Effects of alginate water soluble fertilizer on growth and quality of watermelon

Abstract:【Objective】The effects of alginate soluble fertilizer on watermelon growth with different fer- tilizer types and under reduced application conditions were compared to provide theoretical basis for ra- tional fertilization of watermelon.【Methods】The variety was‘Zhongke 6’, and six treatments were de- signed as follows: CK0 (no fertilization), CK1 (common compound fertilizer), CK2 (traditional water- soluble fertilizer), AF (alginate water-soluble fertilizer), AF1 (20% reduction in alginate water-soluble fertilizer), and AF2 (40% reduction in alginate water-soluble fertilizer). Three repeats were set for each treatment, with a total of 18 plots and random block arrangement. Watermelon planting space was 0.5 m× 2 m. The total nitrogen, phosphorus and potassium and total amount of nitrogen, phosphorus and potas- siuminCK1,CK2andAFwereN100kg·hm-2,P2O5 35kghm-2 andK2O130kg·hm-2,respectively,in which the deficiency of nitrogen, phosphorus and potassium was supplemented by inorganic fertilizer. 40%, 30% and 20% of the total amount of fertilizer were applied in watermelon vine extension stage (5- 6 leaves), early fruit swell stage and final fruit swell stage. In the fertilizer-applying process, drip irriga-tion was used to dissolve the fertilizer in the fertilizer tank before the end of conventional drip irriga- tion, then water slowly dripped around the watermelon root system, and finally dripped at an appropri- ate amount of water. The photosynthetic pigment content, dry matter content, plant nutrient content and fruit quality of watermelon after different treatments were measured.【Results】The reduction of 20% al- ginate fertilizer did not significantly affect the chlorophyll content in watermelon leaves, but the effect on the carotenoid content in watermelon leaves was not significant. The reduction of 40% alginate wa- ter-soluble fertilizer had a significant effect on the chlorophyll content in watermelon leaves, while the effect of 40% alginate water-soluble fertilizer on watermelon carotenoid was not obvious. Alginate wa- ter-soluble fertilizer could promote the formation of photosynthetic pigment in watermelon, compared with traditional compound fertilizers. During the fruit swell period and mature stage, the dry matter ac- cumulation in watermelon increased rapidly, the dry matter accumulation of watermelon treated with AF was the highest and CK0 was the lowest, and the difference reached a significant level (p < 0.05). The dry matter accumulation of watermelon was affected by different kinds of fertilizers, and it was al- so related to the amount of fertilizer applied. For example, 40% reduction and 20% reduction of algi- nate water-soluble fertilizer had significant effects on the dry matter accumulation in watermelon at ma- turity. In terms of nitrogen absorption, the amount of nitrogen absorbed with AF treatment was the high- est, but there was no significant difference, compared with CK1 and CK2 treatments. The nitrogen con- tent of watermelon treated with AF2 after 40% reduction of alginate fertilizer was significantly lower than that of AF treatment, but there was no significant difference compared with CK1 and CK2 treat- ments of conventional compound fertilizers and water-soluble fertilizer. It was suggested that alginate fertilizer can promote the absorption of nitrogen to a certain extent. In terms of phosphorus absorption, watermelon showed no significant difference under different fertilizer treatments, even if no topdressing had effect on the absorption of phosphorus, and the content of phosphorus was lower than that of the other two elements. It suggested that the amount of phosphorus absorbed by watermelon during the growth period was less, and the phosphorus in the base fertilizer can meet the demand for phosphorus during the whole growth period. In terms of potassium, the content of potassium in watermelon with AF treatment was significantly higher than that of CK0, CK1, AF1 and AF2 treatments, but there was no significant difference with CK2 treatment, indicating that alginate fertilizer may promote the absorption of potassium in watermelon. After AF, AF1 and AF2 treatments with different alginate fertilizer con- tents, the pericarp thickness did not decrease significantly, but the fruit refractive sugar content in water- melons treated with AF were the highest, significantly higher than that of AF1 and AF2 treatments, even so, the central soluble solids content and edge soluble solids content of watermelon treated with AF1 and AF2 were significantly higher than those of the blank control CK0. The above results showed that topdressing can significantly improve the fruit quality of watermelon: alginate fertilizer > water-soluble fertilizer > compound fertilizer, and especially the central soluble solids content of watermelon was most easily affected by topdressing. Principal component analysis was carried out on 13 indicators of 6 treatments, and a total of 3 principal components Y1, Y2 and Y3 were obtained in this study. The corre- sponding variance contribution rate was 72.30%, 11.12% and 7.77%, respectively, and the cumulative contribution rate was 91.18%. The average value of the membership function was calculated according to the results of principal component analysis, and the 6 treatments were ranked according to the value: AF>CK2>AF1>CK1>AF2>CK0.【Conclusion】The application of alginate water soluble fertilizer in watermelon field could obviously promote the growth of watermelon compared with ordinary chemical fertilizer, and the stable yield can be ensured under the condition of reducing 20% alginate water solu-tassium fertilizers. Compared with ordinary compound and chemical fertilizers, 20% reduction of algi- nate water-soluble fertilizer can still ensure the absorption efficiency of nitrogen, phosphorus and potas- sium. Finally, in the aspect of fruit quality, alginate water-soluble fertilizer could improve fruit quality, but the decrease of fertilizer application rate had a significant effect on watermelon fruit quality.