Stay on Top of Your Game-Do Top Dressing

If you are going to plant maize, then it stands to reason that you intend to get the best yield possible off the plants growing in that field. This means you will have carefully considered all your seed, fertilisation and weed control requirements. One of the most important factors to consider is plant nutrition. It is important to use the right fertiliser to ensure the plant roots can take up all the nutrients available in the soil and convert this into grain. It is therefore necessary to take regular soil samples, so you know how much fertiliser to apply. There is still more to the science of fertilisation though, because it is equally important to apply the necessary nutrients at the right time, so the plant can use it as efficiently as possible.

What does it mean when we say the amount and type of fertiliser is used optimally?
The effective use of fertiliser applied at the correct time means you are more likely to extract the maximum amount of grain possible. It is also most likely to result in improved water efficiency so that none of the water available to the plant is wasted. This means the plant will produce more grain per millimetre of water available – in other words secure ‘more crop per drop’!

Some important factors to bear in mind when topdressing

  • Ensure that the fertiliser does not come into direct contact with any part of the plant to avoid burning or scorching.
  • The best method to top-dress is band placement as it is much more economical.
  • The earlier you can do your topdressing the better e.g. once before it reaches knee height and then again when the plant is waist height and still in its pre-tasselling stage.
  • It may be necessary to top-dress at least twice in areas where soils are less fertile.
  • It is a good idea to split the dressing so that your fertiliser concentration is decreased and less likely to cause sub-soil acidification which will scorch the roots and harm the plant’s potential to uptake nutrients anyway.
  • Top dressing should preferably be done when the soil is moist.
  • Avoid top dressing during heavy rains as the fertiliser will be leached from the soil or washed away.
  • Weed control should be done prior to top dressing. This simply means the weeds will not get a chance to take up any of the nutrients intended for the crop.
  • Weeding should always be done to avoid competition for both nutrients and sunlight.
  • Do not be tempted to apply all the fertilisation prescribes in one application process. The negative effects are too serious to take this risk as not only scorching of the roots but also fertiliser will fall outside of the optimum band area and nutrients will be wasted.
  • Remember the maize plant’s nutrient requirements increase steadily and the final yield potential is determined in the V12 stage. This is the stage when maize is rapidly growing, and a new leaf appears every two days as well as significant root development.
  • It is important to do accurate calibration of the fertiliser spreader before you start your application. It is crucial to apply the prescribed amount of fertiliser in order to achieve optimum results.

These factors are important to keep in mind when applying your topdressing fertiliser. But the most valuable factor is to be pro-active and to get it done! Often, we don’t apply at the correct time or we don’t apply the correct amounts which result in poorer yields. As mentioned before; in order to achieve the best possible yields, we need to consider all the growing factors of a plant. Don’t neglect the top dressing factor.

Application strategies in maize production
Broadcasting of fertilizer is suitable for high fertility soils.

Broadcasting
Broadcasting is a low risk method of application, if the fertilizer is applied pre-planting or during early growth stages. But, after the crop has developed a leaf whorl there is an increased risk of fertilizer particles lodging and causing leaf burning. While the effects of this scorching rarely adversely affects yield as a result of plant recovery and regrowth, French research shows that broadcasting is best carried out prior to the V6 stage. Broadcast application or surface banding of urea will also increase the risk of high ammonia losses, particularly in high temperature conditions.

Band applications
In grain maize production systems, practices that place the fertilizer in bands within 5cm of the seed row allow better targeting of nutrients such as nitrogen, phosphorous and zinc during establishment when the root system is not as effective at taking up nutrients.

Pneumatic spreaders that place ammonium nitrate on top of the soil, underneath the plant leaves are particularly effective and minimize the risks of scorch due to broadcasting.

Banding in the soil enables growers to provide a high nutrient concentration in the vicinity of the developing roots where the crop can take it up more easily. It is a good way of top dressing ammonium nitrate fertilizers (e.g. NPK), reducing the risk of leaf scorch.

Starter fertilizers
Starter fertilizers target the emerging plant and are used to encourage good early establishment and growth. Starter fertilizers based on phosphorus, with low amounts of nitrogen improve rooting and speed early development, helping maximize grain production. In most situations, the biggest starter effect comes from phosphorus. However, the best synergy can be achieved with nitrogen applied up to an equal amount of phosphorus.

Any high-yield production system for maize should also consider zinc fertilizer as a matter of course to target early development.

1. Pop-up Application
Pop-up application places starter fertilizer in the row with the seed. It is so named because in theory it leads to faster emergence and establishment. Good responses are found from using phosphorus and nitrogen applied close to the seed alongside limited levels of potassium.

NPKs are commonly used as pop-up fertilizers to improve early plant development. However, care is needed with some nitrogen forms and urea should be avoided, especially on high pH soils, as they can injure the seed and inhibit or delay germination.

2. Fertilizer Placement
An alternative method is to use starter fertilizers applied below and/or beside the seed. This approach is particularly useful in helping overcome temporary nutrient deficiencies in cold and low phosphorus soils.

Placement varies according to local experience. In most instances starter fertilizers are placed below and at the side of the seed.

Seed treatment
Nutrients needed to boost initial growth are increasingly applied around the seed prior to planting. These commonly include zinc and phosphorus, both of which have a direct effect on root growth and which can be unavailable in difficult planting conditions.

Foliar application
Foliar application is used to address an immediate nutritional need or where soil conditions restrict availability of specific nutrients. Properly formulated products are increasingly important in ensuring balanced maize crop nutrition. Applications can be made as soon as sufficient leaf area is available – usually from the V2 stage onwards, perhaps applied in a tank mix with compatible herbicides.

Fertigation
Fertigation, by providing nutrients through the irrigation system, delivers fertilizer direct to the plant. Most common fertigation method in maize is through centre pivot irrigation systems.

This allows nutrients to be timed closer to peak demand – a practice which is difficult to achieve through other means because of difficulties of travelling through the crop with the farm fertilizer spreader or sprayer once it has passed the V8 stage. Where centre pivot irrigation is employed, growers can usefully split nitrogen and potassium use, specifically tailoring applications, to suit plant needs at each phase of growth.

SOURCE: https://www.yara.co.ke/cropnutrition/maiz