The utilisation of gamma ray spectrometry, a soil mapping technology, to improve dryland crop production

[Truncated abstract] Annual and perennial crop production systems can be enhanced by the incorporation of spatial information to improve decision making. In broad terms, this is referred to as precision agriculture. Examples of specific applications include the application of variable fertiliser rates in an annual cropping system and the site selection of perennial plants for establishing a perennial cropping system. These specific applications are termed "site specific management" within the precision agriculture literature. Site specific management requires knowledge of the spatial variation in site conditions. The growth of annual and perennial crops can often be related to intrinsic soil or landscape properties, such as the capacity of the soil to store moisture and nutrients. This can be represented by a number of parameters (depending upon the site) such as soil texture, soil (rooting) depth or a combination of both, in plant-available water capacity. There are significant difficulties in spatially defining the soil-water holding and soil-fertility properties at the farm scale. Gamma ray spectrometry (radiometrics) is a soil sensing technique that has the potential to improve the prediction of these properties in a cost effective manner. t ... Alternatively, when benefits were assessed under conditions estimated from the wheat yield map, the benefit was $31/ha, under non-optimal N rate conditions. The utility of the radiometric based information was dependant upon the season and magnitude of plant available Thesis abstract iii water capacity. The use of radiometric data to improve N-management decisions has the potential to increase gross margins and is worth further investigation. In summary, radiometrics collected at sufficient resolution can reliably depict some of the soil factors related to plant growth for grain and woody crops at the scale suitable for precision agriculture. For deep rooted crops, radiometrics is useful when the near surface properties mapped are correlated with critical soil properties within the root zone. However, the successful calibration of soil or plant properties with radiometric data is dependant upon the regolith properties of the surveyed area. Where suitable, radiometrics can improve crop production through more efficiently identifying, sites for woody crop establishment and N fertiliser rates for wheat management. To fully evaluate the utility of radiometric data to dryland agriculture, an evaluation that covers other site conditions is recommended. Other recommendations include further testing of bio-economic farm models to assess the sensitivity of site specific management and a probabilistic, value of information analysis.