So, why is it easier for grafted watermelon to turn yellow at the leaf edge?
Before getting down to business, we need to know the following two points:
What is grafted watermelon? Grafting watermelon is a planting technology that uses pumpkin (gourd) seedlings with stronger disease resistance than watermelon root system and adopts grafting method to replace watermelon root system. Generally speaking, it is watermelon head and pumpkin (gourd) root.
Why should watermelon be grafted? In fact, no one wants to plant grafted watermelons. In addition to the trouble of seedling raising, the taste of grafted watermelon is obviously not as good as that of self-rooted melon. In order to solve the contradiction between watermelon continuous cropping and less stubble land in this area, grafting cultivation came into being.
Factors leading to yellowing of watermelon leaves and "Phnom Penh" phenomenon of old leaves 1. Soil salinization
Due to the continuous use of chemical fertilizers, a large number of cations such as calcium, sodium and magnesium in fertilizers accumulate on the soil surface and react with chloride ions, sulfate ions and carbonate ions. Metal ions in fertilizer accumulate all the year round, and with the increase of planting years, secondary salinization is easy to occur. After watering, the white stains on the soil surface are typical salinization, which farmers call "pan-alkali".
In saline soil, organic matter decreases, salt increases, air permeability decreases, nutrient mobility slows down, root activity decreases, and absorption function is blocked, resulting in various physiological obstacles of watermelon plants.
2. Potassium deficiency
? Symptoms? When watermelon is deficient in potassium, the plant grows slowly, the stems and vines are thinner, the leaves are dark and dull, the leaves curl backwards, and the edges and tips of the lower nodes turn yellow. Symptoms usually develop from bottom to top. In severe cases, the heart leaves turn light brown or even brown, which leads to difficulties in fruit setting, small fruit shape, reduced sugar content and quality.
Analysis? According to the analysis of fertilization habits of local melon farmers in Pucheng, there is no shortage of potassium fertilizer. If watermelon plants lack potassium, there are two aspects:
① Excessive use of other fertilizers or long-term accumulation of other elements in the soil may inhibit the absorption of potassium by watermelon due to antagonism between nutrient elements.
② Although the amount of potassium fertilizer is quite large, a large amount of potassium can't be absorbed by crops due to the weak absorption function of watermelon roots, resulting in the "lack" of potassium. Just like people, there are many delicious things, and it is no use not digesting and absorbing them.
3. The root system of pumpkin rootstock is not resistant to high temperature.
Watermelon has been planted in a large area for many years, and there are few so-called "stubble fields". Although some people go to neighboring counties and cities dozens of kilometers away to plant melons, most melon farmers still choose hybrid pumpkin grafting seedling technology to replant.
Grafted pumpkin seedlings have the advantages of low temperature tolerance, developed root system, strong ability to absorb water and fertilizer, and strong growth potential of watermelon, which is suitable for early spring and early maturity cultivation. But at the same time, the biggest disadvantage of pumpkin root system is that it is not resistant to high temperature. In Pucheng, the temperature rose in mid-May. Once improperly managed, the roots of grafted pumpkin seedlings are prone to premature aging, showing old leaves "inlaid with gold", which melon farmers call "leaf aging"
The main reason for the yellowing of grafted watermelon leaves was found, and a set of solutions was needed to improve the soil.
The soil has good air permeability and high organic matter content, and with scientific management, it is sure to grow a good watermelon. The problem is that continuous cropping has become more and more common with the extension of planting time and the continuous expansion of the main watermelon producing areas in China. Planting the same crop year after year, the soil is seriously short of various nutrients suitable for watermelon growth, and the excessive use of chemical fertilizers makes the soil overwhelmed.
① The practice of deep ploughing to improve soil and reasonable rotation stubble shows that reasonable rotation stubble can effectively change the physical and chemical properties of soil. Watermelon has been rotated for more than 5-8 years, and the rotation crops are: wheat, rice, corn, radish, sweet potato and green manure. (2) Fertilize scientifically, improve soil fertility, replant seedlings and plant watermelons. It is suggested to carry out soil testing and formula fertilization according to different plots. Fertilization principle: apply organic fertilizer again, increase biological fertilizer and soil conditioner, and appropriately reduce chemical fertilizer input. Improve soil fertility and eliminate residual toxins in the soil year by year. ? Improve and protect the roots
In the process of grafting watermelon planting, it is beneficial to "squat seedlings" in the extension period, to root down and to induce new lateral roots. However, too many "squatting seedlings" may lead to root aging and blocked nutrient supply.
① Planting, watering, drip irrigation and applying rooting biological agents or humic acid nutrient solution promote new roots, which is beneficial to delaying seedlings and preventing the use of rooting powder products. (2) Combined with vine-stretching water, a small amount of all-element water-soluble fertilizer is applied under drip irrigation to ensure the normal growth during the whole vine-stretching period, and there is no need to worry about the phenomenon of "squatting seedlings" and causing root injury. ③ Careful use of water-soluble fertilizers and irrigation fertilizers In recent years, the market of water-soluble fertilizers and irrigation fertilizers is chaotic, and the quality of products is mixed. Although some fertilizers have obvious effects after use, they are easy to lead to premature root senescence and decreased absorption function. ? 3 foliar spraying fertilizer
Grafted watermelon leaves turn yellow, usually in the middle and late growth period, after the watermelon grows to 7-8 kg. It is what melon farmers often say, "When the vine is heavy, play with the motor." Therefore, grafted watermelon should be combined with pest control and sprayed with high-quality foliar fertilizer to maintain leaf vitality.
? 4. The watermelon in the shed should be properly ventilated and cooled in the middle and late stage, and the temperature should be controlled at about 32 degrees.
In Pucheng, according to the different planting areas, the watermelon expansion period is generally from late April to mid-May, when the daytime temperature is often around 30 degrees. It is necessary to release air in time to cool down, reasonably adjust the daytime temperature management, and adjust the size of the tuyere in time to keep it at 28-32℃.
It has also been suggested that the lack of medium and trace elements (magnesium, calcium) or diseases and pests may also lead to this situation. Through years of observation, these factors are not excluded, but they are not the main reasons.
? abstract
The yellowing phenomenon of grafted watermelon leaves in the middle and late growth stage is mostly caused by soil salinization in continuous cropping land, which leads to the obstruction of root absorption function and malnutrition. As long as we improve the soil, protect the roots, manage the temperature and humidity, and try our best to prolong the growth vitality of grafted watermelon in the middle and late stage, it can basically be effectively avoided.