| Sorghum,as the fifth largest cereal crop in the world,has obvious drought resistance,salt tolerance,barren tolerance,and waterlogging tolerance.In addition,sorghum is also an important dryland crop and can be widely used in brewing industry,green mowing forage,bio-energy,and functions.However,continuous cropping has limited the output and farmers’ enthusiasm for planting sorghum to a certain extent.According to survey statistics,the yield of continuous cropping sorghum could be reduced by 50%-69%,compared with non-continuous cropping sorghum.Therefore,sorghum-maize rotation system is of great significance to solve the obstacles of continuous sorghum cropping.The sorghum-maize rotation has been tested by the research team for many years,and it has become a rotation system that can effectively overcome the obstacles of sorghum continuous cropping in the sorghum-maize producing areas of Shanxi Province.In addition,many studies had determined that long-term fertilization had certain effects on crop growth and development,soil fertility,soil microbial populations,and fertilizer efficiency.Therefore,based on the long-term positioning experiment(2011-2016)platform,the study of the effects of different fertilization treatments on crop growth under the background of long-term fertilization is in line with the agriculture production..Besides,based on multi-year fixed-point sorghum-maize rotation system test platform,the effects of different fertilization treatments on crop growth and soil chemistry and microbial changes after the two crops multi-year rotation need to be further explored.So,T long-term different fertilization in the sorghum-maize rotation system was used as background,on the one hand,we aime to explore the effects of long-term different fertilization on the growth and development of sorghum and corn from the perspective of growth phenotype and grain quality.On the other hand,we analyzed the response effects of the sorghum-maize rotation system to different long-term fertilization modes from the perspective of fertility,microbial diversity and weed occurrence,to provide theoretical foundation for finding a suitable long-term fertilization mode.The main results were as follows:1.Based on growth phenotype and grain quality analysis,the results determined that NPK combined application treatment was significantly better than other treatments.Among N,P,and K fertilizer,N had the greatest impact on the phenotype and yield of sorghum and maize.Lack of nitrogen fertilizer could cause the root system of sorghum and maize to grow,the surface area increases,and the roots accumulate to the surface.In terms of quality,the between of nitrogen fertilizer,phosphate fertilizer,sorghum grain total starch,amylopectin and tannin accumulation showed a significant negative correlation,but between the nitrogen fertilizer,total protein and amylose accumulation showed a significant positive correlation.For maize,nitrogen,phosphate,and potassium fertilizers had positive correlation with the amylopectin and total protein accumulation,and a negative correlation with amylose content.Nitrogen fertilizer and maize kernel total starch content accumulation showed a negative correlation,while phosphate and potassium fertilizers showed a positive correlation with the accumulation of total starch.These results showd that in the sorghum and maize rotation system,NPK combined application was the better fertilization mode,but under the premise of ensuring yield,the input of nitrogen fertilizer and phosphate fertilizer could be appropriately reduced in order to increase the starch content of grains.2.Based on nutrient absorption and utilization analysis,the result determined that PK and CK treatment significantly reduced the accumulation of nitrogen in harvested plants and grains of sorghum and maize.The lack of nitrogen fertilizer had significantly effect on the nitrogen and phosphorus transferring to sorghum and maize grains.The accumulation of N in sorghum stems under NP and NPK treatments was significantly higher than the treatment of PK,NK and CK.The accumulation of K in sorghum stems treated with K was significantly higher than that of PK,NK and CK.The K accumulation of sorghum stalks treated with K was significantly higher than the K-deficient treatment.In the maize stalks,under the same NP and NPK treatments not only the N accumulation was significantly higher than the other treatments,but also the change rule of the stalk K accumulation was similar to sorghum stalks.In sorghum grains,the accumulation of N under PK treatment was the largest,followed by NPK and NK treatments,which indicated that the application of K fertilizer could promote the transfer of N to the grain.In terms of K accumulation in sorghum grains,the accumulation under PK treatment was also the largest,followed by NPK treatment,and NK and NP treatment were the lowest.In maize kernels,the N accumulation under NPK treatment was significantly higher than other treatments,followed by NK and NP treatments.Except for the significant differences in N and K accumulation of maize cobs with different fertilization treatments,the accumulation of other nutrients in sorghum and mazie cobs had no significant correlation with fertilization treatments,but also had the same rules in maize cobs.The accumulation of N and K under nitrogen treatment and potassium application treatment was higher,which was significantly higher than under nitrogen deficiency and potassium deficiency treatment.3.The results of coupling analysis between nutrient absorption and different fertilization treatments show that in sorghum,the interaction strength between nitrogen fertilizer application and leaf N accumulation,stem N/P/K accumulation,ear core N/P/K accumulation,and grain P accumulation was stem_K> stem_N> leaf_N> ear_P> ear_K= stem_P> ear_N> grain_P.The interaction intensity order between nitrogen fertilizer and the accumulation of leaf_P/K and grain_N/K was grain_K>leaf_K>seed_N>leaf_P.In maize,the interaction intensity between nitrogen fertilizer and nutrient accumulation in different tissue parts of maize was leaf_N> stem_N> ear_N> grain_N> stem_K> ear core_K> ear core_P>kernel_K.In sorghum,the interaction strength of the positive correlation between phosphate fertilizer and leaf_N,stem_N,and grain P/K was stem_N>grain_K>grain_P>leaf_N,and the negative correlation interaction intensity with other parts of the nutrient accumulation was core_P>leaf_P>stem_P>core_N>leaf_K >grain_N> stem_K> ear core_K.The positive correlation between phosphate fertilizer and leaf_N/P,stem_N/P,grain_N/P/K,ear core_N/P/K,and the interaction intensity in maize were grain_P >grain_K>grain_N>Stem_N>spike core_N>spike core_K>leaf_N>leaf_P>spike core_P>stem_P.The interaction intensity of negative correlation was leaf_K>stem_K.In sorghum,the positive correlation between potassium fertilizer and grain_N/P/K,ear core_N/P/Kwas grain_N>ear core_P>seed_K>ear core_K>grain_P>ear core_N,and the intensity of the negative correlation with leaf_N/PK and stem_N/P/K was leaf_N>leaf_K>stem_N>leaf_P>stem_P>stem_K.The positive correlation between long-term application of potassium fertilizer and leaf_N/K,stem_N/P/K,kernel_N,ear core_N/P/K and the interaction intensity of potassium fertilizer in maize was ear core_P> ear Core_N>leaf_K>leaf_N>ear core_K>grain_N>stem_N>stem_K>stem_P,and the negative correlation between leaf_P and grain_P/K was grain_P>grain_K>leaf_P.4.After coupling analysis of the fertilizer utilization efficiency and different fertilization,it was found that in sorghum,nitrogen fertilizer had greatest impact on fertilizer utilization efficiency.Nitrogen fertilizer had a very significant positive correlation with the absorption and utilization rate,agronomic efficiency,and contribution rate.The correlation intensity was in the order of N absorption and utilization rate > K absorption and utilization rate > P absorption and utilization rate;N agronomy efficiency > K agronomy efficiency > P agronomy efficiency;N contribution rate > P contribution rate > K contribution rate.The phosphate fertilizer was significantly positively correlated with N harvest index,P absorption and utilization rate and K contribution rate.The correlation intensity was in order of K contribution rate > P absorption and utilization rate > N harvest index.Potassium fertilizer only showed a significant positive correlation with K absorption and utilization rate but had no significant impact on other evaluation indicators for fertilizer absorption efficiency.In maize,the nitrogen fertilizer also had the greatest impact on fertilizer utilization efficiency.It had a very significant positive correlation with maize N,P,K absorption and utilization rate,agronomic efficiency,and contribution rate.The correlation intensity showed that N absorption and utilization rate > K Absorption and utilization rate > P absorption and utilization rate;N agronomy efficiency > P agronomy efficiency > K agronomy efficiency;N contribution rate > P contribution rate > K contribution rate.Phosphate fertilizer had no significant effect on fertilizer utilization efficiency of N,P,K in corn.Potassium fertilizer only showed a significant positive correlation with the corn P harvest index,but not significantly correlated with other evaluation indicators of fertilizer use efficiency.5.After coupling analysis between fertilizer utilization rate and crop yield,it was found that the interaction intensity between sorghum yield and fertilizer utilization efficiency was P agronomic efficiency > N efficiency > K efficiency > P absorption and utilization rate > N contribution rate > P contribution rate> K contribution rate > N absorption utilization rate > K absorption and utilization rate > K harvest index > N harvest index > P harvest index.The correlation intensity between corn yield and evaluation index of fertilizer utilization efficiency was in order P agronomy efficiency > P contribution rate > N agronomy efficiency > N absorption and utilization rate > K contribution rate > N contribution rate > K agronomy efficiency > K absorption and utilization rate > P absorption rate utilization rate > P harvest index > N harvest Index > K harvest index.6.Different fertilization treatments had important effects on the nutrient content and the metabolic activity of microbial communities of sorghum and maize rhizosphere soil.Under the sorghum/maize rotation system,the PK fertilization strategy had positive effect on the nutrient content of sorghum rhizosphere soil,as well as carbohydrate,alcohol,amine,acid carbon sourced metabolic activity,metabolic diversity of microbial community in sorghum rhizosphere soil.Nonetheless,its effect of improving sorghum rhizosphere soil enzyme activity was significantly lower than that of NK and NPK treatments.NPK treatment increased the nutrient content,enzyme activity,carbohydrate,alcohol,amine,carbon sourced acid metabolic activity metabolic diversity of microbial community in sorghum rhizosphere soil.Therefore,after comprehensively considering various factors,PK treatment was recommended as the sorghum fertilization mode under the sorghum/maize rotation strategy.NPK was recommended as the long-term fertilization mode for maize.The combination of two different fertilization modes was of great significance to reducing nitrogen fertilizer input in the rotation system.7.In the sorghum-corn rotation system,there were certain differences in weed types and densities among different fertilization treatments.The total weed density in the field was in the order of CK > PK >NK > NP > NPK.N affected the occurrence of most weeds.Chenopodium,Amaranthus retroflexus,and Barnyardgrass were the dominant weeds in the sorghum and corn rotation system,in which,the Chenopodium occupied an absolute dominant position,and NPK treatment significantly reduced its relative abundance.Branch amaranth,abutilon,barnyardgrass and crabgrass finely adapted to the low P and N soil and had strong barren tolerance.The balanced application of N and P promoted the development of Sonchus Brachyotus to the dominant species.Among the fertilization treatments,the weed communities between NP and PK treatments were similar,and similar with CK treatment.The similarity of weed community between NPK and NK was the lowest,with 0.649 Sorenson similarity index,yet showed Sorenson similarity index 0.870,0.857 and 0.816 with PK,CK and NP,respectively.The order of total weed density in the rotation field under different tillage methods is crushed straw to field + autumn rotary tillage(CK)> crushed straw to field + deep loosening > crushed straw to field + Deep tillage + autumn rotary tillage.The farming system of crushing straw to field + deep tillage + autumn rotary tillage effectively reduced the weed density in the rotation system.8.In terms of soil enzyme activity,pendimethalin herbicide promoted the activity of invertase,polyphenol oxidase and alkaline phosphatase to a certain extent,activated the activity of soil urease,and inhibited the activity of catalase.After considering the activities of various enzymes,400 and 600 g ai/hm2 were recommended as the optimal concentration of the crop rotation system,which could minimize its weakening effect on soil enzyme activity.In terms of changes in microbial populations,dimethylpentene Lingling mostly activated soil bacteria and fungi,and this effect changed with the concentration of pendimethalin,and long-term application easily damaged soil fertility.Among the 8 different concentrations in the potted environment,the bacterial community diversity at a concentration of 600 g ai/hm2 was the highest,and the Shannon index was higher.However,in a field environment,the bacterial diversity at 200 g ai/hm2 was higher,and the Shannon index was significantly higher than other concentrations.Among the 8 different concentrations in potted environment,the fungal population diversity is the highest at 1400 g ai/hm2 and the Shannon index is the largest.However,in the field environment,the fungal diversity was highest at 600 and 800 g ai/hm2 treatment,along with a high Shannon.Therefore,it is recommended that 600 g a.i./hm2 is the optimal concentration of pendimethalin to maximize the activation of soil microbial populations. |
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