Maize And Fertilizers

 

For farmers to attain high yields in maize ( 11 tons and above) it is not only top dressing fertilizer that is critical, but a whole range of nutrients including phosphate potash and the micronutrients as well.

The question frequently asked by farmers is how much fertilizer to apply to attain the said 11 tons per ha.

Quantities

Nitrogen:

The nitrogen requirements of your maize crop come from both applied compound and top dressing fertilizers. Only that at initial growth maize plants require very little nitrogen, with the rest being applied at vegetative to flowering stages. Bearing in mind that the total applied nitrogen should be in the region of  180 kg N. 

Nitrogen taken up by a plant is made up of two forms; that portion applied by the farmer and that part already resident in the soil ( also called residual fertility).

One of the purposes of soil analysis is to ascertain how much fertility is held in the soil and therefore how much is needed as additional.

So How much fertilizers should a farmer add to reach the required nitrogen content?

1 . Basal Fertilizer

If a farmer applies 400 kg (8 bags) of compound D 7:14:7

The total applied nitrogen will be 28kg.

2. Top Dressing

If a farmer applies again 400 kg of AN (34.5%)  the actual nitrogen applied will be  138 kg  ( the rest will be inerts).

So adding the 28kg from basal fertilizer to the 138kg from the top dressing the total amount will be 166 kg.

Assuming the soils are sandy and could have held 20kg residual nitrogen then the total available to the plant is 186kg, well within range to hit 11 tons and above.

If a farmer does not afford 8 bags per ha should they stop growing maize?

No, not all. Farmers applying less fertilizer ( in the region of 250 to 350 kg) can still be profitable. What is important is to do soil analysis. Clay and clay loams can hold up to 60 kg of residual nitrogen on their own.

Fertilizes and plant Population

 Consider a farmer who uses cup size number 8 to apply their top dressing fertilizer. If their population is  50000 plants per ha then by scooping to the very plant they would have applied 400 kg of AN.

However, if their population was 44000 plants then by still using the same cup and scooping to every plant they would have applied 350 kg or 7 bags per ha by end of the day. What I am saying is it is not the farmer who decides what amount of fertilizer to apply rather it is the plant and its population that dictates. 

So far we have been talking of nitrogen only and not much of phosphate and potash. Why , because the compound fertilizers that supply nitrogen also supply enough of these . However farmers are urged to occasionally apply cereal blends high in P and K such as 6:23:23 instead of continually relying on 7:14:7.

Fertilizer and pH

Farmers are urged to correct their soil pH to a minimum of 5.5 or better up to 6.8.  

Acidic conditions will result in soil fertility not being efficiently taken up by the maize plants.

Foliar Sprays

A frequently asked question by farmers is whether foliar sprays work or whether farmers can replace conventional fertilizers with foliar sprays.

The first thing to note is there are two types of foliar fertilizers; the first type supplies micronutrients and the second type supplies predominantly macronutrients.

Foliar sprays for *Micro nutients

These supply micronutrients such as Magnesium, iron, copper, boron, zinc and manganese. These cannot replace your conventional basal and top dressing fertilizers. Rather their role is to help the crop manage stress and minimize loss of water during drought conditions. In addition to providing energy to the plant micro mix foliar can also aid root development in the early stages of crop development. 

Macro Foliar Sprays

As their name suggests macro Foliar Sprays supply your maize plants with predominantly the major elements NPK as well as a reasonable amount of microelements.

An example of macro mix is Wuxal foliar spray which contains NPK in the ratio of 16:16:12. Additionally, Wuxal also supplies the crop with micronutrients namely Mn Zn Fe Bo and Mo . When you use a macro mix you need to adjust your NPK basal rate slightly downwards since both contribute substantial amounts of NPK.

To attain 11 tons and above not only the macronutrients are important but also the micro ones.

 Fertilizer and Soils

Farmers growing maize on sandy soils need to split apply their top dressing to reduce leaching. Whereas the first application can come in as early as the 6 leaf stage a repeat application should follow 3 to 4 weeks later. For the very serious farmer, a 3rd last application should come in just before or at the start of flowering. This may surprise farmers but a maize plant only uses 60% of the applied nitrogen during vegetative stages. The balance is taken and used during flowering and grain filling stages.

Not only do sandy soils need to be split as incessant rains may also fall on heavier soils. As a precaution, I would say farmers on all types of soils should split apply their top dressing.

So farmers clearly we have seen that it's not as easy as asking how much fertilizer should one apply. There are a whole lot of other factors that impact on your applied fertilizers .....from pH to plant population through balancing up to timing.

Varieties with the potential to yield 11 tons and above are there ....the sc 555, sc 649, not to mention the blockbusters sc 657, sc 659, sc 661, sc 719, sc 727 and sc 729.

It is my hope that this small article has helped and will continue helping you as you prepare for the 2021/22 season.

 Acknowledgement  Hacked And Posted from Whatsapp By 

Trust Muzvozviona

Seedco Agronomist

Sept 2021