Soil management Tony Pitt

Six years of soil testing In 2005/06, recycled water use was fairly minor – just 47 farms with more than 1 ML/ha. For 2006/07, recycled water underpinned crop production for Werribee For the following 4 years, recycled water was by far the dominant source of irrigation water for the district. The salinity of the recycled water is 1700 to 2300 EC –1,700 uS/cm to 2,300 uS/cm – units used for irrigation water –1.7 dS/m to 2.3 dS/m – units used for soil water.

Average surface soil salinity is back to baseline values District average chloride has fallen by 40 % in 12 months Sodium values however are unchanged Sodicity is apparent when collecting soil samples Winter rainfall better but still below average In 2010

The Red Brown Earth soils of Werribee South are very forgiving and very responsive to rain The late summer and autumn period are the most important times for salinity management For every irrigated crop some leaching is required A negative impact of rainfall on sodic soils is the dispersion and sealing of the soil surface Short term

Natural leaching from rain will remove the surface salinity provided the soils are kept permeable Rain or low salinity water doesn’t improve sodicity Sodicity requires continuous on-farm management Gypsum dosing of the irrigation water could be better option than broadcast gypsum Long term

Adding calcium –Gypsum broadcast –Gypsum added to water –Other calcium fertilizers Sodicity management

In summary Werribee South soils can handle 2,000 to 2,200 EC water for a season or two with very good farm management Evidence from six years of soil testing indicates 1,300 EC –1,800 EC, with minimal leaching should be sustainable provided soil sodicity is kept under control Above 1,800 EC leaching has to increase and be planned for each crop Lower salinity water may increase the problems of surface sealing and poor aeration On-going sodicity management important