Late planting and a cold June have left most forage maize crops “three to four weeks” behind on maturity when compared to the same date in 2023, farmers at a Fane Valley event on Tuesday were told.

“Last year was an exceptional year for maize. There were some crops ready by 22 September. This year has been challenging,” said Gary Spence from Fane Valley at the event held on Jack Dobson’s farm outside Moy, Co Tyrone.

There is a wide range in crop maturity across NI, with some maize in the east, planted in late April under plastic, ready to cut in the next two weeks. However, further west, it might be well into October before crops can be ensiled. On the Dobson farm, a relatively early variety, KWS Severus, was planted in May with no plastic. The crop has grown well since June, but is still “six to seven weeks away,” said Spence.

He estimates that around half of maize crops in NI this year have been grown without plastic, compared to around 35% to 40% in 2023.

“It costs around £200/acre for biodegradable plastic – it is a big cost, but it is an insurance policy. We are not advocating one or the other,” he said.

The Fane Valley representative quoted an example from a Co Down farm where a proportion of a field of maize was grown under plastic this year. The crop that was under plastic has cobs that will be ready two to three weeks earlier.

In general, various studies suggest maize grown under plastic will have higher dry matter (DM) and deliver around 2.5t more DM/ha, which probably just about covers the cost of the plastic, said Spence. Ultimately, a decision on whether to use plastic or not might depend on the plan for the field and whether a winter crop is to be planted post maize harvest.

Seed rate

Other factors that dictate harvest date include seed rate and the variety chosen.

On most sites a seed rate of 40,000 per acre is used and this can be increased to 45,000 on exposed fields or where the crop is intended for biogas production. If the seed rate is too high, plants grow taller and with smaller, less developed cobs.

Maturity

To maximise the value of the crop, early varieties should be grown in NI, with a FAO number (a measure of crop maturity) of 190, or less.

“If you want to get a winter crop in, you might go with a lower seed rate and an earlier variety. We go as far as 190 – that is as far as we are happy to sell,” said Spence.

The aim should be to harvest crops at 30% to 35% DM and when the milk line is one-third to halfway down the kernel within a cob.

Most farmers apply an additive at harvest. “It is an expensive crop to grow and you want to ensure you get the best out of it,” said Spence.

Maize is relatively easy to grow and can be continuously cropped in the same field, but care should be taken to avoid compaction, suggested Dr Stephen Bell from Fane Valley.

“Maize is good at rooting, but if it meets a hard pan it becomes lazy.

“If the soil is compacted, you will have reduced yield,” said Bell.

He told farmers to make sure they control weeds before maize reaches the six leaf stage.

He also emphasised there is a role for biostimulants to encourage early phosphorus uptake, and for foliar feeds that supply phosphorus, zinc, magnesium and nitrogen.

Including maize as a second forage in cattle diets will increase DM uptakes by up to 20%, leading to improved animal performance, confirmed Matthew Armstrong from Fane Valley.

“Maize is the king of second forages. Fifty per cent of the time dairy farmers will see a benefit in milk yield. But either way, you will save concentrate feed on,” he said.

In addition, milk protein should be higher, while most farmers report improved cow health and fertility when maize is fed.

But to get those production responses, maize should make up at least 30% of forage (on a DM basis) in the diet. It is high in fibre and low in protein, so best complements a good quality grass silage. “Ideally, feed 50:50 maize with good quality grass silage. Maize is 7% – 9% protein so you need to increase protein levels in concentrate to balance that out properly,” suggested Armstrong.

However, first cut silage quality is an issue on NI farms this year, with around 1,200 samples assessed by Fane Valley coming in at an average ME of just 10.8MJ.

It might be the case that second, third and fourth cuts are of higher quality and it is this silage that should be fed alongside maize to early lactation cows.