Most soils provide only limited amount of nutrients to the crops, therefore fertilizers need to be applied to compensate the crop nutrient requirement and for increasing the increase grain yield. In some cases, fertilizers are also added to improve the soil’s physical condition specially, the organic fertilisers. The amount and type of fertilizer applied are determined on the assumption that 1 ton of grain will remove 15 kg nitrogen (N), 2–3 kg phosphorus (P), and 15–20 kg potassium (K). These base rates need to be modified according to the soil type, the cropping season, the variety, ecology, the crop condition and prevailing weather conditions, and efficiency of nutrient application. Steps for efficient fertilizer-use are:
- Use organic fertilizers (manure, compost, straw, husk, plant leaves) wherever possible, especially in nurseries.
- Apply fertilizer according to soil type and expected yield. As a guide, apply complete recommended dose of phosphorus and potassium as basal and nitrogen in 2-3 splits. In sandy soils apply K in two splits, with additional 10–15 kg K per ha.
- All quantity of P and K and 1/3rd of N must be incorporated evenly just before seeding or transplanting. For direct-seeded broadcast crop, it is better to apply 10-14 days after crop establishment when there is water in the fields.
- Apply remaining N (urea) in 2 equal splits as top dressing at 25-35 days after transplanting and at panicle initiation.
- Use leaf colour chart (LCC) - a tool that can assess leaf N status and the crop’s need for N.
- In established crops, apply chemical fertilizer only in standing water and evenly across the whole field.
- Do not apply high rates of fertilizer in traditional tall varieties, it may lead to lodging.
- Inorganic fertilizers must be stored under dry and shaded conditions