| The increase of planting density,growing the variety for high density tolerance is one of the main ways to further improve the modern maize yield.It is also one of the key measures for maize production to break through bottleneck by means of the subsoiling tillage for completely breaking the plow bottom,which could change the soil structure of the topsoil and further increase the planting density.Therefore,it is significancant important to explore maize tolerance physiological mechanism and regulation effect of subsoiling.In this study,considering plant type,root-canopy,yield as a research system,different spring maize varieties for density tolerance,under different density and different tillage practice were systematically studied in the root characteristics,photosynthetic characteristics,dry matter accumulation and distribution,yield and the yield components on the density of response,and the subsoiling tillage regulation effect of density tolerance,maize density tolerance evaluation indexes were selected under the conditions.The main results are as follows:(1)In 28 maize varieties,according to the coefficient of variation(CV?15%)in the relative value of 13 index(the ratio of index in high density to low density stress level),7 parameters(relative stem diameter,the relative value of SPAD,relative Pn and relative dry weight,relative bald length,relative kernel per row and relative plant yield)were selected as the evaluation indexes for density tolerance strength.The fuzzy comprehensive evaluation method was also established by the coefficient of variation of the index normalized as the weights.28 maize varieties were divided into 3 goups: 9 varieties for higher density tolerance(0.719-0.965),9 varieties for intermediate density tolerance(0.457-0.592),10 varieties for lower density tolerance(0.038-0.342).(2)After increasing the density,the crowding effect between plants was more obvious,and the plant could actively regulate the growth of leaves and stems.Subsoiling tillage can effectively alleviate the crowding effect for increasing density;improve leaf self-adjustment ability,making the leaf angle become relative smaller above ear,relative bigger under ear.The shading effect caused by the leaf angle in lower ear leaf changing to moderate big for the increasing the density,make leaves in the best light receiving position.Under high density,the varieties with high density tolerance have higher self adjustment ability than those with lower density tolerance.The performance tendency for alleviating the stem diameter decreasing,could increase the internode length above ear for maize varieties with different density tolerance,The internode length above ear more longer,the light received by leaves in upper plant more better.(3)In increased density,subsoiling tillage can significantly alleviate the decreasing LAI and canopy light transmittance declining in late growing stage,which could help to increase LAI and light transmittance in ear layer and above,effectively delaying ear layer leaf senescence for increased density in late growth stage,improve the bottom and ear leaf layer light condition,to maintain a higher LAI for longer time and adequate photosynthetic area.These are favorable to grain filling,laying foundations for increasing maize yield.(4)There are significant root morphological difference among different varieties of density tolerance.Generally,the varieties with higher density tolerance still have a larger root system,and showing extending subsoiling trend under conditions of high density,which is helpful to adapt more density.The varieties with higher density tolerance have slowly aged roots,more subsoiling roots in late growing stage,which meet the demand for water and fertilizer,account for maintaining higher yield in higher density.(5)After increasing maize density,SPAD,Pn and Fv/Fm value were decreased in ear leaf,and accelerate the lowering rate of these parameters above in late growth stage.In increased density,varieties with high density tolerance maintain higher chlorophyll content,and higher photosynthetic rate,higher Fv/Fm,which alleviate the photo inhibition.Photosynthetic capacity decreased slowly is the physiological basis of high yield for those varieties.Subsoiling tillage can significantly improve maize ear leaf SPAD value and Pn;and can effectively alleviate the decreasing rate of SPAD value and Pn,delaying senescence of leaves and Pn decreasing,providing the basis for higher photosynthetic efficiency,which is helpful for dry matter production and accumulation.(6)Dry matter accumulation was decreased significantly,the lower extent varied in different varieties with different density tolerance,with the increase of the density.25.9% yield declining for the varieties with higher density tolerance,42% for varieties with lower density tolerance.Subsoiling tillage can significantly improve dry matter accumulation in different growth stages,and alleviate the decreasing of dry matter accumulation in higher density,maitaining the higher amount of dry matter accumulation after silking,providing adequate supply for grain production,and increasing the ratio of grain dry matter weight of those varieties with higher density in increased density.(7)The maize varieties have significant response of yield on density changing,the varieties with density tolerance have greater yield potential than those with low density tolerance;and have significant higher suitable density than those with low density tolerance.Under increased density,both kernel per ear and thousand kernel weight were decreased,but the varieties with higher density tolerance have relatively smaller yield decreasing than those with lower density tolerance.Subsoiling increased grain yield for 7.8%-11.0% by means of increasing effective ear numbers,slowing the decreasing the kernel per ear and kernel weight.(8)Under subsoiling tillage,adopting maize varieties with higher density tolerance,reasonable increase planting density,are the effective ways to increase production and efficiency. |
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