How to fertilize yam?

Yam seedling and vine stage mainly long branches and leaves, fertilizer mainly nitrogen, bud into the growth peak, underground tubers began to expand, fertilizer needs a large amount, is the key period of fertilization, nitrogen, phosphorus and potassium combined application. 1. Base fertilizer. Select the plot, apply decomposed farm manure 2000- 4000 kg and ternary compound fertilizer 60- 80 kg per mu as base fertilizer before ploughing, and then plough the soil 30 cm and rake it. Second, topdressing. Seedlings mainly nitrogen fertilizer, 10---15 kg per mu of high nitrogen and potassium type compound fertilizer. In the first ten days of July, apply 20- 25 kg of high nitrogen and potassium compound fertilizer per mu, and spray 0.25% potassium dihydrogen phosphate once. From late July, spray 0.25% potassium dihydrogen phosphate 2---3 times, and apply 20---30 kg NPK compound fertilizer per mu in early August.