Detailed Explanation of Key Points for Field Cultivation Techniques of Yam

I. Land Preparation and Fertilization, Timely Planting 

The absorbing roots of yam penetrate relatively shallowly into the soil while the tubers grow deeper, therefore, be sure to select sandy loam or loam soil with deep, loose soil layers that has not been continuously cropped for 3 years. In the first winter, plow more than 35 cm deep, and after spring begins, plant on high beds or in furrow ridges. Since the main absorbing root system of yam is distributed in the upper soil layer, the base fertilizer is applied shallowly in the surface soil layer, adopting the method of planting the seed tubers first, then turning the soil and applying fertilizer. For base fertilizer, dried manure, plant ash or farmyard manure mixed thoroughly with soil is preferable. Manure should be decomposed first, generally applied at 30000-60000 kg/hectare, along with urea at 300-375 kg/hectare, superphosphate at 225 kg/hectare, and potassium sulfate at 375-525 kg/hectare. In areas with a short frost-free period, in order to extend the field growth period and improve yield and quality, the method of raising seedlings and transplanting can be adopted, using protective facilities for seedbed seedling cultivation, then transplanting to the field at the appropriate time.

II. Skillful Application of Topdressing

In the early stage, yam mainly grows aboveground stems and leaves, while underground stems grow relatively slowly and require less fertilizer. Therefore, from sowing or transplanting until the vines are established, decomposed manure can be applied heavily. Generally, when seedlings are fully emerged or after transplanted plants have survived, apply one round of dilute manure urine at about 15000 kg/hectare. After that, apply once every 20-30 days, each time applying decomposed manure urine fertilizer at 15000-22500 kg/hectare or ternary compound fertilizer at 225-300 kg/hectare in furrows. After the plant buds appear, while the underground tubers are rapidly elongating, they also gradually enter a period of expansion, thickening and weight gain, and fertilizer demand increases sharply. At this time, heavy application of a thicker mixture of human manure urine and cake fertilizer at 30000-60000 kg/hectare or three-element compound fertilizer at 600-750 kg/hectare should be applied. This topdressing is the single most critical fertilizer application affecting tuber yield. Afterward, when the stems and vines have fully covered the trellis, if signs of fertilizer deficiency are observed, apply one more round of fertilizer at a lower amount than the previous application. The final application should be made 40 days before harvest, assessing plant vigor, to supplement fertilizer once more to improve tuber yield and quality. After Frost's Descent, when the aboveground stems and leaves turn yellow and wither, harvest should be carried out promptly.