Effect of cumulative fertilizer dressings on the phosphorus status of mineral soils II Comparison of two phosphorus testing methods

Authors

• Helinä Hartikainen Department of Agricultural Chemistry, University of Helsinki, SF-00710 Helsinki, Finland

DOI: https://doi.org/10.23986/afsci.72353

Abstract

Soil samples collected from field plots before onset of fertilization trials and after seven years of cultivation with annual P additions of 0, 30 or 60 kg ha-1, were analyzed for water-soluble P (Pw) and acid NH4-acetate-extractable P (PAAc). In all soil samples, the P test values correlated closely (r = 0.93***). However, they differed significantly in the clay soils where PAAc amounted to 59—96 % of Pw . In the coarser soils, the acetate solution extracted 70—365 % of the water-soluble P, but the difference between the methods remained insignificant. In both soil groups, the molar ratio of NH4F-P to oxalate-soluble Al explained 90 % or more of the variation in the P test values. The soil samples were divided into different P content classes according to the acetate test calibration scheme. In various P classes the test values tended to differ statistically significantly: in the lower classes acetate extracted P more and in the higher classes less than water did. Only in soils ranked as satisfactory in P the test values were about equal. When the rating scale limits given for the advisory soil testing were applied to the water extraction, in most soils the difference between the P testing methods was of one P class. The fertilization recommendations based on the acetate and water extraction tests were compared.