Recommended fertilization rates based on watermelon yield and fertilizer reduction potential

Objectives We studied the nutrient requirements of watermelon for different yield levels in different watermelon production areas in China to propose the key technical measures for reducing fertilizer application rate and increasing fertilizer use efficiency.

Methods We analyzed the nutrient uptake level for producing 1 t economic yield using data from multi-point fertilizer experiments and literature on watermelon yield and nutrient uptake. We surveyed watermelon yield, organic and chemical fertilizer types and application rates, fertilizer and irrigation methods of farmers with large cultivation areas in 22 major watermelon producing provinces, cities and autonomous regions in China, and referred to the watermelon yield of various regions in the national statistical yearbook of China. We proposed recommended fertilizer rate under different yield levels and fertilizer reduction potential in different regions based on the target yield nutrient requirements of watermelon in different regions, the soil fertility level adjustment coefficients, recommended fertilizer rate in literature and the results verified in field experiments.

Results The average yield range of watermelon across the watermelon producing provinces, cities and autonomous regions was 11.9–58.8 t/hm², and the fertilizer inputs (N, P₂O₅ and K₂O) range were 190.7–380.7, 162.9–349.5, and 62.7–492.5 kg/hm² respectively. The average yield of watermelon across provinces and cities in southern China was 32.1 t/hm² and average fertilizer inputs (N, P₂O₅, and K₂O) were 250.2, 217.0, 236.9 kg/hm² respectively. The average yield of watermelon across provinces and cities in northern China was 45.6 t/hm² and the average inputs (N, P₂O₅, and K₂O) were 264.1, 245.8, and 291.9 kg/hm² respectively. The nutrient demands for N, P₂O₅, and K₂O to produce 1 t watermelon were 2.0, 0.83, 3.3 kg respectively. When the yield level was 30–40, 40–50, 50–60, 60–70, and 70–95 t/hm², the recommended fertilizer N application rate was 90–120, 110–150, 130–170, 150–205, and 170–230 kg/hm², the P₂O₅ application rate was 45–65, 55–75, 65–85, 70–95, and 80–110 kg/hm², and the K₂O application rate was 110–150, 125–170, 150–205, 170–230, and 185–250 kg/hm² respectively. The average fertilizer rates of N, P₂O₅, and K₂O applied by farmers in different regions were 1.3–3.0, 1.9–5.5, and 0.3–2.5 times of the recommended rate respectively. The reduction potential of chemical fertilizers (N, P₂O₅, and K₂O) were 22.7%–66.5%, 47.8%–81.7% and –187.1%–59.4% respectively, with an average of 43.0%, 68.7%, and 12.2% respectively. The fertilizer input of nitrogen and phosphorus in the main watermelon producing areas were excessive while both excessive and insufficient were found for potassium fertilizer. The excessive application of phosphorus fertilizer was more common and the fertilizer reduction potential in the southern China was greater than that in the northern China.

Conclusions In view of different yield levels, fertilization status and the related problems in the different regions, it is urgent to establish the comprehensive technical patterns to match the climate, cultivation season, and cultivation modes. The total recommended fertilizer rate for the watermelon should be based on the target yield and the application rates should be rationally controlled according to the nutrient requirements at the different growth periods. We should establish methods targeted at integration of fertigation management, organic fertilizer alternatives, soil testing for fertilizer formulation and other key technologies based on the amount of available nutrients that can be provided by organic fertilizer inputs. We can set up models and support technical protocols, large-scale demonstration and promotion, and ultimately achieve the goal of fertilizer reduction, higher efficiency and green sustainable and healthy development of watermelon industry.