Modelling water and salinity risks to almonds under sustained deficit and saline water irrigation

V. Phogat, J.W. Cox, T. Pitt
The sustainability of irrigated almonds in arid and semi-arid environments depends on rainfall and adequate irrigation volume and quality. The long-term (2000-2015) evaluation of water and salinity risks to almonds under sustained water deficit and marginally saline irrigation was undertaken to understand how best to minimise any harmful impacts on the trees. A numerical modelling exercise testing the risk of salinity to Riverland almond production found that a scenario of 20% sustained deficit irrigation reduced the average seasonal almond transpiration by 14%. Similarly, a 50% reduction in irrigation, such as those experienced during periods of drought, showed 43.5% reduction in the average seasonal transpiration as compared to full irrigation. These simulated reductions in almond water uptake would have direct impacts upon canopy growth and would likely reduce yield potential. Model output also suggested significant reductions in deep drainage (28-85%) and leaching fractions (21-45%) under deficit irrigation with modelled salt accumulation increasing beyond levels known to affect almond production. A simulation with deteriorating river water quality to the upper threshold at Morgan (ECiw = 0.8 dS m-1) was found to increase root zone salinity even under full allocation. Coupling poor water quality with reduced allocations almost doubled the accumulation of salts in the root zone. Model outputs suggest that almond production is well suited to the Riverland conditions providing that water quality remains below 0.5 dS m-1 and that irrigators retain their full allocations. However, simulations also showed that irrigation induced salinity can rapidly escalate through small changes to either quality or availability of River Murray water. This was particularly the case for simulations that included periods of drought when rainfall offered little to no leaching effect.
Phogat, V., Cox, J.W. and Pitt, T. (2018). Modelling water and salinity risks to almonds under sustained deficit and saline water irrigation. Acta Hortic. 1219, 169-176
DOI: 10.17660/ActaHortic.2018.1219.28
almond, water quality, salinity, deficit irrigation, modelling, leaching

Acta Horticulturae