The interests of the farmer and waterways in terms of phosphorus fertilization may be closer to each other than thought so far, discovered Senior Scientist Antti Iho from MTT in his dissertation study.

For plants, phosphorus is a vital nutrient, but phosphorus runoff may accelerate eutrophication in waterways. According to the dynamic calculation model drawn up by Iho, it is possible to optimise phosphorus fertilization to provide a sufficient amount of nutrients to cover the needs of crop cultivation while limiting the amount of runoff phosphorus.

"The phosphorus level optimal from the crop cultivation perspective is not far from the phosphorus level optimal from the point of view of society and the environment. In other words, there is no major contradiction between the good of the farmer and of society," Iho sums up.

Annual fertilization steers soil reserves
The crop response to phosphorus is largely based on the soil phosphorus reserve available to plants and not directly on phosphorus provided in the form of fertilizer.

In his dissertation Iho examines annual fertilization chiefly as a way of regulating the soil phosphorus level over the long term. He developed a theoretical framework for controlling phosphorus fertilization in order to ensure an optimal end result for both the farmer's economy and society.

Farmers have to take into consideration fertilizer price, impact on yield and the price of the end product, such as crop. Society also has to consider the effects of phosphorus runoff on the eutrophication of waterways and the resulting adverse consequences, such as algae blooms.

"From the perspective of environmental protection, the most important thing is to select the correct level of phosphorus fertilizer, not simply to reduce fertilization," Iho stresses.

The price of waterway eutrophication is decisive
Iho applied his dynamic model to the phosphorus fertilization of barley cultivated on clay soil using certain price levels. He discovered that, from a commercial perspective, it was profitable for the farmer to aim at keeping the phosphorus level of fields at slightly over 7. The optimal phosphorus level from the environmental perspective was just under 6.5.

"From the viewpoint of both the farmer and society, unnecessarily high soil phosphorus reserves should be lowered using very similar optimum solutions," Iho notes.

The difference between the desired phosphorus levels depends on the emphasis, or price, placed on the adverse effects of eutrophication. According to Iho, while it may be difficult to find a compromise between the economically and socially sensible solutions on environmentally vulnerable field sections, in other sections the two objectives might be very close to each other.

The researcher points out that the sensible level of phosphorus fertilization depends on the prevailing status of soil phosphorus reserves, which may vary greatly even within one section of the field.

"The determination of the precise fertilization levels and the recommended soil phosphorus levels requires soil type- and plant-specific data on the best indicator of phosphorus reserves available for plants and on the combined crop response of soil phosphorus and phosphorus fertilization."

The doctoral dissertation of L.Ph. (Agriculture and Forestry) Antti Iho, "Essays on socially optimal phosphorus policies in crop production", will be examined at the Faculty of Agriculture and Forestry of the University of Helsinki on 26 November 2010. The opponent will be Professor Angels Xabadia from the University of Girona, with Professor Markku Ollikainen from the University of Helsinki as custodian.

For more information, please contact:
Senior Scientist Antti Iho, MTT, tel. +358 50 572 2059, firstname.lastname@mtt.fi