Having a favourable pH is an important aspect of producing good quality trees and fruit, and to achieve this, Australian growers have been applying conventional lime for years. But how effective is it, and what are the factors to consider when purchasing lime?

A 2020 research paper reported that fine lime achieved and maintained a higher pH increase over an eight-year period, when compared to coarse lime. The field trial, conducted in Wagga Wagga, debunked the myth that coarse lime is more effective over the long term in pH management.

Advantage Agriculture technical agronomist Brian Foster says because conventional bulk lime is made up of a range of particle sizes (0.075mm to 5mm), the release will be uneven, with the coarser particle portion being less reactive, taking longer to work and not penetrating past the top 10cm of soil.

“It is therefore vital that finer soil amendments are utilised and applied in smaller amounts more often to get ahead of soil reacidification, otherwise you will continue to lose money every year through inefficient fertiliser use and yield loss,” he said.

“Even if coarse lime is incorporated at depth, it will not travel far from where it has been placed. This results in variations of pH across the plant root zone, creating uneven fertiliser efficiency and uneven plant growth across the crop.

“Essentially, coarse lime takes so long to release that you are unlikely to get anywhere with one application every three or so years.”

The major constraint with an ultra-fine lime is how to practically apply such a fine, powdery product, and until recent years there had been few options that were effective.

Advantage Agriculture now has a range of granular products designed to make the application of ultra-fine soil amendments practical, while delivering an agronomic benefit.

Ozcal and OzcalMag 3–5mm granules contain ultra-fine particles, 95% of which are below 0.045mm. Upon contact with moisture they break down into the soil delivering a far quicker, robust result.

Mark Duncan of Duncan Macadamia Monitoring in northern NSW started using Ozcal for the first time this year and said the product ticks a lot of boxes for his growers.

“The ability to spread the most effective part of the lime, when and how they choose, is very important,” he said.

“The terrain of some of our farms in the Northern Rivers means that timing is critical due to the risk of runoff and washaway down the hills. The ultra-fine granule seems to break down quickly with the moisture so it can start working, rather than the risk we take with bulk lime washing away.

“We have applied a variety of different liming products in the past 18 months which have shown a limited ability to adjust pH significantly. We put this down to the severe drought conditions we have faced which has resulted in a lack of penetration through the soil profile.

“It's only the first year we have used Ozcal, but it has been a promising start. In one of the crops we are monitoring we applied Ozcal at slightly less than 10% of the rate of bulk lime and achieved a better pH adjustment. The other real short-term benefit we see with Ozcal is its ability to maintain soil and leaf calcium concentrations.”

Gypsum is another product that is used broadly in the management of tree crops, and Ozgyp is the brand name of Advantage Agriculture’s granulated version.

Mr Foster has seen many improvements in leaf tissue calcium levels from growers using Ozgyp on avocados in the Atherton Tablelands and reports of similar results from citrus crops in the Mundubbera region with growers targeting calcium delivery at critical growth stages, such as flowering.

“The high purity and small particle size accelerate and increase calcium delivery into tree crops, reducing the need for calcium foliar sprays that often have unwanted nitrogen and the potential for interfering with pollination,” he said.

It is also been shown in many research articles that calcium is more effectively taken up though the plant roots rather than through the leaf, as calcium is a very large molecule. Growers can also do multiple applications over the season of Ozgyp to maintain a steady flow of calcium into the trees, without major peaks and troughs.

“Our products are not new chemistry; they are still simply lime, gypsum and dolomite organically mined from the earth,” said Advantage Agriculture national sales manager Jason Gadsden.

“The new technology we introduced is the ability to put ultra-fine particles into a robust 3–5mm granule.

“For decades now, worldwide scientific studies have proven that it is the fine particles in soil amendments that drive results, but the powder was just too hard to apply. Now we have a solution for it.”