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Is it worth subsoil testing for Nitrogen?

Oliver, Y., Bowden, B., Scanlan, C. and Bell, R.ORCID: 0000-0002-7756-3755 (2013) Is it worth subsoil testing for Nitrogen? In: 2013 WA Agribusiness Crop Updates, 25 - 26 February, Perth, Western Australia

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In WA, soil testing for mineral N (ammonium plus nitrate) has traditionally been taken from the top 0-0.1 m. Farmers and advisors are now interested in deeper soil testing, in order to know how much mineral N occurs at depth and what this may mean in terms of fertiliser N application decisions. Accounting for topsoil and subsoil test level in N fertiliser use varies markedly among growers and advisors depending on; their own historic applications; use of nitrogen decision support tools (N-DSS’s) such as Yield Prophet simulations or SYN. Other growers use approximate total soil profile N and then add N fertiliser required to reach target yield (i.e. 45 kg N/ha for 1 t/ha of grain).

The main question this paper is addressing is “Do I need to soil test to depth for better N decisions?”

To answer this we needed to understand: 1. Where in the profile the subsoil N occurs and if it is related to topsoil N, 2. How effective is the subsoil in supplying N for the crop – which depends on root access to subsoil N as affected by subsoil constraints and N leaching, 3. What does this mean for N recommendation systems based on soil testing? and 4. Given the seasonal interaction with yield response, will the subsoil N test results reduce the errors in recommendations enough to justify this extra complexity, cost and effort?

Item Type: Conference Paper
Murdoch Affiliation(s): School of Environmental Science
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