Mapping Plant Available Water-Holding Capacity (PAWC) using electromagnetic (EM) and Radiometric Surveying.
Growers Rob and Dan Dempster are working with Wheatbelt NRM on a three year trial to evaluate the use of variable rate technology (VRT) for optimizing nutrient and water use efficiency relative to traditional farming practices. The aim is to increase yields and reduce input costs, particularly on unproductive land.
In order to apply VRT, the Dempsters have used Precision Agronomics to conduct electromagnetic and radiometric surveys to map two paddocks. The mapping identifies the different soils and their corresponding Plant Available Water-Holding Capacities (PAWC). Soil testing is additionally undertaken to baseline and compare the nutritional status of the soil zones.
The soil zonation mapping is then incorporated with yield data and Yield Prophet modelling to identify the optimum input levels required for each zone. This practice allows the Dempsters to deliver targeted inputs at the levels required to maximise yield across the soil zones and avoid spending on nutrients that do not further increase yield.
Crop yield is of course influenced by many factors, some that the grower can control such as fertiliser and application and others the grower cannot, such as the weather. VRT uses precision agriculture to provide the grower with greater insight into optimum input application however yields may not increase as anticipated if other limiting factors are present.
In order to understand how the Dempsters trial is being effected by the season, Wheatbelt NRM is conducting monthly soil moisture testing using an Aquaterr Soil moisture probe throughout the growing period. This gives the percentage of soil moisture per cubic metre. These values are important to determine if there is sufficient soil moisture for the plants to grow. The moisture required for plant growth differs for each soil type; for example heavier soils require a higher soil moisture percentage than in sand.
Preliminary results for 2017, indicate that majority of the soil moisture results are good (between 62 & 63%) however one site was recorded at 25% which is much lower. This site has pale deep sand which means that the % of soil moisture does not need to be as high as soils with more clay content. This particular sample point has been identified as having a high mean yield (t/ha).
For anyone that would like to look at their own soil moisture levels, Wheatbelt NRM has a soil moisture probe available for hire free of charge. Just email Leigh Whisson on lwhisson@wheatbeltnrm.org.au or telephone 08 9670 3136.
By the end of the growing season the soil moisture readings should correlate with yield at the profit points adding further rigour to results from the use of VRT.
The Dempsters trial is supported as part of Wheatbelt NRM’s Trials and Demonstration project funded from the Australian Government’s National Landcare Programme.