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C-Wise did some recent trial work to determine the moisture holding effect of the use of a new category of composts in market garden growing systems.  Market gardeners always have a budget to guide their purchases so any measure designed to lift productivity or save costs has to be of itself cost effective.  

The result of the experiment was a finding that by adding small amounts of a high maturity compost called Humicarb to sand before planting can have a multiplier effect on increasing moisture holding capacity.  Vegetable growers are challenged by cultivating high demand crops in low nutrient, low carbon, sandy soils.  Building the soil's capacity to hold moisture has value in terms of reducing overall water demand as well as offering a buffer for unexpected drought which can arise due to irrigation failures or climate change induced water shortages. 

Baldivis Market Garden growsa range of vegetables in low carbon, low nutrient Spearwood type sand at the junction of Sixty Eight and Eighty roads in Baldivis. Five trial plots of carrots were chosen, each plot was fifteenmetres wide.  One plot had no history of compost product applications and this has been used as the control.

Spearwood sandy soils drain quickly and effectively. Soluble nutrients move through this sand with moisture, meaning that much can be wasted through leaching. Leached nutrients are a major cause of algal blooms in our rivers and waterways.  Summer moisture stress causes herbaceous plants and grasses to shut down growth for days at a time.  Luxury levels of water are applied routinely when plants are under water stress and this has the effect of increasing nutrient leaching.

Sandy soils in the Coastal Plain have a poor moisture buffering ability and when irrigation systems are under pressure during the hot dry summer season and any small difficulty can result in catastrophic moisture stress in crops including carrots. 

Carrots are a significant export crop for WA and most come from the South West.  WA is the nation's largest supplier state and this is largely as a result of our sandy soils.  Eastern States growers have difficulty growing straight carrots due to clay soils which can often blunt and distort the shape of this root crop.  

Slowing moisture movement through the soil profile means plants can make better use of it and the nutrients it contains.  This means thatboth moisture and nutrients inputs can be reduced. 

One result of a more efficient soil is seen as deeper root penetration.  This brings a number of benefits.  Roots are able to access more water and nutrient making for improved growth and resilience in the face of unexpected drought or flooding.  

A 2 mm thick layer of Humicarb was applied to the soil surface, this equates to 20 cubic metres per hectare.   This was then cultivated by rotary hoe to a depth of 200mm before planting. At this rate the Humicarb would have made up less than 1% of the volume of the soil mixture. 

Electronic soil probes were used tomeasure dissolved salts as well as moisture at three different levels. 

The Australian Standards AS4454 - 2012 provided a maturity index for composted products.  The new category of Index 3 Matured composts have gone through a full curing process and are very rich with slow releasing nutrients.  There is no continued decomposition nor unpleasant odour production. These materials provide the most effective improvements in long term moisture savings and stimulate biology to provide all the requirements for healthy productive plants.  This biology delivers increased nutrients and moisture as well as providing protection against pests and disease.

The bottom line result was that the addition to sandy soil of 1% by volume of C-Wise Humicarb can yield a 23% improvement in water holding capacity.