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NOTE: To get off this list, send email to majordomo@aqua.ccwr.ac.za with the body of the message containing the line: unsubscribe sowacs >If so can some one tell me how did they calculate the Field capacity of the >soil in volume (cm3) rather than percentage which what the sensor reads. The total water content in the soil (over a given depth range) can be calculated by multiplying the % moisture (VSW%) by the distance between sensors (integration using Simpsons rule) TotalSoilWater = Sigma( VSW% * DepthIncrement ) Changes in total soil water gives the depletion rate (mm/day). This should be actual crop daily water use (DWU), after making allowances for through-drainage, horizontal flows and surface evaporation. The active rooting depth can also be found from soil moisture measurements - the depth below which the soil moisture is constant. Field capacity is found from the wettest reading above which through-drainage starts to takes place. This will be indicated by an increase in the depletion rate and an increase in the measured soil moisture below the normal rooting depth. Field capacity will be dependant on soil type, but can vary during a growing season. The stress (or refill) point is indicated when the daily water use falls and the crop starts to extract water at a greater depth. This will be indicated by a decrease in the soil moisture below the normal rooting depth. The stress point is a function of soil, crop and stage in the season. Infiltration rates cannot be calculated from just soil moisture, because under steady-state conditions there can be flow with no changes in soil moisture. However, infiltration and through-drainage amounts can be estimated if the amount of water applied is known. If the amount of water applied (irrigation or rain) is recorded, the effective gain and the irrigation efficiency (effective/delivered) can be calculated. These can then be totalled over the season to give total water used by the crop (Integrate(DWU)), and the total water use efficiency. There are many hundreds of growers, throughout the world, who routinely meaure soil moisture in order to calculate the irrigation requirements of their crops. At no extra cost the same measurements can be used to calculate water use efficiency . ------------ Trevor Finch Research Services New England 8/16 Nicholson Street Balmain, NSW 2041 Australia T: +61 (2) 9810 3563 F: +61 (2) 9810 3323 mailto:support@rsne.com.au http://www.rsne.com.au --------------------------