Maize can easily achieve 9 tons/ha (40 bags per acre) with the right agronomy and adequate moisture, but it does require adequate nutrition to achieve this.
The amount of fertilizer required is best calculated by multiplying the target yield in tons per hectare, by 20-25 Kg. For a 30 bag per acre crop this is 160 Kg of nitrogen.
Timing is final part of getting fertilizer right; DAP or a compound fertiliser at planting forms a good base for crop emergence, with the balance applied as urea as a topdressing.
Soil Mineral Nitrogen testing can help too, by accounting for residual nitrogen in the soil profile.