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Matching Nitrogen To Plant Available Water For Malting Barley On Highly Constrained Vertosol Soil
1J. A. Delgado, 2B. Sauer, 1C. N. Guppy, 4M. G. Trotter, 2D. W. Lamb
1. USDA Agricultural Research Service Soil-Plant-Nutrient Research Unit
2. University of New England
3. CRC for Spatial Information and Precision Agriculture Research Group The University of New England
4. University of New Engalnd

Crop yield monitoring, high resolution aerial imagery and electromagnetic induction (EMI) soil sensing are three widely used techniques in precision agriculture (PA). Yield maps provide an indication of the crop’s response to a particular management regime in light of spatially-variable constraints. Aerial imagery provides timely and accurate information about photosynthetically-active biomass during crop growth and EMI indicates spatial variability in soil texture, salinity and/or moisture content. The output of aerial imagery and EMI is often inextricably linked to crop yield.

Spatial variability in the yield and quality of barley (Hordeum vulgare) provides challenges for growers wishing to avail themselves of premium markets associated with producing malting quality (low protein) grain. On a trial farm in northern NSW, Australia, rigorous soil testing and EMI surveying was used to create a ‘soil class map’ with highly variable apparent electrical conductivity (ECa) due to extreme levels of chloride below 60cm. High chloride reduces plant available water (PAW) with anecdotal evidence of significant yield losses and/or high protein grain, especially in seasons with less than average rainfall. We investigated the potential use of in-season EMI sensing to monitor spatially-variable PAW, high resolution aerial imagery and the variable application of in-season nitrogen to optimize the match between spatially-variable PAW and grain quality. Results so far confirm ECa soil class maps are a useful method to interpret spatially variable water demand in dryland grain production. The combined analysis of yield maps and high resolution aerial imagery indicates efficacy of soil class management as a function of yield and quality. Results also suggest that variable rate applications of in-season nitrogen is a suitable practice for reducing variability in barley quality on spatially variable soil types with variable PAW.
Keyword: Plant available water, malting barley, precision agriculture, EMI, aerial imagery
J. A. Delgado    B. Sauer    C. N. Guppy    M. G. Trotter    D. W. Lamb    Precision Nutrient Management    Oral    2010