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USDA-ARS perspective on PAM
Get PDFPolyacrylamide (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
Concentrations of PCDD/PCDFs and PCBs in spent foundry sands. Chemosphere
Get PDFApproximately 10 million tons of spent foundry sand (SFS) are generated in the United States each year,
and their beneficial use in agricultural and horticultural applications is being considered. Other studies
have demonstrated that trace elements are low enough in sands from iron, steel, and aluminum foundries
to allow their beneficial use. Because data were not available on polychlorinated dibenzo-p-dioxins, polychlorinated
dibenzofurans, and polychlorinated biphenyls in SFSs, we analyzed representative spent
sands from 10 foundries to assess the potential for these compounds to limit their use in soil-related
applications. The total TEQ (toxicity equivalent) concentrations ranged from 0.01 to 3.13 ng TEQ kg�1,
with an average concentration of 0.58 ng TEQ kg�1. These concentrations are within the range of natural
background in soils
Effect of timing of a deficit-irrigation allocation on corn evapotranspiration, yield, water use efficiency and dry mass
Get PDFWater regulations have decreased irrigation water supplies in Nebraska and some other areas of the USA
Great Plains. When available water is not enough to meet crop water requirements during the entire
growing cycle, it becomes critical to know the proper irrigation timing that would maximize yields and
profits. This study evaluated the effect of timing of a deficit-irrigation allocation (150 mm) on crop
evapotranspiration (ETc), yield, water use efficiency (WUE = yield/ETc), irrigation water use efficiency
(IWUE = yield/irrigation), and dry mass (DM) of corn (Zea mays L.) irrigated with subsurface drip
irrigation in the semiarid climate of North Platte, NE. During 2005 and 2006, a total of sixteen irrigation
treatments (eight each year) were evaluated, which received different percentages of the water
allocation during July, August, and September. During both years, all treatments resulted in no crop
stress during the vegetative period and stress during the reproductive stages, which affected ETc, DM,
yield, WUE and IWUE. Among treatments, ETc varied by 7.2 and 18.8%; yield by 17 and 33%; WUE by 12
and 22%, and IWUE by 18 and 33% in 2005 and 2006, respectively. Yield and WUE both increased linearly
with ETc and with ETc/ETp (ETp = seasonal ETc with no water stress), and WUE increased linearly with
yield. The yield response factor (ky) averaged 1.50 over the two seasons. Irrigation timing affected the
DMof the plant, grain, and cob, but not that of the stover. It also affected the percent of DM partitioned to
the grain (harvest index), which increased linearly with ETc and averaged 56.2% over the two seasons,
but did not affect the percent allocated to the cob or stover. Irrigation applied in July had the highest
positive coefficient of determination (R2) with yield. This high positive correlation decreased
considerably for irrigation applied in August, and became negative for irrigation applied in September.
The best positive correlation between the soil water deficit factor (Ks) and yield occurred during weeks
12–14 from crop emergence, during the ‘‘milk’’ and ‘‘dough’’ growth stages. Yield was poorly correlated
to stress during weeks 15 and 16, and the correlation became negative after week 17. Dividing the
150 mm allocation about evenly among July, August and September was a good strategy resulting in the
highest yields in 2005, but not in 2006. Applying a larger proportion of the allocation in July was a good
strategy during both years, and the opposite resulted when applying a large proportion of the allocation
in September. The different results obtained between years indicate that flexible irrigation scheduling
techniques should be adopted, rather than relying on fixed timing strategies
Soil genesis and development, lesson 3: Soil forming factors
Get PDFThis lesson explores the five major factors of
soil formation—(1) climate, (2) organisms, (3) time, (4)
topography, and (5) parent material—and their influence
in forming soil. The distinction between active and passive
factors, moisture and temperature regimes, organism and
topographic influences, and parent material sources are
described.
At the completion of this lesson, students will be able to do
the following:
1. Identify the five factors of soil formation.
2. Explain the effects of each of the factors on soil
formation.
3. Explain how types of parent material differ in terms
of mode of deposition and degree of sorting.
The lesson is written to target educational needs of lower-level
undergraduate students and is available for use by the
public and educational institutions
Irrigated small-grain residue management effects on soil chemical and physical properties and nutrient cycling
Get PDFThe effects of straw removal from irrigated wheat and barley fields cropped to wheat and barley on soil properties and nutrient cycling is a concern due to its potential impact on the sustainability of agricultural production. Increasing demand of straw for animal bedding and the potential development of cellulosic ethanol production will likely increase the demand in the future. Previous reviews addressing changes in soil properties when crop residues are removed focused primarily on rain-fed systems. This paper reviews published research assessing the effects of wheat and barley straw removal on soil organic carbon (SOC), and analyzes changes in nutrient cycling within irrigated wheat and barley production systems. The effects of straw removal on bulk density (BD), saturated hydraulic conductivity, and other properties are reported from selected studies. Six studies compared SOC changes with time in irrigated systems in which wheat straw was removed or retained. These studies indicated that SOC either increased with time or remained constant when residues were removed. It is possible that belowground biomass is supplying C to soils at a rate sufficient to maintain or in some cases, slowly increase SOC with time. A separate research review calculated the minimum aboveground residue required to maintain SOC levels (MCS) from nine wheat system studies. Calculations of the MCS values were from rain-fed systems and are some of the best information available presently for use in evaluating residue removal effects in irrigated systems. However, long-term studies are needed to obtain reliable data for diverse irrigated systems. Nutrients removed from the soil/plant system with straw can be worth 20 per Mg of straw removed. Producers will need to determine the cost of the nutrient removal from their systems to determine the value of the straw
Soil and Nutrient Losses from Small Sprinkler and Furrow Irrigated Watersheds in Southern Idaho
Get PDFSediment and associated nutrients flowing to the Snake River with furrow irrigation runoff and unused irrigation water have been a concern in the Twin Falls irrigation tract in southern Idaho. Converting furrow irrigated fields to sprinkler irrigation is one practice that has been promoted, and received financial assistance, to reduce sediment loss. Five small watersheds (330 to 1480 acres) with 10 to 70% sprinkler irrigation were monitored from 2005 to 2008 to determine if converting to sprinkler irrigation reduced sediment and nutrient losses from these watersheds. Eliminating runoff from furrow irrigated fields by converting to sprinkler irrigation will reduce sediment and nutrient losses from fields. However, there were no significant correlations between the amount of sprinkler irrigation and the sediment or nutrient loads from these watersheds. Potential reasons for these results are the flow rate allocation system used by the TFCC, the amount and location of furrow irrigated fields in each watershed, and the management of furrow irrigated fields within each watershed. One significant correlation was decreasing dissolved phosphorus concentrations as relative amount of sprinkler irrigated land increased, presumably because less water flowed across fields in furrows as sprinkler irrigated area increased. A water quality model for irrigated watersheds is needed for more thorough assessment of the variety conditions and management practices within these watersheds
Continuous biosolids application affects grain elemental concentrations in a dryland-wheat agroecosystem
Get PDFContinuous land application of biosolids in a beneficial-use program changes trace-element availability to plants over time. Consequently, what regression model, if any, could best predict wheat (Triticum aestivum L.) grain concentrations in a biosolids-amended dryland agroecosystem? We calculated paraboloid, linear, quadratic, and exponential-rise-to-a maximum equations for grain Ba, Cd, Cu, Mn, Mo, Ni, P, and Zn concentration versus number of biosolids applications and/or soil NH4HCO3-dithethylenetriaminepentaacetic acid (AB-DTPA) extract concentrations for two sites that had each received six applications of Littleton/Englewood, CO, USA Wastewater Treatment Facility biosolids. The paraboloid-regression models were superior (higher R2 values, lower S.E. of the estimate) to other models. Soils classified the same as the Weld soil (used in this study) at the family level (fine, smectitic, mesic Aridic Argiustolls) encompass 25 soil series in 10 US states with an aerial extent of 2.3 × 106 ha. The paraboloid-regression model approach probably would be applicable to these similarly classified soils
Fate of biosolids Cu and Zn in a semi-arid grassland
Get PDFBiosolids land application applies varying trace metal amounts to soils. Measuring total soil metals is
typically performed to ensure environmental protection, yet this technique does not quantify which soil
phases play important metal release or attenuation roles. We assessed the distribution of biosolidsborne
Cu and Zn associated with soluble/exchangeable, specifically adsorbed/carbonate-bound,
amorphous and crystalline Mn/Fe oxyhydroxide-bound, residual organic, and residual inorganic
phases. Biosolids were surface-applied (no incorporation) to experimental plots, at the Meadow Springs
Ranch (40 53'46"N, 104 52'28"W) which is owned by the city of Fort Collins, CO, USA, in 1991 at rates of
0, 2.5, 5, 10, 21, and 30 Mg ha�1. Plots were split in half in 2002, with one-half receiving biosolids at rates
identical to 1991 rates. In 2003, 0–8, 8–15, and 15–30-cm soil depths were collected and subjected to
4 M HNO3 digestion and sequential fractionation. The 4 M HNO3 extraction suggested downward Cu
transport, while Zn was immobilized in the soil surface. The sequential extraction procedure, more
sensitive to changes in soil metal pools, suggested that repeated biosolids application did not affect
vertical Zn movement, but did increase the downward transport potential of organically complexed Cu.
In the given time, organically complexed Cu was likely mineralized and subsequently associated with
soil mineral oxide phases. Because bioavailability of Cu is associated with dissolved phases, and soluble/
exchangeable Cu concentrations were below detection limits in the subsoil, a reduction in
environmental quality should be minimal. Still, we advocate that on coarse-textured semi-arid soils,
biosolids application rates should match the plant N needs to avoid potential downward trace metal
transport
Sugar beet cultivar evaluation for storability and rhizomania resistance
Get PDFTo reduce storage losses and improve resistance to rhizomania caused by Beet necrotic yellow
vein virus (BNYVV), studies were initiated to establish a storage cultivar selection program. In
2006 and 2007, 30 or more commercial sugar beet (Beta vulgaris) cultivars were grown in soil
naturally infested with BNYVV. At harvest, two root samples from each plot were collected and
used to establish percent sugar. Additional samples were placed on top of an indoor pile (set
point 1.7°C) and inside an outdoor pile in a randomized complete block design with four replications.
After 142 and 159 days in indoor storage, sucrose reduction ranged from 13 to 90% in
2007 and 57 to 100% in 2008. Outdoor storage sucrose reduction ranged from 13 to 32% in
2007 and 28 to 60% in 2008. An average of 31 and 45% of the root surface was covered with
fungal growth in 2007 and 2008, respectively. Cultivars that retained the most sucrose had resistance
to BNYVV and the least fungal growth and weight loss. Indoor storage with BNYVV infested
roots allowed for the most consistent cultivar separation and will potentially lead to
selection of cultivars for improved storability and rhizomania resistance
Dairy manure field applications-How much is too much?
Get PDFApplying dairy manure to agricultural fields has
been shown to increase crop yields, improve the
water-holding capacity of the soil, and enhance
soil fertility. However, when manures are applied
to fields at high rates over a period of several
years, nutrients can accumulate, causing
eutrophication in drainage waterways; degradation
of drinking water; nutrient toxicities in plants;
nutrient deficiencies in plants; disruptions in
soil microbial populations; and nutritional
imbalances for grazing animals. Growersand dairy
producers also run the risk of violating state and
federal regulations designed toavoid these issues