Quality of Reclaimed Domestic Water Irrigated Peppers - NPK Coupling Model and Optimized Combination Solution

Focusing on the coupling between the NPK content in Reclaimed domestic water irrigated peppers and capsaicin, a field experiment in the three-factor, five-level quadratic general revolving combination design was conducted for an in-depth analysis of capsaicin content coupling model by testing the significance of regression equation and coefficient with regression equation. The test result shows that : (1) factors affecting the content of capsaicin are in order of nitrogen fertilizer application level (x1) > nitrogen fertilizer application level (x2) > potassium fertilizer application level (x3) according to the main factor effect analysis based on the established capsaicin-NPK coupling model; (2) the nitrogen-potassium interaction effectively improves the content of capsaicin. That is, the content of capsaicin theoretically tend to be 0g.kg-1 when both the nitrogen fertilizer application level and the level of potassium fertilizer application level are at the lowest; when the amount of nitrogen and potassium fertilizers application increases, the content of capsaicin increases accordingly. Medium nitrogen combined with medium potassium may result in the highest level of capsaicin content which can reach 0. 068g.kg-12 when the level of nitrogen and potassium fertilizers application reaches 120 g.kg-1 and 112.5g.kg-1 respectively . Under the circumstance of certain volume of potassium fertilizer application, the content of capsaicin further increases with the decrease in the level of phosphorus application. The maximum capsaicin content of 0. 21g.kg-1 is achieved when the level of potassium and phosphorus fertilizer application reaches 120 kg.hm-2 and 60 kg.hm-2 respectively; and (3) the range of the ideal target content of capsaicin in peppers irrigated with the reclaimed domestic water in China’s Ningxia Region and the optimized NPK combination solution are obtained and developed. And in specific: the level of NPK fertilizers application would be 186.15kg.hm-2, 71.17kg.hm-2 and 122.02kg.hm-2 respectively under the condition that the content of capsaicin being greater and beyond 0.12g.kg-1.