Quantifying The Effects Of Nitrogen And Potassium Coulpling On Growth Dynamics And Quality Of Muskmelon In Plastic Greenhouse

Nitrogen and potassium are two crucial nutrient elements that affect the yield and quality of crops.The aim of this study was to quantitatively investigate the effects of nitrogen and potassium coupling on the growth dynamics and quality of muskmelon.Experiments with different planting dates,different levels of nitrogen,different levels of potassium,and different ratios of nitrogen and potassium on muskmelon?Cucumis melo L.‘Nanhaimi'and‘Xizhoumi 25'?were conducted in plastic greenhouse located at Sanya,Hainan?18°1?N,109°30?E?from Nov.2012 to Sept.2015.By integrated photo-thermal index?PTI?,the quantitative relationship between growth dynamics,yield and quality of muskmelon and the leaf nitrogen content and potassium content was determined.Based on these quantitative relationships,the way and coefficients of nitrogen and potassium coupling were confirmed,and models for predicting the effects of nitrogen,potassium,nitrogen and potassium coupling on growth dynamics,yield and quality of muskmelon were developed and then incorporated into a photosynthesis-driven crop growth model?SUCROS?.Independent experimental data were used to validate the model.?1?Quantitatively analyzed the effects of nitrogen on leaf area index,leaf maximum total photosynthetic rate,dry matter partitioning index of each organ,fruit fresh weight,fruit soluble sugar,soluble protein,Vc and soluble solids for muskmelon.Four experiments with different planting dates,different levels of nitrogen,were conducted in plastic greenhouse from Nov.2012 to Sept.2015.Four levels of nitrogen concentration treatment(N7:7,N10:10,N13:13,and N16:16mmol·L^–1)were used in each experiment.The results showed that the critical leaf nitrogen content at flowering stage for muskmelon‘Nanhaimi'and‘Xizhoumi 25'were 19.8 and 21.0 mg·g^-1.Corresponding to the critical value of leaf nitrogen content at flowering stage,the available nitrogen in the substrate of Expt.1–4 for the two cultivars were,respectively,169,178,196,and 145 kg·ha^–1 for‘Nanhaimi'and 173,193,247,and 132 kg·ha^–1 for‘Xizhoumi 25'.The coefficient of determination?r²?between the predicted and measured values of leaf area index?LAI?,dry weight of shoot?DWSH?,stem?DWST?,leaf?DWL?,and fruit?DWF?,fresh weight of fruit?FWF?,soluble sugar content?SU?,soluble protein content?PR?,vitamin C content?Vc?and soluble solids content?SO?of nitrogen model were,0.91,0.90,0.82,0.76,0.92,0.90,0.91,0.89,0.86,and 0.88,respectively;and the relative root-mean-squared error?r RMSE?were 10.8%,19.6%,21.1%,30.3%,11.9%,10.1%,17.3%,13.9%,27.8%,20.6%.?2?Quantitatively analyzed the effects of potassium on leaf area index,leaf maximum total photosynthetic rate,dry matter partitioning index of each organ,fruit fresh weight,fruit soluble sugar,soluble protein,Vc and soluble solids for muskmelon.Two experiments with different planting dates,different levels of potassium,were conducted in plastic greenhouse from Jan.2014 to Sept.2014.Four levels of potassium concentration treatment(K3:3,K6:6,K9:9,and K12:12 mmol·L^–1)were used in each experiment.The results showed that the critical leaf potassium content at flowering stage for muskmelon‘Nanhaimi'and‘Xizhoumi 25'were 55.0and 46.0 mg·g^-1.Corresponding to the critical value of leaf potassium content at flowering stage,the available potassium in the substrate of Expt.1 for‘Nanhaimi'and‘Xizhoumi 25'were,respectively,765 and 554 kg·ha^–1.The coefficient of determination?r²?between the predicted and measured values of leaf area index?LAI?,dry weight of shoot?DWSH?,stem?DWST?,leaf?DWL?,and fruit?DWF?,fresh weight of fruit?FWF?,soluble sugar content?SU?,soluble protein content?PR?,vitamin C content?Vc?and soluble solids content?SO?of potassium model were 0.93,0.98,0.83,0.96,0.98,0.99,0.94,0.94,0.89,0.85,0.90,respectively;and the relative root-mean-squared error?r RMSE?were 10.8%,19.6%,30.3%,21.1%,11.9%,17.2%,13.9%,27.8%,20.6%,10.1%,respectively.?3?Quantitatively analyzed the effects of nitrogen and potassium coupling on leaf area index,leaf maximum total photosynthetic rate,dry matter partitioning index of each organ,fruit fresh weight,fruit soluble sugar,soluble protein,Vc and soluble solids for muskmelon.Two experiments with different planting dates,different ratios of nitrogen and potassium were conducted in plastic greenhouse from Jan.2015 to Sept.2015.Eight ratio treatments of nitrogen and patassium?N7K3,N7K6,N7K9,N7K12,N13K3,N13K6,N13K9 and N13K12?were used in each experiment.Based on quantitatively analysis of the effects of nitrogen,potassium on the growth dynamics,yield and quality of muskmelon,the coupling way and coupling coefficients of nitrogen and potassium were determined.Nitrogen limit factors,potassium limit factors and coefficients of nitrogen and potassium coupling were multiplied as the way of nitrogen and potassium coupling.The r² between the predicted and measured values of leaf area index?LAI?,dry weight of shoot?DWSH?,stem?DWST?,leaf?DWL?,and fruit?DWF?,fresh weight of fruit?FWF?,soluble sugar content?SU?,soluble protein content?PR?,vitamin C content?Vc?and soluble solids content?SO?of nitrogen and potassium coupling model were 0.78,0.91,0.93,0.94,0.83,0.89,0.92,0.95,0.91 and 0.93,respectively,and their r RMSE were 9.2%,12.4%,11.8%,43.2%,6.6%,7.2%,6.85%,4.98%,6.61%and 4.35%,respectively.Therefore,our research gave satisfactory predictions of growth dynamics and quality for muskmelon under different ratios of nitrogen and potassium treatment,and developed the model of nitrogen and potassium interaction of muskmelon by the multiplicative coupling way was feasible.The results showed that the model developed in this study can prediet growth dynamics,yield and quality of muskmelon satisfaetorily,hence,can be used for optimization nitrogen and potassium management for muskmelon production in plastic greenhouse.