Summary

Baseline soil salinity levels were manipulated in a range of common soil types found in SA in glasshouse trials to determine critical thresholds for pulse crops including beans, chickpea and lentil. Comparisons were made to current critical levels for cereal crops from previous studies and current guidelines for toxicity.

Background

Pulse crops are more sensitive to soil salinity and fertiliser inputs than cereals but there is currently limited information to help growers and advisers estimate the potential yield penalties associated with different salinity levels.

Research Aims

The core objectives of the project were to:

• Determine soil salinity thresholds for emergence and vigour of common pulse crops across a small range of soils by manipulating baseline soil salinity levels.
• Compare pulse salinity thresholds with other cereal crop types for sensitivity and check current critical levels outlined from previous studies through interpretation guidelines for salinity.

In The Field

Three soils were collected from cropping regions in the northern Yorke Peninsula (from SAGIT projects AGS04922 and ACR3923) with appropriate textures and previous herbicide regimes suitable for the crop types to be grown in the trial. Targeted soil types and textures were sand, loam and a calcarosol.

In a glasshouse experiment, eight levels of soil salinity were generated in each soil type by applying high quality sodium chloride. Additional fertiliser treatments were kept to the minimum required to meet basic nutrition requirements in each soil type to avoid additional salts. Crops assessed were chickpea (CBA Captain), bean (Aquadulce Claudia), lentil (Thunder) and wheat (Scepter) and grown for 22 days.

Crop sensitivity to applied salt was assessed via emergence counts, plant dry weights and measurement of tissue sodium and chloride levels.

Results

Salinity treatments reduced crop emergence in all crops. Critical points where soil salinity decreased crop emergence were determined. Two levels of seed emergence penalties were analysed – 20 per cent penalty of crop emergence and 50 per cent penalty of crop emergence.

Bean and chickpea recorded similar ability to emerge under increasing soil salinity with an Electrical Conductivity converted from an EC_1:5 value using soil texture (ECe) of 8.3-9.4 dS/m for the 20 per cent threshold and 12.2-14 dS/m for the 50 per cent threshold.

Wheat was more tolerant of salinity with an ECe of 10.6 dS/m and 16.1 dS/m for the 20 per cent and 50 per cent thresholds respectively.

Lentil was the least tolerant of all crops with critical levels of soil salinity of 3.6 dS/m and 7.7 dS/m for 20 per cent and 50 per cent emergence penalty respectively.

Crop yields (measured by plant dry weights) were also negatively affected by increasing soil salinity. Thresholds were again calculated at 20 per cent penalty of maximum yield (as relative yield) and 50 per cent of relative yield penalty. Again, wheat recorded the highest tolerance to soil salinity with a 50 per cent reduction in growth occurring at 11.7 dS/m. Lentil recorded the lowest tolerance with 50 per cent reduction in growth occurring at 6.1 dS/m.

Soil type appeared to play a small role in the tolerance of different crops to increasing salinity with the conversion of EC_1:5 to EC_E helping improve fitted toxicity curves.