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Variation in ruminant preference for alfalfa hays cut at sunup and sundown
Get PDFDiurnal variation in the concentration of total nonstructural carbohydrates
(TNC) occurs in plants as a result of photosynthesis. Ruminants
have been shown to prefer tall fescue (Festuca arundinacea
Schreber) hays cut in the afternoon but the effect of morning vs.
evening cutting had not been tested in legumes. To test for diurnal
variation in preference for alfalfa (Medicago sativa L.), we harvested
six times in the midbud stage. Harvests were paired so that each time
a cutting of alfalfa was made at sundown (PM) another was made
the next morning at sunup (AM). We harvested in this manner three
times resulting in six hays. The hays were field dried, baled, and
chopped prior to their use 3 to 6 mo after harvest. Three experiments
were conducted [Exp. 1, sheep (Ovis aries); Exp. 2, goats (Capra
hircus hircus); and Exp. 3, cattle (Bos taunts)] utilizing six animals
in each case. During an adaptation phase, hays were offered alone
as meals. In the experimental phase, every possible pair of hays (15
pairs) was presented for a meal. Data were analyzed by multidimensional
scaling as well as by traditional analyses. Multidimensional
scaling indicated that the animals were basing selection on at least
two criteria. Variables associated with preference through multiple
regression varied across experiments but significant coefficients were
found between preference and nitrate, protein, carbohydrate fractions,
lignin, and cellulose. Coefficients varied depending on which other
variables were in the model; however, carbohydrates were associated
with positive coefficients. Shifting hay mowing from early in the day
to late in the day was effective in increasing forage preference as
expressed by short-term dry matter intake
Influence of adverse soil conditions on the formation and function of Arbuscular mycorrhizas
Get PDFThe majority of plants have mycorrhizal fungi associated with them. Mycorrhizal fungi are ecologically significant
because they form relationships in and on the roots of a host plant in a symbiotic association. The host plant provides
the fungus with soluble carbon sources, and the fungus provides the host plant with an increased capacity to absorb
water and nutrients from the soil. Adverse conditions are a pervasive feature in both natural and agronomic soils.
The soil environment is constantly changing with regard to moisture, temperature and nutrient availability. In
addition, soil properties are often manipulated to improve crop yields. In many cases, soils may be contaminated
through disposal of chemicals that are toxic to plants and microorganisms. The formation and function of
mycorrhizal relationships are affected by edaphic conditions such as soil composition, moisture, temperature, pH,
cation exchange capacity, and also by anthropogenic stressors including soil compaction, metals and pesticides.
Arbuscular mycorrhizal fungi are of interest for their reported roles in alleviation of diverse soil-associated plant
stressors, including those induced by metals and polychlorinated aliphatic and phenolic pollutants. Much mycorrhizal
research has investigated the impact of extremes in water, temperature, pH and inorganic nutrient availability on
mycorrhizal formation and nutrient acquisition. Evaluation of the efficacy of plant–mycorrhizal associations to
remediate soils contaminated with toxic materials deserves increased attention. Before the full potential benefits of
arbuscular mycorrhizal fungi to reclaim contaminated soils can be realized, research advances are needed to improve
our understanding of the physiology of mycorrhizae subjected to adverse physical and chemical conditions. This
paper will review literature and discuss the implications of soil contamination on formation and function of
arbuscular mycorrhizal associations
Irrigation: An historical perspective
Get PDFIrrigation can be broadly defined as the practice of applying
additional water (beyond what is available from rainfall)
to soil to enable or enhance plant growth and yield, and,
in some cases, the quality of foliage or harvested plant
parts. The water source could be groundwater pumped to
the surface, or surface water diverted from one position on
the landscape to another. Development of irrigation water
often entails development of large-scale, geographically
significant dams and water impoundments and/or diversions
that can provide additional functions apart from crop
growth enhancement, e.g., flood control, recreation, or
generation of electricity. In many cases sustainable
irrigation development requires concomitant development
of surface and/or subsurface drainage
Aeration measurement
Get PDFSoil oxygen enables aerobic respiration of plant roots and
soil micro- and meso-flora and fauna. Its availability can
be limited by soil wetness, compaction, discontinuous
pores, or high respiration in moist soil due to elevated soil
temperature or incorporation of fresh organic substrate.
With oxygen depletion, soil redox potential shifts from
oxidative to reducing conditions, hampering plant growth
because of less efficient metabolic pathways and release
into soil of toxic by-products of reduction chemistry or
anaerobic respiration. Several texts are excellent sources
for fundamental soil aeration concepts (1-3).
Measurements of soil aeration fall into three categories:
"capacity," volume of gas-filled void space; "Intensity,"
partial pressure or concentration of oxygen (or other gases)
in the voids; and "transport rate," the rapidity at which
oxygen can be supplied to a point in the soil. Measurement
difficulty increases in the order capacity < intensity
< rate, as do the value and insight of the measurements
Evaluating WEPP predicted on-field furrow irrigation erosion
Get PDFThe Water Erosion Prediction Project (WEPP) model
has the ability to predict erosion from furrow-irrigated
fields. A previous evaluation showed that WEPP-predicted
infiltration and soil loss correlated poorly with
field measurements. Our objective was to further
evaluate the WEPP model for furrow irrigation by
comparing on-field distribution of measured and
predicted infiltration, runoff and soil loss. We used data
from three fields with Portneuf silt loam (coarse-silty,
mixed, superactive, mesic Durinodic Xeric Haplocalcids)
near Kimberly, ID. Single-event WEPP simulations were
used so predicted erosion could be evaluated without the
effects of daily model adjustments to effective hydraulic
conductivity, critical shear and rill erodibility. Single-event
simulations showed that the model could only
adequately predict infiltration and runoff within a field
when effective hydraulic conductivity was calibrated for
each irrigation. However even with accurate furrow
flows, the WEPP model could not adequately predict
sediment detachment, transport, and deposition within a
field. Comparing measured and predicted on-field
distribution of soil loss indicated that transport capacity
was over-predicted by the model because deposition was
only predicted when detachment was greatly over-predicted.
More thorough investigation of the WEPP
model programming and more detailed furrow erosion
field data are needed to develop an accurate simulation
model for furrow irrigation erosion
Seasonal phosphate activity in three characteristic soils of the English uplands polluted by long-term atmospheric nitrogen deposition
Get PDFPhosphomonoesterase activities were determined monthly during a seasonal cycle in three characteristic soil types of the English
uplands that have been subject to long-term atmospheric nitrogen deposition. Activities (moll para-nitrophenol ri soil dry wt.
h-1) ranged between 83.9 and 307 in a blanket peat (total carbon 318 mg g-1, pH 3.9), 45.2-86.4 in an acid organic grassland soil
(total carbon 354 mg g-1, pH 3.7) and 10.4-21.1 in a calcareous grassland soil (total carbon 140 mg g-1, pH 7.3). These are
amongst the highest reported soil phosphomonoesterase activities and confirm the strong biological phosphorus limitation in this
environmen
Biotransfer possibilities of selenium from plants used in phytoremediation
Get PDFWe are investigating the biotransfer of accumulated Se by the plant in several
phytoremediation systems. In study I, we evaluated the biotransfer of Se from Indian
mustard, a Brassica species, to the insect-cabbage looper (Trichoplusia ni); mortality,
deterrence, and biomagnification of Se were examined. We determined that
feeding behavior of food chain consumers was affected not only by the plant
concentration of Se, but also by the mobility of the insects and choice of feed
available. In study II, we examined the survival and development of beet armyworm
(Spodoptera exigua) fed Se-enriched plant tissues from different lines of saltbush
(Atriplex spp.) After feeding on lines of saltbush that produced high biomass and
accumulated high concentrations of Se, insect growth and survival was reduced. In
studies III, IV, and V, lambs, dairy cows, and rabbits were fed Se-enriched Brassica
and Medicago (alfalfa) plants as part of their feed ration. None of the tested animals
exhibited any Se toxicity symptoms, but they had increased levels of Se in most
tissues sampled (e.g., organs, blood, urine, feces), excluding milk. In study VI, we
evaluated biotransfer of Se from broccoli to rats to determine efficacy of Se for
reducing colon cancer. We found that Se-enriched plant material was more effective
than inorganic sources of Se for preventing precancerous colon lesions. Results from
all studies clearly show that Se absorbed by plants can be transferred biologically in
an intentional or unintentional manner to insects and animals
Management of irrigated agriculture to increase organic carbon storage in soils
Get PDFIncreasing the amount of C in soils may be one method to reduce
the concentration of CO2 in the atmosphere. We measured organic
C stored in southern Idaho soils having long term cropping histories
that supported native sagebrush vegetation (NSB), irrigated moldboard
plowed crops (IMP), irrigated conservation-chisel-tilled crops
(ICT), and irrigated pasture systems (IP). The CO2 emitted as a result
of fertilizer production, farm operations, and CO 2 lost via dissolved
carbonate in irrigation water, over a 30-yr period, was included. Net
organic C in ecosystems decreased in the order IP > ICT > NSB >
IMP. In this study, if NSB were converted to IMP, 0.15 g C m- 2
would be emitted to the atmosphere, but if converted to IP 3.56 g C
m 2 could be sequestered. If IMP land were converted to ICT, 0.95 g
C m 2 could be sequestered in soil and if converted to IP 3.71 g C
m 2 could be sequestered. There are 2.6 x 108 ha of land worldwide
presently irrigated. If irrigated agriculture were expanded 10% and
the same amount of rainfed land were converted back to native grassland,
an increase of 3.4 x 109 Mg C (5.9% of the total C emitted in
the next 30 yr) could potentially be sequestered. The total projected
release of CO2 is 5.7 X 10'" Mg C worldwide during the next 30
yr. Converting rainfed agriculture back to native vegetation while
modestly increasing areas in irrigated agriculture could have a significant
impact on CO2 atmospheric concentrations while maintaining or
increasing food production
Nutrient losses in surface irrigation runoff
Get PDFRunoff from surface-irrigated fields is typically managed to improve infiltration
uniformity by reducing differences in infiltration opportunity times between the upper and lower
ends of fields. Runoff water not used on other fields within an irrigation tract is discharged to
streams or rivers, along with sediment and nutrients. Return flow nutrient and sediment
concentrations may be greater than in the diverted water, but the total sediment and nutrient
mass returned may be less if most of the diverted water infiltrates within the irrigation tract.
Controlling erosion reduces total phosphorus loss, because total phosphorus concentration
relates directly to sediment concentration. On-farm management practices, such as
polyacrylamide (PAM) application and conservation tillage, reduce erosion from fields, while
sediment ponds in the field or on return-flow streams trap suspended sediment that is not
controlled by on-farm practices. Surface irrigation return-flow water quality can be improved with
an organized effort using a combination of practices
Erosion, controlling irrigation-induced
Get PDFErosion is the greatest threat to agricultural sustainability.
Most irrigation is on fragile arid soils that have enormous
crop yield potential when irrigated. However, that yield
potential is easily lost if the thin veneer of "topsoil" is eroded
(1). Erosion prevention on irrigated land is, arguably, more
important than on rainfed land. Yields from irrigated land
are more than double those from non-irrigated land, with
nearly triple the crop value per hectare (2). In addition,
runoff and irrigation return flows (necessary in many surface
irrigation schemes) deliver sediment; human, animal and
plant pathogens; nutrients and pesticides to downstream
fields and riparian waters. These pollutants accumulate in
runoff primarily as a result of erosion