| Planting density and nitrogen application rate are the key factors affecting maize yield,and mechanized harvesting is an important technical means to realize cost-saving and high-efficiency in maize production.In recent years,with the continuous selection and breeding of close-planting maize varieties suitable for mechanical harvesting,the corresponding planting density and nitrogen application level need to be further discussed.In this study,two close-planting machine-resistant cultivars Xianyu 1171(XY1171)and Jinyu 838(JY838)were selected and applied with different densities(A1:52,500 plants/ha,A2:67,500 plants/ha and A3:82,500plants/ha)and Nitrogen Levels(B1:0 kg/ha,B2:120 kg/ha,B3:180 kg/ha and B4:240kg/ha respectively),the effects of density,nitrogen fertilizer and their interaction on the growth and yield characteristics of machine-harvested spring maize varieties were studied.The main results were as follows:1.Increasing planting density significantly reduced stem diameter,LA and leaf SPAD value,LAI and lodging rate gradually increased,and planting density increased from A1 to A3,stem diameter,LA and SPAD value decreased by 15.20%,22.38%and 5.26%,LAI and lodging percentage increased by 21.78%and 1.12 times respectively;The plant height,leaf SPAD value and LA were significantly increased by N application rate.The plant height was the highest in B3 treatment,which was9.40%higher than that in B1 treatment.Leaf SPAD value and LA per plant were the highest in B4 treatment,which were 10.67%and 17.55%higher than that in B1treatment respectively.2.Nitrogen application significantly increased the length of the 3rd and 5th Internode and the content of cellulose in stalk,and reached the maximum value in B3treatment,which was 14.81%,21.65%and 13.28%higher than that in B1 treatment,the puncture strength and compressive strength of stalk increased at first and then decreased.The planting density increased the length of the third internode and the ratio of length to diameter of each internode,and decreased the internode coarseness,the content of cellulose,the puncture strength and the compressive strength of the stem.The planting density increased from A1 to A3,the length of the third internode and the ratio of length to diameter of each internode increased by 13.54%and 33.08%respectively,while the internode diameter,cellulose content,stem puncture strength and compressive strength decreased by 21.23%,8.51%,14.56%and 39.62%respectively.3.With the increase of nitrogen application rate,the accumulation of dry matter in the population,the transfer rate of dry matter from vegetative organs before silking stage and the contribution rate of the transfer rate to grain yield increased at first and then decreased,which reached the maximum in B3 treatment,compared with B1treatment,the average increase was 29.16%,45.59%and 62.88%respectively.The dry matter accumulation of single plant decreased by 31.72%in A3 treatment compared with A1 treatment,and the dry matter accumulation of the population increased first and then decreased,the highest in A2 treatment,compared with A1treatment,the dry matter transfer rate of vegetative organs and the contribution rate of dry matter transfer rate to grain yield before silking stage increased significantly with the increase of density,there was an increase of 31.75%and 37.61%under A3treatment.The effect of dense nitrogen interaction on dry matter accumulation of cob at R1 XY1171 was very significant.4.Population N Accumulation at R1 stage,NTE and NCP increased firstly and then decreased with the increase of N application rate,and reached the maximum value in B3 treatment,which was 80.83%,21.91%and 17.26%higher than that in B1treatment,compared with B2 treatment,PFP and AE decreased by 43.35%and 44.24%,compared with B1 treatment,the nitrogen use efficiency of B4 treatment decreased by 31.71%.With the increase of plant density,the accumulation of nitrogen increased at first and then decreased,and reached the maximum in A2 treatment,which was 38.85%and 75.78%higher than that in R1 and R6 stages respectively.5.Nitrogen application could increase the ear length,ear diameter,number of grains per row and 1000-grain weight in a certain range,and decrease the bald tip length.Compared with B1 treatment,the ear length,ear diameter,row number of grains and 1000-grain weight increased by 13.55%,8.89%,14.49%and 13.69%,respectively,while the bald tip length decreased by 26.47%.When nitrogen application rate was higher than 180 kg/ha,ear diameter,ear row number and grain number per row did not increase significantly.With the increase of planting density,the length of ear,the diameter of ear and the number of grains per row decreased by6.70%,4.27%and 5.35%respectively.Close nitrogen interaction had no significant effect on yield and yield characters.6.The effects of density and N application rate on maize yield were different,and the yield was significantly affected by N application rate.With the increase of nitrogen application rate,the yield of maize increased at first and then decreased.The highest yield was obtained in B3 treatment,which was 33.12%higher than that in B1treatment.With the increase of density,the yield of maize increased at first and then decreased.A2 treatment reached the maximum value,which was 10.60%higher than A1 treatment.7.The density and nitrogen application rate had no significant effect on most of the mechanically harvesting traits of two maize varieties.With the increase of nitrogen application rate,the water content of grain,the puncture strength and the bending strength of cob increased gradually,compared with B1 treatment,compared with no nitrogen application,B4 treatment increased by 7.97%,26.85%and 35.19%respectively.However,it can be seen that there are obvious differences in the main mechanical properties among varieties,the water content of stem and Sheath and grain of JY838 were 9.70%and 3.51%higher than that of XY1171,respectively.The puncture strength and crushing strength of JY838 were 17.34 N/mm~2and 122.06N higher than that of XY1171,and the impurity rate of JY838 was 0.16%higher than that of XY1171,respectively,the breakage rate of JY838 was 4.67%lower than that of XY1171 on average,When planting density was 67500 plants/ha and nitrogen application rate was180kg/ha,XY1171 and JY838 had the highest yield,SPAD value and LAI both maintained higher level,which was beneficial to dry matter accumulation,it could keep higher stem strength,PFP,AE and NUE,lodging rate is lower,and grain moisture content can reduce to 28%,which could meet the condition of mechanical harvest.Therefore,the recommended planting density and nitrogen application rate of maize varieties suitable for machine harvest in Guizhou are 67500 plants/ha and 180kg/ha respectively. |
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