Effects Of Nitrogen Application On Growth And Photosynthetic Characteristics Of Apple Trees Under Water Storage Pit Irrigation

Nitrogen fertilizer is the most important nutrient for fruit trees.It is very important to apply appropriate amount of nitrogen fertilizer to the growth of fruit trees.Water and fertilizer distribution in soil is changed by water storage pit irrigation method,which makes the utilization of water and fertilizer of fruit trees change.In order to realize the efficient utilization of nitrogen fertilizer by fruit trees under water storage pit irrigation,a fertilization system suitable for this irrigation method should be formulated.Three nitrogen levels(0,20 kg/mi,40 kg/mu)and two top-dressing stages(post-anthesis top-dressing stage,Fruit Swelling top-dressing stage)were set up for seven water storage pit irrigation treatments.The effects of different nitrogen application stages and amounts on Photo synthetic Characteristics of leaves and growth of fruit trees of 7-year-old dwarf rootstock densely planted Red Fuji apple were analyzed in order to determine the suitable nitrogen application sites for fruit tree growth.In order to provide the basis for formulating the fertilization system of apple trees under water storage pit irrigation.The results are as follows:1.Effects of Nitrogen Application on Photosynthetic Characteristics of Apple Leaves under Water Storage Pit Irrigation(1)Applying nitrogen fertilizer effectively increased net photo synthetic rate of apple leaves,and the effect of water storage pit irrigation was more obvious than that of surface irrigation.At the same fertilization stage,the net photosynthetic rate increased with the increase of nitrogen application when the single application of nitrogen was less than 20 kg/mu,and excessive application of nitrogen would inhibit photosynthesis.Under the same nitrogen application rate,the effect of topdressing nitrogen fertilizer after Anthesis on net photosynthetic rate was more significant than that of fruit swelling stage.However,considering the whole growth period,two topdressing treatments were more conducive to the improvement of photosynthetic rate of fruit leaves during the whole growth period.In this experiment,T6 treatment was the best way to improve the net photosynthetic rate of apple leaves.(2)By analyzing the effect of nitrogen fertilizer on stomatal conductance,intercellular CO2 concentration and transpiration rate of leaves,and combining with the change rule of net photosynthetic rate,it is concluded that stomata is the limiting factor of photosynthesis from germination and flowering stage to new shoot vigorous period.Applying nitrogen fertilizer after flowering increases stomatal conductance and transpiration rate,and increases the utilization efficiency of intercellular CO2 by photosynthesis,alleviating this stage.Stomatal limitation;with stomatal development,net photosynthetic rate was no longer affected by stomatal limitation,and nitrogen application affected photosynthetic rate through other non-stomatal pathways.(3)Topdressing nitrogen fertilizer can increase the chlorophyll content and total nitrogen content of apple leaves,and the effect of water storage pit irrigation is also more obvious than that of surface irrigation.The chlorophyll content and total nitrogen content increased with the increase of nitrogen application rate when the single nitrogen application rate was less than 20 kg/mu.The chlorophyll content decreased when the nitrogen application rate reached 40 kg/mu,and the total nitrogen content did not increase significantly compared with the treatment of 20 kg/mu.Under the same nitrogen application rate,the total nitrogen content of leaves increased more significantly after anthesis than that of leaves without nitrogen application,and the chlorophyll content and total nitrogen content of leaves could be maintained at a higher level during the whole growth period by applying nitrogen in stages.Under the experimental conditions,the nitrogen application scheme of T6 treatment was most beneficial to the accumulation of total nitrogen and chlorophyll content in leaves2.Effect of Nitrogen Application on the Growth of Apple Trees Irrigated in Water Storage PitTopdressing nitrogen fertilizer effectively promoted the growth of new shoots,leaves,trunks and roots of apple trees,and under the same fertilization conditions,the cumulative growth of new shoots,trunk diameter,root length density and leaf area index of water storage pit irrigation treatment were greater than those of surface irrigation treatment.At the same fertilization period,the cumulative growth of new shoots increased with the increase of nitrogen application rate;the cumulative growth of leaf area index and root length density increased with the increase of nitrogen application rate when the single nitrogen application rate was less than 20 kg/mu,but did not increase significantly when the latter leaf area index was higher than the latter,but the root length density decreased;the cumulative growth of trunk diameter was greatly affected by the amount of nitrogen application after anthesis,and increased with the increase of nitrogen application rate.Additionally,it increases.Generally speaking,post-anthesis nitrogen fertilizer has a greater impact on the aboveground part of apple trees.The content of nitrate nitrogen in rhizosphere soil increased significantly under nitrogen application,and increased with the increase of nitrogen application.The content of nitrate nitrogen in rhizosphere soil was higher after the second topdressing.Water storage pit irrigation can effectively reduce nitrogen losses and store more nutrients for fruit tree growth.Comparing the differences of growth indices of apple trees after nitrogen application,it was found that T6 treatment was most beneficial to the growth of apple trees during the whole growth period3.Prediction model of photosynthetic rate of apple leaves under water storage pit irrigationThe relationship between net photosynthetic rate and other factors was studied by multiple linear regression and path analysis.The factors which had great influence on photosynthetic rate in two periods were selected to establish the prediction model of net photosynthetic rate of apple leaves after two times of topdressing in water storage pit irrigation.Finally,the net photosynthetic rate after anthesis with stomatal conductance,intercellular CO2 concentration and total nitrogen content of leaves as independent variables was established.The net photosynthetic rate(NPR)model at fruit expansion stage was established with stomatal conductance,atmospheric CO2 concentration,relative humidity and chlorophyll content as independent variables.The correlation coefficient R2 of the measured and predicted values after two topdressing treatments reached above 0.97.