with the advancement of the breeding.2.Under the three planting systems,the photosynthetic characteristics of maize were significantly different.At the early stage of growth and development,the photosynthetic capacity of maize was continuously increased by > soy-maize stubble > under soy-soy-maize rotation.At the later stage of growth and development,the photosynthetic capacity of maize was continuously increased by > soy-soy-maize rotation under soy-maize stubble.The results of this study showed that the light and index of recently developed maize hybrids were significantly higher than those of early developed maize hybrids,indicating that the photosynthetic capacity of maize hybrids increased gradually with the advancement of breeding process.3.The yield of maize increased with breeding progress.The yield of maize hybrids used in this experiment increased by 73.14% in a span of more than 30 years.The yield of recently developed hybrids was significantly higher than that of earlier hybrids,that is,the yield potential of maize hybrids was effectively improved with the progress in breeding.Among the yield components,the increase of 100-grain weight is the main factor.Under the three cropping systems,the yield of maize was the highest under the soy-maize stubble cropping system,followed by the soy-soy-maize rotation cropping system and the lowest under the continuous cropping system.4.Dry matter distribution in different organs of maize was studied under three cropping systems,and the results showed that dry matter in leaves still increased under soy-maize stubble cropping and decreased under soy-soy-maize rotation cropping,but showed no significant change under continuous cropping.The results showed that the dry matter distribution in seeds of the newly released hybrids was significantly higher than that of the earlier released hybrids in wax-ripening stage,and the dry matter distribution was 12.13% higher than that of the earlier released hybrids.5.Nitrogen accumulation and distribution in different organs of maize were studied under three cropping systems,and the results showed that the nitrogen content of vegetative organs in continuous cropping was significantly higher than that in soy-maize stubble and soy-soy-maize rotation at the vegetative growth stage.At the stage of reproductive growth,the proportion of nitrogen content of grain in the whole plant under continuous cropping was significantly lower than that under soy-maize stubble and soy-soy-maize rotation.Studies of the maize under the three planting system in different organs for phosphorus accumulation and distribution showed that in the vegetative growth stage,the phosphorus content of leaf sheath under continuous cropping accounted for the proportion of the whole plant phosphorus content and was significantly lower than soybean low-toxin chemical-maize and soybeans,soybean and maize crop rotation,blade under the soybeans,soybean and maize crop rotation of phosphorus accounts for the proportion of the whole plant phosphorus content was significantly higher than that of soybeans,maize low-toxin chemical.The amount of phosphorus transferred from nutrient organs to grains was significantly higher in soybean-maize rotation than in soybean-soybean-maize rotation.The accumulation and distribution of potassium in different organs of maize were studied under three cropping systems.The results showed that the proportion of potassium content in the continuous cropping of vegetative organs in the whole plant was significantly lower than that in soy-maize stubble and soy-soy-maize rotation in the vegetative growth stage.Among them,the proportion of potassium content in stem under continuous cropping was significantly lower than that in soy-maize stubble,and the proportion of potassium content in leaf in whole plant was soy-soy-maize rotation > soy-maize stubble > continuous cropping.During the reproductive growth stage,the transfer of potassium from vegetative organs to grains was significantly higher under soy-soy-maize rotation than under soy-maize rotation.6.The nutrient accumulation and distribution of maize hybrids released in different years were studied.During the reproductive growth stage,the content of nitrogen and phosphorus in the grain of the newly developed hybrids was significantly higher than that of the other hybrids.At the same time,the nutrient harvest index of the recently developed maize hybrids was higher than that of other maize hybrids.The demand for nitrogen,phosphorus and potassium in 100 g grain of recently developed maize hybrids was 7.96%,4.90% and 4.17% lower than that of early maize hybrids respectively.7.The diversity of soil bacterial community was studied under soy-soy-maize rotation and continuous cropping,and the results showed that the richness and diversity of bacterial community were significantly increased by 9.91% compared with continuous cropping under rotation.At the same time,the effect of maize cultivars in different years on soil bacterial community was studied,and the results showed that the effect of maize cultivars in recent years on soil bacterial community diversity was more obvious than that of maize cultivars in early and middle stages,and the soil bacterial community diversity of maize cultivars in recent years was more abundant.In conclusion,recent maize cultivars are better than other maize cultivars in yield and nutrient absorption.The main factor for the increase of yield was the increase of grain weight.In terms of nutrient absorption and accumulation,harvest index and nutrient demand,the mode of nutrient absorption and accumulation was more optimized in the recently bred varieties,and the harvest index was higher than that of the cultivated varieties in other periods,while the nutrient demand was lower than that of the cultivated varieties in other periods.It indicates that with the advance of breeding process,the application ability of maize varieties to nutrients is gradually improved.In addition,recent maize cultivars improved the community richness and diversity of rotation soil to some extent. |
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