Chasing the RB209 phosphate target index of 2: A fool’s dream?


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RB209 recommends building soil phosphate banks – does this fit modern farming practice?

THE importance of phosphorous for plant growth is well-documented and understood. The lack of it at any stage of plant development can leave the plant’s engine room lacking fuel for growth.


It is, therefore, perhaps understandable that the thinking behind RB209 – The AHDB Nutrient Management Guide - for phosphate and potash management is to maintain the soil at a target Index of 2 or above.


John Sarup, Managing Director of Spud Agronomy, and Simon Fox, a Soil Scientist and Managing Director of Emerald Research Ltd discussed the fundamental flaws in this practice and how, in light of high fertiliser prices, environmental management and the drive for sustainability, this thinking is leading to excessive input use and cost.


The original thinking behind this was to build up reserves to maintain available nutrient sources throughout the crop rotation, a principle driven by the desire to “level up” agricultural soils for food production in the post-war era.

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Under this scenario soils have often been likened to banks, where nutrients are added to the soil (current account), crops withdraw what they need to grow, anything left over is stored within your soil and can be used when needed (savings account).


However, John and Simon believe this to be a very simplistic view. A more apt housekeeping analogy of this approach would be that of someone while ensuring the children are fed (the current crop’s needs are met) then wildly invests in the stock market. They may get lucky, they may break even, but more often they have squandered it for no return.


To read our fuller feature, see the March issue of Potato Review. You can subscribe here.

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