Cropping in the hills

01-09-2010 | Jackie Harrigan

The initial kill of existing pasture and weeds is one of the most important factors in ensuring hill-country cropping success, H&T Agronomics representative Paul Oliver says.

He told sheep and beef farmers at Marton recently a matrix of variables influences successful aerial cropping. But the expertise of the helicopter spray operator is another crucial factor, and one on which farmers need to do their homework.

Get the most experienced person to do the job, not necessarily the person who usually sprays your thistles, because invariably operator experience affects crop success.

The pitfalls of hill-country cropping were highlighted by Oliver at a Central Districts Sheep and Beef Council field day on Making More Money in the Hills.

Aerial cropping can be successful, he told the group, but there were many variables. "Sometimes it works, sometimes it doesn't."

Aerial cropping of hill country gives farmers the opportunity to grow brassicas, setting up finishing areas and increasing the growth rates of young stock, plus the ability to reduce the number of animals on pasture at certain times of the year and the mechanism to change pasture species.

Oliver says the increase in the practice has coincided with a reduction in summer brassicas grown on the flats in the Manawatu for lamb finishing.

"Land-use change over the past five years from summer brassica lamb finishing crops to dairy forage crops or cereals has forced farmers to consider the lamb finishing job back on their own properties," he says.

Success requires planning, accuracy of application and continual management of the crop.

One of the success stories has been swedes in areas with reliable spring and winter rainfall and cold winter environments. Swedes have a relatively small nitrogen requirement, sustaining 1 tonne of leaf growth a hectare compared with a large phosphate requirement for many tonnes of bulb yield. An added success factor is that high swede yields require a low plant population of 10-15 plants a square metre compared with other leafy brassicas. Planted in December for July feeding, swedes also have more time to grow the yield and can recover from setbacks.

Citing reasonable turnip success in summer damp environments, Oliver says November sowing for February feeding requires reliable summer rainfall and has a reasonably high nitrogen requirement. With a shorter growing time, crop establishment and soil fertility need to be much more exact to guarantee success.

Overall brassicas need a reasonable depth of topsoil, because if the roots hit an impenetrable subsoil they will stop growing, and a small root system is not able to get enough moisture or nutrient to grow a reasonable yield.

Oliver says for autumn regrassing, mudstone soils tend to glaze on top after the brassica crop is eaten off and the glaze slows grass growth, allowing faster weed growth. Volcanic soils have much better success rate.

Erosion is a potential problem, as heavy rain events can cause slipping on slopes greater than 28° under crop. At this slope growth is concentrated on the sheep tracks, an inefficient use of crop establishment costs.

Brassicas will not grow well in areas of poor drainage, with poor establishment in wet seeping areas.

"It costs the same amount per hectare to establish the crop, so it makes sense to use the country which will yield the best."

In paddocks with an underlying woody weed problem, cropping can exacerbate the problem, preventing a good establishment of new grass. These paddocks should be avoided.

The initial spray job is important, Oliver says. The paddock needs to be prepared to maximise the uptake of glyphosate, with enough leaf to get a good kill. If bad weather delays the spraying, in two weeks the pasture can go to seed, so plan B will require another grooming job by the sheep to bring it back to an effective leafy state.

Fertility needs to be built up over time to get the best crop result. Fertility can also vary hugely across large hill-country paddocks. Differentially soil testing the paddock would highlight fertility variation and the cropped paddock may need to be redressed with nitrogen or phosphate later to keep the fertility consistent and to maximise the yield.

Top tips for hill-country crop success:

• Crop paddocks with high fertility record and good past management

• Free-draining soils on medium slope

• Close to facilities - yards and water for spraying

• A cluster of four paddocks to get rotation going

• Minimum rate of glyphosate - 6L/ha

• Pelletised seed - better ballistically, but need to double the weight of seed applied

• Use higher H2O rate for spraying herbicide - bigger droplets more likely to hit target

• Keep flying speed slow

• Reliable rainfall - 25ml for establishment, trampling can help

• Beware pests and actively control them - slugs, porina, grass grub, pigs, deer

• Ask if management practices can be put in place to favour new species and discourage the old species?

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