| In order to explore the effects of different straw returning years on spring maize yield,nitrogen absorption and utilization,and soil nitrogen changes,to provide a theoretical basis for reasonable nitrogen fertilizer regulation under continuous straw returning.In 2021,TK601 was used as a test variety in Kailu,Tongliao City,Inner Mongolia Autonomous Region,and adjacent non return maize fields were used as a control,to study the yield,dry matter accumulation and transportation,nitrogen absorption and utilization,and soil nitrogen changes of spring maize after returning maize straw to the field for 3,5,and 7years.The main research results are as follows:1.Returning straw to the field for 5 and 7 years significantly improve the photosynthetic capacity of spring maize leaves,increases the accumulation of dry matter in the plant,especially after silking stage,and has a significant yield increase effects.Compared to CK,the leaf area index significantly increased by 10.23%and 15.45%during the 5 and 7 year silking stage,the SPAD of spike leaves increased by 11.82%and 18.68%,the net photosynthetic rate of leaves increased by 12.35%and 26.88%,the senescence rate of leaves decreased by 5.04%and 5.98%,the population photosynthetic potential increased by 11.78%and 16.85%during silking–milking,the canopy photosynthetic capacity increased by 24.22%and 46.23%during the silking stage,and the dry matter accumulation after silking stage increased by 19.58%and 27.27%compared to CK.The yield of straw returning to the field for 3,5,and 7 years increased by 6.12%,11.09%,and 15.06%compared to CK,respectively.The number of grains per ear and the weight of 1000 grains significantly increased after returning to the field for 5 and 7 years,but the difference between returning to the field for 3 years and CK did not reach a significant level.2.Returning straw to the field promotes root growth,significantly increasing root biomass,enhancing root vitality,and delaying root premature senescence after 5 and 7years of straw returning to the field.The quality of the root stem during the silking and ripening stages was significantly higher than that of CK after returning to the field for 7and 5 years;there was no significant difference in the number of roots between the 10 cm soil layer returning to the field for 7 years and returning to the field for 5 years,both of which were significantly higher than returning to the field for 3 years and CK.The 20 cm soil layer returning to the field for 7 years>5 years>3 years;the total root decay rate of straw returning to the field for 7 years and 5 years decreased by 8.52%,2.84%compared to CK;the differences in root activity and CK between the three years of straw returning to the field during the silking and milking stages were significant,with the highest being 7years of straw returning to the field;the total absorption area and active absorption area of the root system significantly increased,especially during the milking stage,with a difference of 46.56%,66.20%and 43.75%,64.85%higher than CK at 5 and 7 years,respectively.3.Returning straw to the field promotes plant nitrogen nutrient absorption and reduces nitrogen transport efficiency.Compared to CK,the nitrogen content in spring maize leaves increased under three years of straw returning,and the nitrogen accumulation in plants,nitrogen transport in organs,and nitrogen accumulation rate after silking increased.The degree of improvement increased with the increase of straw return years;the efficiency of nitrogen transport and the contribution rate of nitrogen transport to grains decreased when returning straw to the field.The nitrogen absorption efficiency and nitrogen fertilizer productivity increased by 12.16%,24.32%,35.14%,and 6.13%,11.08%,15.12%compared to CK after 3,5,and 7 years of straw returning to the field.4.Returning straw to the field has expanded the soil nitrogen pool,increased soil nitrogen nutrient content,and improved soil enzyme activity.Returning straw to the field increased the total nitrogen,alkali hydrolyzed nitrogen,ammonium nitrogen,nitrate nitrogen,and organic matter content in the 0～60 cm soil layer of spring maize,with an average increase of 7.71%,21.13%,29.87%,24.98%,and 39.10%compared to CK;the soil urease activity,cellulase activity,sucrase activity,protease activity,and catalase activity were all highest after returning to the field for 7 years,followed by returning to the field for 5 years,and there was no significant difference between returning to the field for 3years and CK.The annual increment of soil nitrogen pool decreased with the increase of returning years,significantly increasing compared to the control.Straw returning for 3,5,and 7 years increased by 225.97 kg·hm-2,424.87 kg·hm-2,and 547.60 kg·hm-2compared to CK,respectively.In summary,under the condition of returning straw to the field,spring maize maintains high photosynthetic capacity and strong root activity in the later stage of growth,increases soil nitrogen nutrient content,promotes dry matter and nitrogen nutrient absorption,improves grain yield,nitrogen absorption efficiency,and nitrogen fertilizer partial productivity,and the improvement amplitude increases with the increase of straw returning years. |
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