Delayed sample filtration and storage effects on dissolved nutrients measured in agricultural runoff

Standard water quality analysis methods recommend that sediment-laden runoff waters sampled to determine dissolved nutrient concentrations be filtered immediately after collection. Few research studies have examined the influence of delayed filtration on sample stability or nutrient loss assessments. Twenty eight runoff water volumes were collected from 3 irrigation furrows during a 12-h irrigation set. Four subsamples of each volume were obtained; 2 were filtered (45 µm) in the field and the other 2 were filtered 10 days later, with or without boric acid treatment (1 mL saturated H3BO3 solution per 100 mL sample). All samples were refrigerated at 4 deg. C. Dissolved reactive P (DRP), NO3-N, and NH4-N concentrations were measured in all filtered samples 10 and 107 days after collection. Samples filtered in the field and those with a 10-day delayed filtration had similar dissolved DRP, NO3-N, and NH4-N concentrations, whether or not boric acid was added. After 107 days storage: 1) measured NO3-N concentrations in delayed filtration samples were 3.7-times greater than that in field-filtered samples, regardless of boric acid addition; and 2) boric acid had stabilized DRP and NH4-N concentrations relative to field-filtered samples. When integrated across the entire irrigation, the mean NO3-N and DRP furrow stream concentration and runoff mass losses computed from runoff water samples were similar for field filtered and delayed-filtration/no-boric-acid treatments. However, when these same parameters were computed using delayed-filtration, extended-storage (107-d) sample results, both NO3-N (4.7x) and DRP (1.9x) were greater in magnitude. The field-filtered or 10-d delayed-filtration without boric acid treatments provided the best dissolved nutrient measurements for comparing agricultural management effects at the field edge; however, results suggest that an incubation-type test of field-edge runoff water may provide a more accurate estimate of field management effects on downstream dissolved nutrient loads and aquatic ecosystems

Long-term water retention increases in degraded soils amended with cross-linked polyacrylamide

Polymer hydrogels, cross-linked polyacrylamide co-polymer (XPAM) and K-polyacrylate (XPAA), increase soil water availability under drought, but their long-term effects are unknown even though such knowledge is important for assessing economic feasibility at the farm-scale. This 9-yr, outdoor study amended an irrigated, calcareous silt loam with a one-time, 0.25% or 0.5% dry wt. (5.6 or 11.2 Mg/ha) application of either XPAM or XPAA; and included an untreated control and untreated, uneroded topsoil. Soil water retention and plant available water (PAW, g H2O per g dry soil) were measured in soil samples collected in spring for 7 of the 9 years. Across all years, the 2% XPAM produced the greatest PAW (0.318) and the PAW of other treatments followed in the order: 0.5% XPAM > 0.25% XPAM > Topsoil > 0.25% XPAA = 0.5% XPAA = control (0.224). In all years, the 0.25% XPAM and 0.5% XPAM treatments increased soil PAW relative to the control, i.e. their PAW ratios exceeded unity. Topsoil PAW exceeded that of the control in 6 of the 7 years measured. The PAW of 0.25% XPAM and 0.5% XPAM peaked in year one after application and declined linearly with time (P<0.03), at -0.0036 /yr and -0.0044/yr, respectively. Hence, the half-life of the XPAM-related water-retention benefit is 10 to 16 years. In this study, soil water-retention benefits from XPAM amendments exceeded projections proposed by the industry (5 years in soil) and suggests that the cost-benefit of farm-scale XPAM applications might be more favorable than previously anticipated

Polyacrylamide and biopolymer effects on flocculation, aggregate stability, and water seepage in a silt loam

Researcher’s seek a more renewable and natural alternative for water soluble anionic polyacrylamide (PAM), a highly-effective, petroleum-derived polymer used in agriculture to control erosion and reduce water seepage from unlined irrigation structures. This study evaluated two anionic polymers: a bacteria-produced polysaccharide (biopolymer) with 10-20 Mg/mol molecular weight (MW) and 30% charge density, and a PAM (12-15 Mg/mol MW, 30% charge density) to compare their ability to flocculate soil colloids, stabilize soil aggregates, and influence effective hydraulic conductivity (seepage loss). The biopolymer most effectively flocculated the colloids at a concentration of 1 mg/L, but was still 30% less effective than PAM at 1 mg/L and 50% less effective than 10 mg/L PAM treatments. The aggregate stability test included the polymers listed above as well as lower-MW representatives of each type (MW = 0.2 to 0.5 Mg/mol). Overall, both polymers increased the stability of 1- to 2-mm-diam., silt loam aggregates, though PAM was 1.35x more effective than the biopolymer, 88.7% vs. 65.5%. These results suggested that the biopolymer’s bulkier molecular conformation limited the extension and flexibility of the molecule in solution, compared to PAM. After 140 hr, the biopolymer reduced seepage loss rates 21%, while PAM increased loss rates 1.6-fold, compared to controls. These data suggest that the biopolymer would be less effective than PAM for reducing water erosion owing to its lesser flocculation and aggregate-stabilizing potential. However, the biopolymer could be a more desirable alternative to PAM for controlling seepage from unlined irrigation canals and reservoirs; it (i) can be used effectively at lower concentrations, (ii) is considered more environmentally friendly, and (iii) is produced from a renewable resource

Does turbulent-flow conditioning of irrigation water influence soil chemical processes: I. Laboratory results

Variable effects of irrigation water on soil chemistry, groundwater quality, and crop productivity are primarily attributed to the quantity, rate, or chemical composition of the applied water. Implicit in these explanations is the assumption that the intrinsic behavior of molecular water is invariable, yet accumulating evidence suggests that water behavior can be modified via non-chemical means, such as when water flows through a magnetic field. This foundational study hypothesized that turbulent-flow conditioning (CTap) of a mineralized irrigation water source (Tap water) may alter water behavior and the character of soil-water interactions. Here we provide central evidence demonstrating that CTap irrigation water changes the chemical composition of soil leachate; consistently increasing mean concentrations of K, NH4-N, Mg, and Ca by 1.2- to 1.4-fold compared to untreated Tap water. The effect develops after incubated soil is irrigated for a period of 4- to 8-weeks, suggesting that the treatment impacts on soil properties may accumulate over time, potentially influencing soil productivity and management. The treatment’s capacity to increase soil cation leaching may provide an economical means of managing or remediating degraded and marginally productive soils that contain excess salts. Because water is an integral component of earth’s ecosystems, we anticipate that the phenomenon discovered here may also be implicated in a broad spectrum of abiotic and biotic chemical processes

Automated system for collecting multiple, sequential samples from soil water percolation samplers under continuous vacuum

Manually collecting a series of sequential, discrete water samples from soil water percolation samplers, or similar devices that withdraw water from unsaturated porous media under continuous vacuum, is a logistical challenge, though the resulting collection can provide valuable information on the dynamics present in both laboratory and field studies. This article describes a sequential tension autosampler (STAS) that executes such sampling automatically. The STAS operates on 12 volts direct current (VDC) and can be adapted for laboratory and field applications. A data logger was programmed to operate a series of solenoid valves, which direct soil water collected under tension to seven individual collection bottles. The number of sequential samples, sample period, start time, and between-sample interval are specified by the user. The operator only need to attend the system periodically to transfer water samples to storage vials and program the next sampling sequence. In a laboratory study, the apparatus successfully collected samples overnight or over several days

Irrigation (agriculture)

Agricultural erosion research has focused primarily on rainfall-induced soil loss. but erosion losses associated with surface irrigation practices can be equally severe. Of the estimated 2.5 x 10^8 hectares (6 x 10^8 acres) irrigated worldwide, at least 60% are surface irrigated. In the Pacific Northwest. approximately 1.5 x 10^6 ha (3.7 x 10^6 acres) of the most erosive soils in the United States are surface irrigated. Typically, 5.5-55 tons of soil per hectare per year (5-50 metric tons per acre per year) can be lost from furrow-irrigated fields, and three times that amount from near the furrow inlets at the upper end of fields

USDA-ARS perspective on PAM

Polyacrylamide (PAM) is a synthetic organic polymer derived from petroleum. It is an industrial flocculent used worldwide in several industries. For example, one international manufacturer of PAM markets 31 percent of its PAM product to the municipal potable and waste water treatment industry, 18 percent to paper production, 17 percent to industrial water treatment, 13 percent to oil production (enhanced oil recovery), 9 percent to mining, and the remaining 8 percent to agriculture, animal feed, and cosmetic industries. Since agriculture is a relatively small market, the polymer manufacturers commit only limited resources toward developing or improving agricultural polymer products. This is why the research conducted by the U.S. Department of Agriculture, Agricultural Research Service (USDA-ARS) and others toward developing PAM technologies has been crucial to growing its potential and useful application in irrigated agriculture. The PAM used in furrow irrigation erosion control is a water soluble, anionic, high molecular weight, 12 to 15 Mg mol-1 (i.e., >150,000 repeating units) polymer with moderate charge density (~18 % of the repeating units are negatively charged). This PAM is also referred to as water soluble PAM (WSPAM) or linear anionic PAM (LAPAM). This long, single-chain polymer can be dissolved in water, where it forms a hydrated random coil structure. The size of the PAM hydrated coil increases with increasing molecular weight and charge density, and decreasing salt concentration in the water. Loops and tails of the hydrated polymer extend out into the water. Negatively charged sites on the polymer form electrostatic bonds with negatively charged sites on soil particles through intervening positively charged cations, Ca2+, Mg2+, and others. Thus, the polymer can bind soil particles together via a so-called cationic bridge, which is one of the main mechanisms by which PAM interacts with soil

Optimizing irrigation water

When applied properly, the synthetic organic polymer, polyacrylamide or PAM, can provide substantial water quality, infiltration, and water retention benefits to irrigated agriculture. To achieve peak performance, applications may need to be fine-tuned for individual circumstances. This article discusses how water-soluble PAM (WSPAM) and cross-linked PAM (XPAM) can be most effectively employed in irrigated agriculture. The form of WSPAM, method of application, and rate of application used in furrow irrigation will vary depending on local irrigation water quality and field soil properties. XPAM is comprised of WSPAM polymers cross-linked together to form a massive, porous product, which is not water soluble but can absorb >100+ times its weight in water. XPAM is added to soil to increase water retention and reduce water and nutrient leaching losses. Using XPAM in humid regions could be a challenge, since increased soil water retention during periods of surplus precipitation could create problems associated with excess water, slow soil drying/warming in spring, delayed tillage and planting. The use of XPAM in arid-land, irrigated agriculture may provide the most benefits because water deliveries to fields in these areas are intensively managed and can be limited or delayed

Inhibiting water infiltration with cross-linked polyacrylamide: Seepage reduction for irrigated agriculture

High water infiltration rates in unlined canals, reservoirs, and the inflow end of furrows relative to outflow ends result in excessive seepage losses and reduced furrow irrigation application uniformity. This study evaluated the use of cross-linked, anionic, polyacrylamide hydrogel (XPAM), a water-absorbing, swellable polymer solid, for reducing infiltration and seepage losses though soil. Experiments 1 and 2 measured the influence of soil treatments on seepage rate in soil columns under constant-head conditions: Exp. 1 treated five soils with 0, 2.5, 5, and 10 g kg -1 XPAM; Exp. 2 applied combined XPAM (0-5 g kg-1) and NaC1 (0-5.1 g kg-1) treatments to a silt loam soil, and separately tested the effect ofXPAM granule size and treated soil layer thickness on seepage rate. In Exp. 3, a miniflume was used to determine how a 5-mm-thick, XPAM-treated (0-5 g kg- 1 ) soil layer at the inflow end of the "minifurrow" influenced water distribution. The 21-h seepage rates of all soils except the loamy sand decreased curvilinearly with increasing )(PAM rate, with maximum reductions of 87 to 94% for 5 and 10 g kg -1 XPAM rates, relative to controls. The <300-pm-diam. XPAM granules were significantly more effective than the coarser grained )(PAM for reducing seepage, and reducing the thickness of the treated soil layer from 71 to 24 mm had no significant effect on the seepage reduction obtained with XPAM. The 5 g kg- 1 XPAM treatment applied to inflow-end miniflume soils significantly decreased the "furrow-stream" advance period and reversed the infiltration patterns observed in miniflumes, relative to controls. These XPAM treatments could potentially be used to increase the uniformity of furrow water applications and reduce seepage from unlined irrigation ponds and canals

Polyacrylamide and biopolymer effects on flocculation, aggregate stability, and water seepage in a silt loam

Researcher’s seek a more renewable and natural alternative for water soluble anionic polyacrylamide (PAM), a highly-effective, petroleum-derived polymer used in agriculture to control erosion and reduce water seepage from unlined irrigation structures. This study evaluated two anionic polymers: a bacteria-produced polysaccharide (biopolymer) with 10-20 Mg/mol molecular weight (MW) and 30% charge density, and a PAM (12-15 Mg/mol MW, 30% charge density) to compare their ability to flocculate soil colloids, stabilize soil aggregates, and influence effective hydraulic conductivity (seepage loss). The biopolymer most effectively flocculated the colloids at a concentration of 1 mg/L, but was still 30% less effective than PAM at 1 mg/L and 50% less effective than 10 mg/L PAM treatments. The aggregate stability test included the polymers listed above as well as lower-MW representatives of each type (MW = 0.2 to 0.5 Mg/mol). Overall, both polymers increased the stability of 1- to 2-mm-diam., silt loam aggregates, though PAM was 1.35x more effective than the biopolymer, 88.7% vs. 65.5%. These results suggested that the biopolymer’s bulkier molecular conformation limited the extension and flexibility of the molecule in solution, compared to PAM. After 140 hr, the biopolymer reduced seepage loss rates 21%, while PAM increased loss rates 1.6-fold, compared to controls. These data suggest that the biopolymer would be less effective than PAM for reducing water erosion owing to its lesser flocculation and aggregate-stabilizing potential. However, the biopolymer could be a more desirable alternative to PAM for controlling seepage from unlined irrigation canals and reservoirs; it (i) can be used effectively at lower concentrations, (ii) is considered more environmentally friendly, and (iii) is produced from a renewable resource