| As an important fertilizer cultivation measure,straw returning to the field is of great significance in agricultural production.It can not only solve the problem of insufficient organic fertilizer sources,but also reduce the environmental problems caused by a large amount of straw.However,due to the cold climate in Northeast China,straw decomposition is slow and the improvement of fertilizer application technology for straw returning to the field is insufficient.Therefore,this research adopts the indoor simulation test,compared to conventional fertilization conditions,reducing fertilizer was studied with straw and exogenous humic acid on soil chemical properties,and the influence of the physiological characteristics and nutrient uptake,in order to make clear straw returned to soil and crop system of comprehensive influence in the quarter,and the control effect of the humic acid,provide reference for further perfecting the technology of straw returned.The main research results are as follows:1.The straw returning significantly increased the number of soil fungi and bacteria,and the combined application of humic acid accelerated the decomposition of straw,and further promoted the proliferation of soil fungi and bacteria at tasseling and maturity stages of maize.The number of fungi significantly increased by 133.3%-145.6% and 72.7%-183.5% compared with the conventional chemical fertilizer control,respectively.The bacterial population significantly increased by 59.5%-84.8% and 92.0%-157.1%,respectively.Straw counters-field raised the metabolic activity of the soil,and the application of humic acid effect on soil enzyme activity was not significant,but the straw with humic acid significantly increased soil urease,peroxidase,catalase and acid phosphatase activity,especially raising stage,soil carbon metabolism of maize,its effect is better than that of straw returning alone to deal with.2.Straw returning treatment reduced soil alkali-hydrolyzed nitrogen content by 11.1%-19.0%compared with conventional chemical fertilizer at maize jointing stage.Humic acid can activate soil nutrients,and straw returning combined with humic acid can effectively alleviate the "competition" between straw decomposition and nitrogen before maize jointing,and increase the accumulation of nutrients in soil after jointing.Applying humic acid to the white clay soil with low soil available P significantly increased soil available P by 10.5%-19.6%,alleviating the P absorption stress of maize plants under the condition of straw returning.3.Compared with conventional fertilization,the total nitrogen content of maize leaves at jointing and mature stages with humic acid application increased by 9.4%-21.6% and32.2%-59.0%,respectively.The straw returning combined with humic acid application can alleviate the "nitrogen competition" between straw decomposition and plant growth.Straw returning increased the total phosphorus and total potassium content of maize plants,antagonized the accumulation of sodium,and decreased the absorption capacity of calcium and magnesium,while straw combined with humic acid could improve the ratio of potassium and sodium,and promote the absorption of calcium and magnesium in maize plants.4.The activity of 1,5-bisphosphoenolpyruvate carboxylase and phosphoenolpyruvate carboxylase were significantly increased by 50.0%-82.6%,45.2% and 160.4%,respectively,at jointing-stage and Tasseling stage,and by 21.1%-28.6% and 19.5%-41.4%,respectively,by applying humic acid.However,the activity of phosphoenolpyruvate carboxylase at joisting stage and tasseling stage was significantly increased by 41.3%-48.8% and 32.2%-72.1%,respectively,which enhanced the photosynthetic carbon assimilation ability of maize plants.Straw returning significantly increased the activities of sucrose synthetase and invertase,increased the contents of soluble sugar,reducing sugar and starch in maize plants,and combined application of humic acid further enhanced the activity of photosynthetic carbon metabolism in maize plants.5.The activities of glutamate synthetase,glutamine synthetase and glutamate dehydrogenase in straw returning treatment decreased,while humic acid treatment increased the activities of key enzymes in nitrogen metabolism of maize plants.The effect of straw returning combined with humic acid application was significant,and the activities of nitrate reductase in maize jointing stage increased by 35.1%-46.1%.The glutamate synthetase activity increased by 28.6%-36.5%during tasseling stage,which simultaneously improved the assimilation and transformation process of nitrogen.Straw returning combined with humic acid application increased the ratio of photosynthetic carbon metabolism to nitrogen metabolism,and increased the ratio of soluble sugar to soluble protein by 11.6%-41.7% at the stage of Tasseling.6.The straw returning reduced the activity of antioxidant enzymes in maize plants,resulting in an increase of 46.5%-89.4% and 10.9%-86.4% of superoxide anion free radicals and an increase of malondialdehyde content in maize plants at jointing and tasseling stages,respectively.Applying humic acid increased the activities of catalase,ascorbate peroxidase and reduced glutathione content.The activities of catalase and glutathione reductase increased by29.1%-91.4% and 13.7%-33.6%,respectively,during tasseling stage of maize with straw returning and humic acid application,strengthening the protection of plasma membrane integrity.Straw returning to the field or applying humic acid(replacing 15% potassium in the conventional fertilizer rate with the same amount)can save 15% nitrogen and phosphorus in the conventional fertilizer rate without affecting the growth of maize in the current season.At the same time,humic acid stimulated corn growth.Straw returning combined with humic acid application significantly promoted straw decomposition(decomposition rate increased9.9%-20.8%)and dry matter accumulation in the upper part of maize field(plant dry weight increased 10.0%-76.7%),enhanced the metabolic activity of soil-crop system and improved the quality of straw returning. |
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