Friday, March 29, 2024

Assaying late summer grazing

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Maize is becoming an increasingly popular greenfeed crop for beef and dairy cattle in dryland areas of New Zealand. Fed in February when the cob is just starting to develop, the crop offers a bulk of feed at a time of year when there is often no other greenfeed available. Raewyn Densley, a forage and nutrition specialist with Pioneer brand products, says the big advantage of maize is its water efficiency.
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With an effective rooting depth of up to 1.8m the maize plant can access moisture and nutrients not available to many other forages and the plant itself is three times more water efficient than ryegrass on a kilogram of drymatter (DM) per unit of water basis.

Densley explains that the grazing maize is typically a blend of hybrids of different maturities that can be either sown conventionally or by using a precision planter.

Sown in early November, it can be grazed after six weeks but Densley says maize has an exponential yield curve so the longer it is left the higher the yield.

Grazing when the cob is just starting to develop in early February is ideal from a yield point of view and it fits in with a period of high feed demand.

Densley says in early February a November-sown crop will be yielding 10 tonnes/ha with an energy value of 10-10.5 megajoules of metaboliseable energy (MJME)/kg DM and crude protein (CP) of 8-9. This CP level is below maintenance requirements for most classes of stock and animals grazing greenfeed maize should be given a high-protein supplement such as pasture or lucerne.

“Leave the crop until mid-March and the yield will be closer to 12-14t DM/ha with a similar feed value.”

While Densley admits greenfeed maize doesn’t offer a huge amount of energy it is being fed at a time of the year when there is little else available and at 10-10.5 MJME/kg DM it is comparable to good quality silage.

“The upside is that it is very drought tolerant, disease resistant and once established it looks after itself.” 

So long as there isn’t too much cob development, stock transition easily off grass and on to maize but more care needs to be taken if the cob is well developed.

While some farmers simply run the stock on to the crop behind a wire others will knock the break over with a tractor and then feed it. Stock grazing maize don’t require any extra fibre.

As a crop, maize is very easy to grow with few inputs required. Typically maize seed is coated with an insecticide before drilling and this will protect the plant against its three major pests – Argentine stem weevil, greasy cutworm and black beetle.

The crop needs to be established with DAP or any nitrogen-phosphate-potassium fertiliser. Grass and broadleaf weeds need to be controlled pre and post emergence. 

The big advantage of maize is its water efficiency.

When the crop emerges, Densley says most farmers will broadcast urea but once established maize will not require any more inputs.

There are latitudinal limitations to growing maize. Densley says it can be grown in Oamaru but is less reliable any further south. 

She says grazing maize as a greenfeed crop was a popular practice in the 1990s but maize silage took over from grazing in-situ because of the flexibility it offers. A hybrid maize silage crop can also be green-chopped and some farmers will green-chop a proportion of the crop and ensile the rest.

However, growing maize as a greenfeed crop is becoming popular again and while it has been traditional practice in Waikato, farmers in Canterbury are now growing it.

Densley says her company is seeing a lot of interest in growing greenfeed maize from beef producers in the region as well as from farmers doing dairy support.

System addition

Ruminant specialist Dr Jim Gibbs from Lincoln University says maize is a safe and cheap feed and while weight gains aren’t spectacular because of the relatively low metabolisable energy (ME), it is certainly better than no feed or summer dry pastures.

He says crude protein levels are okay early on but they drop as the drymatter yield spikes.

“The plant is a C4 so is water efficient but with that comes a high fibre content and hence a low digestibility which means the ME value is low, probably 10 at best.”

Gibbs adds that he likes maize as a system inclusion for later summer and early autumn before cattle go on to a feed such as fodder beet.

  • Read more about beef cattle grazing maize in upcoming Country-Wide Beef (formerly Heartland Beef).
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