Effects of Different Colors of Biodegradable Mulch Film on Vegetative Growth, Yield, Fruit Quality, and Soil Properties in Grafted Watermelon

The prolonged use of traditional polyethylene mulch (PM) films has resulted in significant environmental issues, such as soil residues and white pollution, which pose challenges to sustainable agriculture. The transition from PM to fully biodegradable mulch (BDM) films has emerged as a prominent trend in contemporary farming practices. This study investigates the effects of various colors of biodegradable mulches on watermelon production and quality, with a particular emphasis on BDM in comparison to conventional PM. Within the 0.2–15.3 µm wavelength range, transparent variants demonstrate high light transmission, while the silver–black treatment exhibits greater reflectivity. The silver–black surface effectively reduces evaporation, maintaining soil water content 5–8% higher than that of PM. However, its thermal profile reveals periodic temperature increases similar to those observed with PM. The results indicate that BDM silver–black enhances biomass, root N and P levels, and leaf NPK retention compared to PM. Notably, among the BDM treatments, silver–black yielded the highest average fruit weight and width (7.68 kg, 22.83 cm), although these differences were not statistically significant when compared to PM. Additionally, it produced the highest soluble solids content (13.2 °Brix) at a significance level of p < 0.05 relative to PM. This finding suggests an enhancement in the soil’s capacity to retain moisture and its nutrient availability, thereby fostering plant growth. All treatments proved profitable and economically viable; however, the total inputs and outputs associated with BDM silver–black and CK-PM transparent yielded a satisfactory profit, ranging from $1937 to $2503 per hectare. These results advocate for the utilization of sensor-embedded mulch films and the silver–black color to optimize water and nutrient utilization, thereby promoting sustainable watermelon cultivation.