How high should your maize stubble really be and can you really get more by leaving some behind? On the face of it that statement looks ridiculous, surely you need to harvest all the crop you can, but there is good science behind the thinking. In a previous piece in this series we looked at the height of cut focussing mainly on grass stubbles but grass needs to re-grow whereas the maize crop is finished once its been harvested. Previously I stated that “Be it grass, whole crop or maize, the obvious answer to this question is cut all of it – as much as possible. Obviously you need to make sure the header does hit the ground and suck up soil and stones into the silage but that’s all we need to worry about isn’t it?”

This really all depends on what you’re feeding the resultant silage to as we will see later but firstly lets explore the argument for leaving crop behind in the field.

Why not cut maize as low as possible?

It’s well understood that the bulk of the nutritional value of the maize crop is located in the cob but there is still valuable nutrition in the leaves and stem. So at first glace rejecting material that you’ve invested time and money to grow seems madness but there is some good reasoning for this. The varying properties of the maize plant are key here. The kernels and the cob husk or core contain the bulk of the nutrients and dry matter. For a maize silage with 35% bulk dry matter, the cob might have over 55% dry matter. At the same time, the lower sections might be below 25% dry matter. Not only this, but the stem, being mostly lignin, is also low in sugars and protein.

 From a purely nutritional density point of view, the cob, higher stalk and healthy leaves are the most valuable feedstuff. The cob alone may be over 60% of the total dry matter harvested, 50% in the kernels, 10% from the spindle and a little more in the husk. All the valuable nutrients made in the leaves will have been transferred to the cob by the time the crop is ripe. The value in the stem increases the further up the plant with the lower section being particularly low in energy and protein. However the inclusion of the less valuable lower stalks in your silage might be positively detrimental. The lower leaves are more susceptible to mycotoxin zeralenone produced by fusarium infestations. Leaving these leaves back in the field can be really beneficial for maize silage fed to cattle.

Should maize for AD be cut lower?

Not necessarily because the fermentation of maize silage can be inhibited by the lower stalk material. This high lignin part of the crop is more susceptible to acetic acid production and this can slow the pH drop in the clamp. Until a stable pH is reached, the crop dry matter – and in particular the energy rich sugars – are being burnt up by microbes in the silage. Using an inoculant to promote the rapid production of lactic acid can offset this and that might be the best solution for AD silage producers. For livestock farmers, the production of high levels of acetic acid not only slows the fermentation but also makes the silage less palatable leading to reduced forage intakes. Fortunately AD tanks don’t have taste buds or noses so the intake is only limited by the bug’s ability to digest the material.

It’s also important to consider the overall cost of the forage and that includes the costs of storage. Harvesting and clamping bulky material that has little feed value makes no financial sense at all. So maybe you can get more acres into the existing clamps or build smaller clamps in the first place.

 How high can you cut maize?

The aim should be to cut around 100mm below the lowest cob height. This will usually leave 350mm to 450mm in the field (depending on the variety and growing conditions), but exactly how much crop does that equate to? It depends on yield and growth pattern, but typically this will be just 5-7% of the overall crop dry matter. Now 5-7% is not to be sniffed at, but when you consider that in-clamp losses can reach 40% of dry matter in some cases, this is really a small price to pay if it improves silage quality. In addition to this, the resultant silage can have a higher ME level of 0.1 to 0.3 MJ – or a 2-3% increase in energy. There are also additional benefits as crude fibre should drop 1-2% and ash by 1%.

So reducing in-clamp losses and increasing the nutrition density of the silage makes a case for leaving some poor value material behind, but there are associated benefits. Chopping, hauling and clamping all that poor value stalk all costs time and money, as does giving it a home - it takes up valuable clamp space. When feeding to cattle it also takes up belly space, takes longer to be digested and can lead to reduced overall nutritional intake.

How to deal with maize stubbles

 If you’re concluding that it’s sensible to only harvest the nutrient dense part of the crop, how do you deal with the rest? It might well be possible to plough the stubbles straight in but sometimes the residue might need running over with a set of heavy discs or a mulch pass ahead of the plough. Whichever technique is used, you will be returning some organic matter to the soil that can only be a good thing. Soils might benefit on headlands and around gateways too as less loads will have gone over the soil when employing the higher cut height. 

If you want to discuss the pros and cons of different cutting heights for maize silage or any of the other aspects of silage making covered in this series – contact Jeremy Nash at Jeremy@silageconsultant.co.uk