Water use on organic farms

There is ample anecdotal evidence and some experimental evidence that organic farms use less water than conventional farms. Anecdotal evidence from many growers, especially irrigation users, indicates that organic growers apply water less often than their non-organic neighbours. It is reasonable to assume that this is largely due to increased soil moisture storage in soils well supplied with organic matter, and to common cultural practices on organic farms, such as use of mulch. Mulch may directly limit evaporation from the soil surface and prevents soil from forming a water-resistant crust, but also allows plant roots to more effectively use the top five centimetres of soil, by keeping them cool and protected from bright light. Better water use on organic farms may also be due in part to greater awareness of water management issues by organic farmers, including plant requirements and irrigation programming, and a greater willingness to directly observe soil moisture, or to use remote sensing devices to help manage irrigation.

There is some experimental evidence from surveys of organic farms, such as the one that compared conventional and biodynamic dairy farmers in northern Victoria, conducted by the Victorian Department of Agriculture in the early 1990s. Total water use on biodynamic farms averaged 323 Ml/ha/year, compared to 410 Ml/ha/year for the conventional farms. Although total production on BD farms was less (3,436 litres/cow/year, compared to 4,585) and herds were slightly smaller, irrigations were spaced considerably further apart, at 15 days rather than 9.

We may also reasonably speculate that avoidance of very-soluble fertilisers and long-lasting pesticides on organic farms causes organic growers to contribute less to off-farm water quality issues than their conventional neighbours. Again we could assume that significant awareness of environmental impacts, combined with (at least) annual inspection of environmental performance indicators on certified farms will ensure that the most unsustainable practices do not occur on organic farms and that most organic growers are not causing major water quality issues downstream.