Quantifying spatial variation in pasture and crop biomass can help to direct management practices and improve farm productivity, through accurate and informed movements of grazing rotations, crop and pasture nutrient management and yield production. Visual pasture assessments are often subjective, and require a degree of expert knowledge/experience. Quadrat-based plant harvesting determinations of biomass is labour intensive and costly when accurate quantification of pasture and crop variability over large areas is required. Furthermore, quadrats of 1m² or less are not easy to relate to remotely sensed images with spatial resolutions ranging from 4 to 400m². Active optical plant sensors that measure the red and near-infrared radiation reflected from the vegetation canopy offer the potential of deriving objective estimates of the photosynthetically-active plant biomass and may also hold the key to quantifying biomass over large areas with high spatial resolution. Crop Circle™ (Holland Scientific) is one example of an active plant sensor that measures red and near infrared light reflected from the canopy/soil matrix. In this paper we present the results of a project to assess the accuracy of Crop Circle™ for biomass assessment in a variety of agricultural environments including: native, improved and irrigated pasture; and forage and cereal crops.

Nutrient-use efficiency is a key issue for grazing systems in Australia. Spatial variability in soil pH and nutrients at the sub-paddock scale may affect the efficiency of utilisation of, and provide an opportunity for, site-specific management (SSM) of fertiliser and soil ameliorants. However, there has been little research exploring the potential for SSM in grazing systems. This study examines the spatial variability of soil test pH, phosphorus (P), potassium (K) and sulfur(S) in two typical pasture fields (a native and an improved) on the Northern Tablelands of New South Wales and evaluates the potential for SSM based on a comparison with critical values. In both fields, the overall paddock mean from a grid survey containing >80 samples for pH, P, K and S (0-10 cm) exceeded the critical values, suggesting that the addition of fertiliser or lime was not required. However, considerable sub-paddock-scale variability was observed, with CV ranging from 35% to 66% for the key nutrients (P, K and S). The Sprengel-Liebig Law of the Minimum was applied to evaluate the proportion of each field constrained by one or more soil characteristics. Up to 55% of the improved paddock and 78% of the native pasture was potentially responsive to amendments. The results of this study suggest that SSM of fertilisers and ameliorants could provide substantial improvements in productivity and possibly reductions in fertiliser use. The development and application of appropriate systems and tools to effectively quantify this spatial variability remain a challenge, coupled with management strategies that optimise the placement of amendments and account for the variability in other production limiting factors.

Spatial monitoring of livestock and their environment has been a rapidly expanding area of research in Australia, New Zealand and around the world over the past few years. Furthermore, systems for commercial deployment are currently being developed to enable producers to make use of this technology. It's an exciting time to be a researcher; however we need to be aware of the many challenges we face if these technologies are to be successfully adopted by industry. Communication between technology developers, researchers, funding bodies and producers is fundamental to ensuring a coordinated approach to research and to ensure practical outcomes for industry. This is one of the primary functions of this symposium, bringing together all these parties to share knowledge and build working relationships! This symposium has a diverse range of speakers and, as a direct consequence of discussions from last year's GPS Livestock Tracking Forum, keynote speaker Toby Patterson will provide insights into animal movement and behavioural modelling in ecology, an allied research area from which the livestock industry can learn a great deal. So whether you are a researcher intent on using the technology to understand the mysteries of plant and animal interactions, or a producer just wanting to know where your cows are, we hope you will glean something useful from the event!