Soil Management

The two A horizons are somewhat unusual in that they are; dense, sodic, have low soil carbon, and low hydraulic conductivity, yet have remarkably good water retention properties. Due to the absence of roots in the B22 and B3 horizons, and poor moisture retention properties of the subsoil, it should be considered that the trees are really utilising moisture and nutrients from the two A horizons. Consequently, this soil profile should be thought of as only being 37 cm deep. Regardless of this limitation, the two A horizons together hold 47.7 mm readily available soil moisture and have a plant available water content of 94.7 mm. In relation to irrigation, the refill point for the A1 horizon is between 20% (50 kPa) to 16 % (100 kPa) soil moisture. However, the soil has a number of chemical limitations. The CEC is low throughout the profile which indicates this soil has poor ability to retain and supply nutrients, and potential exists for nutrients to leach beneath the root zone. Fertilizer application is advised to be small and frequent to avoid leaching. Apple trees are sensitive to salinity in which research indicates yield losses occur at salinities greater than ECe 1.7 dS/m. As the ECe in the A1 horizon was estimated at 4.3 dS/m, and 2.6 dS/m in the A2 horizon yield and growth losses are expected. The whole soil profile is also strongly sodic with ESP values ranging from 16 to 23 % which promotes hardsetting (and thus the high bulk density), loss of soil structure, dispersion of clays, tunnel erosion, leads to blockage of subsurface drains and reduces availability of calcium and magnesium. As the A1 horizon is slightly alkaline (which may be due to lime application ?) further application of lime will not become available, as such application of gypsum is recommended. Subsurface drainage is not recommended in these soils. The low soil carbon content is also concerning, management should consider increasing levels of carbon residues being applied to the tree row, including grass clipping, manures and mulches, other plant residues.

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