How effective is foliar fertilizer spraying on dragon fruit?

First, dragon fruit can be given foliar fertilizer. Second, to ensure fertilizer efficacy, it must be analyzed from two aspects: the surface characteristics of dragon fruit stems and leaves, and the formulation of the foliar fertilizer together with supporting application techniques. Only with corresponding treatments can it take effect. 

First you need to understand the surface characteristics of the dragon fruit plant. It originated in the arid regions of South America and belongs to the cactus family of perennial vine-like plants, with the physiological and ecological characteristics of drought-adapted plants. As shown in the figure on the right, its stems and leaves have undergone variation, presenting triangular columnar succulent green branches, while the leaf parts have degenerated into needle-like points distributed along the edges of the triangular columns. On the branch surface there are large numbers of brown aerial roots, and together these two constitute all the nutrient organs through which dragon fruit receives foliar fertilizer. The foliar fertilizer is sprayed onto the surface of the triangular column branches. To improve fertilizer efficacy, when spraying foliar fertilizer on dragon fruit, you must spray around the triangular column, and all three sides must be covered. 

Requirements of the dragon fruit branch surface characteristics for the formulation of foliar fertilizer components: the efficiency of foliar fertilizer is closely related to leaf surface traits and structure. The epidermal cuticle is a barrier for mineral nutrients entering the plant body. For leaves with a thick waxy layer on the surface, fertilizer droplets do not easily penetrate the leaf, and after spraying, the liquid fertilizer droplets will slide off the surface, causing nutrient loss with no absorption or fertilizer effect. The triangular column surface of dragon fruit has a thick, hard, and hydrophobic waxy layer, which places special requirements on the formulation and application techniques of foliar fertilizer. To ensure effectiveness, excellent adjuvants must be added to the formulation of the foliar fertilizer. Adjuvants are auxiliary components of foliar fertilizer, referring to additives other than the nutrient elements in the foliar fertilizer. The adjuvant system of foliar fertilizer is relatively complex and important, and it plays a decisive role in maintaining the excellent physical and chemical properties of the foliar fertilizer and ensuring product quality. The main components of adjuvants are surface-active substances, which have a series of effects such as wetting, penetration, emulsification, dispersion, solubilization, and moisture retention. Generally, adding a very small amount of surfactant can significantly reduce the surface tension of the fertilizer solution. Adjuvants are especially important for the fertilizer efficacy of foliar fertilizer specially used for dragon fruit. This is because the hydrophobic waxy layer on the surface of dragon fruit triangular column branches is thick and hard, and ordinary water-soluble foliar fertilizers are not easily able to wet and penetrate it, which directly affects the absorption of nutrients. Only by adding adjuvants with excellent performance can the foliar fertilizer adhere to and spread over the triangular column surface, prolong the wetting time, and achieve the purpose of nutrient absorption. Although there are many types of surfactants on the market, experimental studies at home and abroad show that adjuvants such as organic fertilizers and betaine have better effects. These are also suitable for foliar fertilizer specially used for dragon fruit. 

Second, the selection of nutrient components in foliar fertilizer should be based on the principle of mainly supplementing medium and trace nutrient elements while combining them with major nutrient elements. During the long production period from April to November each year, in the early fruiting stage, the main supply should be magnesium, boron, and nitrogen, while in the middle and late fruiting stages, more attention should be paid to the successive supplementation of potassium, nitrogen, magnesium, calcium, iron, and boron. They are all beneficial for improving the stress resistance and quality of dragon fruit. In addition, to improve the targeted nature of foliar fertilization, you should also refer to the types of limiting nutrients in the local soil. It is best not to choose an all-purpose tonic liquid, which is both expensive and not targeted, and the effect may not necessarily be good. 

Attention should also be paid to the requirements of the photosynthetic metabolic characteristics of dragon fruit for foliar fertilizer application techniques. Dragon fruit, which originated in arid regions and has succulent characteristics, belongs to the crassulacean acid metabolism type of plant. Their stomata are open at night and closed during the day. This opening and closing pattern of the stomata is opposite to that of other C4 plants. Since the main pathways for foliar fertilizer nutrients to enter the plant body are through stomata and cracks in epidermal tissues, the best time for foliar spraying on dragon fruit is after 5 to 6 p.m. Spraying fertilizer when the sun sets is conducive to nutrient absorption. In addition, regarding the nutrient concentration of foliar fertilizer, according to the characteristics of dragon fruit, it can be appropriately increased by 10% to 20%, giving a better effect. 

In short, the effect of foliar spraying is faster than root fertilization, and it can directly and quickly reach the nutrient body of dragon fruit, avoiding the fixation of fertilizer nutrients in the soil. But the disadvantage is that the amount of fertilizer applied is limited and the effect is relatively short-lived. Therefore, foliar fertilization is an auxiliary method of fertilizing dragon fruit. It may as well be applied in coordination with root fertilization, which can increase yield.