Unlocking soil secrets | My Machinery
CASE Agriculture
Unlocking soil secrets

Australian farmers are slowly beginning to understand the importance of soil tests, but for Soil Management Systems principal Brenton Byerlee there is still a lot of room for improvement. “There’s more people getting soil tests done now, and that’s good, but we need to move away from just this focus on the major nutrients,” he said. He pointed to the over-reliance on the Colwell phosphorus (P) test as an example. “There was this focus on getting a Colwell reading of 30, but people don’t understand that the Colwell reading is very reliant on your soil type,” he said. “Some types of soil can easily get up to 30 parts (milligrams per kilogram), and some soils will easily get up to this level and some soils will never get up there.” Mr Byerlee said a “one size fits all” approach to soils and soil testing did not work. “With phosphorus levels, or whatever, you need to look at the various toxicities and analysis whether there is anything in the soil stopping nutrients becoming plant available, rather than just simply throwing more and more MAP at it each year,” Mr Byerlee said. Mr Byerlee said rather than just looking at total P levels, part of SMS’ work was to analysis total P levels, including plant unavailable supplies. “If there has been a consistently low Colwell reading in a paddock with a good P history, then there’s a fair chance there’s a high total P level, but that it is just there in plant unavailable form,” he said. “Rather that just throw more super at it and waste your money, the trick is to unlock the P that is already there and get it so it is plant available.” Mr Byerlee said there could be a range of factors that created the soil imbalance that tied up nutrients. “We look at all the trace elements, iron levels and aluminium, they can all influence how the major nutrients are taken up by the plant,” he said. Along with testing all the factors that can influence soil fertility, Mr Byerlee said an assessment was made on the optimum fertility level of the soil. “If a soil is fairly sandy, then there’s no point putting out heaps of P on it, only to see it leach away. “It might be better to try and target lower yields, which have better gross margins because you are not wasting money on unnecessary inputs, or you can look to alter the soil structure through a process such as clay topping, if it is economic to do so. “However, we certainly don’t believe its sustainable to keep farming basically hydroponically, and keep putting out large amounts of synthetic fertiliser to bolster yield on inherently infertile soil.” In terms of nitrogen, Mr Byerlee said Australian soils generally had very poor nitrogen efficiency rates. “It’s a problem that can be solved by getting the soil balance right, with trace elements such as zinc, but again, just by testing for nitrogen levels, you’re not getting the whole story, you have to see what else is missing.” He said his clients had achieved massive efficiency gains in terms of their fertiliser costs just by focusing on micro-nutrients such as zinc and copper. “Plants can’t take up nitrogen and use that unless they have sufficient micro-nutrients, and in the right amount, too much creates toxicities, so we look at that to check the soil is in balance when creating a nutrient plan.” “We’ve got growers that have managed to reduced their N inputs by half with no cut-back in yield, just by getting the soil to make more N plant-available.” He said the underlying message was to get as much information about soil conditions as possible. “It’s so important to get a full soil analysis, and not just focus on the major nutrients, soil and its microbes is far more complicated than just getting your N, P and K levels.”

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