Assessing organic phosphorus status of Cerrado oxisols (Brazil) using ³¹P-NMR spectroscopy and phosphomonoesterase activity measurement

Abstract

Chapuis-Lardy, L., Brossard, M. and Quiquampoix, H. 2001. Assessing organic phosphorus status of Cerrado oxisols (Brazil) using 31 P-NMR spectroscopy and phosphomonoesterase activity measurement. Can. J. Soil Sci. 81: 591-601. Plant production in the Brazilian savannas, also known as the Cerrados, is limited mainly by low P availability in soils. Little is known about the P status in the Cerrados region, despite its increasing significance for the country's agriculture.31 P-NMR spectroscopy of alkali extracts and phosphomonoesterase (PME) activity measurements were used to study forms of P and their stability in oxisols of natural and pasture systems. Total P content (Pt) in topsoils ranged from 301 to 456 mg kg -1 and organic P content (Po) from 84 to 194 mg kg -1 with the highest values under natural vegetation. The estimation of forms of soil P with different lability (provided by NaHCO 3 and NaOH extractions) showed little difference between natural vegetation and pastures, but the proportions of Po extracted suggest the importance of organically bound P as a source of plant-available P. All NMR spectra showed signals of organic P (monoesters and diesters) and inorganic P forms (orthophosphate and pyrophosphate), with little influence of land use. Organic P appears to be mainly in the form of stable phosphomonoesters. The most marked effect of land use was a decrease in PME activity under recent pastures, indicating an increase of PME stability in topsoils after the maize-grass ley plantation. The importance of the pH of the PME activity measurement is also discussed.Key words: Organic P, labile P, 31 P-NMR, phosphosmonoesterase, Cerrado, Oxisols.Chapuis-Lardy, L., Brossard, M. et Quiquampoix, H. 2001. Détermination du statut du phosphore organique d'oxisols de la région des Cerrados (Brésil) par RMN du 31 P et mesures d'activité phosphomonoestérase. Can. J. Soil Sci. 81: 591-601. La production des savanes brésiliennes connues sous le nom de Cerrados est principalement limitée par une faible disponibilité du phosphore présent dans les sols. Malgré l'importance croissante de cette région pour l'agriculture brésilienne, le statut du phosphore reste peu étudié. Cette étude a été réalisée sur des échantillons d'oxisols prélevés sous végétation naturelle de savanes et sous pâturages. Les formes du phosphore et leur stabilité ont été étudiées par résonance magnétique nucléaire (RMN du 31 P) et mesures de l'activité phosphomonoestérasique (PME). Le contenu en phosphore des horizons superficiels s'échelonne respectivement de 301 à 456 mg kg -1 sol pour le phosphore total (Pt) et de 84 à 194 mg kg -1 pour le phosphore organique (Po) ; les valeurs les plus élevées étant observées sous végétation naturelle. La quantification des formes de phosphore plus ou moins assimilables présentes dans les sols (extraites par NaHCO 3 et NaOH) montre peu de différences entre la végétation naturelle et les pâturages ; Les quantités obtenues suggèrent cependant l'importance des formes organiques comme source de phosphore assimilable p...

Phosphorus analysis in soil under herbaceous perennial leguminous cover by nuclear magnetic spectroscopy

“…Forster & Zech (1993) found that, in tropical rain forest soils, persistent orthophosphate P monoester makes up an even greater percentage of soil phosphorus. Similar results were observed for Brazilian savannah soils, cultivated or not, and could be explained by the stabilization on Al and Fe hydroxides and other clays (Chapuis-Lardy et al, 2001). In a primary tropical forest, Möller et al (2000) verified that soil organic phosphorus (SOP) is constituted mainly of orthophosphate diesters on the organic layer, whereas on the mineral horizons orthophosphate monoesters dominated the chemical composition of extractable SOP.…”

Nutritional adaptations of native plants of the cerrado biome in acid soils

“…Soil properties of two typical Latosol (Oxisol) profiles associated with natural vegetations of a cerrado sensu stricto in central Brazil and a terra firme forest in the Amazon in northern Brazil (RadamBrasil, 1976a, b (Lathwell and Grove,1986;Davidson and Howarth, 2007;Elser et al, 2007). Phosphorus is a limiting factor for most agricultural crops and the organic fraction of P is considered to be an important source of plant available P in native soils (Chapuis-Lardy et al, 2001). Nitrogen is reported to be limiting in tropical savannas .…”

Ecophysiology of forest and savanna vegetation

“…Malhi et al [2009] also differentiated between "rain plant ordination studies [Ribeiro and Tabarelli, 2002;Miranda et al, 2003] and points to soil fertility being a major determinant of woodiness in Brazilian savanna at the landscape scale Cox, 1977a, 1977b]. For example, it is well established that some woodland types, cerradão, tend to occur only on unusually fertile soils Morriera, 2000;Chapuis-Lardy et al, 2001], and on the basis of soil pH and exchangeable cation measurements, a distinction is sometimes made between "mesotrophic facies cerradão" and "dystrophic facies cerradão," which are characterized by different species compositions. Nevertheless, despite these differences, both vegetation forms seem to be characterized by relatively high soil-soluble phosphorus concentrations .…”