SAARELA, I., Y. SALO, and M. VUORINEN. “Effects of Repeated Phosphorus Fertilisation on Field Crops in Finland 1.Yield Responses on Clay and Loam Soils Relation to Soil Test P Values”. Agricultural and Food Science 15, no. 2 (January 2, 2006): 106-123. Accessed August 26, 2019. https://journal.fi/afs/article/view/5835.