| Monitoring for Broadacre Production | ||
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| Why Do It? |
Soil moisture monitoring developed around irrigated crops, with soil moisture probes being used to improve the scheduling of irrigation - saving water and improving yield and/or quality. Whilst working for SANTFA in the 2000's, Greg Butler came to the realisation that the probes could also be used in a dryland farming environment. His work was part of the development of techniques to minimise soil disturbance, improve soils and improve water use efficiency and opened up a whole new industry sector.
In dryland farming, moisture comes only from rain and that is an input that farmers have no control over. But the level of moisture held in the soil profile - in conjunction with expectations of future rain - control the crop's growth and ultimately yield. Prior to this, farmers used their intuition and the occasional dig to estimate how much water was available, but this was ralrely better than guesswork. A soil moisture probe helped take the guesswork away. Whilst irrigation managers are making decisions on a daily basis, broadacre farmers tend to use the probes at critical growth stages - making critical, one- off decisions. A poor decision from an irrigation manager may ultimately have only a small impact, but one poor decision from a dryland farmer can cost tens or hundreds of thousands of dollars. But the soil moisture probe does not do all the work: it must be conencted to a solar/battery powered telemetry unit, which reads the sensor at regular intervals and sends the results to a remote software platform, form where it can be viewed. The real power comes from being able to see those "near real-time" readings in the paddock when driving your machinery. |
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| Wet and Dry Years | The one thing that farmers can be assured of, is that each year will be different. Sure there are similarities between years and it helps to be able to classify each according to its decile level (which of the 10 bands does the current year fall in to) but there is no guarantee that the rain pattern of the last 3 months will dictate the pattern of the next (just as investment companies have to declare that past returns are no guarantee of future returns). As a result, cropping decisions must be made using risk management techniques. You may not be able to predict how much rain will come in the next 90 days, but if you know how much moisture is stored in your profile, you can make informed estimates of what the likelihood of achieving a certain yield is. Fertiliser is one of the most expensive inputs - in both its cost of purchase and the costs to apply it. If the profile is dry and there is little chance of decent rain, adding more fertiliser is a waste. But if the profile is holding plenty of moisture, the fertiliser will give a dramatic yield boost. There are plenty of examples of farmers using their probes to make successful fertiliser management decisions. |
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| Soil Temperature | All of the commonly used soil moisture probes also measure soil temperature. Many nutrients can't be taken up by plants unless the temperature is above a threshold. Similarly, crops won't germinate unless the soil temperature is above a minimum level. Which means that the soil temperature data which comes as an adjunct to the soil moisture data, can also be used to improve decision making. |
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| Adding Sensors | If rain is the primary source of water for crop growth, then it makes obvious sense to measure it. And in recognition of that, the first thing that we began to add to soil moisture probe sites in broadacre agriculture, was a rain gauge. See our Rainfall Sensors page for more details, but tipping spoon and tipping bucket rain gauges are cost effective and reliable. Because they use a small reed-switch to close a pair of contacts each time 0.2 or 0.25mm or rain falls, they are cheap to interface to. And just about every telemetry unit on sale, has pulse inputs. Because the in field telemetry unit is sending data regularly (typically every 15 minutes) you can monitor rain as it happens. But more importantly, you can create additional summaries: such as daily or weekly rain and the growing season rain. |
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| Weather Sensors | The next obvious step was to add sensors for air temperature and relative humidity, because it makes sense to understand the conditions in which the crops are growing. From there, it didn't take long for people to start to request wind sensors as well. Which meant that before long, a broadacre monitoring station could carry a soil moisture probe (tyically 80 to 120cm), which also returned soil temperature, a rain gauge, temperature and humidity sensor and a wind speed and direction sensor. Some went further, adding a solar radiation (sunshine) sensor as well. With all of this in place, a probe site becomes a full automatic weather station. |
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| Doing More with the Data | Once you start to collect all that information, you open things up to a range of other questions, the most pertinent being, what can I do to add value to the data - to make it more useful. And this is where we move into the field of modelling: using the sensor readings to calaculate other parameters, which are in turn used to aid decision making. | |
| Fire Behaviour Index | In most jurisdictions, farmers operate under a Code Of Practice, which specifies that if conditions were such that if a crop fire broke out, it would not be able to be controlled, machinery movements must cease. In the first implementations of the Code, the fire risk was calculated using data from the nearest Bureau of Meteorology weather station. If the calculated Fire Danger Index (FDI) exceeded the agreed threshold, all farmers in the district would cease operations. Text messages were the primary means of delivering alerts to farmers. The initial Grassland Fire Danger Index has now largely been replaced with a mor representative Fire Behaviour Index, but it is still calculated from the same weather paramaters: air temperature, relative humidity and wind speed. Situations occur where conditions on an individual farm will still be favourable when a district wide alert is called. So the Code allows for farmers who installed their own local weather station, to continue operating until their station reaches the alert stage. Having a weather station which can record all the raw sensor readings, make the calculation of the FBI and save the results, gives owners the confidence that if a fire does occur, thet they have safe, verificable records fo the conditions at the time. |
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| Delta-T | Delta-T is a measure of the humidity of the air and was developed before electronic humidity sensors became common place. It is a measure of the difference in temperature between a bulb thermometer in the air and a second one whose bulb is wrapped in a wick which is dipped in water. Evaporation cools the air around the wick, which reduces the temperature seen by this "wet bulb" thermometer. The lower the humidity, the drier the air and hence the higher the avaporation rate and higher the Delta-T. Even though it is now very easy to measure relative humidity directly, many chemical labels still define the safe application limits in terms of the delta-t rather than the relative humidity. But now, rather than measure Delta-T with two thermometers, it is calculated from the measured values of temperature and relative humidity. |
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| Inversion Monitoring | An inversion occurs when the air at ground level cools faster than the air above it. Which leaves a layer of cold air, trapped below a layer of warm air. Normally the temperature will decrease as you move higher above ground level. But in an inversion, the temperature at height will be warmer than that below. Inversions represent a risk to farmers in two ways: firstly, they often accompany frost, and frosts can damage plants causing a reduction in yield. Secondly, in an inversion event, any chemicals in the air, will be trapped under the layer of warm air and can't disperse. They can move laterally over large distances, damaging other plants as they do so. It is thus very important not to apply chemicals when an inversion is present. In agriculture, an inversion is said to exist if the temperature measured by a sensor at a hieght of 10m is higher than that of a sensor at 2m height. The presence of an inversion can be detected either on the telemetry unit of the weather or in the software platform used to view the data. Alerts can then be notified by text or email. At a more complex level again, it is also possibe to distinguish between an inversion which will cause harm to crops and one which will not. |
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