Determining the Causes of Spatial and Temporal Variability of Wheat Yields at Sub-field Scale Using a New Method of Upscaling a Crop Model |
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Authors: | M T F Wong S Asseng |
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Institution: | (1) CSIRO, Underwood Avenue, Floreat, WA, 6014, Australia |
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Abstract: | Wheat yields in the Mediterranean climate of Western and Southern Australia are often limited by water. Our measurements on
a 70 ha growers field showed linear relationships between grain yield and the plant available soil water storage capacity
(PAWc) of the top 100 cm of the soil profile. PAWc was linearly related to apparent soil electrical conductivity measured
by proximal sensing using electromagnetic induction (EM38). The APSIM wheat model also employs PAWc as one of the systems
parameters and simulated linear relationships between PAWc and yield. These relationships were used to transform an EM38-derived
PAWc map of the field into yield maps for three major season types (dry, medium and wet) and nitrogen (N) fertiliser management
scenarios. The results indicated that the main cause of temporal and spatial yield variability within the field was due to
interactions of seasonal rainfall, PAWc and N fertiliser applications. Spatial variability was low in low rainfall years when
yields across the field were low and the higher soil water storage capacity sites were often underutilised. With adequate
N, spatial variability increased with seasonal rainfall as sites with higher PAWc conserved more water in wet seasons to give
higher yield response than sites with low PAWc. The higher yield response of high PAWc sites to rainfall gave rise to larger
temporal variability compared with sites with low PAWc. Provision of adequate N is required for the water limited yield potential
to be expressed and this increased both spatial and temporal variability. Sites with low PAWc performed poorly irrespective
of rainfall and N application. PAWc is inherently low on deep coarse sands; these sites should be considered for a change
in land use. Elsewhere, strategic management interventions should aim to improve PAWc through sub-soil amelioration and deep
root growth to increase the capital asset of the farm. The resulting increase in yields will occur in favourable seasons and
with adequate fertiliser provisions. The largest grain yield response to water and N will be obtained on sites with the highest
PAWc and it is at those sites that the greatest profits from fertiliser use could be achieved in wet seasons. |
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Keywords: | APSIM EM38 nitrogen plant available soil water precision agriculture yield mapping |
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