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Growing Maize Under Plastic

Some farmers choose to plant maize under a photodegradable polythene film (method developed in France). The film is a mulching agent used to conserve soil moisture. In Ireland, this method is employed on 30% of the total land area used for growing maize. When deciding whether to use plastic or not, one should consider the following:
1. Would the crop mature without the use of plastic?
2. The cost of the plastic.
3. The degradability of the plastic.

Advantages:
1. Yields on average are increased by 3.5tonnes/ha.
2. Dry matter yield is increased by 3.7tonnes/ha (5%).
3. Starch content is increased by 2.5tonnes/ha (10%).
4. The crop can be planted earlier (usually by the end of March) as the soil temperature is increased by 5C.
5. Germination occurs more quickly and growth is faster.
6. Harvest date is advanced by 2 3 weeks. This is important, as the crop is ready for harvesting before the first heavy autumn frosts.
7. The season is lengthened.
8. Frost damage is reduced.

The increased cost (250/ha) is compensated for by the additional output and quality.

If conditions are very suitable in that particular year of growing maize, the use of plastic does not have such huge advantages over conventional growing methods. Therefore, plastic is a bit like an insurance in case bad conditions prevail.


Kildare 2002 (bad year):

DM%

With plastic

15

Without plastic

10

Starch%

With plastic

38

Without plastic

24

Yield tonnes of DM/ha

With plastic

28

Without plastic

19


Cork 2004 (good year):

DM%

With plastic

30

Without plastic

32

Starch%

With plastic

29

Without plastic

26

Yield tonnes of DM/ha

With plastic

18

Without plastic

18

Two varieties that are planted under plastic are Benica and Justina. Benica is planted at the end of March and Justina at the beginning of May.

One of the techniques used is called Punched Plastic and involves laying two sheets of a 1.5 metre wide photodegradable polythene film on the soil surface. The rows are kept 70cm apart. The seeds are then sown through the plastic. The seeding mechanism punctures the film at the exact seed position, which allows the seedling to emerge through the hole completely free of the plastic.

The other technique used is called Complete-Cover. This involves sowing the seeds and then covering them with plastic. As the seeds grow, they puncture the plastic themselves. It is important that the plastic is slightly elevated from the ground to allow room for the seeds to germinate.
This is the system used by Fachtna Collins.

The fact that the film is photodegradable means that it is broken down by sunlight during the growing season and virtually disappears by harvest time.

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