Simulation Of The Effects Of Leaf Nitrogen Content On Greenhouse Cucumber Leaf Area

Leaf is the most important apparatus of transpiration and photosynthesis, it play an important role in the growth and development of plant. Leaf area index (LAI) is one of the most important crop parameters in photosynthesis driven crop growth simulation models and transpiration models. Besides temperature and radiation, nitrogen is the most important factor affecting leaf area and leaf area index. Crop growth and development simulation model is a useful tool for the optimization of greenhouse crop and climate management, and cucumber is one of the most popular crops of greenhouse production. The purpose of this paper is to develop a Simulation of the affects of leaf nitrogen content on greenhouse cucumber leaf area and find out the most suitable nitrogen fertilization way.In this study, a series of field experiments with greenhouse cucumber (Cucumis Sativus cv. Deltastar) including different nitrogen treatments were carried out in a Venlo-rype greenhouse, a multi-span PVC greenhouse in Shanghai (E121.5°, N31.2°) from 2003 to 2005 to collect data for model development and validation. After the analysis of the experiment data, a leaf area model of greenhouse cucumber that affected by different leaf nitrogen content using intercepted product of thermal effectiveness and photosynthetically active radiation (TEP) by canopy was developed. This model includes two subsystems: the model of unfolding leaves and the model of leaf length increasing rate.The TEP (product of thermal effectiveness and photosynthetically active radiation) that intercepted by canopy is calculated by formula as follows:TEP=ΣDTEP_iDTEP_i=CPAR_i * RTE_iCPAR_i=Σ(PAR_j*(1-exp(-k*LAI_i-1))))PAR_j=Q_j*0.5*1800*10^-6DTEPi is the i'th day's TEP that intercepted by canopy; CPARi is the i'th day's photosynthetically active radiation that intercepted by canopy;RTEi is the i'th day's relative thermal effectiveness after unfolding of the first leaf; PAR_j is the photosynthetically active radiation of j'th hour in i'th day's; LAI_i-1 is the leaf area index of (i-l)'th day; Q_j is the radiation of j'th hour in i'th day's; 0.5 is the convert coefficient from radiation to photosynthetically active radiation; 1800 is the convert coefficient from J m^-2 -s^-1 to J m^-2·h^-1; 10^-6 is the convert coefficient from J to MJ.Then, a leaf area model of greenhouse cucumber that affected by different leaf nitrogen content using intercepted TEP by canopy was developed. Leaf area plant was calculated as follows:LA=Σ(0.9272* (LLi)²) -LAoLLi=Lmax(i)*(1-EXP(-VLi*TEPij/Lmax(i))Lmax(i)= Lmax(p)*(1-EXP(-8.74*i/ Lmax(p)))Lmax(p)=28.99*(1-exp(-1.91*N/28.99))VL(min)=-0.05+0.02*NTEPij=TEPj-TEPiATEP=10.32-0.16*NLA is the leaf area of any day after unfolding the first leaf, LAo is the extirpated leaf area, LLi is the observed length of i'th leaf, Lmax(i) is the maximum leaf length of i'th leaf, Lmax(p)is the maximum leaf length of the whole plant, N is the leaf nitrogen content, VLi is the increasing rate of leaf length, VL(min) is the minimum increasing rate of leaf length in the whole plant, TEPij is the intercepted TEP by canopy of i'th leaf in the j day after unfolding the first leaf, TEPj is the cumulate TEP that intercepted by canopy from unfolding the first leaf to the j'th day after unfolding the first leaf.,TEPi is the cumulate TEP that intercepted by canopy when unfolding the i'th leaf, n is the number of leaves unfolding, ATEP is the average intercepted TEP by canopy that unfolding one leaf. LAI=LA*d/10⁴LAI is the leaf area index, d is the planting density (plant/m2), 10 is the convert coefficient from cm² to m².When using the above formulas to predict leaf area index, the coefficient of determination (R²) and RMSE between simulated and observed LAI of experiment 1 based on the 1:1 line were 0.9715 and 0.14,as the same while, the R2 and RMSE of experiment 2 and experiment 4 were 0.9825, 0.13 and 0.9579. 0.18.The model of this study can be used to calculate the increasing rate of leaf length and numbers of unfolding leaves, and finally can be used to forecast the LAI under different nitrogen fertilization. It also can be connect with t dry matter partitioning and yield prediction model and photosynthesis model to predict the dynamic change of the LAI, the drymatter weight and the yield. The model will be useful to the management of nitrogenous fertilizer in greenhouse cucumber cultivation.