Farm Ireland

Thursday 23 November 2017

Why do we persist with planting costly maize on marginal sites?


Dr Richard Hackett

As planning for the upcoming spring cropping programme is taking place, one of the crops that seems to be in a state of uncertainty is maize. Maize grew very well in 2013 but 2012 was a disaster.

Given that it's a tropical crop trying to grow to potential on a rock in the middle of the North Atlantic, it is only to be expected that results will vary from year to year.

Maize has the potential to produce big yields of very high quality material, and those in other sectors know a lot more about the added benefit of adding maize to a finishing diet. However, it is a very expensive crop to grow and has a very late harvest. It can also be very detrimental to soil structure if harvested in very wet conditions and the build of up problem weeds as a result of continuous maize production is a growing problem.

The general trend in maize production is to cover the crop with plastic. There is a line of thought that maize can be grown in any site, in any location and under any conditions, as long as it's covered with plastic. While plastic covering can have its merits, the environmental footprint of this practice has often perplexed me.

Covering the land with such an energy intensive and non-renewable material such as plastic in order to feed cows is very questionable at the best of times, but using the technology to attempt to overcome a natural impediment for the crop such as poor site selection seems to me to be looking at the problem from the wrong way round.

I looked at the maize variety results from the Department of Agriculture crop variety evaluation trials from 2008 to 2013 and compared the results between the covered and uncovered trials.

The first point to make is that these are completely different trial programmes and really are not comparable at all. They have different protocols, sowing dates, locations and different varieties are used.

That said, these trials are planted in optimum sites and in optimum conditions using optimum varieties for each respective system, so a rough comparison can be made.

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It shows that between 2008 and 2013, the three year rolling average difference in yield between the uncovered and covered trials amounted to 3.12tDM/ha or 1.45tDM/ac in favour of the covered plots.

The differences ranged from 1.4t/ha in 2008 to 5.7t/ha in 2012. Given the cost of plastic, and all the associated problems such as weed proliferation and sometime unreliable rates of plastic breakdown, it's not a spectacular difference.


Proponents of covering will always point to an area of crop in a covered field where the plastic has blown off and show that the crop is far inferior to the rest of the field.

However, use of plastic entails use of varieties that are only suitable for growing under plastic.

A variety that requires covering is not suitable for use in the open in any conditions. Proponents will also point to the 2012 year and say that it's necessary as an insurance policy to cover the crop.

But no crop did well in 2012 and if similar conditions were to become a regular feature, cropping in Ireland would cease to be a feature of the landscape, regardless of covering or not.

The final point they will make is that in unsuitable sites, the only option is to cover with plastic to protect the crop. If a site is so marginal for maize production, why do you have to grow maize on it?

Spring wheat, barley or triticale can be grown and whole cropped and are much more tolerant to suboptimal conditions. The other major advantage of whole-cropped cereals is that the crop is in the pit in August, rather than having to wait until November to see what feed is available for the year.

If spring barley cannot be grown successfully on a site, grass that is managed correctly will yield very well over the course of a season, with no ongoing establishment costs.

If you cannot manage grass successfully, taking on the extra expense of maize production is hardly likely to increase profit.

Maize can be grown very successfully and profitably on an ongoing basis on many sites in Ireland. These sites are generally located east of a line drawn from Cork city to Drogheda.

There are a very limited number of suitable sites outside this area. There are also certain situations where covering with plastic will enhance the quality of a crop.

For example, if the crop is to be brought to maturity for ground ear maize or for combining. However, if the only way that maize can be grown successfully on a site is by covering it with plastic, it seems a very high risk strategy to secure feed.

Natural impediments such as cold sites will overcome the best efforts, and imposing a very high cost crop on a constrained site is unlikely to be a profitable exercise. Sometimes the best way to make money is not to spend so much of it in the first place.

Dr Richard Hackett is an Agricultural consultant and is a member of the ITCA and ACA.

Irish Independent