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

A Järvi,H Hakkola,I Saarela

doi:10.2137/1239099042643099

Abstract

Fertilising with phosphorus (P) ensures continuous supply of an essential growth factor as necessary for productive and sustainable agriculture. The amounts of P required to attain and maintain an adequate P status in the soil were investigated in field experiments at 22 sites in Finland on soils containing large amounts of residual fertiliser P. The effects of five rates (0, 15, 30, 45 and 60 kg ha-1) of annual P application were measured in the soil by chemical methods after 9 to 15 experimental years, and the changes in soil test P values (STP) were compared with P balances. Stratification of P in ley soil by broadcast application of fertilisers was assessed at four sites. The mean changes of STP in the whole topsoil caused by P fertilisation expressed as per cent of the balance difference were 3.5% (0.0159 mg dm-3)/(kg ha-1) in the acid ammonium acetate test (PAc), 4.7% (0.0214 mg dm-3)/(kg ha-1) in water extraction (Pw) and 9.7% (0.058 mg kg-1)/(kg ha-1) in sodium bicarbonate extraction (modified Olsen P). Initially high PAc values tended to slowly decrease at zero P balance, while low values did not change without some particular reason, such as soil acidification or mixing of the topsoil with some of the less fertile subsurface soil. A thin layer of the uppermost soil was quickly enriched by broadcast application of P fertiliser.;

Highlights

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)
The amounts of total P and the soil test P values (STP) values summed in Table 2 and presented in Figs 1–4 which were obtained from smaller numbers of samples are less reliable
The changes of total P and soil test P values caused by different rates of repeated P fertilisation were monitored for 22 diverse Finnish soils enriched with large amounts of accumulated fertiliser P

Summary

Introduction

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). The long-term balance surplus which markedly improved the P status in a major part of the cultivated soils in Finland has primarily increased the secondary inorganic fractions assumed to be bound to Al and Fe (Al,Fe-P). The relative changes in the inorganic P fractions have been still larger in organic soils than in mineral soils. Repeated broadcast applications of fertilisers on untilled soil according to the common practice in ley enrich the surface efficiently with extractable and potentially transportable P (Saarela 1992a), while mixing the rich topsoil with the poorer subsurface soil by deep tillage decreases the STP values (Saarela et al 2000, Peltovuori 2002)

Methods

Results

Conclusion