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Polymer additives in irrigation water to reduce erosion and better manage water infiltration
Get PDFWater-soluble polyacrylamide
(PAM) was identified as an
environmentally safe and highly
effective erosion preventing and
infiltration-enhancing polymer
when applied in furrow irrigation
water at 1-10 g m-3, i.e.
1-10 ppm. The agricultural use of
polyacrylamide, PAM, as an
additive in irrigation water has
grown rapidly since commercial
introduction in 1995 because it
improves water infiltration and
reduces erosion-induced soil
losses up to 97%, saving tons of
topsoil per hectare per year.
Various polymers and biopolymers
have long been recognized as
viable soil conditioners because
they stabilize soil surface structure
and pore continuity. The new
strategy of adding the conditioner,
high molecular weight anionic
PAM, to the irrigation water in the
first several hours of irrigation
enables a significant costs savings
over traditional application
methods of tilling soil conditoner
into the entire (15 cm deep) soil
surface layer. By adding PAM to
the irrigation water, soil structure is
Unproved in the all-important
1-5 mm thick layer at the
soil/water interface of the 25 to
30% of field surface contacted by
flowing water. Recent studies with
biopolymers such as chitosan,
charged polysaccharides, whey,
and industrial cellulose derivatives
show potential as biopolymer
alternatives to PAM. Their success
will depend on production
economics
Squeezer: A device for indirect pressure measurement in thin-walled microirrigation tubing
Get PDFA simple device was developed for measuring pressure in thin—walled collapsible emitting hose or tubing in the
field. The device, called a "Squeezer," senses pressure by measuring the force necessary to compress a short section of tubing
between two parallel plates to 50% of its original diameter. The force can be measured by either an electronic load cell or
a spring balance, and the output, calibrated for a particular size of tubing, read directly in pressure units. The device provides
a convenient, non—intrusive and low—cost means for irrigators to assess pressure variations within their microirrigation
laterals without installing special fittings or puncturing the tubing
Aeration, tillage effects on
Get PDFFew land management practices have the potential to
impact upon soil aeration as directly or rapidly as tillage.
Indeed, often, the reason for performing tillage is to modify
or improve soil physical properties including aeration. The
problems associated with inadequate aeration have been
comprehensively reviewed elsewhere (1, 2). Important
effects of limited soil aeration in crop production are:
altered nutrient dynamics, a shift from oxidative to
reductive chemical/biological reactions, impaired plant
growth, and changes in gas equilibria affecting both soil and
ambient atmospheres. For example, consider the soil
nitrogen cycle which aeration effects via its influence on
denitrification and gaseous nitrogen losses, decreased
nitrogen mineralization rate and a reduction in nodulation
and symbiotic fixation by leguminous plants (3). If the
oxygen supply is sufficiently limited, and anerobosis sets in,
then the products of reduction reactions may accumulate to
toxic levels. In addition, a depleted oxygen supply may
constrain root form and function, such as water and nutrient
uptake, and therefore plant shoot performance even when
many other soil physical factors are favorable (4).
Unfortunately, relatively short periods of oxygen shortage
can seriously compromise crop performance if they
coincide with critical stages of crop growth (1). Finally,
there are the effects of gas sources and sinks in the soil and
transformations of soil gaseous components, and the
exchange between soil and above ground air, on the
atmosphere, e.g., diminished soil aeration may enhance the
emission of greenhouse gases (5).
While the tillage-related literature is voluminous, little
of it directly addresses soil aeration. Of necessity, this
short article critiques only research which has measured
aeration status directly—particularly indices of concentration
and rate—and will make little or no attempt to draw
inferences about the effect of tillage on soil aeration from
studies reporting other related soil characteristics.
Although bulk density, moisture content, and pore size
distribution are related to soil aeration, and so may be
indicative of aeration status, their direct relevance to a
nuanced understanding of soil aeration is problematical.
For instance, measurements of pore space convey little
about pore continuity, tortuosity, or stability (6), whereas
these effects are largely integrated de facto in measurements
of oxygen diffusion rate (ODR)
Arbuscular mycorrhizal response to adverse soil conditions
Get PDFAdverse conditions are a pervasive feature in both natural as well as
agronomic soils. The soil environment is constantly changing with regard
to moisture, temperature and nutrition. In addition, soil properties such
as fertility, pH and aeration are often changed to improve crop yields.
Soils have been unintentionally contaminated as a result of accidents that
occur during agronomic operations or intentionally contaminated in mining
or manufacturing operations by disposal of chemicals that are toxic
to plants and micro-organisms. Mycorrhizal associations in terrestrial
ecosystems influence organic and inorganic nutrient relationships, water
relations and carbon cycling in plants. Relatively little is known about
factors that control the vigour and extent of mycorrhization. This lack of
understanding arises in large part from the difficulty of studying the
intact association, which is a functionally and anatomically distinct structure
comprising two biologically different organisms, e.g., plants and
arbuscular mycorrhizae (AM) fungi. The formation and function of
mycorrhizal relationships are affected by edaphic conditions such as soil
composition, moisture, temperature, pH, cation exchange capacity. They
are also affected by anthropogenic stressers such as heavy metals, pesticides
and soil compaction.
An organism's response to stress may involve interactions among
various avoidance and tolerance mechanisms (Taylor, 1978; Tingey and
Taylor, 1982; Tingey and Anderson, 1991). Stress avoidance mechanisms
influence the amount and rate at which stress will reach the target site in
the plant. Stress tolerance is defined as resistance via an ability "to come
to thermodynamic equilibrium to the stress" without being killed (Levitt,
1980). In this chapter, we shall review the effects of a number of soil-associated
stressers, including soil moisture, temperature, pH, heavy
metals, agricultural practices and pesticides on AM development and
function and host plant tolerance to these stresses. Several publications
have reviewed the impact of various stresses on plant-mycorrhizal
interactions (Anderson and Rygiewicz, 1991; Read, 1991; Van Duin et al, 1991;
Sylvia and Williams, 1992), which provide additional information on this subject
Influence of irrigation water properties on furrow infiltration: Temperature effects
Get PDFFor surface irrigation, the rate and spatial
characteristics of infiltration processes influence crop
productivity, water use efficiency, and erosion potential
of stream flows. A change in infiltration rate alters
furrow stream flow velocity and shear, and hence
irrigation-induced erosion. Furrow irrigation models
may be improved if they can account for the influence of
water properties on these processes. Water temperature
may influence furrow infiltration by altering fluid
viscosity. We conducted laboratory soil column intake
(constant head), and field recirculating furrow
infiltrometer experiments, to determine whether
irrigation water temperature significantly altered
infiltration. The soil was Portneuf silt loam (coarse-silty,
mixed superactive, mesic, Durinodic Xeric Haplocalcids).
Soil column intake increased by 0.8 to 3.0 percent per
degree C. This increase was not significantly different
from that observed for furrows, 2.0 to 2.9% deg.-1. While
more field studies are needed, these data show that
diurnal and seasonal changes in irrigation water
temperature can significantly alter furrow infiltration
and stream flow. These effects may help explain observed
field-infiltration variability. Inclusion of temperature
algorithms in furrow irrigations models may increase
their predictive accuracy
Registration of HiMag Tall Fescue Germplasm
Get PDFHiMag (Reg. no. GP-79, PI 615587) tall fescue (Festuca
arundinacea Schreb.) was developed and released by the Missouri
Agricultural Experiment Station and the USDA-ARS
in 1997. HiMag has relatively high Mg and Ca concentrations
and low tetany ratio [K/(Ca + Mg)] expressed as moles of
charge.
Parental germplasm for the Co cycle of selection for HiMag
included 950 plants from 'Kenhy' (Buckner et al., 1977), 831
plants from 'Kentucky-31', and 688 plants from `Missouri-96'
(Asay et al., 1979). All plants were endophyte free [ Neotyphodium
coenophialum (Morgan-Jones and Gams) Glenn, Bacon,
and Hanlin comb. nov.]. Parental plants were transplanted to
the field near Columbia, MO, in the fall of 1983. The soil was
a Mexico silt loam (a fine, montmorillonitic, mesic Udollic
Ochraqualf) with a pH of 6.4. Selection was applied against
crown rust (caused by Puccinia coronata Corda. var. coronata),
leaving 1011 plants which were harvested in the fall of
1984 and analyzed for elemental concentrations of Mg, Ca,
K, and the tetany ratio. Sixty-five plants (11 from Kentucky-
31, 54 from Missouri-96, and 0 from Kenhy) were chosen to
generate the C1 cycle of selection. These 65 plants contained
5.0 to 7.0 g kg-1 Mg, 5.0 to 10.2 g kg' Ca, 20 to 33 g K,
and had K/(Ca + Mg) values of 0.61 to 0.99. These were
allowed to open-pollinate in the greenhouse during the winter
of 1985/86. Harvested seeds were germinated in the greenhouse
and seedlings were transplanted to the field in the fall
of 1986. During the fall of 1987 approximately 1000 plants
were analyzed from the CI cycle to determine elemental concentrations
of Mg, Ca, K, and the tetany ratio. Forty-six plants
chosen for the C2 contained 4.4 to 6.1 g kg -' Mg, 5.5 to 8.1 g
kg-' Ca, 17.2 to 30.9 g kg' K, and had tetany ratios of 1.06
to 2.13. These were allowed to open-pollinate in the greenhouse
in the winter of 1988-1989. Approximately 1000 seedlings
were transplanted to the field having areas of Creldon
silt loam (Mollic Fragiudalf) and Hobert silt loam (Umbric
Fragiaqualf) at the Southwest Research Center, located near
Mt. Vernon, MO, in the fall of 1989. In the summer of 1990,
seed was harvested from these spaced plants and planted into
an irrigated Portneuf silt loam soil (Durinodic Xeric Haplocalcid)
to establish a seed increase block at Kimberly, ID, in
April 1991. In 1992, seed from HiMag was harvested with the
following characteristics: 1635 kg ha-1, 400 seeds g-1, 2.5 g
1000 seeds-1, and 302 kg m-3
A novel technique for the pre-concentration and extraction of inositol hexakisphosphate from soil extracts with determination by phosphorus-31 nuclear magnetic resonance
Get PDFInositol hexakisphosphate (IP6 ) is often the dominant form of soil
organic phosphorus (P), but is rarely investigated because of the
analytical difficulties encountered in its extraction, separation, and
detection in environmental samples. In particular, recent advances in
the study of soil organic P with 31 P nuclear magnetic resonance (NMR)
have been of limited use for the study of IP6 , because the technique
does not discriminate between IP6 and other forms of P. This was
addressed by developing a novel analytical procedure using the retentive
properties of gel-filtration gels for IP6, which allows the combined
selective extraction and pre-concentration of IP 6 from soil extracts
with determination by 31 P NMR. While the technique is still in the
developmental stage, the results demonstrate that the gel does not
interfere with 31 13 NMR analysis and retains IP6 to concentrations well
above those required to give clear spectral signals. The technique has
considerable potential for application to the study of IP6 in soil extracts
and water samples and, with development, could help to answer fundamental
questions regarding the dynamics of organic P in the environment
Hydraulic modeling of irrigation-induced furrow erosion
Get PDFIn the experimental Version 4.xx series, erosion
science is introduced into the surface-irrigation
simulation model, SRFR. The hydraulics of water flow in
furrows for individual irrigation events is predicted by
numerical solution of the unsteady equations of mass and
momentum conservation coupled to generally applicable
empirical equations describing infiltration and soil
roughness and to a known furrow configuration and
inflow hydrograph. Selection of appropriate field values
for the infiltration and roughness coefficients yields
infiltration distributions and surface flows (including
runoff) in reasonable agreement with measurements. The
erosion component consists in applying the simulated
hydraulic flow characteristics to site-specific empirical
determinations of soil erodibility, to general empirical
sediment-transport relations, and to general physically
based deposition theory to provide estimates of soil
erosion, flux, and deposition at various points along the
furrow as functions of time. Total soil loss off the field
and ultimate net erosion and deposition along the furrow
follow. At this initial stage of the investigations, a single
representative aggregate size is assumed adequate for the
analysis. Results are compared to measurements of
sediment concentrations in the furrow quarter points
and in the tailwater. For a given representative aggregate
size, the results are heavily dependent on the choice of
transport formula. The Laursen (1958), Yang (1973), and
Yalin (1963) formulas are programmed for investigation,
as are a variety of computational options. Preliminary
comparisons suggest the superiority of the Laursen
formulation, with the Yang and Yalin formulas
significantly over-predicting transport
Nonstructural carbohydrates: Challenges and progress in forage testing
Get PDFForage testing has evolved by adapting new technology but acceptance of different tests
for forage quality is slow and some tests are impractical. Reliance on technology has replaced
intuition and experienced knowledge in some cases. For example, alfalfa grown at high
elevations was preferred as dairy hay in the 1960's and 1970's. The use of forage testing in the
1980's and 1990's appears to favor alfalfa hay grown at lower elevations. Moreover, the forage
tests of acid detergent fiber (ADF) and neutral detergent fiber (NDF) do not consistently
predict animal intake or performance across cuttings. For example, hot season cuttings usually
have finer stems, are greener in color, and conventional tests show similar values of ADF and
NDF to first (cool season) cuttings, yet animal intake is less for the hot-season cuttings. Using
current forage testing to compare high versus low elevation grown hay, or to compare hays
from different cuttings, is not dependable. There are some promising developments which
should improve our ability to predict animal performance. The testing for nonfibrous
carbohydrates (NFC) or total nonstructural carbohydrates (TNC) are additional tools you may
want to use. Nonfibrous carbohydrates are defined by the National Research Council (2001) as
NFC = 100 - (%NDF + % CP + %Fat + %Ash), where CP is crude protein. Total nonstructural
carbohydrates are determined by a fractionation of the sample and are calculated as the sum of
monosaccarhides, disaccharides, short chain polysaccharides, and starch. This paper reviews
the underlying principles of forage quality and the development of testing; environmental,
genetic, and harvest management effects on forage quality; and reviews diurnal cycling of total
nonstructural carbohydrates and related animal preference studies
Mineral uptake of high-Mg cultivars of Italian ryegrass and tall fescue grown under different level of potassium
Get PDFMagnesium and potassium interactions affect the concentration of Mg in forages. By
evaluating the performance of high-Mg cultivars under different nutrient levels it is possible
to understand interrelationship, of nutrients as well as to find out optimum K levet for
screening forage plants. For this purpose. Italian ryegrass and tall fescue eultivars were
studied using nutrient solution culture to evaluate the growth and mineral uptake under
different K levels