Effects Of Rice Straw Return On Growth And Yield Formation Of Common Buckwheat

China is a large agricultural producer,and as our rice production increases,so does the production of rice straw year by year.In past decades,unused straw was usually disposed of in the form of incineration,which has caused serious pollution to the environment.At present,straw return technology has been widely used on farmland and has become the main way to reduce fertilizer use and improve the quality of arable land,playing a major role in achieving the efficient use of China’s straw resources,achieving cost savings and efficiency gains,developing quality and efficiency agriculture,and sustainable development of farmland ecology.The aim of this study was to screen the optimal combination of rice straw and fertilizer application to provide a theoretical basis for the resourceful use of straw,reduce the impact on the agro-ecological environment and provide high yield and quality cultivation techniques for common buckwheat（Fagopyrum esculentum Moench.）.In this study,the high-yielding common buckwheat variety’Fengtian1’was used as the test material to investigate the effects of different concentrations of rice straw decomposition solution,different amounts of rice straw returned to the field,and the amount of rice straw returned to the field with fertilizer treatments on the physical and chemical properties and enzyme activities of the inter-root soil,root morphology and root activities,plant nutrient content,non-structural carbohydrate accumulation and translocation,filling characteristics of superior and inferior grains,key enzyme activities of the sucrose-starch metabolic pathway,fertilizer utilization,yield and quality.The results obtained are as follows:1.Effects of different concentrations of rice straw rotting solution on seed germination and seedling growth of common buckwheatThe effects of different concentrations of rice straw decomposition solution（0,6.25,12.5,25,50 and 100 mg/m L）on seed germination,root morphology and vigour,plant nutrient uptake and utilization and antioxidant enzyme activity were investigated.The results show that rice straw decomposes on common buckwheat seed germination and seedling growth and development with"low promotion and high inhibition"of the chemosensory effect.Compared with control treatment,different concentrations of decomposition solution treatment will reduce seed germination rate,germination potential and germination index;compared with high concentrations of decomposition solution,low concentrations of treatment on germination rate,germination potential and germination index to promote the effect of 12.5 mg/m L treatment is the most obvious.Treatment under the common buckwheat seedling root activities,root surface area and volume were improved.The increased concentration of decomposition solution significantly inhibited the activities of superoxide dismutase（SOD）and peroxidase（POD）and significantly increased malondialdehyde（MDA）content in the leaves.The amount of fast-acting nutrients in the decomposing solution and the nutrient content of the seedling plants continued to rise with increasing levels of straw decomposing solution.Therefore,it is necessary to consider the appropriate amount of straw to be returned to the field during the subsequent actual straw return process to avoid excessive straw return having a negative impact on seed germination and seedling growth and development.2.Effects of different rice straw returns on the growth and yield of common buckwheatFour different straw return treatments were set up:no straw return 0kg/hm²（CK）,half amount of straw return 4500 kg/hm²（HT₁）,full amount of straw return 9000 kg/hm²（HT₂）,high amount of straw return13500 kg/hm²（HT₃）,to study its effect on inter-root soil enzyme activity,root morphology and activities,seed filling characteristics,leaf antioxidant enzyme activity,agronomic traits and yield of common buckwheat.The results show that the maximum grain filling rate(G_max)and average grain filling rate(G_mean)of common buckwheat seeds are HT₂maximum;each treatment under the leaf SOD,catalase（CAT）activity with the increase in the amount of straw returned to the field to show a trend of first increase and then decrease in the activity of the HT₂treatment to reach the maximum.Compared with the control treatment,the straw treatment increased the soil alkaline phosphatase,sucrase activity.With the increase in the amount of straw returned to the field,the agronomic traits and yield indicators of common buckwheat showed a trend of increasing and then decreasing,all reaching a maximum with HT₂treatment.Therefore,when planting common buckwheat in Guizhou Province,the recommended amount of rice straw returned to the field is9000 kg/hm²,which is conducive to yield improvement.3.Effects of rice straw combined with inorganic fertilizer on soil nutrients and plants nutrient uptakeThe study set up six treatments:no straw and no fertilization（CK）,no straw with normal fertilization（SF）,full straw with 20%reduction in conventional fertilization（SH）,full straw with 40%reduction in conventional fertilization（SM）,full straw with 80%reduction in conventional fertilization（SL）,full straw with no fertilization（HT）,and the effects on soil physical and chemical properties,soil enzyme activity and plants nutrient uptake were studied.The results showed that both HT treatment and straw combined with fertilization treatments（SH,SM and SL）significantly increased the available N,available K,available P and organic matter content in the inter-root soil compared CK treatment.Urease and alkaline phosphatase activities in the inter-root soil were higher in the straw return treatments（SH,SM,SL,HT）than in the CK and SF treatments;The Invertase activities of the straw return treatments（SH,SM,SL and HT）was higher than that of the CK treatment,and showed a decrease followed by an increase with decreasing fertilizer application,with the maximum sucrase activity being achieved under the SH treatment.Compared to CK,SH treatment increased total nitrogen content in stems,fast-acting phosphorus,and fast-acting potassium in leaves.It can be seen that the straw return treatment can effectively improve the inter-root soil environment of common buckwheat and increase fertility,but the effect on total phosphorus and potassium in the plant is not significant.4.The effect of rice straw return with inorganic fertilizer on the yield and quality of common buckwheatThe study set up six treatments:no straw and no fertilization（CK）,no straw with normal fertilization（SF）,full straw with 20%reduction in conventional fertilization（SH）,full straw with 40%reduction in conventional fertilization（SM）,full straw with 80%reduction in conventional fertilization（SL）,full straw with no fertilization（HT）,and its effects on superior and inferior grain filling,starch synthase activity,non-structural carbohydrate accumulation and translocation,agronomic traits,fertilizer utilization,yield and quality of common buckwheat.The results showed that the initial growth power（R₀）,maximum and average grain-filling rate,and starch synthase activity of the superior grains were higher than those of the inferior grains.SH and SF treatments remarkably improved the fertilizer contribution rate and fertilizer agronomic utilization rate,promoted root growth,and enhanced the starch branching enzyme and soluble starch synthase activities of superior and inferior grains.Compared with CK,SH treatment increased the translocation rate and contribution of NSC at flowering,which in turn increased the number of grains per plant,grain weight per plant,100-grain weight and yield;SM treatment increased the accumulation of flavonoids,starch and amino acid content in the seeds and improved the quality of the seeds.Thus,the common buckwheat planting can be considered when the full amount of rice straw returned to the field when the inorganic fertilizer reduction of20%or inorganic fertilizer reduction of 40%,should be recommended as an agronomic method for promoting yield or quality.