Improving irrigation practice for growing vegetables on sandy soils Rohan Prince and Robert Deyl

Background Efficient irrigation is required to maximise yield, water and nutrient use efficiency and therefore, often profit An irrigation system is only as efficient as the way it is operated Many tools are available to help predict the water movement in soil e.g. Dripgame and Wetup (CSIRO or CRC for Sustainable Sugar Production) Our sandy soil have an average of 95% coarse sand.

Root zones of crops Crops have an effective root zone where they remove the majority of water and nutrients This root zone is determined by crop type, soil type and structure, and cultural practice Pictures courtesy of DAFWA

Water movement Water movement is influenced by soil types, structure, irrigation method and volume and cultural practices What happens on the surface is not what always happens below the surface Blue dye test shows you the movement of water through soil Zwart, P, ‘Tracing Irrigation Water with Blue Dye and a Shovel’ Ministry of Agriculture, Food and Rural Affairs. Ontario. Simonne et al, ‘How to Conduct an On-farm Dye Test and Use the Results to Improve Drip Irrigation Management in Vegetable Production’. Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences,University of Florida HS980.

Results on sand on the surface On the soil surface the spread of the dye looked good 0.3 L water applied resulted in 20 cm radius from the dripper 2.0 L applied resulted in 30 to 40 cm radius indicated 4.0 L applied resulted in 40 to 60 cm radius indicated But this result was only skin deep

Results on sand below the surface Depth and spread of dye in trial Volume applied (L) Application rate L/hrSpread (cm)Depth (cm) >

Daily water application (mm) = Crop factor x Epan Scheduling using evaporation Crop factor curve for irrigating tomatoes on sand Weather data from DAFWA remote weather station network Date Air Temp Degree C Relative Humidity Soil 4cm Solar Radiation Wind Speed Total Rain Total Evap MinMaxMinMaxMinMaxtot. kJavg. km/hrmm 17-May May May May May May May

The Vegetable Irrigation Scheduling System (VISS)

Scheduling using evaporation Weeks after planting Proportion of Evaporation replacement tomato demonstration crop irrigation

Tools

Soil moisture monitoring Fine tuning, not scheduling 0–15 cm15–30 cm40–70 cmDepth Soil Moisture (%) Good PracticeGrower Practice

Demonstration trial 2 weeks after transplant 8 weeks after transplant 6 weeks after transplant 4 weeks after transplant Good Practice scheduled using VISS left of each picture Vs Grower Practice right

Grading and pack out Nutrient NPKCaMgS Good Practice Grower Practice Grading Medium-Lg.Medium No1MediumSmall-MedLargeRed RipeCocktailGreenWaste Good Practice16%24%15%6%4% 3%4%16% Grower Practice13%23%17%8%2%3%4%7%13% Nutrient applications

Demonstration Results Good Practice compared with Grower Practice Similar yields 108 t/ha compared with 105 t/ha 40% less water applied 983 mm compared with 1651 mm 73% less drainage 250 mm compared with 950 mm Similar plant water use 733 mm compared with 701 mm 45% less leaching of nutrients 265 kg/ha compared with 477 kg/ha

Thank you and the funding bodies