Fosforgödslingseffektivitet i långliggande bördighetsförsök

Abstract: Rapid population growth and the fact that phosphorous is a limited resource implies that the question regarding an efficient use of phosphorus is of great importance, and consequently,that the phosphorous use efficiency should be as high as possible. The view on phosphorous use efficiency, and how this is calculated, has varied over time. This has had great implications on what type of research that has been conducted, which have resulted in an inconsistency between the academic’s view on the subject and recommendations received by farmers. The purpose of this paper is to calculate the phosphorus use efficiency in the Swedish long term fertility experiments. Calculations are made using different methods in order to evaluate which method is most suitable for calculating phosphorus use efficiency. Furthermore, the purpose is to determine at which P-AL you receive the highest efficiency for different soils and crops. Calculations made using the difference method consequently demonstrate lower phosphorus use efficiency than calculations made using the balance method. This implies that phosphorus is reversely fixed in the soil. The efficiency obtained using the difference method is strongly dependent on the yield in a references patch left unfertilized. Calculations on phosphorus use efficiency should therefore be made using the balance method. The highest efficiency achieved was 72 %, after correcting for an increase in P-AL. Nearly all of the sites had a phosphorus use efficiency over 25 %, which is commonly recognized as the upper limit. Yield in relation to P-AL differs greatly between different soils, differences that cannot be explained by simple soil parameters, such as content of clay and organic matter. According to Jodbruksverkets recommendations, replacement fertilizing should be done on soils graded as having phosphorus class III. The calculations show that the yield-effect of fertilizing decreases around P-AL 4, which corresponds to the lower regions of phosphorus class III. For some of the soils, this effect is observed at lower P-AL levels. There are significant differences between P-AL level required for a certain yield when different crops are compared. Calculations show that winter wheat is more tolerant to lower P-AL levels than spring barley and spring oilseeds. This is something that should be considered when planning phosphorus fertilization.