We all budget to make the best use of a resource, be it money, time or an asset like water. Water budgeting is an essential part of risk management on farms. We use water budgeting to try and foresee any risks with our water use decisions and plan to minimise any negative aspects of our decisions.
Irrigators need to budget their water so that they can reduce or eliminate the risks of not having enough to water their crops. Water budgeting is generally done at the beginning of each irrigation season when you estimate the amount of crop you can grow with the available water (particularly relevant for annual crops) or determine how much water you will need to grow an intended area of crop (particularly relevant for perennial crops).
The amount of water that you can supply to a crop is determined by crop water requirements, irrigation system efficiency and the availability of water.
The following formula can be used to estimate the area of crop that can be irrigated.
Area = Irrigation available + Annual crop water requirement X Irrigation System efficiency.
The estimated Efficiencies of various Irrigation Systems are shown in this table.
Here is an exercise to test your understanding of water budgeting.
You are growing a crop of maize in a paddock with a travelling irrigator and you have 60ML of water available for the season. Your irrigation system is about 80% (0.8) efficient.
From your research, you determine that maize needs about 10ML of water per hectare in a season. In an average (or median) season rainfall in your area will provide about 3ML of water per hectare to the crop. This means that your annual crop water requirement from irrigation is about 7ML per hectare.
From these figures, calculate the maximum area of maize that you could irrigate.
Irrigation Available 60 ML
Crop Water requirement 7 ML
System Efficiency 80% (0.8)
Area = B / C X D
Area = 60/7 X 0.8 = 6.86 ha
Thus the maximum area that you could sow using your allocation of water would be 6.9 ha.
