By: Gary Kruger, P.Ag - Irrigation Agrologist
Irrigation scheduling is the process of determining the frequency and amount of irrigated water required for application to a growing crop.
Good water management provides many benefits including higher yields, better-quality crops, conservation of water and efficient uptake of nutrients. The goal of irrigation scheduling is to apply the proper amount of water at the proper time to meet crop needs without flushing soil moisture and nutrients below the rooting zone. The water must be applied slow enough to allow the soil to absorb the moisture without ponding of water on the soil surface. Ponding leads to runoff of water into depressions of the field.
Soil texture is an important factor to consider when determining the rate and quantity of irrigation applications. Texture determines how quickly water will soak into the soil profile and how much water the soil will hold. Coarse textured soils will have more rapid infiltration rates but will not be able to hold as much moisture. Conversely, heavier textured soils have lower infiltration rates but higher capacities for holding moisture. Irrigation scheduling seeks to maintain the reservoir of water in the crop rooting zone above 50 per cent of the maximum storage capacity of the root zone.
It is important for irrigators to monitor soil moisture in order to ensure that it is applied when needed. Numerous techniques have been developed to assess the soil moisture status in a field. However, most producers still prefer the traditional hand feel method to determine the soil moisture status. This involves the producer using a hand auger or soil probe to take a core sample and determine the moisture content by feeling the soil.
Irrigators can also support their on-site field moisture measurement with rainfall data and use a check-book approach or a computer modelling program to predict crop water use. This allows the irrigator to predict moisture needs for the coming week and schedule water accordingly.
An updated version of the Irrigation Scheduling Manual has been published by the Ministry of Agriculture. For weekly crop water use updates throughout the growing season follow @ICDC_SK on twitter.