Study On Density Tolerance Character Of Super High-yielding Population

【Object】Higher planting density is one of the key measures for Higher Yield in maize production all over the world.Many findings revealed that planting density is more than 7.5×104plants·hm-2 on both ton-grain field and super-ton-grain field.However,lodging is a major constraint to limit planting density.At present,there is less varieties which can stably obtain high-yield and super high-yield in the case of close planting.Therefore,study the law of lodging resistance and the relationship between dry matter production and distribution and stem strength, have important significance to exploit "structural production potential"of maize populations and,subsequently,obtain high-yield and/or super-high-yield in the different high-yield maize varieties.【Methods】In this experiment,we employed four different density-tolerant maize cultivars,Jingke 518,Jingke519,Denghai3719,Nongda108 under five densities,3.00,5.25,7.50,9.25,and 2.00×104plants·hm-2,respectively.Samples were measured at before tasselling stage,silking period,21 days after silking and physiological maturity stage.Stem strength,root character,dry matter production,ear characters and yield components of different density-tolerant maize cultivars were studied by methodology of morphological physiology and biological mechanics under the condition of close planting.Finally,we discussed on mutual relations between stem lodging resistance capacity and the populations production potential.【Results】The main results are as follow:1.Lodging was classified into two types in maize,stem lodging and root lodging.The extent of lodging increased with the increase of planting density,especially in the7.5×104plant·hm-2.The type and extent of lodging were different between different varieties.The type of Jingke518 was root lodging and the extent serious.The type of Jingke519 was stem lodging and that of Nongda108 inclined to stem lodging and the extent slight.Denghai3719 was a lodging-resistant cultivar.Before tasselling stage,the 3rd and 4th internodes were easier to stem lodging,especially in 20~40cm height.However,the 5th,6th and 7th internodes were easier to stem lodging under physiological maturity stage.The most lodging-resistant was Denghai3719,followed by Jingke519,Nongda108,andJingke518.Creeping-roots lodging had negative effect on the yield mostly.The quality of root declined rapidly with the increase of planting density,especially in 5th to7th layers of root trait.The negative effect of root diameter is highest on root lodging,followed by the total number of crown roots and root-layers.Also,fresh matter and dry matter of root had effects on root lodging.2.With increasing planting density,the changes of diameter and length of stem were significantly,dry weight of units long stem reduced,the crushing strength and puncture strength of stem reduced.When planting density increased to above 7.5×104plant·hm-2,the stem mechanical strength of sparse planting variety decreased quickly,especially in the 4th and above 4th internodes.For the dense planting variety,with increasing planting density the variation coefficient of the stem quality was less and the plant stem strength maintained homogeneity,which had advantage of resistance to environment.3.Compared to dense planting density,the LAI and LAD of the large-size spike maize variety were higher under low planting density.Although NAR was slightly lower,the single plant production and the dry matter accumulation were higher.When planting density increased to above 7.5×104plant·hm-2,lodging of dense planting variety Denghai 3719 was slightly.Furthermore,LAI,LAD and NAR were significantly higher than the lower planting variety.The individual and population of dry matter accumulation and the proportion of the roots were higher,thus which was beneficial to enhance their lodging resistance.4.Some of ear characters were contributed to yield per plant,which included ear weight,ear axis weight,ear length,effective ear length,ear diameter,and were greatly effects on grain number per ear,which included ear weight,ear length,effective ear length and ear axis weight,and were greatly effects on1000-kernel weight,which included ear diameter,ear weight,ear axis weight,ear axis diameter.The feature of large-size spike maize varieties under lower density cultivation were the bigger ear diameter and ear axis diameter,the shorter ear length and effective ear length.In high-density conditions,due to lodging kernel development was hindered,subsequently,row grains decrease.Thus,such varieties were not the type of dense-resistance and high-yielding . However , The feature of dense-resistance varieties Denghai3719 was the little change of row grains,ear diameter,ear axis,and the longer ear length and effective ear length,better dense-resistance capacity of ear,longer barren ear tip。Such varieties had high-yield potential in the case of close planting.5.In low-density conditions,yield of sparse planting variety was higher or slightly higher than the dense-resistance variety.Its harvest ears and grain number per ear was not significant lower than the dense-resistance variety,yield of plant and 1000-grain weight were higher significantly.When planting density increased to above 7.5×104plant·hm-2,harvest ears of sparse planting variety was lower 34~40% than the dense-resistance variety.Its yield and grain number per ear decreased significantly.Although 1000-grain weight was slightly higher than the dense-resistance variety,the final yield was lower significantly.It showed that effectively increase of population quantity was a main factor to improve the yield under close planting conditions.【Conclusion】In low-density conditions,the sparse planting variety had good individual development,stronger photosynthetic capacity,higher harvested ears number and 1000-grain weight.Although grain number per ear was slightly lower than the dense-resistance variety,the final yield was slightly higher.When planting density increased to above 7.5×104plant·hm-2,stem mechanical strength decreased and lodging was seriously.Due to photosynthetic productivity capacity hindered,some of traits were lower,which included dry matter quantity per ear,the dry matter partitioning ratio of root and ear was lower.Subsequently,yield was lower than the dense-resistance variety.However,the dense-resistance variety had lodging-resistance.With increasing of planting density,photosynthetic productivity capacity and effective harvest ear number increased significantly.Moreover,bareplant percentage was lower and ear weight,grain number per ear and 1000-grain weight decreased slowly.Its population increasing yield effects was significantly.So that selection of lodging-resistant high-yield varieties was the key to achieve sustainable high-yield under high-density conditions...