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Phosphate sorption by Pacific Northwest calcareous soils
Get PDFUnderstanding phosphorus (P) sorption of calcareous soils is important
for the development of successful fertilizer and manure management
practices. This study was conducted to identify soil chemical properties
controlling P sorption in semiarid calcareous soils of the Pacific Northwest.
Sorption isotherms of 18 primarily calcareous soils ranging widely
in soil physical and chemical properties were constructed by equilibrating
4 g of soil with 40 mL of 0.01M CaC12 containing between 0 and 700
mg P 1.- 1 for 24 h. The P sorption isotherms at low to medium P concentrations
fit the Freundlich isotherm (r2 � 0.93). The slope of the
isotherm generally increased abruptly at high P concentrations, suggesting
Ca-P precipitation. The maximum P sorption prior to Ca-P precipitation
was closely related to organically complexed Fe and Mn (R2 >
0.98), suggesting that such complexes may regulate P sorption in these
soils. The equilibrium P concentration at the point where Ca-P precipitation
begins to dominate was closely related to pH and organic carbon.
A better understanding of the role of organically complexed metals in
controlling P sorption in calcareous soils is needed to determine how P
solubility is affected by organic matter additions and how this will ultimately
impact the plant availability and potential off-site transport of P
from these soils
Separation of soil organic phosphorus compounds using reverse-phase ion-pair chromatography
Get PDFMethods were developed for the extraction and separation of soil organic
phosphorus compounds using reverse-phase ion-pair chromatography
(RP-ICP). Nucleotides (ATP, ADP, and AMP) were separated using a
mobile phase of 15 mM TBAHS, 15 mM KH2PO4, and 7% acetonitrile.
Inositol hexakisphosphate was separated using a mobile phase
composition of 0.05 M formic acid:methanol (49:51 v/v) and
1.5 mL/100 mL of TBAOH. Extraction procedures were developed for
the nucleotides which would be compatible with the RP-ICP system
developed for their separation
Organic phosphorus composition and potential bioavailability in semi-arid arable soils of the Western United States
Get PDFThe organic P composition of semi-arid arable soils is largely unknown,
but such information is fundamental to understanding P dynamics
in irrigated agriculture. We used solution "P nuclear magnetic
resonance (NMR) spectroscopy and phosphatase hydrolysis to characterize
organic P in semi-arid arable soils from the western USA (organic
C 2.0-30.7 g C kg' soil, clay 2-48%, pH 5.2-8.2, CaCO 3 <1-480 g
kg -' soil). Total P concentrations ranged from 220 to 1210 mg P kg-1
soil, of which between 12 and 45% was extracted with NaOH-EDTA.
Inorganic orthophosphate was the dominant P compound, but concentrations
determined by solution 31P NMR spectroscopy were consistently
greater than those determined by molybdate colorimetry. Concentrations
of organic P were relatively small, and were dominated
by orthophosphate monoesters (11-130 mg P kg-1 soil), with smaller
concentrations of orthophosphate diesters (0-7 mg P kg-1 soil). Pyrophosphate
was present in almost all soils at concentrations up to 14 mg
P kg-1 soil. Bicarbonate-extractable organic P ranged from 1.7 to
22.8 mg P kg-1 soil, of which between 37 and 87% was hydrolyzed
by phosphatase enzymes, suggesting its bioavailability. Soil organic
P concentrations were positively correlated with mean annual precipitation,
organic C, clay, and oxalate-extractable metals (Al, Fe, Mn),
and negatively correlated with mean annual temperature and soil pH.
However, CaCO3 concentrations were not significantly correlated with
any soil property. These results indicate that equilibrium levels of
organic P in semi-arid arable soils are controlled by a balance between
the physical protection offered by the soil matrix and the suitability
of the environment for biological productivit
Deficiencies in the soil quality concept and its application
Get PDFSoil quality is a concept that has deeply divided the soil science community. It has
been institutionalized and advocated without full consideration of concept weaknesses and
contradictions. Our paper highlights its disfunctional definition, flawed approach to
quantification, and failure to integrate simultaneous functions, which often require contradictory
soil properties and/or management. While the concept arose from a call to protect the
environment and sustain the soil resource, soil quality indexing as implemented may actually
impair some soil functions, environmental quality, or other societal priorities. We offer the
alternative view that emphasis on known principles of soil management is a better expenditure of
limited resources for soil stewardship than developing and deploying subjective indices which fail
to integrate across the necessary spectrum of management outcomes. If the soil quality concept
is retained, we suggest precisely specifying soil use, not function or capacity, as the criteria for
attribute evaluation. Emphasis should be directed toward using available technical information to
motivate and educate farmers on management practices that optimize the combined goals of high
crop production, low environmental degradation, and a sustained resource
Quality soil management or soil quality management: Performance versus semantics
Get PDFIn the past 200 years, soil science has used reductionist research to develop agricultural technologies that have unlocked the hidden potential of earth's natural systems to feed, clothe, and provide raw materials to the human population of over six billion. The soil quality paradigm seeks to change that scientific approach, the nomenclature of soil science, and institutional priorities for soil management and research. The definition of soil quality is elusive and value-laden. Concerns exist for the paradigm's policy overtones, regional and taxonomic biases, failure to reconcile conceptual contradictions, as well as its ambiguous definitions that are confounded by countless circumstance-specific, function-dependent scenarios. The paradigm does not recognize or offer practical means to manage conflicting, and often contradictory soil management requirements for the multiple functions of soil that occur simultaneously. Implementation of the concept has delivered low index ratings for many of the most economically productive and least subsidized US soils and agricultural sectors, and high ratings for soils and regions with some of the lowest economic return and greatest subsidization. The paradigm's focus on arbitrarily selected function assessment has diverted research and management resources from efforts aimed directly at developing improved management capable of solving existing identified and prioritized problems. We attempt to articulate the dangers of shifting soil science away from the value-neutral tradition of edaphology and specific problem solving to a paradigm based on variable, and often subjective, societal perceptions of environmental holism. We submit that over-arching, philosophically driven indexing of soil status, as opposed to focused, specific soil status and property characterization, carries risks to the scientific assessment process, and to the scientist's role as a data interpreter and science mediator. Value intrusion in umbrella-style indices erodes the individual manager's access to objective data to make decisions. We suggest emphasizing quality soil management rather than soil quality management as a professional and scientific goal
Seasonal phosphatase activities of mosses from Upper Teesdale, northern England
Get PDFChanges in tissue nutrient concentrations and surface phosphatase activities of eight moss species were measured
over one year in terrestrial and semi-aquatic environments on Widdybank Fell, Upper Teesdale National
Nature Reserve, northern England. Rates of phosphatase activity in apical regions of moss shoots differed
markedly between species, but were generally greatest in the winter and least in the summer in most species.
Mean values for phosphomonoesterase activity (umol para-nitrophenol g-1 d.wt h-1) ranged from 18.2 for
Polytrichum commune to 85.8 for Palustriella commutata var. falcata. Mean phosphodiesterase activity ranged
from 3.1 for Polytrichum commune to 86.2 for Hylocomium splendens. In contrast, tissue nitrogen and phosphorus
concentrations remained relatively constant throughout the year. Phosphatase activities were negatively
correlated with tissue phosphorus concentration for several species, although few relationships were detected
between ambient nutrient concentrations and phosphatase activity, tissue nitrogen, or tissue phosphorus
concentration. These results demonstrate that phosphatase activities can provide a sensitive indicator of nutrient
stress in terrestrial and semi-aquatic mosses, notably in the ectohydric Hylocomium splendens. However,
further studies at sites with a wide range of nutrient levels are required to determine whether the technique can
be used to indicate ambient nutrient status
Irrigation increases carbon in agricultural soils
Get PDFIrrigated agriculture sequesters significant amounts of organic C. Irrigation may also
sequester significant amounts of inorganic C. Inorganic C reactions are important chemical reactions
in irrigated soils and may contribute to the total amount of C sequestered. Calcium content of arid and
semi-arid soils tends to be higher than rainfed temperate soils due to calcium rich parent material and
low rainfall. Carbonate formation is usually controlled by carbonate equilibrium reactions in the solid
and g as phase CO2 . Respiration in plant roots and soil microorganisms continually produce CO,
increasing its concentration in the soil atmosphere, modifying carbonate solubility. Since irrigation
water flows through a series of canals, where smaller amounts of water are directly exposed to
incoming radiation, irrigation water usually has higher temperatures than stream or ground water.
Carbon dioxide dissolves in water to form both CO2 as a gas and H2CO3 in solution. Warmer water
increases reaction time and, in favourable conditions, precipitates CaCO3 .We measured organic and
inorganic C stored in southern Idaho soils having long term land use histories that supported native
sagebrush vegetation (NSB), irrigated mouldboard ploughed crops (IMP), irrigated conservation -
chisel- tilled crops (ICT) and irrigated pasture systems (IP). Inorganic C and total C (inorganic +
organic C) in soil decreased in the order IMP>ICT>IP>NSB. We use our findings to estimate the
amount of possible organic, inorganic and total C sequestration if irrigated agriculture were expanded
by 10%. If irrigated agricultural land were expanded by 10% worldwide and NSB were converted to
IMP, a possible 1.90 x 10' Mg total (organic +inorganic) C (2.72 % of the total C emitted in the next
30 yr) could be sequestered in soil. If irrigated agricultural lands were expanded by 10% worldwide
and NSB were converted to ICT, a possible 1.30 x 10' Mg total C (2.24 % of the total C emitted in the
next 30 yr) could be sequestered in soil. If irrigated agricultural land were expanded worldwide and
NSB were converted to IP a possible gain of 1.7 x 10 8 Mg total C (1.174 % of the total C emitted in
the next 30 yr) could be sequestered in soils. Altering land use to produce crops on high output
irrigated agriculture, while selected less-productive rainfed agricultural land were returned to
temperate forest or native grassland. there could be meaningful reductions in atmospheric CO 2
Potential contribution of lysed bacterial cells to phosphorus solubilisation in two rewetted Australian pasture soils
Get PDFSoil drying renders considerable amounts of phosphorus soluble upon rewetting, which may be partly derived from lysed microbial cells.
Using direct bacterial cell counting in water and tetra-sodium pyrophosphate extracts of two Australian pasture soils, we found that almost all
extractable cells were lysed following the rewetting of dry soils. The amounts of phosphorus in the lysed cells corresponded closely to the
increases in water-extractable phosphorus following soil drying, suggesting that bacterial cell lysis is a major source of the released
phosphorus
Quantification of myo-inositol hexakisphosphate in alkaline soil extracts by solution 31P NMR spectroscopy and spectral deconvolution
Get PDFInositol phosphates are the dominant class of organic phosphorus (P)
compounds in most soils, but they are poorly understood because they
are not easily identified in soil extracts. This study reports a relatively
simple technique using solution 31P NMR spectroscopy and spectral deconvolution
for the quantification of myo-inositol hexakisphosphate
(phytic acid), the most abundant soil inositol phosphate, in alkaline soil
extracts. An authentic myo-inositol hexakisphosphate standard added to
a re-dissolved soil extract gave signals at 5.85, 4.92, 4.55, and 4.43 ppm
in the ratio 1:2:2:1. Spectral deconvolution quantified these signals accurately
(102 ± 4%) in solutions containing a mixture of model P compounds
by resolving the envelope of signals in the orthophosphate monoester
region. In NaOH-EDTA extracts from a range of lowland
permanent pasture soils in England and Wales, concentrations of myo-inositol
hexakisphosphate determined by spectral deconvolution ranged
between 26 and 189 mg P kg- 1 soil, equivalent to between 11 and 35%
of the extracted organic P. Concentrations were positively correlated
with oxalate-extractable aluminum and iron but were not correlated with
total carbon, total nitrogen, clay, or the microbial biomass. This suggests
that myo-inositol hexakisphosphate accumulates in soils by mechanisms
at least partially independent of those controlling organic matter stabilization
and dynamics. Furthermore, myo-inositol hexakisphosphate concentrations
were positively correlated with plant-available inorganic P
and negatively correlated with the carbon-to-organic P ratio, suggesting
that biological P availability may, in part, regulate myo-inositol hexakisphosphate
concentrations in soils, perhaps because organisms capable
of degrading this compound are favored in more P-limited environments.
Solution 31P NMR spectroscopy and spectral deconvolution offers
a relatively simple method of quantifying myo-inositol hexakisphosphate
in soil extracts
A new tall fescue with a beneficial endophyte
Get PDFResearchers from the University of Arkansas, University of Missouri, and the USDA Agricultural
Research Service cooperated in an effort to produce a new cultivar of tall
fescue (Festuca arundinacea Schreb.) containing an endophyte (Neotyphodium
coenophialum) which does not produce ergot alkaloids. Our objective was to select and
introduce an endophyte which was not toxic to livestock be that retained the beneficial
characteristic of enhancing plant drought tolerance. Studies were conducted in Arkansas
and Missouri to test the safety and persistence of the cultivar HiMag with a nontoxic
endophyte, referred to here as ArkPlus. ArkPlus was shown to produce steer weight
gains as high as HiMag fescue without endophyte, and significantly higher than
Kentucky-31 fescue with its natural, toxic endophyte. Stand persistence of ArkPlus was
as good as toxic Kentucky-31 and better than endophyte-free HiMag in southwest
Arkansas. ArkPlus Brand tall fescue is currently being marketed by FFR Cooperative
and through its associated cooperatives throughout most states in the southeast