Expert advice . . . DairyNZ scientist Paul Edwards presents nitrogen research information, while AgResearch scientist Robyn Dynes operates the data projector. PHOTO: SALLY BROOKER

Plantain shows promise for helping both dairy and sheep farmers to reduce nitrogen leaching from their land.

A two-hour seminar organised by the North Otago Sustainable Land Management group (Noslam) at Weston on Tuesday revealed research findings that could be useful for meeting new environmental regulations without lowering productivity.

Two scientists from the Forages for Reduced Nitrogen Leaching discussed a six-year programme that worked across the dairy, sheep and beef, and arable sectors.

Paul Edwards, from DairyNZ, said the study looked at plants that were better able to take up nitrogen from the soil and that contained less nitrogen themselves. Pasture that would reduce the amount of nitrogen a cow took in and had improved metabolisable energy content would improve animal performance and reduce leaching from urine patches.

Pasture that had greater root depth, to reach nitrogen lower down in the soil, and that grew in the cool season would also help reduce leaching, Dr Edwards said.

A study tested leaching from two types of pasture. One was a ryegrass-white clover mix and the other was Italian ryegrass-plantain-white clover. A standard amount of urine was applied in autumn.

The latter showed a 45% reduction in nitrogen because of the winter-active ryegrass species and the deeper roots that could pick up more nitrogen. The urine from cows eating that pasture also had less nitrogen in it.

The total effect, half from the effect of the plants and half from the different urine composition, was an 89% reduction in nitrogen leached.

“This trial demonstrates the principles,” Dr Edwards said. “In reality, it’s a lot more complicated.”

Where fodder beet made up 23% of the cattle diet, nitrogen leaching was reduced. If fodder beet was 45% of the diet, it was reduced further due to lower concentrations in urine.

However, when dry cows were fed 85% fodder beet with straw, there was a high risk of rumen acidosis.

Catch crops could help mop up soil nitrogen from urine or a crop, Dr Edwards said. The earlier they were sown, the better.

It was important for “self-starters” such as those who attended the seminar to pick up on research findings and spread the word, Noslam member Lyndon Strang said.

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