Monitoring soil moisture in broadacre cropping

Saddleworth Reinstall

Monitoring soil moisture in broadacre cropping

EnviroSCAN Plus systems were installed into a range of cereals crops in different soil types around South Australia to monitor the dynamics of water content changes during the growing season, and to develop strategic management mechanisms for dryland growers.

During the very first year of monitoring, one grower noticed that soil water reserves in the middle profile from 20 – 50cm depth were very low late in the season (Graph 1). The crop was mainly using water from a depth of 70 cm. With little prospect of impending rain in the short to medium term the grower made the decision to withhold a planned nitrogen application, preferring to accept a lower yield.

Within days of making this decision, the crop showed signs of significant water stress (wilting and browning). In the grower’s own estimation, the planned fertiliser application would not only have been a waste of time and money, but would also have amplified the wilting and browning, potentially inhibiting the crop’s recovery even further.

At another site (Graph 2), seasonal soil water data from 2 1/2 successive years was plotted one above the other in IrriMAX to demonstrate the marked differences in the timing of rainfall events, and the way in which it was distributed within the soil layers.

Graph 1: Each line in the chart represents a sensor at a different depth. The top line shows the 10cm sensor and is useful for monitoring effective rainfall.  The sensors at 70cm and 100cm allow us to see root zone development, and the exact moment water is taken up by the roots.
Graph 1: Each line in the chart represents a sensor at a different depth. The top line shows the 10cm sensor and is useful for monitoring effective rainfall. The sensors at 70cm and 100cm allow us to see root zone development, and the exact moment water is taken up by the roots.
It was possible to make a prediction that there would be sufficient water reserves at depth to carry the crop through to a high final yield.

Monitoring of the water content with EnviroSCAN Plus probes within the soil profile is helping cereals farmers to make better informed decisions regarding those aspects of crop growth under their direct control.

This enables them to develop management strategies to reduce their level of risk and make savings wherever possible.

Graph 2: Summed data from EnviroSCAN probes plotted in IrriMAX shows how water reserves can be used to predict crop yield.
Graph 2: Summed data from EnviroSCAN probes plotted in IrriMAX shows how water reserves can be used to predict crop yield.
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