Increasing productivity on high country farms

Daniel Hendrie has hit upon the ideal formula for applying lime to increase phosphorus availability.

The Lincoln University PhD student has spent the past three years experimenting with fertiliser and lime on high country soil, which is light and friable, and known to contain high levels of aluminium.

“We rely on growing legumes in the high country because they fix nitrogen rather than having to apply nitrogen fertiliser,” says Daniel. “But legumes are restricted by aluminium toxicity in the soil and phosphorus and sulphur deficiency.”

As part of his research Daniel conducted two different field experiments. One examined fertiliser interactions with lime and how that affects pasture growth. The other major field experiment, conducted at three sites, focussed on injecting lime directly into subsoil where there’s low pH and high aluminium to see how that affects plant growth.

Daniel, who expects to have his findings written up by the end of the year, explains some general outcomes from his research. “The results are very site- and soil-specific, so what happened on one farm is not necessarily going to happen on a neighbour’s farm. But we generally found that liming improves phosphorus availability. And quite often you need a smaller amount of lime than you think you’ll need to see a phosphorus response.”

While adding lime to soil can neutralise high levels of aluminium and lead to a good increase in phosphorus uptake, Daniel’s research reveals that adding too much can be counterproductive.

“The ideal pH to maximise phosphorus availability is between 5.8 and 6 and you definitely don’t want to go over 6.3. But you can always mitigate that by putting more fertiliser on, although that’s expensive.

“It is not advisable to apply phosphorus with lime when liming a soil with high levels of aluminium. This can result in the phosphorus binding with the aluminium as the aluminium precipitates.”

Aluminium is toxic to legumes at concentrations of >3 mg/kg. Some plant species have a greater ability to tolerate high aluminium concentrations in soil and take up phosphorus than other plants. Daniel advises farmers to find the most suitable plants for their farming system and soil conditions. Some legumes that can tolerate high levels of aluminium include Russell lupins, lotus and some annual clovers.

“Often aluminium concentrations in the soil become toxic deeper down the soil profile. So, farmers intending on growing a deep rooting crop like lucerne, which is sensitive to aluminium, or who have acidity issues on their farm should carry out deeper soil tests beyond the standard 7.5 centimetres before planting.

“It’s important to find the most suitable plant that fits in with your farming system – and looking at soil conditions is the best place to start.”

Daniels’ research is funded by the Fertiliser Association of New Zealand, a Callaghan Innovation Business Research and a Development Student Fellowship Grant, AGMARDT, the Don Hulston Foundation Scholarship and Mr Roland Stead. His main supervisor is Associate Professor Jim Moir.