Temperature, concentration, and pumping effects on PAM viscosity

As polyacrylamide (PAM) use in irrigated agriculture increases, new methods are being sought to accurately and automatically apply PAM with irrigation water. PAM is also beginning to be used in sprinkler irrigation. However, little information is available about flow characteristics of PAM solutions. This study was conducted to investigate temperature, concentration and pumping effects on viscosity of two agricultural PAM formulations: a dry powder and an inverse oil emulsion. Flow tests, using solutions prepared from the dry powder PAM, showed that viscosity decreased as flow rate increased for concentrations greater than 400 ppm. Thus, accurately predicting PAM viscosity at concentrations greater than 400 ppm is difficult because viscosity varies not only with concentration and temperature, but with flow conditions. Flow rate changes due to temperature fluctuations, however, should be minimal for the oil emulsion PAM over typical temperature ranges occurring under field conditions if tubing diameter is greater than 10 mm and tubing length is less than 1 m, which should be adequate for all surface irrigation applications. The two PAM products tested had similar viscosity relationships with temperature and concentration. PAM viscosity for solutions with concentrations < 24 ppm only increased about 5% relative to water for each 10 ppm increase in PAM concentration. Pumping a 2400 ppm PAM solution just once through a centrifugal pump reduced viscosity 15 to 20%; pumping five times reduced viscosity approximately 50%. The viscosity reduction is thought to result from breaking or shearing the PAM molecules, reducing its effectiveness to stabilize the soil surface and reduce soil erosion

Water temperature in irrigation return flow from the Upper Snake Rock watershed

Water returning to a river from an irrigated watershed could increase the water temperature in the river. The objective of this study was to compare the temperature of irrigation return flow water with the temperature of the diverted irrigation water. Water temperature was measured weekly in the main irrigation canal, 24 return flow streams and one ephemeral stream from 2005 to 2008 in the Upper Snake Rock (USR) watershed. The USR is an 82,000 ha watershed in southern Idaho, USA with about 60% of the area surface irrigated and the remaining area sprinkler irrigated. Median annual water temperatures in irrigation return flow streams were not greater than the water diverted from the river, suggesting that water flowing through the canal system and furrow irrigated fields does increase temperature. Water in seven of the 14 return flow streams that received flow from subsurface drains had significantly lower temperatures than the main canal in at least two years of the four years. Significant differences were generally only two to three degrees Celsius. Results of this study indicate that water can be diverted from a river for surface irrigation without increasing the temperature of the irrigation return flow

Irrigation: Erosion

Irrigation is essential for global food production. However, irrigation erosion can limit the ability of irrigation systems to reliably produce food and fiber in the future. The factors affecting soil erosion from irrigation are the same as rainfall—water detaches and transports sediment. However, there are some unique differences in how the factors occur during irrigation and in our ability to manage the application of water that causes the erosion. All surface irrigation entails water flowing over soil. Soil type, field slope and flow rate all affect surface irrigation erosion, with flow rate being the main factor that can be managed. Ideally sprinkler irrigation will have no runoff, but application rates on moving irrigation systems can exceed the soil infiltration rate, resulting in runoff and erosion. Using tillage practices to increase soil surface storage and selecting sprinklers with lower application rates will reduce sprinkler irrigation runoff. Irrigation can be managed to minimize erosion and maintain productivity

Evaluating WEPP-predicted furrow irrigation erosion

The Water Erosion Prediction Project (WEPP) model allows users to predict furrow irrigation erosion. However, an initial model evaluation showed that 1) WEPP default erodibility values had to be reduced for simulating furrow irrigation erosion and 2) the WEPP model overpredicted sediment transport capacity. Therefore, the purpose of this study was to investigate the applicability of the governing equations used in the WEPP model to calculate sediment detachment and transport. Sediment detachment data were collected from 53 irrigation furrows, 9 m long, on a Portneuf silt loam with flow rates varying from 2 to 50 L min-1 among furrows. Hydraulic shear measured in irrigation furrows varied from 0.4 to 1.7 Pa, which is less than the 2.6 to 8.8 Pa shear measured during WEPP rainfall simulation on the same soil. The linear relationship between shear and detachment rate used by the WEPP model may be appropriate for predicting both rainfall and furrow irrigation erosion as long as separate erodibility values are identified for furrow irrigation. A power function relating shear and detachment rate may allow one relationship to be used for both the low shear conditions in irrigation furrows and the high shear conditions in rills during intense rain storms. Although transport capacity could not be thoroughly evaluated with this data set, sediment detachment seemed to be limited by factors other than transport capacity,. Additional model evaluation is needed with data from other soils before changes to the model can be recommended or the model can be implemented for predicting furrow irrigation erosion

Intercropping in maize silage versus solo-seeding for alfalfa establishment in Wisconsin and Idaho

Alfalfa (Medicago sativa L.) intercropping with maize (Zea mays L.) silage is being developed in the northern United States to improve the profitability and environmental sustainability of forage production. This study, conducted under rainfed conditions inWisconsin and semiarid irrigated conditions in Idaho, compared the establishment of alfalfa and dry matter yield of four intercropping systems to three conventional systems. The former systems included alfalfa interseeded at planting or the vegetative emergence (VE) stage of maize and grown with or without prohexadione growth retardant. The latter systems included alfalfa seeded in spring, summerseeded after barley (Hordeum vulgare L.), or late summer-seeded after maize silage. Spring seeded and interseeded alfalfa inWisconsin also received foliar fungicide and insecticide during establishment. During alfalfa establishment, yield of intercropped maize silage was 1.8- to 4.4-fold greater than spring-seeded alfalfa. Compared to spring-seeded alfalfa, interseeded alfalfa had similar or somewhat lower stand density but similar first cut yield the following year, provided that intercropped maize was harvested near September 1 to allow ample alfalfa fall regrowth. Shifting interseeding from maize planting to the VE stage decreased early-season alfalfa growth, but improved maize silage yield, with minor effects on alfalfa fall growth, stand density, and first cut yield. Prohexadione application had little impact on establishment or yield of interseeded alfalfa. While having high plant density, alfalfa seeded after barley or especially maize had less fall growth and low first cut yield. Overall, alfalfa establishment and yield of intercropping systems compared favorably with conventional systems

Antimicrobial resistance in escherichia coli and enterococcal isolates from irrigation return flows in a high-desert watershed

Irrigation return flows (IRFs) are of interest because they collect surface runoff and subsurface drainage, causing them to have elevated contaminant and bacterial levels, and making them a potential point source of pollutants. The purpose of this study was to determine antibiotic susceptibility profiles of E. coli and Enterococcus spp. that were collected from IRFs in south-central Idaho. Environmental isolates can be a potentially important source of antibiotic resistance (AR) and IRFs may be one way resistance genes are transported out of agroecosystems. Water samples were collected from nine IRFs and one background site (canal water from Snake River) on a biweekly basis during 2018. Escherichia coli and Enterococcus were enumerated via a Most Probable Number technique, then subsamples were plated on selective media to obtain isolates. About 185 of 800 unique isolates for E. coli and Enterococcus were tested for antimicrobial susceptibility using the Sensititre broth microdilution plates. For E. coli, 11% of the isolates were resistant to tetracycline, with fewer numbers being resistant to the 13 other antibiotics, with none resistant to gentamicin. While 77% of the E. coli isolates were pan-susceptible, 9 MDR patterns with resistance up to 7 drug classes (10 antibiotics) occurred in 11 isolates. For the enterococcal species, only 9% of isolates were pan-susceptible and the single highest resistance was to lincomycin (75%) followed by nitrofurantoin (31%) and tetracycline (11%). In addition, 13 enterococcal isolates were determined to be MDR to up to 5 different drug classes and it was only prevalent among E. faecalis, E. faecium, E. casseliflavus, and E. thailandicus. Due to the potential for human contact, routine monitoring of E. coli and Enterococcus in the IRFs could be a useful tool to understand the long-term trends of AR in this mixed-use watershed

Evaluation of Potential Runoff and Erosion of Four Center Pivot Irrigation Sprinklers

The operational characteristics of center pivot sprinklers are well documented but few studies have been conducted to evaluate the effects that operating characteristics of a particular sprinkler have on infiltration, runoff, and erosion for specific soil types. The objective of this study was to evaluate potential runoff and erosion from four commercial center pivot sprinklers on three widely distributed, south central Idaho soils. A modified commercial irrigation boom system was used to emulate center pivot irrigation on experimental runoff plots. Sprinklers used in the study were: 1) Nelson R3000 with brown plate, 2) Nelson R3000 with red plate, 3) Nelson S3000 with purple plate, and 4) Senninger I-Wob with standard 9-groove plate. Based on manufacturer’s published sprinkler nozzle flow rates, up to 12% variation in applied water was measured between sprinkler types. Testing of sprinkler nozzle flow rates revealed up to an 8.6% difference between measured nozzle flow rate and manufacturer’s published data. Significant differences in runoff and erosion between sprinkler types were observed but were not consistent across all runoff tests or soil types. In general, sprinkler types that visually appear to more uniformly distribute sprinkler droplets over the wetted area with respect to time exhibited the greatest measured erosion rates. This functional difference in water application may cause sediment to remain in suspension in overland flow for a longer duration allowing sediment to be more readily transported down slope. A 50% reduction in sprinkler flow rate reduced runoff and soil erosion 60 to 80% for the same volume of water applied over six irrigations. Reducing sprinkler flow rate early in the growing season prior to crop canopy development could be an effective management tool for reducing sprinkler runoff and erosion

Effects of sugarbeet processing precipitated calcium carbonate on crop production and soil properties

Precipitated calcium carbonate (PCC) lime is a byproduct of sucrose extraction from sugar beet processing factories in Idaho. Each year 351,000 Mg PCC is produced and stockpiled at sugarbeet factories in Idaho. There are currently no viable disposal strategies for the PCC and these stockpiles continue to grow in size each year. The simplest solution would be to apply this PCC directly to agricultural fields each year, however the effects of PCC on high pH soils and southern Idaho crop rotations are not well understood. A study was conducted at the USDA-ARS laboratory in Kimberly, Idaho to determine the effects of PCC application to an alkaline silt loam soil on sugar beet, dry bean and barley production and soil properties. Three PCC treatments (rate and timing) and an untreated control were compared. The PCC had no effects on crop production factors and most soil properties. The only significant effect of PCC treatments was an increase in soil phosphorus (P) concentrations compared to the control. The PCC can serve as a P fertilizer. For all crops in this study, PCC was applied at rates that resulted in applied P levels that were 1.6 to 5.3 times greater than even the highest published recommended P rates. Compared to the control, bicarbonate soil P concentrations increased by 25% and 73% for the final PCC application amounts of 26.9 Mg per ha (6.7A treatment) and 89.7 Mg per ha (6.7A and 89.7T treatments), respectively. The PCC used in this study can safely be applied (at rates up to 87.9 Mg per ha) to heavier textured alkaline soils in the local growing area. Disposing of PCC in this way represents a viable strategy for reducing PCC stockpiles

Potential runoff and erosion comparison of four center pivot sprinklers

The operational characteristics of center pivot sprinklers are well documented but few studies have been conducted to evaluate the effects that operating characteristics of a particular sprinkler have on infiltration, runoff, and erosion of specific soil types. The objective of this study was to evaluate potential runoff and erosion from common commercial center pivot sprinklers on three widely distributed, south central Idaho soils. A modified commercial irrigation boom system was used to emulate center pivot irrigation on experimental runoff plots. Sprinklers used in the study were: 1) Nelson R3000 with brown plate, 2) Nelson R3000 with red plate, 3) Nelson S3000 with purple plate, and 4) Senninger I-Wob with standard 9-groove plate. There were significant differences in measured runoff percentages and measured erosion rates between center pivot sprinkler types for the soils tested and experimental conditions. The magnitude of the differences among sprinklers was equal to or greater than the differences between the soils tested. The I-Wob and S3000 sprinklers exhibited the greatest measured runoff percentages and measured erosion rates and the R3000 sprinklers exhibited the least runoff and erosion for the three soils tested. In general, sprinkler types that visually appear to more evenly distribute sprinkler droplets over the wetted area with respect to time exhibited the greatest measured runoff and measured erosion rates. The relative ranking of the sprinklers in terms of measured runoff percentages and measured erosion rates was consistent when four and six irrigation events were used to apply 75 mm of water. The relative differences in runoff between the sprinklers tested were not directly proportional to sprinkler droplet kinetic energy per unit water volume applied. This outcome is in conflict with conventional theory on soil surface sealing from droplet impact. Possible explanations include incorrect representation of sprinkler droplet kinetic energy, conventional soil surface sealing theory does not apply to the soils used in this study, or some unknown factor is dominating the infiltration and runoff process for the study conditions

Phosphorus loss with surface irrigation

Definition: Surface irrigation uses gravity to deliver water across the field, contrary to sprinkler or drip irrigation that uses pipe or tubing as the conveyance system. Water flows across the field in small streams for furrow irrigation or in a sheet for border and basin irrigation. Problem: In some surface irrigation systems, runoff is desirable to improve the uniformity of water infiltration between the upper and lower ends of the field. Containing all runoff from sloping fields (>1 percent) is also impractical. During the irrigation event, water flowing over soil detaches, transports and deposits sediment and nutrients that are often attached to sediment. Phosphorus (P) can also desorb from the soil and transported sediment, increasing soluble P in surface irrigation runoff. Therefore, there are two main mechanisms that influence P transport in these systems: erosion and desorption of P into runoff water