A new guide to managing pulse and legume crops in acid soils offers growers strategies to address the constraints of subsurface acidity and produce more profitable pulse crops, with flow-on benefits to other crops in the rotations.
The Grains Research and Development Corporation (GRDC), in partnership with the NSW Department of Primary Industries (DPI), has produced Legumes in acid soils, based on findings from crop surveys across Victoria, South Australia, Tasmania and New South Wales.
NSW DPI development officer, Helen Burns, said forward planning and proactive management of soil acidity was fundamental to improving the production potential of acid-sensitive pulses.
"If subsurface acidity is not corrected, poor nodulation may result, even in cases where good inoculation practices are followed," Ms Burns said.
Strategies growers can use to improve production potential, yield and nitrogen fixation of pulses include:
- Select paddocks at least two years before sowing acid sensitive crops to allow for effective lime treatment.
- Test soil pH at 5cm intervals to a depth of 20cm, to detect any acidic layers.
- Apply appropriate rates of fine-grade lime and incorporate lime to a depth of 10cm, 12 to 18 months prior to sowing or 24 months in drier areas. This strategy hastens the lime reaction and increases the depth of lime effect.
- Select crops best adapted to the soil and climatic conditions of your region; avoid soils with shallow topsoil and impermeable subsoil that limit root development and restrict drainage.
- Sow acid sensitive crops early in the recommended sowing window for your location to ensure vigorous early growth.
Ms Burns said growers should use pH levels within the 0-20cm soil surface layer to guide crop choices and liming programs.
"Most pulses and associated rhizobia are sensitive to low pH levels and producers need to accurately measure and target lime applications to lift soil pHCa (measured in calcium chloride) to levels above 5.0," she said.
"The surveys revealed issues in detecting pH stratification and managing severely acidic subsurface, commonly at 5-15 cm, were major reasons for lower than expected yields experienced by many growers.
"Although 90 per cent of paddocks surveyed had a history of lime application, traditional pH testing collected samples at depths of 0-10cm and 10-20cm and failed to detect acidic layers at 5-15cm.
"The common practice of spreading lime without incorporation, and sowing with knife point press wheels or disc seeders, confined the lime effect to the shallow soil surface, resulting in an elevated pH in the 0-5 cm layer and limited movement of the lime effect below 5cm."
Root growth, nodulation, plant vigour and nitrogen-fixing potential of acid-sensitive pulses are reduced in soils with a pHCa of less than 5.0 – the lower the pH, the greater the risk.
Ms Burns advised growers to follow manufacturers’ guidelines for storage and application of inoculant to ensure rhizobia survival in storage, during application, at sowing and during the nodulation process.
"It is important growers get the basic agronomy right and avoid plant stresses which compromise early plant vigour, such as delayed sowing, poor nutrition, disease and pest damage and herbicide injury," she said.
"Results from this project, reinforced by grower experiences, indicated that well nodulated, vigorous pulse crops are more tolerant of multiple environmental stresses than poorly nodulated pulses.
"By focussing on agronomic practices that minimise the negative impacts of low pH and other stress factors on nodulation and the early growth, growers have a far greater chance of achieving their production potential in terms of yield and nitrogen fixation."
Legumes in Acid Soils booklet
