Simulation of the effects of nitrogen on after anthesis dry matter partitioning and yield of greenhouse cucumber

Quantifying the effects of nitrogen (N) on dry matter partitioning and yield of greenhouse cucumber is essential for the optimization of nitrogen management in greenhouse cucumber production. For this purpose, experiments with different planting dates and levels of nitrogen application rate after anthesis for greenhouse cucumber (Cucumis sativus) were conducted in a greenhouse in Shanghai during 2005. First, the seasonal time course of the partitioning indices of shoot dry matter to stem, leaf and fruit were derived using the experimental data. 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 (NL). 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 NL. 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 coefficient of determination (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 0.945, 0.943, 0.990, 0.955, respectively, and the relative prediction error (RE) were 13.0%, 12.3%, 9.2%, 16.8%, respectively. The results showed that the model developed in this study can give satisfactory prediction of dry matter partitioning and yield of greenhouse cucumber under different nitrogen application level, hence, can be used to support decision-making for nitrogen management in greenhouse cucumber production.