Are soil moisture probes worth the investment

Background

Soil moisture probes have been used successfully for decades in irrigation and are essentially a must have piece of equipment to maximise water efficiency and productivity. There use in broad acre dryland farming is increasing but of interest is whether they are able to provide a return on capital and assist with critical on farm decisions?

Probes are starting to become more common place but there still seems to be a good deal of confusion around how to utilise the information to make money.

Discussion

There are a number of ways to utilise probes in dryland agriculture to assist in making better decisions. 

Key ways of achieving this are by knowing:

• How much water is in your ‘bucket’ at critical times of the year (pre-planting and spring)?

• How effective rainfall events have been at pushing moisture to depth?

• What depth your crops are able to access moisture from?

• Whether nitrogen or moisture is likely to be your greatest limiting factor?

• Whether sub-soil constraints are stopping complete moisture draw down.

Understanding these factors will assist in making smart decisions around nitrogen management, risk mitigation, marketing, hay and true crop potential.

Key factors to consider when looking to install a soil moisture probe:

• Is the soil type you are looking at representative of other areas of the farm?

• The most valuable information is gained at the end of a full crop rotation so view installation as a long term investment. Learning what the extraction limit is for each of the crops in your rotation is a critical piece of information.

• Ensure that the installation methods suit the soil type (ie slurry or direct install). Slurry installs work well in clay but tend to produce poor data in sand.

• Is the system scalable? Determine whether you may want to add other sensors at some stage, ie temperature sensors, weather stations, etc.

• What is the software package being offered? Does it suit how you want to view the data? Do you want to view the data on a mobile device or from your desktop computer? Are there multiple people who need to login and view the data?

• Is there assistance available to help interpret the probe data? Data interpretation is the most critical factor once you own a soil moisture probe. Ensure that you have access to the expertise required to decipher what the probe graphs are telling you. Data expressed in a simplified version will lead to simplified interpretations and poor decisions. Take the time to learn what the graphs are telling you and make informed decisions.

Knowing what depth your crop is drawing moisture is a key factor in being able to maximise crop yields. A study by Dr John Kirkgaard has shown that moisture available to crops below 1.25m after anthesis has the capacity to produce up to 60kg/ha/mm compared to 30-40 kg/ha/mm for water used at all other depths before this time. This is a critical piece of information to know and also understand how it fits in with the standard ‘French Schultz’ model at 20-25 kg/ha/mm which has been the baseline figure.

Useful resources

J.A. Kirkgaard, J.M. Lilley, G.N. Howe and J.M. Graham. Impact of subsoil water use on wheat yield. CSIRO Publication

Soil moisture sensing technologies in broad acre crops.

Contact details 

Shane Oster
Alpha Group Consulting Pty Ltd
6 Dugan St Keith SA 5267
0419 400 461
shane@thealphagroup.com.au