In field monitoring devices – soil, crop and weather

Take home messages

• Calculating plant available water content (PAWC) can be challenging and it can vary from year to year depending on crop growth.
• Normalised difference vegetation index (NDVI) imagery is starting to give a good indication of evapotranspiration change across a field.
• New sensors, such as canopy temperature and 10m towers for inversion monitoring, are providing interesting data.
• Selling of aggregated on-farm data is here and will increase in the near future.
• The Internet of Things (IoT) and LoRaWAN™ networks will impact how these sensors are adopted on-farm.

Content

With an increasing number of grain growers adopting soil moisture probes and weather sensors on-farm, the challenge for service providers is to extract maximum value from these sites. Many growers now have access to at least one weather station and soil moisture probe on-farm with some opting for additional soil probe sites on different soil types.

PAWC

Understanding what a soil moisture probe can actually show a grower can be refined by accurately calculating PAWC, but this can vary from season to season and thus potentially be misleading in some conditions. Typically, a stratified soil core is taken alongside the soil probe and analysed for physical and chemical constraints that may be present, including particle size analysis. This can cost from $400 per sample to $800 per sample depending on the analytes assessed. Most display software can then ‘back calibrate’ the soil probe data to reflect the PAWC figure.

However, observations show that PAWC can be a moving figure depending on timing of planting, early season crop growth, fluctuations in chemical constraints (for example, boron) and heat shock events during spring. Heat shock events can result in plants progressing to senescence more quickly, even though moisture may be available at depth (90cm and below) as the roots do not have the ability to draw moisture up into the plant at the rate it is being lost through evapotranspiration. Thus, a ‘fuel gauge’ view, a graphical display of relative soil moisture, is useful.

Soil moisture mapping

With new satellites being launched every month, there are many imagery providers who are willing to provide their interpretation of NDVI crop growth to assist growers in making farm management decisions. More satellites (such as the Sentinel group) mean that cloud free imagery is becoming available most weeks in the southern cropping region. This allows ‘change’ maps to be looked at to view where crop growth has changed from the last image. Together with real time weather and soil moisture probe observations, software can then carry out whole field crop evapotranspiration calculations. An additional step is to use meteorology forecasts that can look ahead for 10 days to show modelled moisture use by the crop. At the end of the season, with known observations, comparisons can be made of the efficiency of a soil type or crop type to convert rainfall into grain yield, which varies from season to season.

Bureau of Meteorology (BoM) maps of soil moisture that are calculated from weather station observations, as well as using radar satellite data, are available. These are updated regularly. While the maps are interesting to observe, they are quite coarse and are not at the paddock scale where they may be useful for making in field decisions.

Canopy temperature sensors

A canopy temperature sensor looks down onto a crop from a height of two or more metres and generates data showing the temperature of what it is looking at — either the growing crop or stubble or ground after harvest. These sensors are providing interesting data that shows the effects of radiative cooling on cloudless nights, where the crop canopy may be 2°C to 3°C cooler than the surrounding ambient air temperature. Whilst this data is currently not being used to make management decisions (for example, whether or not to cut a wheat crop for hay), it is helping growers understand more about frost. It is providing a quantitative figure, which when coupled with frost duration, can give an indication of frost severity.

The effect of frost on a growing crop is driven by numerous factors including winds, slope and crop stage and therefore the spatial distribution of frosted plants across a field or farm varies significantly. Using a canopy temperature sensor that only senses a small patch on a whole farm needs to be put in context; however, the sensor provides a new method of assessing the impact of frost on a plant. Conversely, they also provide data during summer that shows how much hotter the soil surface is than the ambient temperature, which can affect soil biota.

10 metre towers for inversion monitoring

Off-target spray drift causes problems across the countryside every year and is particularly noticeable during summer when phenoxy herbicides drift sideways and adversely affect grape vines, cotton crops, and the home orchardist. Spray drift is a waste of money, but it also has a significant negative impact on the social license of farm businesses to operate. The Grains Research and Development Corporation (GRDC) and others are working on the complex interaction between wind, temperature and localised topography that cause temperature inversions and how as an industry, we can be better informed about what to do when inversion conditions are present (for example, not spraying).

An air temperature sensor mounted up a 10m tower is the simplest way to monitor if an inversion is present. Similar to how spray operators are now diligent at using Delta T and wind speed to help make decisions about spraying; having a guide to the variation in temperature between the ground and 10m is another tool to use. Many will understand what an inversion event looks and feels like, for example, as the dust drifts sideways on a calm night during harvest, but to have an actual quantitative figure from the weather station readout will reinforce this. There is still a fair way to go before a definitive alerting system is in place that takes into account wind, temperature and geography, but growers have found that a 10m tower is a good place to start.

Aggregated data for sale?

Grain growers and service providers are starting to realise the value of aggregated data from weather and soil moisture sensors on-farm. Whilst these devices are valuable in assisting a site owner with on-farm decision making, aggregating the data with neighbours or across a wider region, can also potentially be of immense value. Agribusiness, the insurance industry and grain marketing, as well as governmental organisations such as the Country Fire Service and Natural Resource Management (NRM) boards, are showing interest in acquiring data that is reliable and that fills in the gaps between BoM sites.

There is still some way to go in regards to the legal agreements between site owners > aggregators > end point users, but the wheels are in motion. Grain growers have various opinions about access to their data and the type of reimbursement that should be offered to a site or device owner. Much of this is being currently played out between the machinery manufacturer and dealer. Australia is watching the US to see how the situation unfolds there. It seems to be common that people do not actually own data; rather they own access to the data. There have been very few cases in Australia relating to ag data ownership before the courts to fully know where the law stands.

Internet of things (IoT) and LoRaWAN™ networks

Much has been said in the past few years about IoT changing the way growers monitor what is happening on their farms. There are a number of regions now that are starting to see the benefits of low power, wide range networks that sensors can connect to. As with the GPS guidance roll out, there will be issues with compatibility and reliability, but the ability to connect sensors to more things and to be able to track these on phones is an exciting prospect.

Modern telemetry systems and display software should have the following features:

• Show current readings (at least every half hour).
• Log historic data so it can be readily referenced (such as spray drift complaint).
• The ability to have additional sensors added in (scalable).
• Data displays to be intuitive for users so that decisions can be made readily.
• Viewing platforms that can be shared readily (via SMS), so there can be multiple users.
• The ability to manipulate data so it can be kept personal for the site owner, or aggregated for business or community benefit (for example, Fire Danger Index alerting).

Useful resources

Agbyte 

Contact details

Leighton Wilksch
Agbyte
0408 428714
leet@agbyte.com.au
@agbyte_leet