236 research outputs found
Aggregate Stability and Size Distribution
An aggregate is a group of primary particles that cohere to each other
more strongly than to other surrounding soil particles. Most adjacent
particles adhere to some degree. Therefore, disintegration of the soil mass
into aggregates requires imposition of a disrupting force. Stability of aggregates
is a function of whether the cohesive forces between particles
withstand the applied disruptive force
Soil Cohesion as Affected by Time and Water Content
Cohesion increased for several months after disruption in moist
soils. Rate at which cohesion increased was slower in airdry soil,
but continued for years. Moduli of rupture of soils also increased
with time. Effects of water content on the rate at which cohesion
increases are compatible with an explanation of the bonding mechanism
in terms of slightly soluble components diffusing to and
cementing points of contact between particles. Cohesional forces due
to water are estimated and found to be large enough to provide a
major portion of the cohesion measured in soils. These estimates
are supported by decreased cohesion of a silty soil when dried. However,
cohesion of soils with larger amounts of clay generally increases
when they are dried, indicating that other bonding mechanisms
predominate
Turbulent Flow Self Cleaning Trash Screens
Trash and weed seeds are a major problem to irrigators, particularly those
using gated pipe or siphon tube irrigation systems. Trash in surface irrigation
systems often stops or reduces flow through gates or siphons resulting
in inadequate irrigation of the furrows served. Constant surveillance
to clean trash out of these orifices is impractical. Weed seeds passing
through an irrigation system are distributed throughout the field causing
extra tillage operations and reducing yields
Cablegation: II. Simulation and Design of the Moving-Plug Gated Pipe Irrigation System
THE hydraulics of a moving-plug gated pipe irrigation
system are analyzed. A relationship was developed
for predicting orifice discharge coefficients for a range of
typical pipe flow velocity and head conditions. A simulation
model was developed to predict the time distribution
of orifice flows, the distribution of infiltrated water
across a field, and runoff rates. The model can be used to
design cablegation systems for fields having variable pipe
slopes and variable furrow lengths. Orifice sizes are
varied along the pipe line and the plug travel speed is
varied in order to obtain optimum net water application
for all furrows and to keep the furrow stream sizes within
acceptable limits
Using straw in steep furrows to reduce soil erosion and increase dry bean yields
Furrow-irrigated fields often have different slopes along a furrow, which
tend to cause different water intakes and erosion rates. Irrigated furrows on the steeper
slopes develop narrow channels that reduce the wetted perimeter in the furrow. This results
in lower infiltration, and crops growing on the steep acres do not receive adequate water
for the highest crop yield. Plants growing adjacent to straw-treated furrows received 1.3
to 2.1 times as much irrigation water as plants growing next to untreated furrows. Dry
bean yield increases on the straw-treated furrows, compared to the untreated furrows,
ranged from 614 kg/ha to 1,306 kg/ha—a 21 % to 62 % increase, respectively. Also, sediment
yield reductions in the straw-treated furrows ranged from 69% to 90 % compared
to untreated furrows
Cablegation IV: The Bypass Method and Cutoff Outlets to Improve Water Distribution
TWO techniques of improving the water distribution
characteristics of cablegation systems are proposed
and evaluated. The bypass method, which largely
eliminates the problem of end effects, involves starting
the plug at the first outlet and initially bypassing most of
the flow to the downstream end of the pipeline, which is
plugged. As the plug moves down the pipe, the bypass
flow gradually decreases to zero. This method nearly
equalizes the inflow distribution to all furrows and allows
the use of a constant outlet opening size. The bypass can
be accomplished by using a parallel bypass pipe and
weir, or with a flow-through bypass plug. The bypass
plug appears to be the lower cost method and is as
effective as the weir in controlling the bypass.
The second technique deals with the low outlet flows
during the final stages of a "set" which are insufficient to
reach the end of the furrows such that excess water is
applied to the upper ends of the furrows. Two types of
cutoff outlets, a gravity valve and a siphon type outlet
were designed to abruptly cut off the flow at about the
same time that runoff ceases, thus maximizing the
uniformity of infiltration. The cutoff outlets are
recommended for soils having relatively high sustained
intake rates
Factors Which Affect Furrow Intake Rates
To apply irrigation water efficiently, the water must be absorbed evenly
across the field. In surface irrigation systems, this requires either that
the water be spread quickly across the soil surface so that each portion of
the field has a nearly equal time to absorb water, and that all portions of
the field absorb water at the same rate; or that water intake rate varies
across the field to compensate for differences in intake opportunity time.
Water distribution in surface irrigation systems is determined by: 1) the
water application system capabilities and management, and 2) the infiltration
characteristics of the field soils. Improved application systems and design
procedures for surface irrigation are being developed. But unless soil
infiltration rates can be managed to achieve uniform water intake at desireable
rates, high surface irrigation application efficiencies cannot be achieved.
Although the problem of nonuniform soil water intake can be solved by applying
the water through sprinkler or trickle systems at rates lower than the
lowest intake rates, with the present high energy costs, this option is often
not economical.
The objective of this study is to evaluate several farmer manageable factors
which can affect water intake rates into irrigated furrows. The long term
research goal is to quantify the effects of farmer practices which decrease
intake uniformity, practices he can apply to improve uniformity, and practices
which can change intake rates. Intake rate modification can be useful to
accelerate advance (thus decreasing variations in intake opportunity times),
counteract the effects of variations in intake opportunity times, or better -
adapt a field to a fixed or desireable water application system or schedule.
The manageable factors which will be discussed are:
1) wheel compaction of furrows
2) surface soil water content
3) flow rates, and
4) intermittent application, such as "surge" irrigation
Soil cohesion as affected by freezing, water content, time and tillage
This study was developed to determine whether there are substantial
annual changes in soil cohesion and to identify major factors
causing those changes. Aggregate stability was measured throughout
the year on soils in Utah and Idaho using wet sieving techniques.
Stability generally increased during spring and summer months.
Major decreases of cohesion, found when minimum daily air temperatures
fell to or below 0 °C during winter and early spring months,
were attributed to pressures and associated shearing forces caused
by freezing at high water contents. Equivalent disruption occurred
when confined soils were frozen in controlled laboratory studies.
Disruption also increased as water content at the time of freezing
increased for all soils studied. Disruption of soil by rototilling and
compaction significantly decreased soil cohesion
Furrow Intake Rates and Water Management
FURROW intake rates and their effects on the uniformity
of water distribution throughout the length of
run are examined. Yields are substantially reduced by
nonuniformities. Several treatments are discussed which
can increase or decrease infiltration rates to improve
uniformity.
Furrow compaction is suggested as a method of compensating
for intake opportunity time differences resulting
from advance time requirements. Computations
show that differentially compacting the furrow along the
length of run could provide more uniform application
and increase the length of run without increasing erosion.
This reduces the farmer's investment in the irrigation
system and the time and energy required for planting,
cultivating and irrigating
Cohesion development in disrupted soils as affected by clay and organic matter content and temperature
Soils were dispersed and separated into sand, silt, and clay fractions
that were reconstituted to give mixtures of each soil with 5 to
40% clay. In the range from 0 to 35% clay, higher clay contents
resulted in greater stability. Rate of cohesion recovery was over 10
times as fast at 90°C as it was at 23°C, showing that the processes
Involved are physical-chemical rather than biological. Maximum rates
of cohesion recovery occurred at moderate soil water tensions, probably
because some tension is needed to pull the particles into direct
contact, but a continuous water phase is also essential to allow diffusion
of bonding agents to the contact points. Since diffusion rates
in water increase 300%, while rate of cohesion recovery increased
1000% when temperature was raised from 23 to 90°C, other factors,
such as higher Mobilities at higher temperatures of compounds
contributing hooding ions to the solution. probably play a role In
the rate of cohesion recovery. Recovery of cohesion was more rapid
in the soil with organic C contents of 0.004 kg/kg than in the soil
with 0.012 kg/kg. When the organic matter was removed with H2O2
from the soil with 0.012 kg C/kg, its rate of cohesion recovery increased.
Rate of cohesion recovery of this high organic matter soil
was also increased by aging it at 0.1 kg H2O/kg soil compared to
0.2 kg/kg. A possible explanation is that organic coatings, tending
to prevent direct contact and bonding of adjacent projections of mineral
surfaces, are forced away from contact points by extremely strong
forces that pull the adjacent minerals together when soil water tensions
are high. When the higher organic matter soil had been consolidated
by air-drying and rehydrated, its rate of cohesion recovery
was just as rapid as that of the soil with low organic matter
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