Water is the key for optimising or maximising plant growth. It is needed in much greater quantities than any other input, carries all the nutrient in solution to the plant leaves for photosynthesis and is instrumental in cooling the leaves so as plant growth is not constrained.
Rainfall is the most variable facet of weather, more so than evapotranspiration (ET). Rainfall alone does not supply sufficient moisture for plant growth and can be a major risk for growers. Irrigation is necessary to supplement soil moisture to optimise production.
Not only is irrigation essential, so is the proper management of the irrigation. Rarely during any growing season on any soil type in any region will irrigation not benefit crop yield and quality Soil moisture monitoring (make this a link to (Soil Moisture Monitoring) is the key to ensuring good irrigation management decisions are made to maximise the benefit of irrigation.
Irrigating farmers are most likely to get behind when irrigation is too late starting and/or during a westerly weather cycle. Starting too late can result in “never catching up” until there is a significant rain. Rainfall only allows a catch up on soil moisture content, yield loss is never caught up. During windy westerly conditions water use by crops can be as high as 7–8mm, much greater than the ability of the irrigation system to keep up. Once soil moisture drops below the critical deficit (the soil moisture content when plants struggle for water) plant growth is affected. Production will decrease by 0.2–0.3% for every potential mm transpired (the mm/day used before reaching the critical deficit) below critical deficit. For example, pasture production could fall from 70–80kg/ha/day dry matter to 50–55kg/ha/day dry matter in 7-10 days if irrigation is too late or unable to be applied.