Application of fertilizers
Fertilizers are most effective in the deeper layers of most soils, where the roots are found.
Contrary to nitrogen and to some extend potassium, phosphates are transported very slowly by water in the soil.
For this reason especially phosphates are more effective when placed in the root area.
Row-placement of fertilizers
Row-placement of fertilizer is advantageous:
- when the fertility status of the soil is low
- when fertilizer levels are kept relatively low
- where fixation may occur
- where fertilizers are relatively expensive
Nitrogen and potassium containing fertilizers should not be placed nearer than 4 cm to the side of and 2.5 cm under the seed to avoid damage during germination.
Large amounts of fertilizer in close contact with seed will cause scorching, especially under dry soil conditions.
Placement and broadcasting of fertilizers
Three safe methods of fertilizer placement are:
- bands of fertilizer 4 cm away from and below the seed
- distribution of fertilizer on the bottom of the furrow and mixed with the soil before the tubers are planted
- placing the fertilizer in small heaps between the seed pieces on the bottom of the furrow
Broadcasting
- Broadcasted fertilizer on fertile soils is efficient if applied before the main soil tillage operation. This places the fertilizer in deeper layers and moist conditions.
- Broadcasting of fertilizer is considered as a drawback in areas where phosphorus and potassium become fixed quickly when mixed with the soil.
- Surface application is often a disadvantage, particularly so when the fertilizer is subject to volatilization losses (Ureum). Therefore a split application of N as Ureum can be best applied as a side dressing, followed by re-ridging and irrigation soon after the application
Time of application
- Phosphorus and potassium are applied before or at planting.
- Nitrogen is given shortly before, or at planting but a split application may be better if there is a risk of leaching, or if the application of large quantities of fertilizer under dry conditions may cause scorching.
- The second nitrogen application should, in general, be given no later than 3 weeks after emergence.
- For crops with sprinkler- or drip-irrigation systems (+ fertilizer distribution equipment) nitrogen is applied in small quantities with each irrigation. This application is continued until about 4 weeks before the haulm is killed.