Effect of phosphate fertilizer management strategies on soil phosphorus status and crop yields in some European countries

Continuous applications of P fertilizers over many years resulted in the buildup of soil P in many soil types under different cropping systems. The management of these soils in an agronomically and environmentally acceptable way must take into account the relevant factors affecting plant growth, yield and crop quality. Among these factors are the P demand of the crops, the importance and evolution of the soil P reserves, and the crop quality responses to the soil P status.

In 1991, IMPHOS established a network of experimental sites with the following objectives: Evaluate the effect of withholding phosphate applications on crop yield and soil phosphorus content; Compare the tests used in routine analysis to measure plant available phosphorus; Monitor phosphorus movement and distribution through the soil profile; and Investigate the concept of maintenance fertilization.

The experimental sites were located in the United Kingdom (Broom's Barn), the Netherlands (Marknesse), Belgium (Tinlot), and Germany (Volkenrode). Field experiments were carried out from 1991 to 1999.

Crop responses to P were observed for high P demanding crops such as potatoes and sugar beet, even on soils with medium to high P levels. Potatoes and sugar beet are high P demanding crops and respond well to fresh P applications even in soils with rather high P level. This contrasts with the general perception that the "P enriched" soils in Western Europe do no more need P fertilizations.

The efficient use of P fertilizers is a key issue. The results indicate that the application of mineral P of about 50 kg.ha-1 on most arable soils does not have negative effect on the environment. On livestock farms where the use of organic manure results in high P inputs, the use of mineral P needs much more in-depth analysis as detrimental side effects might occur. These specific cases should not be addressed with the view of generalizing the results to all production systems.

The fate of the soil P and applied P fertilizers were monitored using routine soil P tests. Continuous phosphorus applications over several years of maintenance fertilization rate did not result in measurable P movement down into the soil profile. On non-P fertilized soils, routine soil P test methods did not indicate the extent of the P depletion of the soils. On P fertilized soils these methods revealed little increase in P content even under large P balances.

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