A holistic approach to understanding the desorption of phosphorus in soils

The mobility and resupply of inorganic phosphorus (P) from the solid phase were studied in 32 soils from the UK. The combined use of diffusive gradients in thin films (DGT), diffusive equilibration in thin films (DET) and the “DGT-induced fluxes in sediments” model (DIFS) were adapted to explore the basic principles of solid-to-solution P desorption kinetics in previously unattainable detail. On average across soil types, the response time (Tc) was 3.6 h, the desorption rate constant (k–1) was 0.0046 h–1, and the desorption rate was 4.71 nmol l–1 s–1. While the relative DGT-induced inorganic P flux responses in the first hour is mainly a function of soil water retention and % Corg, at longer times it is a function of the P resupply from the soil solid phase. Desorption rates and resupply from solid phase were fundamentally influenced by P status as reflected by their high correlation with P concentration in FeO strips, Olsen, NaOH–EDTA and water extracts. Soil pH and particle size distribution showed no significant correlation with the evaluated mobility and resupply parameters. The DGT and DET techniques, along with the DIFS model, were considered accurate and practical tools for studying parameters related to soil P desorption kinetics

Inter- and intra-species intercropping of barley cultivars and legume species, as affected by soil phosphorus availability

Aims Intercropping can improve plant yields and soil phosphorus (P) use efficiency. This study compares inter- and intra-species intercropping, and determines whether P uptake and shoot biomass accumulation in intercrops are affected by soil P availability. Methods Four barley cultivars (Hordeum vulgare L.) and three legume species (Trifolium subterreneum, Ornithopus sativus and Medicago truncatula) were selected on the basis of their contrasting root exudation and morphological responses to P deficiency. Monocultures and barley-barley and barley-legume intercrops were grown for 6 weeks in a pot trial at very limiting, slightly limiting and excess available soil P. Aboveground biomass and shoot P were measured. Results Barley-legume intercrops had 10–70% greater P accumulation and 0–40% greater biomass than monocultures, with the greatest gains occurring at or below the sub-critical P requirement for barley. No benefit of barley-barley intercropping was observed. The plant combination had no significant effect on biomass and P uptake observed in intercropped treatments. Conclusions Barley-legume intercropping shows promise for sustainable production systems, especially at low soil P. Gains in biomass and P uptake come from inter- rather than intra-species intercropping, indicating that plant diversity resulted in decreased competition between plants for P

Linking the depletion of rhizosphere phosphorus to the heterologous expression of a fungal phytase in Nicotiana tabacum as revealed by enzyme-labile P and solution 31P NMR spectroscopy

Root exudation of phytase could improve the ability of plants to access organic forms of soil phosphorus (P), thereby minimizing fertilizer requirements and improving P use efficiency in agroecosystems. After 75 days growth in a high available P soil, shoot biomass and P accumulation, soil pH, and rhizosphere P depletion were investigated in Nicotiana tabacum wild-type and transgenic plant-lines expressing and exuding Aspergillus niger phytase (ex::phyA), or a null-vector control. Solution 31P NMR analysis revealed a 7% to 11% increase in orthophosphate and a comparable depletion of undefined monoester P compounds (-13 to -18%) in the rhizosphere of tobacco plants relative to the unplanted soil control. Wild-type plants had the greatest impact on the composition of rhizosphere P based on the depletion of other monoester P, polyphosphate, and phosphonate species. The depletion of phytase-labile P by ex::phyA plants was associated with decreased proportions of other monoester P, rather than myo-InsP6 as expected. Rhizosphere pH increased from 6.0 to 6.5–6.7 in transgenic plant soils, beyond the pH optimum for A. niger phyA activity (pH=5), and may explain the limited specificity of ex::phyA plants for phytate in this soil. The efficacy of single exudation traits (e.g., phytase) therefore appear to be limited in P-replete soil conditions and may be improved where soil pH matches the functional requirements of the enzyme or trait of interest

Body-composition reference data for simple and reference techniques and a 4-component model: A new UK reference child

Background: A routine pediatric clinical assessment of body composition is increasingly recommended but has long been hampered by the following 2 factors: a lack of appropriate techniques and a lack of reference data with which to interpret individual measurements. Several techniques have become available, but reference data are needed. Objective: We aimed to provide body-composition reference data for use in clinical practice and research. Design: Body composition was measured by using a gold standard 4-component model, along with various widely used reference and bedside methods, in a large, representative sample of British children aged from 4 to ≥20 y. Measurements were made of anthropometric variables (weight, height, 4 skinfold thicknesses, and waist girth), dual-energy X-ray absorptiometry, body density, bioelectrical impedance, and total body water, and 4-component fat and fat-free masses were calculated. Reference charts and SD scores (SDSs) were constructed for each outcome by using the lambda-mu-sigma method. The same outcomes were generated for the fat-free mass index and fat mass index. Results: Body-composition growth charts and SDSs for 5-20 y were based on a final sample of 533 individuals. Correlations between SDSs by using different techniques were ≥0.68 for adiposity outcomes and ≥0.80 for fat-free mass outcomes. Conclusions: These comprehensive reference data for pediatric body composition can be used across a variety of techniques. Together with advances in measurement technologies, the data should greatly enhance the ability of clinicians to assess and monitor body composition in routine clinical practice and should facilitate the use of body-composition measurements in research studies. © 2012 American Society for Nutrition

Response-based selection of barley cultivars and legume species for complementarity:root morphology and exudation in relation to nutrient source

Phosphorus (P) and nitrogen (N) use efficiency may be improved through increased biodiversity in agroecosystems. Phenotypic variation in plants’ response to nutrient deficiency may influence positive complementarity in intercropping systems. A multicomponent screening approach was used to assess the influence of P supply and N source on the phenotypic plasticity of nutrient foraging traits in barley (H. vulgare L.) and legume species. Root morphology and exudation were determined in six plant nutrient treatments. A clear divergence in the response of barley and legumes to the nutrient treatments was observed. Root morphology varied most among legumes, whereas exudate citrate and phytase activity were most variable in barley. Changes in root morphology were minimized in plants provided with ammonium in comparison to nitrate but increased under P deficiency. Exudate phytase activity and pH varied with legume species, whereas citrate efflux, specific root length, and root diameter lengths were more variable among barley cultivars. Three legume species and four barley cultivars were identified as the most responsive to P deficiency and the most contrasting of the cultivars and species tested. Phenotypic response to nutrient availability may be a promising approach for the selection of plant combinations for minimal input cropping systems

The Mineral Composition of Wild-Type and Cultivated Varieties of Pasture Species

Mineral deficiencies in livestock are often prevented by using prophylactic supplementation, which is imprecise and inefficient. Instead, the trend for increased species diversity in swards is an opportunity to improve mineral concentrations in the basal diet. Currently, there are limited data on the mineral concentrations of different species and botanical groups, particularly for I and Se, which are among the most deficient minerals in livestock diets. We grew 21 pasture species, including some cultivar/wild type comparisons, of grasses, legumes and forbs, as single species stands in a pot study in a standard growth medium. Herbage concentrations of Co, Cu, I, Mn, Se, Zn, S, Mo and Fe showed no consistent differences between the wild and cultivated types. There were significant differences between botanical groups for many minerals tested. Forbs were highest in I and Se, grasses in Mn and legumes in Cu, Co, Zn and Fe. Comparing species concentrations to recommended livestock intakes, the forbs Achillea millefolium, Cichorium intybus and Plantago lanceolata, and the legumes Medicago lupulina, Trifolium hybridum and Lotus corniculatus, appear to be good sources of Co, Cu, I, Se and Zn. Further work is required to ensure these results are consistent in multispecies mixtures, in different soil types and in field trials

Body composition by 2H dilution in Gambian infants:comparison with UK infants and evaluation of simple prediction methods

Gambian infants show growth faltering, but the underlying body composition is unknown. The present study aimed to compare body composition in Gambian and UK infants using H-2 dilution; and to evaluate accuracy of bioelectrical impedance analysis (BIA) and creatinine excretion for estimating lean mass (LM), using H-2 as the reference. Body composition was measured in thirty Gambian infants, aged 3-18 months. using (1) anthroporrietry, (2) H-2, (3) BIA (equation of Fjeld et at. Pediatr Res (1990), 27, 98-102) and (4) 5 h urinary creatinine excretion. Compared with UK reference data, Gambian infants were light, short and had reduced BMI and skinfolds. The subscapular skinfold standard deviation score (SIDS) was greater than the triceps SDS (P<0.01), indicating central fat preservation. Both LM and fat mass were reduced in Gambian infants, with or without adjustment for length. However, whereas the Gambia-UK difference in LM increased with age, that in fat mass decreased. Average creatinine excretion was similar to that expected (95.5 (SD 23.2) % recovery), but LM estimates showed unacceptable error in individuals. BIA using Fjeld's equation overestimated total body water and LM (P<0.001), hence a new equation was developed, with standard error of 0.47 kg LM. In conclusion, Gambian infants characterised by growth faltering had LM deficits that increased with age. However, adiposity increased with age, and showed indications of a more central distribution than in the reference infants. A new BIA equation for LM prediction is presented however, creatinine excretion is not recommended for LM estimation in this population

A meta-analysis of organic and inorganic phosphorus in organic fertilizers, soils, and water:implications for water quality

Phosphorus is known to be an important contributor to eutrophication of aquatic systems, but the role of organic phosphorus is often overlooked. This review uses a meta-analysis approach to investigate inorganic and organic phosphorus in organic fertilizers, soils and waters, including the quantification of organic phosphorous forms such as monoesters, diesters, and inositol hexakisphosphate. Across these media, organic phosphorus comprised 22–46% of the total phosphorus (by mass of phosphorus). Bioavailable organic phosphorus appears to be more mobile than recalcitrant forms. Organic phosphorus may represent a significant risk for eutrophication, and the risk may vary according to the season, but conclusions are hampered by a lack of data