Topdressing is to replenish nutrients for corn and ensure its continued growth. Whether to use urea or compound fertilizer depends on the specific situation.

First, for plots with poor soil, corn leaves are prone to yellowing, purple-reddish leaves, etc. In this case, topdressing with compound fertilizer is recommended.

Second, for normally growing corn, where the soil is not poor, the corn is not growing vigorously, and base fertilizer is applied regularly, topdressing with urea is recommended.

Third, for plots without base fertilizer, only compound fertilizer should be applied; urea alone cannot guarantee continued growth.

Fourth, for plots that have been fully fertilized at one time, topdressing is unnecessary, or a small amount of urea can be applied later.

The above four situations are common during corn growth. It is important to note that compound fertilizer refers to a three-element compound fertilizer (containing nitrogen, phosphorus, and potassium), not a two-element compound fertilizer.

How should compound fertilizer be selected? What is the appropriate per-mu usage rate of urea or compound fertilizer?

How should compound fertilizer be selected?

First, the nitrogen content should be high. After all, corn is a nitrogen-loving crop. You can choose a high-nitrogen, low-phosphorus, medium-potassium fertilizer, or a high-nitrogen, medium-phosphorus, low-potassium compound fertilizer, or a compound fertilizer with equal phosphorus and potassium content. In actual production, some farmers use urea mixed with diammonium phosphate and potassium chloride, which is also feasible.

What is the appropriate amount of urea or compound fertilizer per mu?

The amount of urea and compound fertilizer used for topdressing is important. Too little will result in insufficient nutrients, while too much will cause excessive growth, which is not conducive to normal corn growth. The amount should be tailored to local conditions, and the amount will vary from plot to plot.

For urea, a general topdressing amount of 15-20 kg per mu is sufficient. For relatively poor soil, where corn grows stunted, the amount can be increased to 25-30 kg per mu. Conversely, for more fertile soil, the amount can be reduced to 10-15 kg per mu. Flexibility is required. As for compound fertilizer, if you choose to apply it as topdressing, based on the aforementioned scenarios, first, the corn is very weak and lacks nitrogen, phosphorus, and potassium, and second, no base fertilizer was applied before planting. In both cases, the topdressing rate for compound fertilizer is around 30-40 kg per mu, with some farmers even using 50 kg.

In addition to the above, some farmers adopt a strategy of applying small amounts frequently, applying 5-10 kg of urea or compound fertilizer each time, and applying three or four times. Of course, this is limited to farmers with smaller planting areas. For larger farms, labor costs are high, so they either apply topdressing once or apply a sufficient base fertilizer before planting and avoid applying any more fertilizers later.

Also, some farmers, even when base fertilizer is insufficient, do not apply topdressing because they consider the overall cost of investment and believe that spending a few dozen yuan on urea or compound fertilizer for topdressing will not significantly increase yield, making it worse to not apply at all. Or, they simply don't have the time or energy to apply topdressing.