Detailed Explanation of Key Points of Soil Testing and Formula Fertilization Technology for Sweet Potato

1. Nutrient Requirements Characteristics:

Among the three essential elements of nitrogen, phosphorus, and potassium, sweet potato has the highest demand for potassium, followed by nitrogen, and then phosphorus. Sweet potato prefers potassium, and increasing potassium fertilizer application has a significant effect on both yield and quality. Sweet potato absorbs few nutrients at the seedling stage; from the branching and tuber-setting stage to the vigorous growth stage of stems and leaves, the rate of nutrient uptake accelerates and the amount absorbed increases, then gradually decreases toward the later stage. During the rapid tuber expansion stage, the absorption of nitrogen and phosphorus declines, while potassium absorption remains at a relatively high level. With nitrogen deficiency, older leaves first show chlorosis, the number of leaves and branches decreases, leaves become smaller, internodes shorten, and leaves tend to yellow and senesce prematurely, seriously affecting yield. With phosphorus deficiency, leaves become smaller, appear dark green, and lose their luster; stem and vine elongation is hindered; large yellow patches appear on older leaves, which turn purple and soon drop off. With potassium deficiency, leaves are small, internodes and petioles shorten, leaf color is dark green, and brown spots appear on the underside of leaves in the later stage. Sweet potato is sensitive to chlorine; when chlorine-containing fertilizers are applied beyond a certain amount, the starch content of tubers decreases, and the tubers are less suitable for storage.

2. Fertilization Technology:

At a medium fertility level, the fertilization amount for sweet potato throughout the entire growth period per mu is 2500-3000 kg of farmyard manure (or 350-400 kg of commercial organic fertilizer), 12-14 kg of nitrogen fertilizer, 6-8 kg of phosphorus fertilizer, and 9-11 kg of potassium fertilizer. Nitrogen and potassium fertilizers are divided into base fertilizer and two topdressings, while phosphorus fertilizer is all applied as base fertilizer. Chemical fertilizers and farmyard manure (or commercial organic fertilizer) are applied together.

Base fertilizer: Apply 2500-3000 kg of farmyard manure or 300-400 kg of commercial organic fertilizer per mu, 4-5 kg of urea, 13-17 kg of diammonium phosphate, and 5-7 kg of potassium sulfate. Slow-release fertilizers are recommended.

Topdressing: Apply topdressing during the tuber expansion stage, with 16-19 kg of urea and 13-15 kg of potassium sulfate per mu.

Foliar topdressing: In the middle and late growth stages of sweet potato, spray the leaves with a 0.5% urea dilution, or 2%-3% superphosphate solution, or 5% wood ash water, or 0.2% potassium dihydrogen phosphate solution. Spray once every 6-7 days, for 2-3 times. Huang Chunrong