Fifty Years of Fertilization Experiments on Pinus pinaster in Southwest France: The Importance of Phosphorus as a Fertilizer
Data from 50 years of fertilization trials on Maritime pine (Pinus pinaster) were compiled to investigate how growth was affected by fertilization or improved nutrient availability. The results demonstrated that only trees fertilized with phosphorus (P) fertilizers showed an overall improvement in productivity. The effects were significant mainly at wetter sites and were less effective at drier sites. The form of P fertilizer does not seem to be important, and a rate of about 17‐35 kg of P ha−1 applied as a single dose at stand establishment was found to be sufficient to obtain a significant improvement in growth. Foresters can expect an increase of 20‐40% cumulative volume at rotation age or a reduction of 4‐5 years in rotation length due to fertilization with P. The duration of the effect of P fertilization on the annual increment varied (up to 20 years after application in the best cases). The high P-fixing capacity of these soils appears to be the most important factor in explaining differential responsiveness to P fertilizers, but stand developmental stage or the appearance of other limitations such as nitrogen may also explain the decline in the effectiveness of P fertilization with age.