| The current increase in maize production is partly due to an increase in planting density.Increasing the planting density and improving the utilization efficiency of the plant to the light and temperature resources is the key to obtain high yield.However,with the further increase of planting density,groups become crowded and the competition of water and fertilizer between group and individual becomes fierce,resulting in waste of resources,therefore,the risk of production-decreasing will increase.The removal of leaves,which based on the theory of plant growth redundancy,as a new cultivation measure provides a feasible way to alleviate the contradiction between the group and the individual plant.It was found by other researchers that the middle and lower leaves of the maize population were blocked by the upper leaves,resulting in the decrease of the photosynthetic performance of the middle and lower leaves,and the removal of some leaves above the functional leaves would be beneficial to the improvement of photosynthetic performance and the grain yield.In our study,the field experiment was conducted in the Northwest A&F University Agricultural Center and the Key Laboratory of Crop Physi-Ecology and Tillage Science in Northwestern Loss Plateau in three years(2015 to 2017).we selected compact corn Zhengdan 958 and semi-compact Qiangsheng 101 as materials.The planting density is 82500/hm~2,which is reported as high yield density.we remove part leaves above the functional leaves,the treatment as remove a quarter of all leaves above functional leaves(D1),2/4(D2),3/4(D3)and 4/4(D4)and no leaf removal plant as control(CK).The effects of treatments on population leaf area,population light transmission,the enzyme activity and content of malonaldehyde,hormone content,grain filling performance and yield were measured and analyzed.As a new way to solve the contradiction between population and plant under close planting condition,we also provided technical support for selecting high yield maize cultivar.The main findings are as follows:(1)Two years(2015 and 2016)of field trials showed that removing leaves at the silking stage reduced the leaf area index of the population and increased the light transmittance of the middle and lower layer of the population.The moderate leaf removal(D1)slowed down the rate of decline of the leaf area index The leaf senescence rate and the functional period were prolonged,which ensured a higher photosynthetic source area for grain filling.However,leaf area index decreased significantly after 3/4(D3)and 4/4(D4)treatments,which accelerate the rate of leaf senescence.(2)The canopy photosynthetic rate(CAP),single leaf photosynthetic rate(Pn),stomatal conductance(GS)and transpiration rate(Tr)of the two maize varieties were significantly affected by leaf removal under close planting condition.The treatment of moderate leaf removal(D1)could significantly increase the CAP,Pn and GS of leaf population,with the increase in the degree of leaf removal,the CAP,Pn and GS showed a decreasing trend,and the effect in Corn Zhengdan 958 is more obvious.(3)The activity of SOD and POD decreased gradually,while the content of MDA gradually increased after silking stage,and the effect in moderate leaf removal(D1)was the most obvious.The treatment D1 significantly increased the activities of SOD and POD and significantly decreased the content of MDA significantly.It indicated that moderately leaf removal D1 treatment under close planting condition could effectively improve the protective enzyme activity of ear leaf and delay the leaf senescence process.(4)The changes of different hormones in dense planting of popcorn showed that the content of IAA in leaves of the ear gradually decreased,and the content of ABA increased gradually,while the content of ZR increased first and then decreased.IAA and ZR contents decreased significantly with the increase of leaf removal,while ABA content increased significantly.The moderate leaf removal D1 could effectively increase the content of IAA and ZR in ear leaf and decrease the content of ABA,indicating that moderate leaf removal of D1can stimulate the regulation of different hormone levels in the corn and effectively prolong the functional period of the leaves.(5)After simulating the process of grain filling,we found that grain filling rate of the two different plant types of maize showed single peak curve,and the maximum filling rate appeared about 35 days after anthesis.In the early filling stage,there was no significant difference between the treatment's grain filling rate.With the progress of grain filling,the filling rate of moderate leaf removal(D1)treatment increased significantly,and the change of grain filling rate in the middle and top part were more obvious.The filling rates of 3/4(D3)and 4/4(D4)kept at a relatively low level during the early filling stage.The results showed that moderate leaf removal(D1)treatment can effectively improve the filling rate of grain in the middle and upper part of the cob.(6)Under the condition of high-density planting,different degrees of leaf removal have different effects on the yield traits of two plant types of summer maize.Moderate leaf removal D1 could increase the grain yield of maize,but the increase degree was different between the two plant types of maize and varied a lot in there years.For example,the output of Zhengdan958 D1 increased by 25.8%,12.0%and 16.0%respectively over CK in 2015,2016 and 2017,while that of Qiangsheng 101 D1 increased by 19.2%,12.5%and 1.5%respectively in three years.It showed that effect of moderate leaf removal(D1)on compact Zhengdan 958 was more effective.Excessive leaf removal(D3 and D4)significantly reduced grain yield due to a significant reduction in photosynthetic source area in the grain filing stage.In the year of2016,the treatment D1 had no significant difference in cob diameter and cob length with CK,but the grain weight increased significantly.For example,the grain weight of Zhengdan 958D1 increased by 7.4%compared with CK,and the grain weight of Qiangsheng 101 D1increased by 4.1%,indicating that moderate leave removal can significantly increase the grain weight in close planting conditions,and then increase the yield. |
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