Is it better to surface apply lime or incorporate lime?
This is the question faced by farmers with increasing amounts of acidity being detected at 10 to 20 centimetres soil depth.
Sustainable Farming Systems’ (SFS) Lisa Miller is working on soil acidity projects and said one trial site located on the Bellarine Peninsula, which had a soil pH (Ca) in the topsoil of 4.2 and a subsurface soil pH of 4.4, was facing a dilemma.
“We surface applied lime at 3 tonnes a hectare and found lime had changed the pH to 5cm depth in the first year but then lime movement slowed to about 1cm/year in the loamy soil,” Lisa said.
“After liming in 2014 we grew an extra 1.3t/ha of barley and 0.4t/ha of canola in 2015, with lime only treating acidity in the top 6 to 7 cm of the soil,” Lisa said.
Lisa said the problem with surface liming was the additional yield penalties incurred from the deeper acidity which was restricting root access to moisture and nutrients. Also with that method, the lime will be used up treating the acidity in the top 10cm and none will remain to change pH at 10-20cm depth.
SFS has established an additional trial this season looking at lime movement using deep ripping to 20cm, discing to 10cm and surface applying lime.
We want to mix the lime through the soil to maximise pH change throughout it. We didn’t want to band the lime in because it can’t move sideways.
- Lisa Miller, SFS
“We want to mix the lime through the soil to maximise pH change throughout it. We didn’t want to band the lime in because it can’t move sideways,” Lisa said.
Lisa expects if the acidity can be addressed in a one-off cultivation, then the grower can return to surface applied liming provided they prevent future acidity from increasing in the subsurface by keeping the pH in the topsoil above a pH of 5.5.
“This will create the alkalinity that’s needed to treat both acidity in the topsoil and subsurface soil,” Lisa said.
The incorporation treatments will add to the cost of lime application (approximately $55 to $70/ha higher than surface spreading at $20/ha) but are expected to be paid off by increased yields.
