Effect Of Fertilizer Application Depths On Resource Utilization And Yield Increase Of Rainfed Summer Maize Under Straw Mulching

Guanzhong dry farming area is an important grain producing area in China,which plays a vital role in ensuring food security.In this area,the traditional shallow fertilization has caused problems such as poor farmland soil,low resource utilization efficiency and crop yield decline.Optimizing fertilization depth has become an important technical means to improve crop yield.However,there is a lack of systematic research on the effects of different fertilization depths on the utilization of light,water and fertilizer in summer maize under straw mulching,which not only restricts the tapping of yield potential of summer maize,but also aggravates resource waste and environmental risks.Therefore,based on the ecological conditions of dryland farmland in Guanzhong double cropping area,this study combines straw mulching planting measures with fertilization depth,sets four fertilization depths（5 cm deep fertilization:D5;15 cm deep fertilization:D15;25 cm deep fertilization:D25;35 cm deep fertilization:D35）under straw mulching and bare land planting,and systematically analyzes the regulatory effects of planting methods and fertilization depth on"soil crop environment",The influence mechanism of fertilizer depth under straw mulching on the synergetic utilization of light,water and fertilizer resources and yield increase was discussed.The results can provide a theoretical reference for optimizing fertilization management of summer maize in dryland areas.The main results of this study are as follows:（1）The effect of changing the depth of fertilization on soil temperature was weaker than that of straw mulching.Straw mulching has obvious seasonal effect on the regulation of soil temperature,that is,it reduces the soil temperature in the middle growth stage（tasseling stage）of summer maize,but increases the soil temperature in the late growth stage（milk and mature stages）,which helps to mitigate the adverse effects of seasonal fluctuations of soil temperature on crop growth.At the same time,straw mulching increased the soil water content during the main growth period of summer maize,weakened the fluctuation range of soil water storage,and reduced the water consumption coefficient of farmland.The effect of fertilization depth on farmland water consumption is to some extent affected by precipitation,and its effect decreases with the increase of precipitation.Compared with D5,both D15 and D25 can increase water consumption during the growth period of summer maize under the two planting modes,while reducing the water consumption coefficient.It shows that D15 and D25 can improve the ability of crops to absorb and use soil water at the same time,which is conducive to improving the water conversion rate of farmland.（2）Straw mulching increased nitrate nitrogen（12.8%-17.1%）in 0-100 cm soil layer and available phosphorus（1.4%-3.6%）and available potassium（0.6%-3.1%）in 0-60 cm soil layer compared with bare land planting.Compared with other fertilization depths,D15effectively increased soil nitrate nitrogen content in root layer（0-40 cm）,7.9-30.7%under bare land planting,and 5.8-28.5%under straw mulching.Moreover,D15 significantly increased the content of available phosphorus and available potassium in the root layer（0-40 cm）under the two planting methods.Straw mulching increased the nutrient uptake of summer maize.Compared with bare land planting,nitrogen uptake increased by 4.6-10.7%,phosphorus uptake increased by1.8-11.7%,and potassium uptake increased by 3.0-5.0%.The change of fertilization depth had a significant impact on crop nutrient absorption.Specifically,D15 can promote the absorption of nitrogen,phosphorus and potassium nutrients of summer maize under the two planting modes in each experimental year;The regulation effect of D25 and D35 on nutrient absorption of summer maize was significantly affected by planting mode and test year,and there was a phenomenon of reducing crop nutrient absorption.（3）Straw mulching promoted root growth and leaf photosynthetic characteristics.Compared with bare land planting,root length density（RLD）,root surface area density（RSD）and root bleeding sap rate in 0-60 cm soil layer under straw mulching were significantly increased by 8.2-19.1%,12.7-19.3%and 6.7-15.5%respectively;The leaf nitrogen content,chlorophyll content（SPAD）and net photosynthetic rate（Pn）increased by3.7-12.3%,4.3-9.1%and 7.5-15.4%.The change of fertilization depth significantly affected the root architecture,function and leaf photosynthesis of summer maize.Compared with D5,RLD,RSD and root sap flow rate of D15 increased by 7.5-11.9%,5.5-11.6%and7.3-14.7%respectively;The leaf nitrogen content,SPAD and net photosynthetic rate increased by 4.5-13.2%,6.1-9.2%and 2.5-9.1%respectively.The effect of D25 on root growth and leaf photosynthetic rate of summer maize was weaker than that of D15,but D35 had no obvious effect.（4）Straw mulching significantly reduced the light transmittance of the canopy bottom（10.8-17.4%）by promoting the growth and development of crops above ground.Therefore,straw mulching increased the canopy interception of photosynthetically active radiation（IPAR）,which was 3.1-7.3%higher than that of bare land planting.D15 increased plant height,stem diameter and leaf area index（LAI）of summer maize under both planting modes,and then increased dry matter accumulation.D25 promoted the aboveground growth and dry matter accumulation of summer maize under bare land planting,while it had the opposite effect under mulching planting.D35 restricts crop growth and dry matter formation under both planting modes.At the same time,D15 effectively reduced the light transmittance at the bottom of crop canopy and increased IPAR.However,D35 increased the light transmittance at the bottom of the canopy（2.4-4.5%）and decreased the IPAR（1.3-4.3%）.（5）Straw mulching increased the yield of summer maize（5.0-13.3%）by increasing the grain filling rate（8.8-14.3%）.In addition,the light,water and fertilizer utilization efficiency of summer corn planted with straw mulch was higher than that of bare land planting.Under the same planting mode,the grain filling rate of summer maize increased first and then decreased with the increase of fertilization depth,and reached the maximum at D15.Both D15 and D25 increased the yield of summer maize under the two planting modes.Compared with D5,the yield of summer maize under D15 increased by 13.0-18.3%,and that of D25 increased by 6.0-9.0%.However,the yield of D35 summer maize was slightly lower than that of D5.And D15 significantly promoted the synergetic and effective utilization of light,water and fertilizer in summer maize.（6）Straw mulching is beneficial to reduce N₂O emissions from dryland summer maize fields,but it increases CO₂emissions.Compared with bare land planting,straw mulching planting increased the nutrient accumulation in the upper soil and decreased the nutrient residue in the lower soil when summer corn was harvested.Under the same planting mode,D15,D25 and D35 reduced N₂O and CO₂emissions from farmland.Therefore,the GWP and GHGI of deep fertilization treatment（D15,D25 and D35）were significantly lower than those of D5.Moreover,D15 improved the nutrient accumulation and distribution of summer maize during harvest.Compared with other fertilization depth treatments,D15increased nitrate nitrogen content in 0-30 cm soil layer and available phosphorus and available potassium content in 0-40 cm soil layer,while significantly reduced nitrate nitrogen accumulation in 60-300 cm soil layer and available phosphorus and available potassium residues in 40-60 cm soil layer.Therefore,15 cm deep fertilization under straw mulching has the most obvious effect on the biomass and yield of the later crop（winter wheat）.To sum up,straw mulching has the advantages of regulating soil temperature,storing water and improving soil nutrient content.Optimizing the depth of fertilization can significantly improve the content and distribution of soil nutrients.Under the condition of straw mulching,optimizing the depth of fertilization can further promote the growth and development of summer maize,improve the ability of crops to absorb and capture key production resources（light,water and fertilizer）,help to increase the net photosynthetic rate of leaves,grain filling rate,number of ears,grain weight and number of ears,improve the cooperative and effective utilization of crop yield and resources,and reduce greenhouse gas emissions and nitrate nitrogen residues in deep soil.Among them,the effect of applying fertilizer at a depth of 15 cm under straw mulching is the most significant,which is the best combination of crop,soil and environmental benefits.It can effectively improve the productivity of dryland summer maize and synergize the use of key production resources,which is of great significance for achieving agricultural production increase,efficiency increase and emission reduction.