Soil-based, field-specific fertilizer recommendations are a pipe-dream
2020
Schut, A.G.T. | Giller, K.E.
Fertilizer recommendations are key for farmers: the investment is relatively large for smallholders and risky with unknown yield responses and variable fertilizer prices. Are agronomists able to provide useful site-specific fertilizer recommendations that reduce these uncertainties? We evaluated the influence of errors introduced due to soil sampling and chemical analysis procedures both within- and among laboratories on fertilizer recommendations. Using what we consider to be conservative estimates of the uncertainty in estimating soil supply of N, P and K in a single composite soil sample, the resulting 90% confidence interval of fertilizer recommendations ranged from 86 to 186, 0–58 and 38–114 kg N, P and K ha<sup>−1</sup> respectively. The numerous laboratory services and digital applications providing field-specific recommendations appear to promise more accuracy than soil analysis can realistically deliver. We conclude that a field-specific fertilizer recommendation based on a single composite soil sample is indeed a pipe-dream.
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