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.
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 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.
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.
YaraMila 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.
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 (see diagram below). When using low amounts of fertilizer, the distance from the seed in Argentina is commonly 3cm x 3cm. In the USA, South Africa and on loam soils in Europe greater, 5cm x 5cm distances between the seed and the fertilizer are more common.
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 (see Yara Teprosyn Seed Treatment).
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, 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.