Plantain and the action of stock feeding on it has been found to slow the nitrification process. By Anne Lee.

Bioactive compounds in plantain appear to be acting like natural nitrification inhibitors scientists are finding.

At a recent Lincoln University Dairy Farm (LUDF) focus day, Dr Trish Fraser from Plant and Food Research told farmers scientists have been looking at what’s happening in the soil when animals are grazing plantain.

The work is part of the larger plantain potency and practice study being funded by the Ministry of Primary Industries, DairyNZ, Fonterra and PGG Wrightson Seeds.

It appears both the plant itself and the urine of animals fed plantain are helping to slow the nitrification process where ammonium is converted to more readily leached nitrate.

Trish says scientists have looked at the urine of sheep fed plantain or ryegrass. They’ve been able to identify more than 2000 compounds, but they’ve found 75 that are unique to, or are present in much higher concentrations, in the urine of the sheep fed plantain.

Laboratory experiments have been carried out using the urine from sheep fed plantain to compare its effects on nitrate production over time in the soil with urine from sheep fed ryegrass and with the application of urea as well as the natural nitrogen mineralisation in the soil.

The amount of nitrogen present in each treatment was the same, to allow the rate of nitrate production to be accurately compared.

Trish says nitrate production where urea was applied was similar over a six-week period to the rate where grass-fed urine was applied.

But in the soil where the urine from sheep fed plantain was applied, the rate of nitrate production was much slower.

By the end of the six-week period the total amount produced was similar but slightly lower.

She says the slower rate means more nitrogen remains in a form that is less likely to be leached for longer.

“It (the effect) isn’t lasting for a long time, but it is lasting for about a month and that’s quite a long time for a plant to be able to take up that nitrogen.”

The first step after urea is applied – either as fertiliser urea or urea in animal urine – is the conversion of urea to ammonium.

That happens fairly rapidly but that’s okay because the ammonium isn’t readily leached and is available to the plants, she says.

The nitrification process, carried out by soil microbes, converts the ammonium to nitrate which is readily leached.

Compounds found in the urine appear to be acting on the nitrification process, slowing it down. Trish says plantain contains unique secondary compounds such as aucubin, catapol and verbascoside which are known to have antimicrobial, antifungal, anti-inflammatory and anti-oxidative properties.

Those antimicrobial properties from some of these compounds are believed to extend to inhibiting the microbes that carry out nitrification and are therefore acting as biological nitrification inhibitors. Plantain also exudes compounds from its roots such as vebascoside and aucubin and those exudates have also been linked directly with biological nitrification inhibitory activity in the soil around the roots.

“Roots usually do that (exude chemicals) to get something in return, so we think the plant is conserving nitrogen for itself.”

Plant and Food scientists are carrying out further studies to develop a quick test that can correlate the level of biological compounds in the leaves of the plantain with those in the roots to give a good indication of the biological nitrification inhibitor activity in a cultivar.

Trish says different cultivars are believed to have different levels and a quick test will make selection and identification of effective cultivars possible.