Status-quo and reduction potential of chemical fertilizer application for facility cultivation of early maturing watermelon and sweet melon

Objectives Investigating the status of fertilization of watermelon (Citrullus lanatus) and sweet melon (Cucumis melo) in Shaanxi to provide scientific basis and technical strategy for reducing the use of fertilizer and enhancing nutrient use efficiency.

Methods We surveyed the types and rates of applied fertilizers, and fertilizing methods of watermelons and sweet melons in Shaanxi to make the reasonable fertilizer recommendation based on the target yield and the fertilizer experiments from literatures at the study regions. We also conducted the field trial to verify the recommended fertilizer rates, and evaluate the potential of reducing fertilizer rates.

Results The total inputs of N, P₂O₅ and K₂O in the main cultivation areas in Shaanxi were 582, 412, and 541 kg/hm² for watermelon and 1059, 763 and 842 kg/hm² for sweet melon. And the average application rates of chemical N, P₂O₅ and K₂O were 266, 213, 304 kg/hm² for watermelon, and 315, 317, 281 kg/hm² for sweet melon, which were 1.8, 3.6, 2.3 times of the recommended chemical N, P₂O₅ and K₂O rats for watermelon and 2.9, 6.3, 3.1 times of those for sweet melon, respectively. Apparent surpluses of N, P₂O₅ and K₂O were 455, 369 and 388 kg/hm² for watermelon, and 980, 728 and 692 kg/hm² for sweet melon, respectively. The application rates of N, P₂O₅ and K₂O in both higher and too high grades accounted for 79.6%, 88.9% and 79.6% for watermelon, and 74.9%, 91.0% and 74.9% for sweet melon, and the nutrient utilization efficiency was thus low, in range of 4.6%–28.3% in the surveyed area. The general nutrient reduction potential of N, P₂O₅ and K₂O was 46%, 72%, and 57% for watermelon, and 65%, 84%, 68% for sweet melon, respectively. The proportion of N from organic manures in watermelon and sweet melon was 39.5% and 65.8% in average, so the over input nutrients were mainly from chemical fertilizer. The ratios of N∶P₂O₅∶K₂O from chemical fertilizers for watermelon and sweet melon were 1.0∶0.8∶1.1 and 1.0∶1.0∶0.9, respectively, and P₂O₅ ratio was too high for both crops. The basal applied chemical N + P₂O₅ + K₂O nutrients in watermelon and sweet melon accounted for 91.2% and 59.4% of total chemical fertilizers, which were too high, especially for those using fertigation technology.

Conclusions In the total nutrient input of watermelon and sweet melon in the surveyed area, the proportion of organic nutrient are generally in suitable range, over input is mainly caused by chemical fertilizers, especially that of P. In addition, the ratio of basal fertilizer is too high, and that is worse when using fertigation technology. It is urgent to make the optimum fertilization systems based on nutrient requirements of watermelon and sweet melon, and the application rates of N, P₂O₅ and K₂O fertilizers of farmers could be reduced by 46%, 72% and 57% for watermelon, and by 65%, 84% and 68% for melon, respectively