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Long‐term P Fertiliser application increases soil phosphorus (P) labile fractions, which can be associated with crop P uptake and grain yield and are useful to improve fertilizer recommendations. Research aims were to evaluate in long‐term experiments with different P Fertiliser application in a Mollisol and a Vertisol: (a) the changes of soil P fractions and (b) the relationship between soil P fractions with long‐term P Fertiliser application, with accumulated apparent P budget, grain P, total P uptake, soybean (Glycine max L.Merr.) and maize (Zea mays L.) grain yield. Soil P fractions were measured after 1 and 9 year since the beginning of the long‐term experiments. Experiments included an initial Fertiliser application rate of 200 kg P ha−1 and annual P Fertiliser application rate of 36 kg P ha−1. Bray1‐P, total, organic, and inorganic P in fine (<53 μm) and coarse (>53 μm) (CF) soil fractions, and in NaHCO3 extract were measured. Initial P Fertiliser application increased inorganic and total P fractions. However, Bray1‐P, total P in NaHCO3 extract and in the CF were the fractions that most increased with continuous long‐term P Fertiliser application in both sites. In the Mollisol, maize grain yield was unrelated to long‐term P Fertiliser application. In the Vertisol, total P in NaHCO3 extract, and total and organic P in the CF were more closely related to soybean grain yield than Bray1‐P. We proposed soil P indices of labile inorganic and organic P that showed close relationships with soybean grain yield and may be useful to improve the diagnosis of P soil fertility. [ABSTRACT FROM AUTHOR]

The efficient use of phosphorus (P) in agriculture should rely on accurate soil P tests (SPT). Organic P contributes to P supply to plants; however, it is not usually taken into account in assessing P fertilizer requirements. We hypothesized that there would be an increased accuracy of bicarbonate extraction as SPT in predicting P uptake by plants if total P (TP) in this soil extract is taken into account. We conducted a soil P depletion experiment with 36 soils involving four consecutive crops in pots. Molybdate‐reactive P (MRP) and total P were determined in extracts centrifuged at 19,000 g (Bic‐MRPC and Bic‐TPC) or not (Bic‐MRP and Bic‐TP). MRP in extracts explained <47% of the variance in the cumulative P uptake, while total P (centrifuged at 19,000 g or not) provided the most accurate estimation of P uptake (59% with Bic‐TP) and threshold values for fertilizer response (R2 = 0.58 with Bic‐TPc). When soils were separated in two groups according to their Ca carbonate equivalent to clay ratio, the variance in the cumulative P uptake explained by Bic‐MRP was above 63%, and that explained by Bic‐TP was above 73%. This separation also enabled more realistic estimation of the threshold values for fertilizer response. It can be concluded that the use of total P instead of MRP in bicarbonate extraction was promising in terms of improving its accuracy in assessing P fertilizer requirements. [ABSTRACT FROM AUTHOR]

Phosphorus (P) K‐edge X‐ray absorption near‐edge structure (XANES) spectra of orthophosphate (oPO4) bound to soil FeIII minerals (e.g. ferrihydrite, goethite) show a pre‐edge signal at 2148–2152 eV. It is unknown whether organic P bound to FeIII oxyhydroxides also show this feature. Otherwise, Fe‐bound soil P may be underestimated by P K‐edge XANES spectroscopy, because a large portion of Fe oxyhydroxide‐bound P in soils is organic P. K‐edge XANES spectra were obtained for different organic P compounds present in soils [inositol hexaphosphate (IHP), glucose‐6‐phosphate (G6P), adenosine triphosphate (ATP)] after sorption to ferrihydrite or goethite and compared with spectra of oPO4 adsorbed to these minerals. P sorption to ferrihydrite increased in the sequence IHP ≪ G6P < oPO4 < ATP. P sorption to goethite increased in the sequence G6P < oPO4 ≪ ATP = IHP. Pre‐edge signals in P K‐edge XANES spectra of organic P adsorbed to Fe oxyhydroxides were markedly smaller compared with those of oPO4 adsorbed to these minerals and absent for FeIII oxyhydroxide‐bound ATP as well as goethite‐bound IHP. Linear combination fitting (LCF) performed on spectra of IHP, G6P or ATP adsorbed to ferrihydrite or goethite, using only spectra of FeIII oxyhydroxide‐bound oPO4 as reference compounds for Fe‐bound P, erroneously assigned >93% (ferrihydrite) or >41% (goethite) of Fe‐bound P to non‐Fe‐bound P species. Inclusion of FeIII oxyhydroxide‐bound IHP as reference compounds markedly increased the recovery of oxyhydroxide‐bound organic P. Thus, Fe‐bound soil P has probably often been underestimated by LCF in soil XANES studies where IHP adsorbed to ferrihydrite and to goethite were not included as reference compounds. Fe‐bound soil phosphorus (P) is probably often underestimated by LCF (linear combination fitting) conducted on P K‐edge X‐ray absorption near‐edge structure (XANES) spectra, unless inositol hexaphosphate (IHP) adsorbed to ferrihydrite and IHP adsorbed to goethite are included as reference compounds. [ABSTRACT FROM AUTHOR]

The bioavailability and stability of organic phosphorus (P) in the soil may be affected by exogenous phytase (EPase) activity and distribution, but remain poorly understood. The distribution of EPase activity and hydrolysis ability of EPase on organic P in soil solid-liquid phases was investigated. The EPase addition to soil suspension (1:20, w/v) from three soil types (red soil, brown soil, and cinnamon soil) under three treatments (untreated soil, removing clay from soil, and removing organic matter from soil) with different characters in the solution and solid phases was assayed. The results showed that the disappearance pattern of EPase activity from solution was similar for all soils, whereas the enzyme activity on the solid phase was dependent on soil types and treatments with the greatest in red soil and untreated soil. When EPase was added to soils, the adsorption ratio of organic matter and clay was 10 to 25% and 3 to 7%, respectively, with sorption capacity of organic matter being significantly ( p < 0.05) stronger than that of clay. Additionally, soil dehydrogenase activity, which is the indicator of overall soil microbial activities, increased after EPase addition and the two enzymes showed significant negative relation in the soil suspension and solution. At the same time, the organic P decreased significantly ( p < 0.05) after the addition of EPase in the soil solid, which had a varied rate under -40% after incubating 192 h, whereas organic P in the solution phase increased significantly ( p < 0.05). This study demonstrated that organic matter had a strong protective and adsorptive effect on EPase effectiveness and microbes mightbe directly affect EPase longevity and decay. This finding suggests that EPase activity in the solid phase played a more important role in organic P hydrolysis. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is a major plant nutrient, however, its availability in volcanic ash soils is presumed to be small, due to its specific sorption on short-range order minerals. We analyzed distinct P fractions in volcanic ash soils of different age (60 to > 100,000 y BP) under pine forests in Central Mexico to investigate their changes along a chronosequence of Regosols, Andosols, and Lixisols, and to evaluate if P availability limits tree growth at any particular stage. Top soil and subsoil samples were first analyzed by the Tiessen and Moir method, which failed to extract exhaustively 'organic' and 'occluded P', and 'P associated with apatite'. Therefore, we modified the fractionation scheme by including a 'recalcitrant organic P' fraction obtained from the difference between P determined in air-dried subsamples and subsamples burned at 300°C; P adsorbed to short-range order minerals was assessed in an extraction with NH4-oxalate, and P in primary minerals by subtracting the sum of all other fractions from total P contents determined by XRF. This we did after discovering that primary P occurred in the form of fluorapatite included in plagioclase, volcanic glass or olivine. We also measured P contents in pine needles and related these with the 'mobile soil P' fractions. The results show that 'organic P' reaches maximum contents in 10,000-y old soil, as does P associated with short-range order minerals, while P occluded into crystalline oxides increases constantly over time. After 100,000 y, 31% of total P still remains in the form of primary P in A horizons. 'Mobile P' was constant > 40 mg kg−1 in Regosols and Andosols and related positively with foliar P contents, which were within adequate nutritional ranges. Only in Lixisols small 'mobile P' concentrations in soil correspond with inadequate P contents in pine needles. [ABSTRACT FROM AUTHOR]

The effect of tillage systems and crop rotation on microbial biomass phosphorus (MBP) and acid phosphatase (P-ase) activity, and the amount of different phosphorus (P) forms measured by P-NMR spectroscopy were studied on a field experiment carried out in a temperate Ultisol from southern Chile. Two tillage systems, no tillage (NT) and conventional tillage (CT) and two crop rotations, oat-wheat (OW) and lupine-wheat (LW) were evaluated 4 yr after the start of the experiment to determine the effects of such management on some soil biological parameters and P forms at three depths (0-5, 0-10 and 10-20 cm). Microbial biomass P ranged from 6.5 to 22.6 mg/kg, whereas the mean total P (P) was 1995 mg/kg for all treatments (OW and LW). Microbial biomass carbon (MBC) and surface P accumulation (at 0-5 cm depth), including Olsen P, MBP, orthophosphate monoesters (monoester-P), were larger under NT than CT. Tillage effects were greater than crop rotation effects in enhancing P availability. The LW rotation showed enhanced P-ase activity and increased monoester-P forms (57 vs. 30% of the total integral area of the spectra, in average) compared with OW. Nevertheless, OW rotation increased orthophosphate (ortho-P), especially at 10-20 cm. Microbial biomass carbon ranged from 532 to 2351 mg/kg, which represented 1.2-4.5% of total organic C (C). Furthermore, MBP correlated positively with MBC ( r = 0.80), Olsen P ( r = 0.77), C ( r = 0.77), pH ( r = 0.65), P ( r = 0.65) and P-ase activity ( r = 0.57), suggesting the importance of the microbial biomass on soil P availability. [ABSTRACT FROM AUTHOR]

Reactive (RP) and organic phosphorus (OP) losses from grazed paddocks were determined on a volcanic soil during 2004 and 2005. Paddocks were grazed by Holstein Friesian steers (3.5 steers ha−1) and received N (67.5 kg ha−1) and P fertilizer (30 kg P ha−1). Total losses ranged between 4 and 15 g P ha−1 year−1 and were greatly affected by incidental P losses associated with spring P fertilizer application. Reactive P constituted 90% of the total losses on average. Due to the high water infiltration capacity of the soil, run-off was <1% of total drainage, therefore, phosphorus losses in run-off were small. [ABSTRACT FROM AUTHOR]

TransgenicNicotiana tabacumplants expressing a chimeric phytase gene (ex::phyA) from the soil fungusAspergillus nigerwere generated. Three independently transformed lines showed increased extracellular phytase activity compared with a vector control and wild-type plants, both of which had no detectable extracellular phytase. TransgenicN. tabacumplants grown in sterile agar supplied with phosphorus (P) as phytate accumulated 3.7-fold more P than vector control plants. Despite this, the expression ofex::phyAin plants did not lead to an improved accumulation of P from two unamended P-deficient soils. However, when soils were amended with either phytate or phosphate and lime, transgenic plants accumulated up to 52% more P than controls. Positive responses by transgenic plants were, in some instances, coincident with a putative increase in soil phytate. We conclude that the development of plants that exude phytase to the soil may not ensure improved plant P nutrition, as the availability of phytate in the soil also appears to be critical. Nevertheless, if plants that expressex::phyAare combined with soil amendments that promote the availability of phytate, there is the potential to enhance the P nutrition of crop plants and to improve the efficiency of P fertilizer use in agricultural systems. [ABSTRACT FROM AUTHOR]

TransgenicTrifolium subterraneumexpressing a phytase gene (phyA) fromAspergillus nigerwere generated. Five independently transformed lines showed an average 77-fold increase in exuded phytase activity in comparison with null segregant and wild-type controls. Unlike other phosphatases, exuded phytase activity was unaffected by P supply, verifying the constitutive expression ofphyA. TransgenicT. subterraneumgrown in agar with P supplied as phytate, took up 1.3- to 3.6-fold more P than controls and had equivalent P uptake to plants supplied with orthophosphate. This unique phenotype was compromised when the plants were grown in soil. None of the five lines showed increased shoot biomass or total P uptake in an unfertilized, low-P soil taken from under permanent pasture. With addition of P, one of the five transgenic lines had consistently greater P nutrition compared with control plants. Despite variable growth and P nutrition responses, P uptake per root length was on average greater for transgenic lines. Exudation of phytase by transgenicT. subterraneumallowed utilization of P from phytate in non-sorbing, sterile laboratory media, but was less effective when plants were grown in soil. Release of extracellular phytase is therefore not the only requirement for the acquisition of P from endogenous soil phytate by plants. [ABSTRACT FROM AUTHOR]

Abstract A variety of native Western Australian legumes produced root clusters in sand culture confirming field and published observations. In general, these legumes grew equally well when supplied with organic or inorganic sources of phosphorus. The nitrogen content of shoots and roots varied little among treatments for all species, however, phosphorus content was always greater in plants supplied with inositol-P. The plasticity of root growth in response to localized placement of organic and inorganic sources of phosphorus was demonstrated using a simple ‘split root’ technique. Total root dry weight was, on average, more than doubled in P-amended sand when compared with non-amended sand. Root clusters tended to be produced in areas of relatively high phosphorus concentration and nodules in areas of low phosphorus concentration. Levels of phosphorus in lateral roots grown in P-amended sand were significantly different from lateral roots grown in the corresponding non-amended sand. Growth increases averaging 70% for white sand to over 100% for yellow sand indicated a large degree of ‘plasticity’ in roots under conditions of heterogeneous supply of phosphorus. Spatially exclusive development of organs for the acquisition of nutrients is discussed in relation to requirements for carbon in organ production and maintenance. [ABSTRACT FROM AUTHOR]