Topdressing is a thin layer of material spread over the surface of soil or grass, rather than dug into it. For crops, that material is fertilizer, added while the plants are already growing so they get food at the moment they need it. For lawns and sports fields — golf courses, football pitches — it is usually fine sand or a sand-and-soil mix, spread to level out bumps and keep the grass healthy. The key idea is 'on top': the material stays on the surface and works its way down with rain and watering. That is what separates it from fertilizer mixed into the ground before planting. It is both a noun (the material itself: 'spread a topdressing of compost') and a verb (the job: 'we topdress the greens twice a year'). It is a farming and gardening word — you will find it on fertilizer bags, in gardening books, and in the mouths of groundskeepers, but almost never in ordinary conversation. Spelling varies: 'topdressing', 'top-dressing', and 'top dressing' all appear, with the hyphen common in British writing.

追肥、表層施肥（作物生長期間撒在土表的肥料）；草坪的鋪面材料（沙土混合）