Lime grade key to effective pH control, and trials look at pulses, acid tolerant crops

Pulse crops growing on a lime trial at Condobolin Agricultural Research Station, NSW.

Grower Gary Somers can testify to the benefits of working with researchers on his farm, Trelawney', 12 km north-east of Parkes NSW, in the middle of an area suffering from acid soils. The work helped him solve an expensive puzzle in regard to his liming program.

With surface pH levels as low as 4.2 in some paddocks, Mr Somers started liming in 1996 at 2.5 t/ha, only to find that in some years the crop response just wasn't as high as it should have been. "At that rate we should have been lifting the pH by a whole unit, and it shouldn't have needed reliming for around 10 years," says Mr Somers.

Instead he saw only half the benefit. By coincidence, he had already invited Neil Fettell and Catherine Evans from NSW Agriculture to run some trials on his property.

Four lime trials

Dr Fettell established four lime trials — two on the Condobolin Agricultural Research Station in 1996, and two at 'Trelawney' in 1997. The trials were initially set up to look at pulses, the effect of lime on their yield and the subsequent nitrogen input for the next year's wheat crop.

A variety of pulses were grown in the first year on each lime rate. In the second year the whole trial was sown to wheat. In the third year a variety of pulses was sown again (on different plots to the first year) and wheat was grown in the fourth year.

Wheat yield benefits from previous pulses

The results, according to Ms Evans, showed that in all cases, the wheat yield was significantly affected by the pulse crop grown earlier (either in the year prior or three years prior).

"We also showed that the yield of Janz wheat (acid-sensitive) was significantly increased with lime application, but Hartog wheat (acid-tolerant) showed no significant increase with lime," says Ms Evans.

This type of response was found consistently through the trials, with acid-tolerant crops showing a much reduced response to lime compared to crops that are acid-sensitive (see table).

"At the extremes, lentils had yield increases of up to 41 per cent with lime application of about 3 t/ha, whereas lupins showed no yield increase with lime application," says Ms Evans.

Ms Evans points out that acid sensitivity or tolerance is important when considering species and varieties to be sown on limed paddocks, even several years after liming, and so it is worth closely monitoring soil pH levels when planning the next season's crop.

Tolerance doesn't solve acid problem

"Growers can use acid-tolerant crops like Dollarbird, Diamondbird, Swift or Sunstar wheat, narrow-leaf lupins, oats, cereal rye, triticale, or subclover to cope with soil acidity but that doesn't reverse the problem. Liming is the answer to reversing soil acidity," says Ms Evans.

"Relying on acid-tolerant crops will actually give growers soil that, with no liming, will end up more acidic," she adds. "Liming is the only solution we have for increasing the soil pH."

At both research sites about 3 t/ha of superfine lime raised the pH from 4.64 to 5.82 in the first year, with a subsequent decline of 0.1 to 0.3 pH units per year.

Lime grade answers the puzzle

It was the use of superfine lime that gave Mr Somers and researchers a clue about the poor crop responses he had seen earlier. "Work at Wagga Wagga found that some lime was too coarse, and this reduced the pH benefit," says Mr Somers. "It was something I would not have found out about without these trials."

"We were planning on reliming every ten years," says Mr Somers, who crops canola and wheat in rotation with barley, lupins or triticale, and a four-year pasture phase. "But we will have to relime soon on the paddocks with the coarser lime."

Since that time, the lime supplier has refined the production process to supply much finer lime.

High acidity in NSW central west

With as much as 57 per cent of central western NSW red soils having a surface pH of less than 5.0, small details like lime particle size are important to continued crop production and profitability.

Another cost saving for Mr Somers was the realisation that he needs to monitor only the surface soil pH as part of his liming program. Like many soils in the region, his soils are alkaline at depth.

SpeciesNil lime (pH 4.6)3 t/ha lime (pH 5.82)Tolerant/ sensitive
Field pea2.853.19Sensitive
Faba bean3.243.82Sensitive
Lupins - narrow3.022.85Tolerant
Lupins - albus3.923.95Tolerant
Wheat - Janz3.854.30Sensitive
Wheat - Hartog2.482.60Tolerant

Program 3.5.2 Contact: Ms Catherine Evans 02 6895 2099