How to fertilize sweet potatoes for high yields? A full breakdown of the key techniques

Sweet potato roots are deep and wide, and the vines can root where they touch the ground, giving them a very strong ability to absorb nutrients. They can still produce a certain yield in poor soil. This often leads people to mistakenly believe that sweet potatoes do not have high fertilizer requirements. Practice has proven that sweet potato is a crop with very high fertilizer requirements, and the order of the yield-increasing effect of fertilization is: nitrogen-phosphorus-potassium greater than nitrogen-potassium greater than nitrogen-phosphorus greater than phosphorus-potassium greater than nitrogen. This shows that potassium fertilizer has the greatest effect on sweet potato yield, followed by nitrogen, and then phosphorus. However, the functions of the three elements nitrogen, phosphorus, and potassium are all different and irreplaceable. Topdressing of sweet potatoes should be determined according to soil fertility, the amount of base fertilizer applied, and the different growth stages and growth conditions of sweet potatoes. If the amount of nitrogen applied as base fertilizer is insufficient, or phosphorus and potassium fertilizers are also insufficient, in the spring and summer sweet potato region of North China, the growth period of spring and summer sweet potatoes is short, so early-stage nitrogen topdressing should be the main approach; in the autumn and winter sweet potato region of the south, topdressing should be applied in multiple split applications, mainly at the mid-stage. It should also be divided into:
1. Seedling-promoting fertilizer. This is an effective fertilization technique for ensuring a full stand, promoting early growth, and accelerating sweet potato seedling growth. This fertilizer is generally applied as topdressing once the seedlings have survived. In ordinary plots, the main focus is topdressing small and weak seedlings so that the small seedlings catch up with the large ones and grow uniformly. Apply 2--3 kg of standard nitrogen fertilizer per mu or 250 kg of decomposed human manure and urine. It can be watered onto the plants or applied in holes opened beside the ridges followed immediately by watering.
2. Vigorous plant and tuber-setting fertilizer. This is a fertilization method used during the branching and tuber-setting stage and before the peak stem and leaf growth period. Its purpose is to promote vigorous stem and leaf growth and tuber formation. Therefore, the people call it "vigorous plant fertilizer" and "tuber-setting fertilizer." In high-yield fields in the spring and summer sweet potato region of North China, phosphorus and potassium are generally the main nutrients, with nitrogen as a supplement (this is different from field crops, which often receive only nitrogen topdressing and no phosphorus or potassium topdressing). In plots with better water and fertilizer conditions, topdressing too early or too much can also cause excessive mid-season growth, hinder nutrient transport to the roots, and instead delay tuber setting. Therefore, in fertile soil, it is better to topdress nitrogen after tubers have already formed, 30--40 days after tuber setting. However, topdressing too late also cannot exert its fertilizer effect in time. In the summer sweet potato region of the south, the sweet potato growth period is long, and regular drought often occurs in July and August. Under early planting conditions, two peak tuber enlargement periods often occur during the growth period. The vigorous plant and tuber-setting fertilizer can be appropriately advanced, preferably 10--30 days after transplanting the sweet potato vines. Research also shows that under drought conditions, topdressing should be done 20 days after transplanting, and under conditions with suitable rainfall, it should be done 30--40 days after transplanting. Generally, 10 kg of standard nitrogen fertilizer per mu or 800 kg of decomposed human manure and urine can be applied.
3. Tuber-promoting fertilizer and tuber-growing fertilizer. Side-dressing fertilizer is generally applied about 45 days after planting, when the aboveground part has already spread its vines down the ridges and the tubers have basically taken shape. On one side of the ridge, use a plow to break open 1/3, then apply fertilizer immediately. Breaking the ridge and applying fertilizer improves soil aeration and also helps tuber expansion. Crack fertilizer: in the late growth stage of sweet potatoes, when tubers are growing vigorously and cracks appear on the ridge backs, the topdressing applied is called crack fertilizer, White Dew fertilizer, or tuber-growing fertilizer. Generally, human manure and urine water or chemical fertilizer water is used at 500--750 kg per mu, poured into the cracks. When base fertilizer is insufficient, it has a good yield-increasing effect. However, it should be applied about two months before harvest; if too late, it can easily cause sweet potato leaves to wither and turn green, with no increase in tuber weight, and other consequences. Foliar fertilizer: in the late growth stage of sweet potatoes, root absorption capacity weakens, so foliar topdressing can be used to make up for nutritional deficiencies. This method takes effect quickly and has good results. Spray 0.5% urea dilute solution, 2%--3% superphosphate solution, and 0.2% potassium dihydrogen phosphate solution on the leaves. Apply in the evening, spraying once every 7 days for a total of 2--3 sprays, with 75--100 kg of solution per mu each time. Generally, this can increase yield by about 10%.