Effects of controlled/slow-released nitrogen fertilizers on physiological characteristics and quality of melon under substrate cultivation

【Objectives】 Nutrient release rates of slow/controlled nitrogen fertilizers vary with different medium. Types of slow release fertilizers should be selected according to crop species, cultivation model and soil environment, etc. To provide theoretical basis for high quality and simplified cultivation ofmelon in non-cultivated land of northwestern China, effects of five controlled release nitrogen fertilizers, including Iso-butyl diurea (IBDU), sulfur-coated urea (SCU), urea formaldehyde (UF), methylene urea (MU) and polyolefin-coated urea (ESN), on physiological characteristics and qualities of melon were investigated in special fertilizers at the same level of whole nutrients, and suitable slow/controlled release nitrogen fertilizer in substrate culture was screened. 【Methods】 Seven treatments were included in this study, namely, no N fertilizer treatment (CK), common urea (U), Iso-butyl diurea, sulfur-coated urea, urea formaldehyde, methylene urea and polyolefin-coated. At the two-leaf stage, muskmelon seedlings were transferred to pot (height 30 cm, diameter 30 cm) within 5 kg substrate. One pot had one muskmelon seedling. The nutrient concentrations of substrate in a pot were N 7.5g, P2O5 3.25g and K2O 7.5g. The formulation of matrix was peat ∶vermiculite ∶perlite=3 ∶1 ∶l (in volume). All the slow/controlled release nitrogen fertilizers were applied as basal fertilizers. For the common urea treatment, 40% urea was used for basal application and 60% amount of urea was used as topdressing. Calcium superphosphate was supplied once at the beginning for all treatments. 40% potassium sulfate was fertilized as basal dressing and 60% used as top dressing. The top dressing was supplied at the fruit setting and fruit-development stages, and the same amount was applied for the two times. Leaf samples were collected randomly at the flowering stage of melon for testing. Three replicates for each treatment were laid out in a random design. 【Results】 Compared with the ordinary urea, the five kinds of slow/controlled release fertilizers increase the leaf chlorophyll content, net photosynthetic rate, transpiration rate, nitrogen content and root activity at different degrees. The slow/controlled release nitrogen fertilizer treatments significantly increase the single fruit weight and improve fruit quality, and the order of the fertilizers effects from high to low are methylene ureas iso-butylene diurea urea formaldehyde polyolefin- coated sulfur-coated urea. In a word, the chemical slow/controlled fertilizers are better than physical type. Compared with the ordinary urea, the chlorophyll a, chlorophyll b and total chlorophyll contents of plants under the methylene urea treatment are increased by 41.0%, 31.0% and 38.3%, the net photosynthetic rate and transpiration rate of plants are increased by 28.9% and 95.5%, the leaf total nitrogen content, soluble protein content, nitrate content and root activity are improved by 23.7%, 24.3%, 269.7% and 37.5%, and the average fruit mass, the central soluble solid content, the soluble sugar content and Vc content are increased by 54.5%, 4.1%, 10.6% and 16.7%, while the nitrate content is decreased by 9.9%. 【Conclusions】The slow/controlled release nitrogen fertilizers could increase the content of chlorophyll and photosynthesis of muskmelon leaves, enhance the function of muskmelon root absorption, promote the absorption and assimilation of nitrogen, and improve yield and quality. The yield and quality of the slow/controlled fertilizer treated melon are correlated with physiological indices, such as chlorophyll content, photosynthetic rate, leaf total nitrogen content, soluble protein content, nitrate content and root activity, etc.