Determination of available soil phosphorus by chemical methods

In order to update phosphorus (P) fertiliser recommendations for the Finnish clay and loam soils enriched with applied P, the effects of repeated P fertilisation on the yields of cereal and other crops were measured at eight sites over a period of 12−18 years. Yield results of some earlier field studies were also used in calibrating the soil test P values determined by the Finnish acid ammonium acetate method (P Ac ). Significant yield responses to P fertilisation were obtained on soils which had low P Ac values or medium levels of P Ac and too low or too high pH values (< 6.0 or 7.5 in water suspension). The mean relative control yield (RCY, yield without applied P divided by yield with sufficient P multiplied by 100) of the eight sites was 94.6% (n = 128, mean P Ac 15.5 mg dm -3 ) varying from 87% at P Ac 2.8 mg dm -3 to 100% at high P Ac . A P Ac level of 5−7 mg dm -3 was adequate for cereals, grasses and oilseed rape on the basis of the RCY value of 95% at optimal pH. At this P Ac replacing the amounts of P in the crops (14 kg in 4 t grain) and the fixation of extractable P (about 6 kg ha -1 a -1 ) produced almost maximum yields in favourable seasons and were considered optimal.

Section: Saarela I Et Al Effects Of Repeated P Fertilisation On Fimentioning

confidence: 71%

Effects of repeated phosphorus fertilisation on field crops in Finland 1.Yield responses on clay and loam soils relation to soil test P values

Saarela¹,

Salo²,

Vuorinen³

2008

“…According to SCHACHTSCHABEL and BEYME (1980), water soluble phosphorus reflects the quantity of total phosphorus relatively easily dissolved and, thus, the phosphorus supplying power of the soil. In the pot experiment made by AURA (1978) with some Finnish soils, the phosphorus extracted by water quite well correlated with the phosphorus uptake by the oats.…”

Section: Introductionmentioning

confidence: 82%

Watersoluble phosphorus in Finnish mineral soils and its dependence on soil properties

Hartikainen

1982

Abstract. Water soluble phosphorus ranged from 0.2 mg to 117.8 mg/kg in 104 surface soil samples studied. On the average, water extracted less P from the heavy clay soils (4.8 ± 2.2 mg/kg) than from the coarser clays (12.8 ± 4.6 mg/kg) and non-clay soils (13.3 + 7.2 mg/kg).Water extraction seemed to illustrate ''the effective" P status, it is that determined by the quantity and quality of sorption components in soil, soil pH and the content of organic carbon. These factors did not affect the amounts of P dissolved in water directly but inderectly by controlling the nature of P bonding which, in turn, seems to be of decisive importance in the extractability of P into water.The P supplying power of a given fraction is obviously controlled by the quantity of corresponding sorption agent. Water extractable P correlated most closely with the molar ratio of NH,F soluble P to oxalate extractable A 1 (r=o.93***, n= 103). However, according to the theory presented, with progressing desorption, P starts to mobilize also from the NaOH soluble fraction, its significance being the more apparent the greater the corresponding molar ratio NaOH-P/Fe is. In addition, the role and significance of other inorganic P fractions were discussed.

“…The ratio of soil to solution was 1 to 20 and the extraction time was two hours. Phosphorus desorption experiments were made using the anion exchange resin method described earlier (Aura 1978). The ratio of anion exchange resin to soil, however, was greater than earlier so that the sorption of phosphorus into resin would not be a limiting factor in extraction.…”

Section: Methodsmentioning

confidence: 99%

“…Pot experiments with oats (Aura 1978) indicated that the extraction of phosphorus from soil using anion-exchange resin and water seems to be a suitable method for measuring the phosphorus level of Finnish soils. Good results have been obtained earlier in other experiments (e.g.…”

Section: Introductionmentioning

confidence: 99%

Phosphate desorption from soil in anion-exchange resin extraction

Aura

1978

Self Cite

Abstract. An attempt was made to clarify the mechanisms of phosphate desorption using the anion exchange resin method for extraction of phosphorus from soil. It was shown that there is a linear dependence between the amount of phosphorus desorbed and the square root of the desorption time. Through theoretical examination it was concluded that the above-mentioned relation between the desorption and time is a result of the diffusion of phosphate from porous soil medium. Using this interpretation of the desorption curve as a basis, the activation energy of the phosphate desorption was calculated from the experimental results obtained with resin extraction at different temperatures. The activation energy values were 32-64 kj/mol depending on soils involved. In application of the results, the mechanisms and rate at different steps of the desorption were examined.