Phosphorus speciation in temperate basaltic grassland soils by solution ³¹P NMR spectroscopy

Abstract

SummaryPhosphorus (P) speciation in 21 basaltic and four non-basaltic Irish grassland soils was determined by NaOH-EDTA extraction and 31 P NMR spectroscopy. Organic P in basaltic soils ranged between 30and 697 mg P kg À1 and consisted of phosphate monoesters (84-100%), DNA (0-16%) and phosphonates (0-5%). Inorganic P was mainly phosphate (83-100%) with small concentrations of pyrophosphate (0-17%). Phosphate monoesters were more important as a proportion of extracted P in basaltic soils, probably because of their greater oxalate-extractable Fe and Al contents. Phosphate monoesters appeared to be strongly associated with non-crystalline Al and increased with total soil P concentration, indicating that they do accumulate in grassland soils. In non-basaltic soils myo-inositol hexakisphosphate constituted between 20 and 52% of organic P, while scyllo-inositol hexakisphosphate constituted between 12 and 17%. These compounds were not quantified separately in basaltic soils because of poor NMR resolution in the phosphate monoester region, but appeared to represent a considerable proportion of the organic P in most samples. DNA concentrations were greater in basaltic soils compared with non-basaltic soils and were associated with acidic pH and large total C contents. The inability of the Olsen P test to assess effectively the P status of basaltic soils may result from strong phosphate sorption to Fe and Al oxides, inducing plant utilization of soil organic P. Phosphorus nutrient management should account for this to avoid over-application of P and associated financial and environmental costs.

Assessment of phosphorus status influenced by Al and Fe compounds in volcanic grassland soils

“…In addition, the soil with the highest Al ox and amorphous Al contents (Pemehue) presented the highest monoester P, myo-IP 6 and NaOH-P o contents. Thus, Al ox might promote monoester P retention in soil (Murphy et al, 2009).…”

Soil organic phosphorus in lowland tropical rain forests

“…This method is no longer used for stronglyweathered soils, because it overestimates organic phosphorus in such soils by increasing the solubility of inorganic phosphate contained within secondary minerals following high temperature ignition (Williams and Walker 1967;Condron et al 1990) and by including alkali-labile inorganic phosphate in the organic phosphorus fraction . It is commonly assumed that organic phosphorus, especially in the form of phosphate monoesters, is stabilized in soils by association with amorphous metal oxides (Harrison 1987;Celi and Barberis 2007) and there are several reports of strong correlations between soil organic phosphorus and oxalate-extractable aluminum and iron in temperate systems (e.g., Harrison 1987;Murphy et al 2010). There is less information for manganese oxides, although amorphous manganese, rather than aluminum and iron, was most strongly correlated with organic phosphorus in the soils studied here.…”

The composition of organic phosphorus in soils of the Snowy Mountains region of south-eastern Australia

“…Furthermore, in three separate studies, soils from cold temperate (<88C) and humid (520-600 mm rainfall) climates in Sweden were found to contain considerable amounts of IP 6 ; myo-IP 6 comprised 19-36% of organic P and scyllo-IP 6 comprised 3% of organic P along a chronosequence (Vincent et al 2013) and myo-IP 6 was also a prominent form of IP 6 in both a long-term fertiliser experiment (Ahlgren et al 2013) and in organic soils (humus) in a boreal forest (Vincent et al 2012). The myo-and scyllo-IP 6 were predominant in non-basaltic grassland soils in north-east Ireland (Murphy et al 2009) and in permanent grassland and cropped soils from Switzerland, where average annual temperatures were in the range of 2.2-9.48C and annual rainfall was 1042-2400 mm, myo-and scyllo-IP 6 comprised up to 25% of soil organic P (Jarosch et al 2015).…”