An evaluation of the Olsen test as a measure of plant-available phosphorus in grassland soils derived from basalt parent material

Abstract

Anecdotal and circumstantial evidence have suggested that the Olsen test underestimates plantavailable phosphorus (P) in basaltic soils in Northern Ireland. Therefore, the ability of this test to predict plant-available P in basaltic (and non-basaltic) soils was investigated by regressing Olsen-P data against herbage P indices calculated from plant tissue test data using the diagnosis and recommendation integrated system. The average Olsen-P concentration for a range of fields situated on basaltic soils was considerably lower than the average Olsen-P concentration for a range of fields situated on non-basaltic soils, and yet mean sward P status, as given by the herbage P indices, was similar for both groups of fields. Herbage P indices were also much better correlated with Olsen-P measurements in non-basaltic soils than in basaltic soils. Furthermore, at low Olsen-P values (59mgPL-') some swards on basaltic soils were genuinely deficient in P, while others were sufficient or even in surplus for this nutrient. The results confirm that Olsen-P is inadequate as a predictor of plant-available P in basaltic soils. It is concluded that an alternative soil test is needed to provide a reliable assessment of plant-available P in basaltic soils, to prevent overuse of fertilizer and manure P and to minimize the amounts of P entering local watercourses.

Phosphorus speciation and fertiliser performance characteristics: A comparison of waste recovered struvites from global sources

“…Olsen-P measurements of plant available P. Methods for Olsen P extraction were as reported by Bell et al (2005). Soil samples were dried (30 o C) and sieved to <2mm.…”

“…Soil samples were dried (30 o C) and sieved to <2mm. Olsen P was extracted using 5% bicarbonate buffered at pH 8.5, in a soil solution ratio 1:20 v/v (Bell et al 2005, Olsen et al 1954). The extraction time was 30 minutes at a controlled temperature (22 o C) and samples were then centrifuged to remove the supernatant.…”

“…P bioavailability and plant uptake is a complex disequilibrium, as the balance between varying P sorption mechanisms continually changes, with no single technology or methodology mimicking exactly the in situ elemental flows. Agronomic and environmental tests for soil bioavailable P are often based on measurements of sodium bicarbonate extractable-P (Olsen-P), but this methodology has been shown to underestimate bioavailable P in acidic or Fe and Al rich soils (Bell et al, 2005) and operates far outside the norms of pH (8.5) usually encountered within most soils. An alternative advanced speciation method, namely DGT (Diffusive Gradients in Thin films), which is a passive sampling technology has been compared with Olsen-P (Mason et al, 2010) in field trials and yields an enhanced representation of the plant available P pool and supply flux for labile solutes.…”

Recent developments in fast spectroscopy for plant mineral analysis

“…No correlation was found at all between extracted P and early dry matter yield, as the amount of extracted P is highly dependent on soil mineralogy and on the types of chemical bonding between P and soil inorganic and organic fractions. This complicates the use of soil testing for general analysis of fertilizer requirements ( Bell et al, 2005 ; Debnath et al, 2010 ). In other words, the plant availability of essential plant nutrients may often not be assessed through traditional soil testing methods as they cannot reflect the complex soil chemistry and rhizosphere effects involved.…”

An evaluation of Colwell‐P as a measure of plant‐available phosphorus in soils of volcanic and non‐volcanic origins in the highlands of Papua New Guinea

“…But this process is resource consuming and very costly. An alternative less costly approach, previously used in the UK by Bell et al. (2005a), is to collect survey data for soil‐P and crop‐P concentrations across the region of interest and then determine if a useful statistically significant relationship exists between these two variables.…”