Sandy soils are the main types on the Swan Coastal Plain from Eneabba to Busselton. Phosphorus fertiliser should be applied before planting on all but deep grey sands. The rate of phosphorus should be determined from soil test results.
Trace elements and magnesium should also be applied before planting if not applied in the previous 12 months. There is a wide range of fertilisers available for post-planting use. Discuss the best options for your situation with your local advisor or consultant.
Urea and potassium fertilisers are commonly applied to the soil or by fertigation through trickle irrigation or sprinklers.
Loamy, gravelly and clay soils
In their natural state, loams, gravels and clay soils (found at Geraldton, Jarrahdale and in the south-west of Western Australia) have little available phosphorus. Soil testing before planting should be used to determine that rate of phosphatic fertiliser to apply before planting. Post-planting nutrient programs will vary with soil type and cropping history. Discuss crop nutrient needs with qualified advisors or consultants.
Alluvial soils are common in the Carnarvon vegetable growing area. These soils contain adequate phosphorus, potassium and many other nutrients, and only nitrogenous fertilisers may be needed.
Starting three weeks after transplanting, apply 35kg/ha of urea every two weeks, which may be injected into the trickle irrigation system. Crops planted in August respond to foliar sprays of calcium nitrate at 2g/L.
Capsicums need uniform soil moisture conditions for high production. Dry periods may cause shedding of flowers and young fruits, and blossom end rot on the fruit. During hot weather, water crops in sandy soil twice daily. In warmer months, apply three-fifths of the water in early to mid-morning and two-fifths in early to mid-afternoon. In cooler months, apply all of the water in early to mid-morning.
Water used for irrigation should preferably contain less than 1000 parts per million (ppm) of total dissolved salts, or have an electrical conductivity (EC) reading of less than 180 millisiemens per metre (mS/m).
Apply water to replace 130% of evaporation. To calculate how much water a crop grown on a sandy soil needs refer to the ‘See also’ links on this page.
An increasing area of capsicums is being watered by trickle irrigation in Perth. When combined with black plastic mulch, this results in fewer weeds and a saving in water. It is also useful for capsicums under cloches to increase soil temperatures in cooler weather. However, trickle irrigation may result in more mites and powdery mildew on the plants compared with using sprinklers. There may be two rows of capsicums per cloche, each with its own row of trickle irrigation.
An evaporation replacement factor of 60-90% is suggested for trickle irrigation of capsicums in Perth. Growers may also plant a double row on black or reflective plastic mulch, without clear polythene protection, and water by sprinkler irrigation from planting onwards.
When using trickle irrigation and polythene mulch, water at 25% daily evaporation replacement rate during early growth and at 40–50% of daily evaporation replacement rate from flowering onwards. Tensiometers may be used for irrigation scheduling to apply irrigation at a suggested soil tension of 30–35 centibars (cb).