Optimising Pasture for Dairying in Northland

DairyNZ is just completing the last season of a four-year trial on the Northland Agricultural Research Farm. The trials compare the management and profitability of three farmlets – ryegrass dominant; kikuyu dominant with autumn mulching and undersowing with Italian rye; and kikuyu dominant without mulching and with oversowing with Italian rye.

Two seasons have been dry and two have had good rain. The mulched kikuyu has performed best each season in terms of DM production and cost. Ryegrass performed poorly in dry seasons and well in good seasons. Non-mulched kikuyu performed reasonably well in the dry seasons but poorly in wet seasons because it could not be controlled well enough by grazing alone.

This project has been supported by the Northland Dairy Development Trust, the T.R. Ellet Trust and Hine Rangi.

For many farmers in Northland kikuyu pastures are a fact of life. Many are in a quandary wondering whether to attempt to spray it out and re-establish conventional pasture or simply learn to live with it.

The Northland Dairy Development Trust along with a couple of other charitable organizations has contracted DairyNZ to compare ryegrass and kikuyu pastures and determine which are the most practical and profitable options for the region.

Kate Wynn, Northland Regional Science Manager for DairyNZ, has been conducting trials on the 84 ha Northland Agricultural Research Farm near Dargaville. Half the farm has kikuyu pastures and half is in ryegrass, so the farm has been divided up into three unequal trial areas:

• Ryegrass farmlet – 42ha

• Kikuyu mulched and undersown farmlet – 22ha

• Kikuyu non-mulched and oversown – 21ha

Ryegrass and kikuyu both grow well in Northland but have different strengths. Rye performs well as long as there is enough rain, and continues to grow and provide feed in Northland’s benign winters. However, it performs poorly in dry periods. Kikuyu thrives in summer even during droughts but grows so vigorously that if not controlled, its stolons become coarse and indigestible and form a blanket that smothers everything else. Once cooler weather comes it completely stops growing.

The vast majority of Northland farmers, says Kate Wynn, face the dilemma of how best to manage their pastures and whether or not to try to get rid of kikuyu where it is not already dominant.

“What we’ve been trying to determine is the productivity and profitability of the three different systems, so in the same environment what can you expect pasture to do and your cows to do, and what is the best practice around managing kikuyu and getting the best out of it,” she says.

“The farmlets have been run as you would run any normal farm trying to meet targets for pasture cover, cow condition, milk production and budget.”

The ryegrass block has been managed conventionally. The kikuyu-mulched block has generally been grazed hard in autumn, then mulched, then (depending on moisture levels) the area has been drilled with Italian rye to provide feed when the kikuyu is dormant.

The non-mulched kikuyu area is like a lot of Northland farmland where the kikuyu is rampant but for various reason such as steepness, the use of a mulcher is not practical and stock grazing pressure is the only means of control. Once the residuals were down as low as possible in autumn, the area was oversown with Italian rye.

The mulcher has flails like a forage harvester which cut and break up the kikuyu stolons.

“First we put the cows in to graze off as much as possible, and then mulch. In the last two seasons we have had to mulch in January/February as well to control the massive growth. After autumn mulching we drill in Italian rye because we find that it lasts a bit longer than annual rye. We still feed winter supplements but the rye provides a lot of extra grass that we wouldn’t get on a kikuyu-only system,” she says.

“With non-mulching if you have low residuals you can get good seed establishment by oversowing, but in good years when the kikuyu is growing really well establishment has been poor. We used a similar sowing rate for both mulched and non-mulched, and it might have helped to put up our seeding rate for the non-mulched area.”

Bearing in mind that the first two years were dry and subsequent two were favourable, costs and returns have been calculated for each year of the trial. The major difference between the systems has been the cost of undersowing the mulched farmlet. There is also the cost of grazing off because mulching takes the area out of production until the Italian rye comes through, so the wintering costs for both kikuyu farmlets are a little higher than for the rye farmlet. However, a lot more supplements were used in the ryegrass trial because in the drought years the ryegrass didn’t grow.

“The three major cost differences are in grazing off, supplement use, and regrassing while other farm costs are the same. Over the first three years the mulched area performed best producing about $1000 per hectare more than the ryegrass, while the non-mulched area produced about $800 more. So the ryegrass cost the most cost and produced the least,” says Kate.

“However, the current year is different owing to poor Italian rye establishment in a good growing year in the non-mulched area because the kikuyu could not be grazed short enough, and we have had to use a lot more supplements. Final figures are not yet in but it looks as though the mulched area will do about $500 more per hectare than the ryegrass, and the non-mulched will be about $100 less than the ryegrass.”

“We have made other changes to optimise the ryegrass system – we’ve reduced stocking rate and so we haven’t had to feed as much supplement, and we have had more pasture available so per-cow performance is better. The mulched farmlet has the highest stocking rate and so there will need to be more supplement fed per cow.”

Kikuyu can be farmed quite profitably as long as you’re willing to use supplements and you’ve got a plan in place around mulching and regrassing. Where kikuyu is dominant and tractor access is possible, mulching followed by undersowing is the best option. Ryegrass pastures perform well in winter but poorly in droughts. Controlling kikuyu without mulching is difficult and in a good season is the least profitable option.

“The ryegrass has performed well this year because we have had good steady rain, and we will probably be growing around 14 to 15 tonnes per hectare which is pretty good for Northland. However, that is one year out of four so it is worth looking at alternative species such as fescue or plantain or chickory mix that will provide another option for some feed and help the ryegrass system,” says Kate.

“So this is Phase 2, and we have got funding to do another three-year project looking at optimising the ryegrass system. It seems that the variation in seasons is too much for it, so what can we add into the mix to improve the whole farm system? In the coming seasons we will have the mulched best practice kikuyu management on half of the farm, and the other half will be predominantly ryegrass with some cropping and whatever else we decide would be beneficial.”