Phosphorus in Finnish soils in the 1900s with particular reference to the acid ammonium acetate soil test

Abstract

Comprehensive research into phosphorus (P) in soils and crops began in Finland in the early 1900s. The average amount of total P in the ploughed topsoil layer of mineral soils was about two tonnes per hectare in the 1930s, before the abundant use of fertilisers. The main chemical fractions of P in mineral soils were organic matter, primary apatite and secondary complexes of the hydrous oxides of Al and Fe. Of the smaller amounts of P in light peat soils, as much as 80% was present in stable organic compounds. Field experiments showed that the native P reserves of Finnish soils are poorly available to plants, and that P fertilisers are inefficiently utilised because of the strong fixation of applied phosphate in soils. In evaluations before the late 1950s, all simple chemical tests appeared to be rather unreliable indicators of the supply of P from soils to plants, but later research has shown that the results were impaired by errors implicit in the research materials. Some soil test P values (STP) obtained from old samples stored for more than ten years evidently were too high, particularly for organic soils, and many of the soils studied were strongly acidic and therefore biologically less fertile than the chemical P tests indicated. The acid ammonium acetate method (pH 4.65) was introduced in the early 1950s and has since been used in routine soil testing in Finland, not only for P but for all macronutrients except N. In later evaluations of different methods used for estimating the requirement of P fertilisation, the acid ammonium acetate method has proven equal or superior to any other simple chemical method.

Phosphorus status of diverse soils in Finland as influenced by long-term P fertilisation 2.Changes of soil test values in relation to P balance with references to incorporation depth of residual and freshly applied P

“…According to recalculation of the data published by Vuorinen and Mäkitie (1955), the P Ac values of mineral soils are closely correlated with the P values determined by the better-known Morgan's sodium acetate method from which the Finnish method was modified (Saarela 2002), (P Morgan = 0.694 * P Ac -0.27, n = 40, w = 1.5 -12, R 2 = 0.89). A very simple correction factor (0.7) can be used in comparing these methods in mineral soils.…”

“…The amounts and chemical fractions of phosphorus (P) in Finnish soils were discussed in a recent review (Saarela 2002) and reported for 24 experimental sites (Saarela et al 2003). Native P reserves are fairly abundant in Finnish soils but occur mostly in stable inorganic and organic compounds which are poorly available to plants.…”

“…During the last decades the input in manure has been almost 10 kg ha -1 and the offtake in crops somewhat larger. The balance surplus is small but probably positive though all outputs including the reforestation of fertilised fields are taken into account (Saarela 2002). In spite of the improved supply of P from the soil, significant yield responses to P fertilisation were common in almost all field crops (Saarela et al 1995).…”

Sensitivity of soil phosphorus tests in predicting the potential risk of phosphorus loss from pasture soil

“…Acid ammonium acetate extraction, found to provide a good estimation of plant-available P in acidic Finnish soils (Saarela 2002), is also reported to be a suitable indicator for critical source areas of P load in pastures (Jansson and Tuhkanen 2003). Our results support this conclusion.…”

Variability of herbage production in mixed leys as related to ley age and environmental factors: a farm survey

“…Also other nutrients, such as P and K, can be lost from the field either by leaching or in surface runoff (Ulén andMattsson 2003, Kayser et al 2007). The amounts of plant nutrients mineralised from mulched herbage are relatively small compared to those mobilised from previous applications of animal manure (Uusitalo et al 2007) and from the soil stock (Kaila 1967, Saarela 2002. Therefore, the residual effect of mulched herbage on subsequent ley growth may be minimal (cf.…”