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 ($n+2$)-dimensional static and hyperplane symmetric thick slice of matter, with constant and positive energy density $\rho$ and thickness $d$, surrounded by two different vacua. We explicitly write down the pressure and the external gravitational fields in terms of $\rho$ and $d$, the pressure is positive and bounded, presenting a maximum at an asymmetrical position. And if $\sqrt{\rho}\,d$ 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