Abstract
The native reserves of phosphorus (P) in Finnish soils are sizeable but poorly available to plants. The P status has been generally poor, but large rates of P applied since the 1940s have substantially enhanced the supply of P from the soil. As a means of optimising P fertilisation of crops grown in the improved soils and promoting agro-environmental sustainability of agriculture, long-term field experiments were established in 1977-1981 on various soil types around Finland, between the latitudes of 60 and 65 N. The experimental sites (8 Cambisols, 9 Regosols, 6 Histosols, 1 Podsol) were moderately acidic (pH w 5.6, range 4.6-6.6) and contained 1.6-31.2% organic C, and (mineral soils) 3-74% clay. The concentration of total P was 1.22 (0.66-1.87) g kg -1 , and the inorganic fraction separated with fluoride and hydroxide extractions (Al,Fe-P) was 8.2% (4.5-12.4%) of oxalate extractable Al+Fe (P saturation index). In mineral topsoil the pool of Al,Fe-P was 850 kg ha -1 , which is 300 kg ha -1 larger than was obtained in the early 1960s and 600 kg ha -1 larger than found in virgin soils. The soil test P value was 13.1 (3.7-60) mg dm -3 by the acid ammonium acetate method, 11.5 (1.6-42) mg dm -3 by a water extraction method (1:60 v/v) and 61 (23-131) mg kg -1 with a modified Olsen method. The intensity factor of soil P status has remained at a relatively low level in a major part of the cultivated area.;
Highlights
Extractable soil phosphorus was determined for all samples (20 or 40/site/layer/sampling) by the acid ammonium acetate method (P Ac, soil test P values (STP))
Much smaller portions of P were extracted with strong acid from organic soils (Table 3), but even these values, 180 to 580 mg dm-3, mean mg dm-3, were many times higher than the inorganic fraction of P found by Kaila (1956) in different virgin peat soils, 35–63 mg dm-3, which is equal to no more than 70–128 kg ha-1 0.2 m-1
The amounts of total P per hectare, which were calculated on the basis of bulk density of ground soil and inexact soil depth (Table 3), are not very accurate, but support earlier estimates that the total amount of P in cultivated topsoils is about three tonnes per hectare (Saarela 2002)
Summary
MTT Agrifood Research Finland, South Ostrobothnia Research Station, Alapääntie 104, FIN-61400 Ylistaro, Finland. As a means of optimising P fertilisation of crops grown in the improved soils and promoting agro-environmental sustainability of agriculture, long-term field experiments were established in 1977–1981 on various soil types around Finland, between the latitudes of 60 and 65 N. Comprehensive experimental research was necessary, to optimise the P fertilisation of crops grown on soils containing large amounts of accumulated P This project was primarily intended for agricultural purposes. Domestic and international surplus production of all main crops had In view of this need for optimisation, a series of long-term field experiments with five rates of annual P fertilisation supplying 0–60 kg P ha -1 was established in 1977–1981 at 24 sites on diverse soil types at MTT Agrifood Research Finland’s research stations.
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