Maize fertilisation, in particular nitrogen fertilisation plays a major part in a crop’s productivity. To better adjust the amounts applied and thus maximise the agronomic and economic effectiveness of the fertilisers, one must be aware of the plant’s needs, at which specific times they need to be met during the plant’s development, and what the soil contribution is.
A lever for productivity
Fertilisers must cover the plant’s core needs at least until flowering. For a summer crop such as maize, the elements (especially nitrogen) that are being released through the mineralisation of soil organic matter take over the role of nutrients.
With regard to the main elements – N (nitrogen), K (potassium), and P (phosphorous) –, the plants’ instant needs are different. Nitrogen and potassium are important for the production of biomass – therefore the plant’s daily uptake of these two elements is high until flowering. As to phosphorous, the plant’s needs of this element are greater at the beginning of its growth cycle.
As far as trace minerals are concerned, the most typical deficiencies (of zinc and manganese) are often induced by improper tillage. Trace mineral deficiencies must be corrected rapidly and right after the first symptoms. Foliar treatments take quick effect (in a matter of hours).
Reasonable Fertilisation: Performance and Environmental Care Working Together
Whatever the cultivation system, soil is an inevitable stage in the nitrogen cycle. The producer’s responsibility is to apply only as much nitrogen as strictly needed for the plants’ development. Beyond that point, any surplus will likely end up in the soil at the end of the crop cycle, in a form that has a high risk of seeping into the water table. Nitrogen fertilisation should therefore be adapted to the envisaged yield potential whilst considering the previous crop residues and the estimated soil contribution.
Note: maize is an efficient user of organic nitrogen coming from livestock waste. At equal amounts, organic N is 30 percent more efficient than its mineral form.
How to Spot Deficiencies
- Magnesium: A frequent occurrence in high-acid soils with a pH below 5,5, this deficiency requires correction through a ground application. Symptoms appear as early as 4-5 leaves. The oldest leaves present a yellow discoloration between the veins, and later on, leopard-like spots. Ca and Mg amendments provide the most appropriate corrections for this type of deficiency.
- Zinc: A frequent deficiency, it manifests itself by a discolouration of the middle third section of the limbs of the youngest leaves in the whorl. It can be corrected by a neutralised zinc sulphate treatment or other foliar products containing zinc, or can be treated preventively – and often more efficiently – through a ground application.
- Manganese: a deficiency that is typical of high-pH soils, “puffy” soils, soils that are high in organic matter and active lime, sandy soil textures, and nematode presence (induced deficiency in that case). The signs include a yellow discoloration between the leaf veins, drooping plants, and curled leaf edges. This indicates a severe deficiency, which in extreme cases translates into stunted corn or absence of ears or kernels. The deficiency is easy to correct by two treatments of manganese sulphate during crop development, done 15 days apart, as early as 4-5 leaves of maize
P and K: Needs and Exports
Grain maize has a moderate uptake of P and its export rate is about 50 units per 100 q of grain. Most of the K that grain maize takes up returns into the soil if stalks are buried. The kernel export of K is rather low, of about 30 units, while the uptake may exceed 250 units, depending on the production potential.
With feed maize, P export stands at about 60 units per 14 tons of DM per hectare. A big portion of the K taken up by the plant will be exported: 162 units out of the 210 units absorbed, for a potential of 14 tons/hectare. However, K will eventually return to the plot along with manure applications.
Calcium, Magnesium, and Other Trace Minerals
Maintaining the Ca and Mg content of one’s fields should be a permanent concern in terms of the overall plot fertility, as it keeps the soil “in good working order”. Striving for a good soil pH will favour the plants’ assimilation of all mineral elements.
Magnesium, zinc, and manganese are elements which maize is most sensitive to. Regular chemical soil testing will allow one to take corrective measures, if necessary. The maintenance and correction of secondary elements should be done through ground treatments rather than applications during crop development – save for manganese, where foliar treatments are effective. Lime treatments – even magnesium lime if needed – should be viewed as a long-term option.
FOCUS : How to Determine Nitrogen Rates
By using a “track record” method, one can calculate the amount of N that needs to be administered to the plant, and by dividing up the rates one can better adjust them to the actual plant’s uptake capabilities. Thus:
• Maize absorbs basically no nitrogen during its first month of development. A small amount of N under the form of starter fertiliser is enough to cover the plant’s needs during its early stages of development.
• Starting with 8 leaves, the maize plant must receive sufficient amounts of nitrogen.
• Dividing up the fertiliser rates is recommended on light soils – and whenever the total dosage administered exceeds 100 units. However, wherever the incorporation of a second treatment is not guaranteed (be it mechanically or through irrigation) – due, for instance, to early drought risk –, it is preferable to apply it all at planting.
• In practice, one should apply 20 to 50 units at planting and then another treatment at 6-8 leaves, in order to maximize the N use coefficient (which goes from 60 percent before 4 leaves to 80 percent after 4 leaves).
How to Determine Nitrogen Rates :
1. Establish a realistic yield target by factoring in the plot specifics and the crop’s agronomic itinerary. For instance, take the mean of yields in the three best years out of five reference years.
2. Apply the N rate, if necessary, per ton of dry matter or quintal of grain (see above diagrams), namely 14 kg of N/ton of DM or 2 kg of N/q of grain (average estimated yield).
3. Consider Soil Reserve and Fertiliser Use Coefficient
• 0,6 for an application from planting to 8 leaves
• 0,8 for an application above 6 leaves
4. In case of high-dosage applications, recommended breakdowns are:
50 kg at planting and the rest at 6-8 leaves, namely:
|Rate = yield x plant’s needs per ton or quintal – 50