Variable Rate P

Author: Dr Brett Whelan

Over the past four years, Brett Whelan, University of Sydney, has run paddock trials on behalf of SPAA to quantify the impact of changing inputs based on management classes. The overall objective of the research is to improve the profitability of each paddock. Six paddocks, two each located at Crystal Brook, Stockport and Snowtown were chosen in 2003 to be part of the SPAA research program. Three additional paddocks (YP, EP and the Murray Mallee) were added in 2004. Each paddock had up to seven years of yield data providing a visual assessment of paddock variability; each could roughly be divided into zones of low or high yield. Here we look at the results for varying the phosphorus rate on Malcolm Sargent’s Road Paddock, Crystal Brook. Background information on this trial can be found in previous issues of Precision Ag News including Volume 2 Issue 1 Winter 2003. Results from other paddocks will be reported in future issues. The management classes in Road Paddock were constructed from an EM38 soil conductivity map, an elevation map and two years of yield map data (Figure 1a). Subsequent soil testing within these classes highlighted a significant difference in phosphorus fertility between the two classes in 2002, and again in pre-season testing in 2003 (Table 2). The fertiliser rate experiment was established with application strips located in Class 1 or in Class 2 providing either 0, 7, 20 or 30kg phosphorus per hectare (Figure 1b). Malcolm decided that from the beginning he would cut back the overall phosphorus applied to Class 1. Instead of applying a blanket rate of 11kg P/ha at seeding, Malcolm reduced the rate to 7kg P/ha on Class 1 the poorer performing zone, and increased the rate to 20kg P/ha on Class 2, the more productive zone. These rates were used for the rotation of wheat, field peas, wheat, barley, grown between 2003 and 2006. Download the article to read more

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