Modifications of Pfeifer's Bird-Control Apparatus

Pfeifer's bird-control apparatus was modified and tested in 1967. Several safety features were incorporated. Also, an industrial timer was added as an interrupter to break the circuit from a high voltage transformer at regular, short intervals providing the arcing and snapping needed in a dry climate

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

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

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

Soil management to prevent earthworms from riddling irrigation ditch banks

Earthworm activities were observed under subdued light in lucite fronted soil filled boxes in which bean plants were growing. They formed their burrows by ingesting a relatively small core of soil about 2 mm in diameter and expanding these holes to a diameter of about 5 mm by flexing their muscles. The compacted zone extended about 4 mm from the radii of these burrows. As shallow bean roots of young plants extracted water from the upper portions of the soil, worms moved downward to moister soil. During furrow irrigation, worms moved toward the water source through existing burrows. A few of them burrowed new holes to the furrow and emerged and swam in the water for up to 20 min before burrowing back into the mud in the bottom of the furrow. In columns with sections packed with pressures of 50, 100, 200, 300 and 600 kPa, worm burrowing was reduced in sections packed at higher pressures and was practically negligible in the sections packed at 600 kPa. Visual comparison of porosity in the compacted soil surrounding earthworm burrows and the soil compacted at 300 and 600 kPa indicated that the worms are able to compact soil with a force between 300 and 600 kPa. Worms were not able to survive long enough to burrow through 15 cm of a subsoil with organic carbon content less than 0.2% that lay between them and topsoil. Both compaction and use of subsoil for the banks show promise for reducing earthworm burrowing and water loss from ditches

Grazing Cow and Calf Responses to Zinc Supplementation

This experiment evaluated weight gain responses to supplemental Zn by cows and calves grazing forage containing Less than 20 ppm Zn. One hundred cow-calf pairs in each of 2 years and 120 pairs in a third year were pastured together over a 63- to 77-day preliminary period during which cows were exposed to bulls. Each experimental period began in mid-June after bulls were removed and continued for 125 to 154 days. During this period, cattle grazed mature dry forage containing <20 ppm Zn and were fed protein supplements with or without added Zn. Estimated Zn intake by each cow-calf pair in the control group ranged from about 140 to 260 mg/pair/day. Daily Zn intake was supplied by forage (100 to 200 mg), basal supplement (32 to 57 mg), water (4 mg), iodized block salt (1 mg) and soil (1 mg). Each cow-calf pair fed the supplement with added Zn received an additional 860 to 900 mg Zn/day. Calves fed Zn gained 6% more (P<.05) weight (.04 kg/day) than did calves in the control group. Weight gains by cows did not differ (P<.05) between the two groups. Clinical signs of Zn deficiency were not observed in any animals. Conception, which occurred before the experimental period, and subsequent calving rates were not affected by Zn supplementation

Root and Sucrose Yields of Sugarbeets as Affected by Mid-to-Late-Season Water Stress

Investigations of the irrigation water requirement of sugarbeets (Beta vulgaris L.) in Arizona and California have shown that water stress several weeks before harvest of fall-planted beets reduces root yields but increases sucrose concentration (2,3). Their studies showed that, since soil and plant water stress late in the season did not significantly reduce sucrose production, irrigations could be discontinued 3 to 4 weeks before harvest for maximum water economy. Mid- to late-season water deficit studies on spring-planted sugarbeets at this Center in 1977 and 1978 clearly showed that sucrose yield was reduced very little in this area, if at all, if irrigations were discontinued after the soil profile was filled with water about 1 August or 10 to 12 weeks before harvest, on soil having a useable soil water reservoir of at least 200 mm (1) . However, if no rainfall occurs, a light irrigation about 1 month after water cutoff may be advantageous. The major difference between these two areas (Arizona-California and Idaho) is that in Arizona and California, potential evapotranspiration rates are higher and increasing when fall-planted beets are harvested; whereas in Idaho, potential rates are lower and decreasing when spring-planted beets are harvested. Allowing mid- to late-season water stress to develop in the Idaho area reduces irrigation water requirements by about 30% during August, September, and October when irrigation water and hydro-electric power for pumping are in shortest supply. Other recent investigations also show the drought tolerance of sugarbeets throughout the growing season ( 8, 11)

Cropping and Fertilizing Wheat and Barley in the Camas Prairie - Fairfield Area

Wheat and barley grown every year with proper fertilization yielded as well as or better than when grown after fallow without fertilizer. Successful annual cropping requires: (1) selecting normal medium-textured (not droughty) soils, (2) controlling weeds, and (3) applying adequate nitrogen and sulfur. In general, annual cropping is a soil-conserving practice

Furrow Erosion and Water and Soil Management

EFFECTS of basic water and soil interactions on erosion are reported. The effects of flow rate and slope on perimeter shear stress are outlined for channels in which the ratio of breadth and depth of the flow cross section stay reasonably constant. Effects of the resulting shear stress on erosion are discussed in terms of coefficients for the equations developed and several data sets. For furrows with a relatively constant breadth to depth ratio, erosion appears to be related to the shear stress by an exponent which varies between two and four depending on the range of cohesive forces holding the soil particles to underlying soil. The data sets studied indicate continuous exponential relationships rather than a "critical shear stress" below which there is no erosion. Following disruption of Portneuf silt loam by tillage or compaction, cohesion increases with time. Maximum rate of cohesion increase occurs when the soils are moist, but have sufficient tension in the water to draw the particles firmly together. Rapid wetting of dry soils disrupts a majority of the bonds between particles, allowing aggregate disintegration which reduces infiltration rates and substantially increases erosion. Considering erosion as an independent factor, not affected by sediment load and carrying capacity, allowed development of equations which appear to describe the whole erosion-deposition process. These findings indicate several management options which can decrease furrow erosion

Silicon in C-3 grasses: Effects on forage quality and sheep preference

Silicon in forage reduces dry matter digestibility and may reduce grazing preference. Two studies were conducted with the following objectives: (1) to evaluate a method of determining grazing preference, and (2) to characterize the distribution and solubility of silicon in 31 accessions of C-3 grasses and relate these traits to grazing preference and estimated forage digestibility. Forage samples were clipped at the beginning of each 7 to 10-day grazing period corresponding to 6 phenological stages of the Agropyron sp. Samples were washed and analyzed for acid detergent fiber (ADF), neutral detergent fiber (NDF), and silicon in ADF and NDF residues. Leaf silicon concentrations increased from the vegetative to seed-ripe stage. Genera were aligned into 3 groups based on the increase in leaf silicon concentration with advancing phenological age. Silicon concentrations in leaves of Agropyron, Pseudoroegneria, and Thinopyrum increased at nearly twice the rate of those in Critesion, Hordeum, Leymus, and Psathyrostachys. Elymus leaves contained higher concentrations of silicon at the vegetative stage than the other groups, but the accumulation rate was intermediate. About 32% of total leaf silicon remained in NDF and 76% in ADF residues at the vegetative stage. These insoluble portions of silicon increased with aging. Preference was positively related to estimated dry matter digestibility at boot and anthesis, but was not related to fiber or silicon measurements. Leaf harshness was negatively related to preference at seed-ripe stage. Further progress in characterizing the role of silicon in C-3 forage grasses should be possible by studying a representative species from each group