How plantain cuts nitrate leaching

New trials have confirmed that plantain can at least halve nitrogen leaching on dairy farms.

Agricom animal nutritionist Glenn Judson says the company’s own trials, studies at Massey and Lincoln universities, and work currently underway in a Plantain Potency and Practice project funded by Sustainable Food and Fibre Futures, continue to suggest a pasture sward containing between 20% and 40% plantain can significantly cut nitrogen leaching.

Judson says Agricom has been researching and developing plantain for more than 20 years and has developed its own cultivar, Ecotain.

It reduces leaching using four mechanisms: reducing the proportion of dietary nitrogen excreted by a cow, diluting the nitrogen concentration of urine, delaying the nitrification process in a urine patch, and restricting or suppressing the nitrification process in the soil.

Judson says up to 90% of all nitrogen leaching on a dairy farm originates from urine patches.

A cow can excrete urine about 13 times a day.

The average dairy cow grazes 140sqm of pasture a day and deposits about half the nitrogen it consumes in an area of about 3sqm.

Concentration does vary, but at its most intense, urine is most regularly equivalent at between 600 to 800 units/N/ha – still too concentrated for surrounding pasture plants to take up.

“It’s these hot spots of nitrogen in urine patches that creates leaching issues,” says Judson.

Ecotain has been bred to enhance the best attributes of plantain.

Typically, about 50% of a cow’s dietary nitrogen is cleared as urine but Ecotain reduces that to between 35% and 40%.

It also dilutes the concentration of nitrogen in urine by increasing urine volume, a consequence of consuming a wet feed that is lower in dry matter, and has a diuretic effect.

Research by Lincoln University shows cows fed plantain produce almost 40 litres more urine than those fed ryegrass, meaning excreted nitrogen is heavily diluted.

Ecotain has also been proven to slow the nitrification process in urine patches, increasing the potential for plants to use it. 

Judson says it does this by delaying the nitrification process by locking the nitrogen in the soil as ammonium, which does not leach – a key attribute for those on light soils.

Ecotain also restricts or suppresses the nitrification process in the soil. This could be through biological inhibitors originating from the roots. That, says Judson, could be a consequence of the plant’s evolution while inhabiting poorly fertile soils such as waste areas. These soils are traditionally light and lack nitrogen, so the plant appears to have developed an ability to retain and store nitrogen for its own use.

Judson says Overseer recognises the reduce-and-dilute functions of Ecotain, and work is underway to get recognition for its other two attributes.

Research shows that pasture containing about 40% Ecotain achieved a 45% reduction in leaching compared to a ryegrass pasture.

Hydrologically isolated paddocks at Massey, in which all runoff and leaching is centralised through one system, shows reductions in nitrogen leaching of 50%, although Judson says this was a site where leaching is not a significant issue.

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Judson says sizeable reductions in leaching can be achieved with swards containing 20% to 30% Ecotain.

“The current target is a 30% Ecotain sward but there is a real possibility that when other mechanisms are recognised, significant reductions in leaching are likely, even when Ecotain makes up a lower proportion of the sward.”

One issue with any plantain is that it can be crowded out by other cultivars, especially ryegrass.

Judson says farm system research shows longevity is enhanced by preventing Ecotain from seeding.

“I fear undergrazing Ecotain more than I do overgrazing. That management is far kinder to the plant than letting it seed.”

It is palatable to stock, has been successfully grown in climates as diverse as North Queensland and Southland, is suited to NZ farm grazing systems, active in cool seasons and has been bred to be upright.

Reseeding a paddock is by simply broadcasting seed and fertiliser, or even adding it to applications of magnesium oxide.

Judson says it has been shown to struggle in fertile, irrigated paddocks, but once the irrigation season is over, it thrives.

In a trial in the Manawatū last autumn, which was dry, the cultivar hung on and took off when the rains came.

As for cost, Judson says Ecotain is cheaper than some Italian ryegrass cultivars.

He says Ecotain’s ability to reduce leaching can assist farmers where they may be struggling to meet their environmental regulations.