Science - February 25, 2010

More phosphates than before found in soil

Farmers and market gardeners have recently been advised by Blgg Laboratories to use less phosphates to fertilize their land. A better method has been developed to gauge the presence of nutrients in soils, thanks to Wageningen PhD student Debby van Rotterdam, who will graduate on Friday.

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Van Rotterdam simulated the uptake by vegetation in the laboratory, and observed the presence of phosphates and potassium in the soil under controlled conditions. Subsequently, she transposed the lab results to the field to gauge their presence. In this way, she created the foundation for a more accurate fertilization advice.
'Roots of plants take in nutrients such as phosphates from the moisture in the soil', says Van Rotterdam. 'But phosphates are also attached to soil particles. During the growing season, these phosphates also find their way into the soil moisture. These additional supplies to the soil - which differ for each soil type - have to be included when issuing an advice.'
Fertilization advice
Blgg Laboratories - active in soil and plant research - has, in the meanwhile, brought out a new fertilization advice based on supplementary field research. It now recommends an average reduction of fifteen kilos of phosphates per hectare, as compared to before, without any loss in harvest and quality. Concrete figures for actual use of potassium are not yet available. 'The formula for arriving at a recommendation for potassium is too complicated', says Van Rotterdam. 'It can be much simplified.' She also expects the quantity of potassium in the fertilization advice to be lower than before, now that she has captured the dynamics of the additional supplies to the soil.
Phosphates are becoming more important in fertilization strategies of farmers and market gardeners. In the past, the strategy was based only on an optimum harvest level. Nowadays, more accuracy is needed because of possible leaching of fertilizers into groundwater. 
Blgg has been using the improved method for some time in its fertilization advice for grassplots and recently, also for agriculture and horticulture. Van Rotterdam will be defending her thesis on 26 February against Willem van Riemsdijk, professor of soil chemistry and soil quality.

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