Simulation Of The Effects Of Nitrogen On Dry Matter Production, Partitioning And Yield Formation Of Greenhouse Fruit Cucumber

Dry matter production,partitioning and yield formation determine the economic benefit of greenhouse fruit cucumber production.Nitrogen is the important nutrient affecting dry matter production,partitioning and yield formation of plants.The aim of this study is to quantitatively investigate the effects of nitrogen(N) on dry matter production,partitioning and yield formation of greenhouse cucumber.Experiments with different planting dates and levels of nitrogen application rate after anthesis for greenhouse fruit cucumber(Cucumis sativus.Deltastar) were conducted in a multi-span PVC greenhouse in Shanghai during 2005.The integrated photo-thermal index,the product of thermal effectiveness and PAR absorbed by canopy(TEP_ab),was used to describe the changes of partitioning index(PI) and harvest index(HI) and fruit numbers with development stages.Effects of N on leaf photosynthesis,the partitioning indices of leaf and fruit,harvest index,factors(the accumulated number of fruits,fruits aborted,fruits setted and growth rate of individual fruits) of yield formation were quantified based on experimental data.Based on these quantitative relationships,a model for predicting the effects of nitrogen(N) on dry matter production,partitioning and yield formation of greenhouse fruit cucumber was developed, and independent experimental data were used to validate the model.The results showed that the model developed in this study gives satisfactory prediction of the total dry weight,dry weight of stem,leaf and fruit and yield formation of greenhouse fruit cucumber.(1) In the dry matter production submodel,the relationship between the maximum leaf photosynthesis rate(Pgmax) and the leaf nitrogen concentration(N_c) under different radiation and temperature conditions was quantified.Based on the quantitative relationship, a process based dry matter production simulation model was developed.Independent experimental data were used to validate the model.The results showed that the coefficient of determination(R²) and the relative prediction error(RE) between the predicted and the measured total dry weight based on the 1:1 line were 0.90 and 12.4%,respectively.(2) In the dry matter partitioning and yield prediction submodel,firstly,the seasonal time course(expressed as TEP_ab) of the partitioning indices of shoot and shoot dry matter to stem,leaf and fruit were derived using the experimental data.Then we found that N has no significant effect on the partitioning index of shoot,while leaf partitioning index increase and fruit partitioning index decrease with the increasing of nitrogen application level.The relative decreasing rate of leaf partitioning index and the relative increasing rate of fruit partitioning index after anthesis were found,respectively,to be an exponential function of leaf nitrogen concentration at middle fruit harvest stage(N_L).The seasonal time course of the harvest index,defined as the ratio of the accumulated dry weight of the harvested fruit to the accumulated total fruit dry weight,was also derived from the experimental data.The relative increasing rate of harvest index was also found to be an exponential function of N_L. Based on these quantitative relationships,a model was developed to predict the effects of nitrogen on after anthesis dry matter partitioning and yield of greenhouse cucumber. Independent experimental data were used to validate the model.The results showed the R² between the predicted and the measured dry weight of stem,leaf,fruit and the yield(fresh weight) based on the 1:1 line were 0.95,0.94,0.99,0.96,respectively,and RE were 13.0%, 12.3%,9.2%,16.8%,respectively.(3) In the process of yield formation submodel,firstly,the effects of N on the accumulated number of fruits(NF),fruits aborted(NAF) and fruits setted(NSF) were quantified.The results showed that,N affects the appearance rate of fruits and the appearance rate of fruits aborted directly.The appearance rate of fruits and the appearance rate of fruits aborted were found, respectively,to be a sigmodel function and a sinusoidal function of N_L,and the appearance rate of fruits aborted was lowest when N_L equals 32 mg(N)·g(DM)^-1.Then the effects of N on the increasing rate of fruit length(cm/MJ·m^-2) were quantified.N affects the increasing rate of fruit length by changing the source-sink relationship(expressed as the ratio of the actual leaf dry weight to the actual fruit dry weight on the plant,AWLi/AWFi).The founction of the increasing rate of fruit length was found to be an exponential function of AWLi/AWFi,and the founction paranwter changed after the ratio of accumulated leaf dry weight to the accumulated fruit dry weight on the plant(WLi/WFi) less than 4.According to the quantitative founction and TEP_ab accumulated after fruit anthesis,fruit length can be calculated.Based on these quantitative relationships,a model was developed to predict the effects of nitrogen on yield formation of greenhouse cucumber.The model gives satisfactory prediction of yield formation,the R² and RE between predicted and measured the accumulated number of fruits,fruit aborted and fruits setted and fruit length were 0.95,0.97, 0.80,0.80,respectively,and the relative prediction error(RE) were 10.6%,18.4%,16.4%, 23.2%,respectively.Using the planting date,nitrogen application rate in nutrient solution,air temperature and radiation in greenhouse as input,the model developed in this study can predict the total dry weight,dry weight of different organs of shoot,yield,fruit appearance date,the accumulated number of fruits setted and fruit size(length) of greenhouse fruit cucumber with the main stem reserved only in Shanghai area,hence,can be used for optimization nitrogen management for greenhouse fruit cucumber production.