1,125 research outputs found
Irrigation-induced erosion reduces yields and muddies rivers
The Snake River plain in southern
Idaho was a desert until ambitious
and far-sighted men built dams and
canals early in this century. The result
was green oases with names like Magic
Valley and Treasure Valley. and world
famous Idaho Potatoes. Nearly four million
acres are now irrigated in southern
Idaho producing a wide variety of crops
Influence of polymer charge type and density on polyacrylamide ameliorated irrigated furrow erosion
Previous experiments have shown that an initial application of 5-10 g m-3 (5-10
ppm) polyacrylamide to furrow irrigation water during flow advance can substantially reduce
sediment loss. This study determined polyacrylamide charge type or charge density
influences on furrow erosion. The study area was located near Kimberly, Idaho; soil was
Portneuf silt loam (coarse-silty, mixed, mesic, Durixerollic Calciorthid); and slope was 1.5%.
Polyacrylamides with contrasting charge type (neutral, anionic, cationic) and charge density
(0, 8-10, 19-20, 30-35%) were employed in the treatments. Polymers were applied at a
concentration of 10 g m-3 (10 ppm) during the initial 30 min of each treated irrigation, and
a 10 min additional application was introduced every 4 hrs (twice) during the remainder of
the irrigation. Inflow rate was 23 L min-1 (6 gpm) during furrow advance, and 15 L min-1
(4 gpm) for the balance of the irrigation. The nature of charge on the polyacrylamide did
influence efficacy of erosion control. On Portneuf soils, the order of effectiveness with
respect to PAM charge type was: anionic > neutral > cationic. Within anionic and cationic
charge types, polyacrylamide efficacy increased with increasing charge density
Influence of irrigation water quality on sediment loss from furrows
Agricultural erosion research has focused on rainfall-induced soil loss, with comparatively little attention to furrow
irrigation-induced erosion. One rationale for this is that rill erosion is mechanistically similar to erosion in irrigated
furrows. However, significant differences exist between the two processes. These are related to soil conditions during
initial stream advance, downstream flow rates, and chemical characteristics of the water stream. The salinity and
sodicity of water in rills are low, owing to its atmospheric origin, whereas, irrigation water quality varies geographically
and seasonall
Imhoff cone determination of sediment in irrigation runoff
There is a need to rapidly quantify erosion from irrigated farmland.
The prevailing method consists of collecting runoff samples, then filtering,
drying, and weighing them to determine sediment concentration.
Labor cost and slow data availability prompted development of
a faster, less expensive technique. Sediment settling volume in a graduated
vessel was expected to correlate well with total mass of suspended
sediment. Eight soils varying in texture, mineralogy, and
organic-matter content were sampled, fragmented, and air dried. A
series of 1-L suspensions was prepared with sediment concentrations
from 1 to 30 g L-1. Samples were either hand shaken for 30 s or
mechanically blended for 60 s. Suspensions were decanted into graduated
Imhoff cones and allowed to settle for 0.5 h (1800 s). The series
was repeated three times for each soil. Settling volume was regressed
against sediment concentration (total sediment, g L-1 ). Field calibrations
for two soils were developed from furrow runoff samples. Laboratory
regressions had a mean r2 of 0.99. Field regressions of two
soils had r2 of 0.94 or higher. Cone design did not permit accurate
volume estimates of the first 1 mL, causing slopes and intercepts to
very among field regressions for sediment concentrations <1.0 g L-1.
These samples, however, represent negligible erosion, and therefore
have little value. Slope and intercept of field regressions corresponded
closely to 30-s-shaken laboratory regressions but different statistically
at P ? 0.05. The technique provided a rapid, inexpensive, and accurate
suspended-sediment determination in the field for concentrations
>1.0 g L-1. Several settling-volume predictions based on textural
components and organic-matter content had r2 > 0.60. Laboratory 30-
s hand-shaken calibrations may be adequate for diagnostic purposes,
but individual field calibrations should be performed for research
purpose
Furrow irrigation water-quality effects on soil loss and infiltration
Irrigation-induced erosion is a serious problem in the western USA
where irrigation water quality can vary seasonally and geographically.
We hypothesized that source-water electrical conductivity (EC) and
sodium adsorption ratio (SAR = Na/[(Ca + Mg)/2]^0.5, where concentrations
are in millimoles of charge per liter) affect infiltration and
sediment losses from irrigated furrows, and warrant specific consideration
in irrigation-induced erosion models. On a fallow Portneuf silt
loam (coarse-silty, mixed, mesic Durixerollic Calciorthid), tail-water
sediment loss was measured from trafficked and nontrafficked furrows
irrigated with waters of differing quality. Treatments were the four
combinations of low or high EC (0.6 and 2 dS m-1) and low or high
SAR (0.7 and 12 [mmolc L-1]^0.5). Slope is 1%. Twelve irrigations were
monitored. Each furrow received two irrigations. Main effects for
water quality, traffic, and first vs. second irrigations were significant
for total soil loss, mean sediment concentration, total outflow, net
infiltration, and advance time. Average tail-water soil losses were 2.5
Mg ha-1 from low EC/low SAR furrows, 4.5 Mg ha-1 from low EC/
high SAR furrows, 3.0 Mg ha-1 from high EC/high SAR furrows;
and 1.8 Mg ha-1 from high EC/low SAR furrows. Elevating water
EC decreased sediment concentration from 6.2 to 4.6 g L-1, but
increasing SAR increased sediment concentration from 6.2 to 8.7 g
L-1. Net infiltration decreased 14% in high SAR compared with low
SAR treatments. Soil loss increased 68% for second irrigations, and
net infiltration fell 23% in trafficked furrows, but water-quality effects
were the same. Water quality significantly influenced infiltration and
erosion processes in irrigated furrows on Portneuf soils
Empty singularities in higher-dimensional Gravity
We study the exact solution of Einstein's field equations consisting of a
()-dimensional static and hyperplane symmetric thick slice of matter, with
constant and positive energy density and thickness , surrounded by
two different vacua. We explicitly write down the pressure and the external
gravitational fields in terms of and , the pressure is positive and
bounded, presenting a maximum at an asymmetrical position. And if
is small enough, the dominant energy condition is satisfied
all over the spacetime. We find that this solution presents many interesting
features. In particular, it has an empty singular boundary in one of the vacua.Comment: 13 page
Cone Penetration Tests (CPTs) in layered soils: a Material Point approach
Cone Penetration Tests (CPTs) can be used to determine in-situ soil properties and represent a practical choice for site investigation offshore, especially for linear infrastructure, such as offshore wind export cables. Information gained from CPTs is key for predicting soil-structure interaction behaviour, for example when predicting the tow forces involved in seabed ploughing, as the CPT provides an analogue to the process. The numerical modelling of CPTs is challenging due to the significant distortion in the soil displaced by the penetrating cone. This means that solving this sort of problem using finite elements, although not impossible, is numerically tiresome in terms of remeshing and mapping of state variables. Therefore, in this paper we adopt the Material Point Method (MPM) to develop a CPT prediction tool in layered soils. This MPM is combined with a novel non-matching mesh frictional boundary to represent the penetrometer. The developed tool will be used to understand the response of layered soils commonly found offshore as a step towards predicting the interaction of ploughs and anchors with the seabed
Root-zone mineral nitrogen changes as affected by crop sequence and tillage
Crop sequence and tillage affect soil mineral N (NH4 plus NO3)
and NO3 leaching below the root zone following alfalfa (Medicago
sativa L.). A 2-yr field experiment was conducted in south-central
Idaho to determine the effect on soil NO3 levels of a corn (Zea mays L.)-
wheat (Triticum aestivum L.) rotation compared with a bean (Phaseolus
vulgaris L.)-bean rotation and to demonstrate improved N utilization
with a corn-wheat rotation. Alfalfa, growing on an irrigated Portneuf
silt loam (coarse-silty, mixed, mesic Durixerollic Calciorthid), was
killed in October 1989 with herbicide. Treatments were: (i) BT-BT:
conventional tilled bean grown in 1990 and 1991; (ii) CNT-WNT:
no-till silage corn grown in 1990, and no-till winter wheat grown in
1990-1991; and (iii) CT-WT: same as CNT-WNT but under conventional
tillage. Similar amounts of soil N were mineralized the first
(275 kg N ha-1) and second (213 kg N ha-1) year after killing the
alfalfa in all treatments. The BT-BT treatment had the highest growing-season
soil mineral N (up to 251 kg ha-1, 0-0.45-m depth) because
the N uptake by bean was lower (187 kg N ha-1) than corn (252 kg
N ha-1, average of CT-WT and CNT-WNT treatments) in 1990 and
later than winter wheat uptake in 1991. Most wheat N uptake had
occurred by late June when bean uptake was just starting. A rotation
that follows alfalfa with corn or a crop with a similar N uptake pattern,
instead of bean, will save N fertilizer, lower soil NO3 levels, and reduce
NO3 leaching potentia
Preventing irrigation furrow erosion with small applications of polymers
Soil erosion is a serious problem threatening sustainability of agriculture
globally and contaminating surface waters. The objective of
this study was to determine whether low concentrations of anionic
polymers in irrigation water would appreciably reduce irrigation furrow
erosion on Portneuf silt loam (coarse-silty, mixed, mesic Durixerollic
Calciorthid), a highly erodible soil. Furrow slope was 1.6%,
furrow length was 175 m, and irrigation rates ranged from 15 to 23
L min-1. Inflow during the first 1 to 2 h of the first 8-h irrigation was
treated. Subsequent irrigations were untreated. Polyacrylamide (PAM)
or starch copolymer solutions were injected into irrigation water entering
furrows at concentrations of 0, 5, 10, and 20 g m-3 . Sediment
loss from polymer-treated furrows was significantly less than that of
control furrows in the first (treated) and second (untreated) irrigations,
but not in the fourth (untreated). The PAM provided better
erosion control than the starch copolymer. Efficacy of PAM treatments
varied depending on its concentration, duration of furrow exposure,
and water flow rate. In the initial (treated) irrigation and at
low flow rates, 10 g m-3 PAM reduced mean sediment load by 97%
compared with untreated furrows. Residual erosion abatement in a
subsequent irrigation, without further addition of PAM, was approximately
50%. The PAM increased net infiltration and promoted greater
lateral infiltration. Effective erosion control was achievable for a material
cost below $3 ha-1 irrigation-1
Seasonal trends in furrow irrigation erosion in southern Idaho
A study was conducted to measure the seasonal irrigation furrow erosion pattern in the absence of
cultivation and a growing crop. This erosion pattern was compared to those of previous measured
plot experiments for different years in the presence of cultivation and a growing crop. Erosion for
sugarbeets, corn and beans was low early in the season and increased to a maximum during the same
3-week period, from 24 June to 10 July over several years. Erosion decreased as the irrigation season
progressed after the erosion peak. The erosion pattern from the uncultivated, non-cropped plots
resembled the pattern from previous studies on cropped soil with the maximum erosion occurring
about the same time of season. The pattern trends differed only after peak erosion. For the cropped
plots, there was a sudden erosion decline after peak erosion, followed by a continual gradual decrease.
In contrast, for the uncultivated, non-cropped plots, there was a sudden erosion decline after peak
erosion, followed by a gradual increase in erosion. Although the seasonal erosion pattern cannot be
completely explained, it is important to report it because of the implication for erosion modeling.
Sediment loss rates measured from these soils in southern Idaho in late June or early July would
significantly overestimate seasonal erosion, whereas sediment loss rates measured in May or early
June or after mid-July would underestimate seasonal erosion. These results show that researchers
cannot rely upon a one-time measurement for model validation if attempting to predict irrigation
furrow erosion over an entire irrigating season
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