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Phosphorus in surface runoff from calcareous arable soils of the semiarid Western United States
Get PDFManagement strategies that minimize P transfer from agricultural
land to water bodies are based on relationships between P concentrations
in soil and runoff. This study evaluated such relationships for
surface runoff generated by simulated sprinkler irrigation onto calcareous
arable soils of the semiarid western United States. Irrigation
was applied at 70 mm h' to plots on four soils containing a wide
range of extractable P concentrations. Two irrigation events were
conducted on each plot, first onto dry soil and then after 24 h onto
wet soil. Particulate P (>0.45 !Lin) was the dominant fraction in
surface runoff from all soils and was strongly correlated with suspended
sediment concentration. For individual soil types, filterable
reactive P (<0.45 !Lin) concentrations were strongly correlated with all
soil-test P methods, including environmental tests involving extraction
with water (1:10 and 1:200 soil to solution ratio), 0.01 M CaCl 2, and
iron strips. However, only the Olsen-P agronomic soil-test procedure
gave models that were not significantly different among soils. Soil
chemical differences, including lower CaCO3 and water-extractable
Ca, higher water-extractable Fe, and higher pH, appeared to account
for differences in filterable reactive P concentrations in runoff from
soils with similar extractable P concentrations. It may therefore be
possible to use a single agronomic test to predict filterable reactive
P concentrations in surface runoff from calcareous soils, but inherent
dangers exist in assuming a consistent response, even for one soil within
a single field
Irrigation, site-specific
Get PDFIrrigation systems have evolved from flood systems to
pressurized sprinkler and trickle systems. In flood irrigation, water is applied to a field in a controlled stream
and allowed to flow over the soil surface by gravity, the
final distribution being affected by variations in surface
slope and water infiltration rates. Well-designed pressurized irrigation systems apply water at sufficiently low
rates that it infiltrates with little or no surface movement,
thus providing a greater degree of control and improved
uniformity of application
Compost amendments in a wood-chip + polyacrylamide medium decreased Verticillium dahliae infection on potato
Get PDFIf the soil around the plant roots could be altered to favor the non-pathogenic indigenous soil
microorganisms overrelative to the plant pathogens, the survival and proliferation of indigenous
soil microorganisms, and thus effectiveness of biological control, may be increased. We used
wood- chip+-polyacrylamide (PAM) cores to alter the soil environment in a greenhouse study to
favor indigenous soil microorganisms in vegetable and manure compost to reduce Verticillium
dahliae infection of potato (Solanum tuberosum L.) plants. Potato plants growing in soils
amended with vegetable compost-wood chip-PAM cores had significantly less disease because of
86 % lower visible (Vvis ) and 66 % lower isolation (Viso ) V. dahliae infection rateings than
control soils and soils with dairy or vegetable compost alone. Soils with wood chip-PAM cores
and soils with wood chip-PAM-vegetable compost had greater 2.5 times greater microbial
biomass/Verticillium dahliae biomass (MBNB) ratios in soil than control soils or in soils
amended with compost alone. MBNB ratios in wood chip-PAM cores and wood chip-PAM-vegetable
compost were 2.5 to 3.2 times greater than in wood chip-PAM-dairy compost cores. Vvis
correlated in a quadratic relationship with the MBNB ratio (r 2=0.76) indicating that as microbial
biomass increased, V. dahliae biomass and symptoms decreased. As MBNB ratio increased,
Vvis decreased
Water use and biomass production of oat-pea hay and lentil in a semiarid climate
Get PDFSuitability of alternative crops in the northern Great Plains remains
a question because of water limitations. Objectives were to compare
water use of an oat (Avena sativa L.)—pea (Pisum sativum L.) mix
grown for hay (OPH) to that of black lentil (Lens culinaris Medikus
cv. Indianhead) grown as green manure (BL). Water use and plant
biomass for OPH and BL were measured near Culbertson, MT (Site
1), during 4 yr. Soil water was measured by neutron attenuation.
Precision-weighing lysimeters were used at Site 2, located 65 km
southeast of Site 1, to measure water use. Soil was a Williams loam
(fine-loamy, mixed, superactive, frigid Typic Argiustolls). Biomass of
crops was measured biweekly. Relative feed value (RFV) based on
measured neutral detergent fiber and acid detergent fiber was calculated.
Biomass under OPH was 34 and 46% greater than with BL at
Sites 1 and 2, respectively. At Site 1, biomass accumulated at a rate
of 14 kg ha-1 mm-1 water used under BL and 23 kg ha -1 mm- 1 under
OPH. Biomass accumulated at a rate of 21 kg ha- 1 mm-1 under BL
and 29 kg ha -1 mm -1 under OPH at Site 2. Hay RFV, at full bloom
in pea, averaged 116 (Number 2 hay), and this did not change appreciably
as the crop matured to soft dough stage in oat. Oat—pea hay fits
the growing conditions in the northern Great Plains and meets the
needs of producers for high quality hay
Soil physics and hydrology: Conditioners
Get PDFThe use of naturally occurring materials as soil-stabilizing
conditioners has been part of agriculture
and general land management for millennia. Some of
the most familiar conditioners in use since ancient
times include animal and green manures, peat, crop
residues, organic composts, and lime. These early uses
of conditioners resulted from knowledge gained from
trial and error long before there was scientific understanding
of how efficacy was derived. Other conditioners
in use for centuries or decades include composted
manures, various organic debris, including sawdust
or other milling residues, food, textile, and paper-processing
wastes and other organic industrial wastes,
as well as mineral materials such as rock phosphates,
gypsum, coal dust, rock flour, and san
Identification of scyllo-inositol phosphates in soil by solution phosphorus-31 nuclear magnetic resonance spectroscopy
Get PDFA large proportion of the organic P in soils can occur as scyllo-inositol
phosphates. These compounds are rarely detected elsewhere
in nature and remain poorly understood, partly because conventional
procedures for their determination are lengthy and erroneous. We
report a straightforward procedure for the determination of scyllo-inositol
phosphates in soil extracts using solution 31P nuclear magnetic
resonance (NMR) spectroscopy. Solution 31P NMR chemical shifts of
a range of synthetic scyllo-inositol phosphate esters were determined
in alkaline solution. Of these, only the signal corresponding to scyllo-inositol
hexakisphosphate at approximately 4.2 ppm was identified
in soil NaOH–EDTA extracts, constituting between 6.5 and 9.8% of
the NaOH–EDTA extracted P. This signal has been previously assigned
to choline phosphate, but we confirmed it to be an inositol
phosphate using hypobromite oxidation, a procedure that destroys
all organic matter except inositol phosphates. Lower order scyllo-inositol
phosphate esters were not identified in the extracts studied
here, and literature reports suggest that they probably occur in insufficient
concentrations to be detected by this procedure. The identification
of scyllo-inositol hexakisphosphate in soils and other environmental
samples will allow its quantification in a range of environments,
and facilitate research into the origins and function of this enigmatic
compound
Colloidal phosphorus in surface runoff and water extracts from semiarid soils of the Western United States
Get PDFoai:eprints.nwisrl.ars.usda.gov:1Colloidal particles in runoff may have an important role in P transfer
from soils to waterbodies, but remain poorly understood. We
investigated colloidal molybdate-reactive phosphorus (MRP) in surface
runoff and water extracts of calcareous arable soils from the
semiarid western United States. Colloidal MRP was determined by
ultrafiltration and operationally defined as MRP associated with particles
between 1µm and 1 nm diameter, although a smaller pore-size
filter (0.3 nm) was used to define the lower size limit of colloids in
water extracts. In surface runoff from three calcareous soils generated
by simulated sprinkler irrigation, colloidal MRP concentrations ranged
between 0.16 and 3.07 1LM, constituting between 11 and 56% of the
MRP in the <1-gm fraction. Concentrations were strongly correlated
with agronomic and environmental soil-test P concentrations for individual
soils. Water extracts of a range of similar soils contained two
size fractions of colloidal MRP: a larger fraction (1.0-0.2um) probably
associated with fine clays, and a smaller fraction (3-0.3 nm) probably
associated with Ca–phosphate minerals. Colloidal MRP was solubilized
in the acidic medium of the colorimetric detection procedure,
suggesting that a fraction of the filterable MRP in runoff from calcareous
soils may not be as readily bioavailable as free phosphate in
waterbodies. Our results suggest that colloidal MRP is an important
but poorly understood component of P transfer in runoff from calcareous
western U.S. soils and should be given greater consideration in
mechanistic studies of the P transfer process
An automated vacuum extraction control system for soil water percolation samplers
Get PDFA vacuum applied to soil water percolation samplers permits collection
of both macro- and matrix-pore liquids. Performance of these
field samplers is improved when the extraction vacuum is adjusted in
accordance with the tension in the surrounding soil. This is particularly
important when monitoring a network of spatially distributed samplers
and for samplers installed in medium to fine textured soils. We designed
a vacuum extraction system to more efficiently collect vadose-zone
soil solution samples. A single vacuum pump, vacuum tank, and
air dryer provided a vacuum supply for 12 soil water sampling sites
via a branching polyethylene pipe network. A vacuum controller containing
two inexpensive pressure transducers, a voltage regulator,
relay, and solenoid valve was developed and tested for field installation.
Data loggers operated the controllers, monitored extraction vacuum
and ambient soil water potential, and adjusted relative vacuum
at each percolation sampling site. The automated vacuum controllers
successfully maintained sampler extraction pressures at levels proportional
to ambient soil water potential and provided the added benefit
of recording the pressure values for use in subsequent data interpretation
The relationship of leaf strength to cattle preference in tall fescue cultivars
Get PDFLow values of leaf blade tensile and shear strength have been
related to herbivore preference and intake in perennial ryegrass (Lolium
perenne L.) and other forage grasses. This study examined relationships
between leaf strength and cattle (Bos taunts) preference
for eight cultivars of tall fescue (Festuca arundinacea Schreb.). Both
tensile strength and shear strength of tall fescue leaf blades were
measured, along with several leaf blade anatomical characteristics.
Leaf tensile strength was negatively correlated (r = –0.20, P 5 0.01)
with preference in this study. `Mozark', the cultivar with the highest
leaf tensile strength, also had the highest proportion of structural tissue
in leaf blade transverse sections. Shear strength was also negatively
correlated with preference (r = –0.16, P s 0.05). Leaf strength of
both chamber- and field-grown plants was negatively correlated with
both leaf blade width and thickness. Leaf width and thickness increased
together and were positively correlated with preference in
all experiments. Wider leaves also had greater distance between veins
and therefore more mesophyll tissue volume. We concluded that leaf
width would be a useful trait in the selection of grasses for cattle
preference, since it would result in grasses with a higher proportion
of cell contents to fiber. This conclusion is supported by the positive
correlation of preference with total nonstructural carbohydrates in
an earlier study of the same tall fescue cultivars
On-farm evaluation of a phosphorus site index for Delaware
Get PDFThe contribution of phosphorus (P) to non-point source (N PS) pollution of surface
and groundwaters is a serious environmental problem in Delaware. In 1999, the Delaware
Nutrient Management Act was passed limiting application of P on "high" P soils to a "three year
crop removal" rate or to the amount recommended by a University of Delaware P site index. The
Delaware P site index was developed and evaluated on seven farms in Delaware, through a joint
effort between the universities of Delaware and Maryland. Results showed that 78% of fields
evaluated were in the "low" risk category, with the remaining 22% falling into the "medium"
(6%), "high" (7%), and "very high" (9%) risk categories. The components of the index found to
have the greatest influence on P site index ratings were soil erosion, subsurface drainage,
leaching potential, distance from field to surface water, soil test P and organic P application rates
and methods. P site index ratings were found to vary by year, depending on manure
applications, suggesting a need for yearly P site index evaluations or averages over a cropping
rotation. The P site index worked well for identifying fields with differing relative potential risks
of P loss; however, validation of these P loss assessments is needed to ensure that the risk
categories assigned are sufficiently protective of water quality. Continual monitoring, analysis,
and improvement of the P site index are needed to ensure that it remains a useful tool for P
based nutrient management planning in the future