David R. Bouldin

Land Application of Sewage Sludges: An Appraisal of the US Regulations

This paper was published in the peer reviewed INT. J. OF ENVIRONMENT AND POLLUTION, 1999, Vol. 11 No. 1 pp 1-36. The journal is available in both hard copy and on-line PDF format. For more information and sample copy of IJEP, visit their web site at http://www.inderscience.com/.

Mass balance and distribution of sludge-borne trace elements in a silt loam soil following long-term applications of sewage sludge

Soil samples were collected at 15-cm increments to a depth of 75 cm from plots on a silt loam soil where until several years earlier and for 14 years, anaerobically digested sewage sludge had been annually applied by furrow irrigation. The study protocol consisted of four replications of 6.1 x 12.2-m plots with 0 (T0), 1/4-maximum (T1), 1/2-maximum (T2) and maximum (T3) sludge application rates randomized within blocks. When sludge applications were terminated, maximum sludge-treated plots had received 765 Mg ha-1 (dry weight equivalent) of sludge solids. Total soil concentrations of Cd, Cr, Cu, Ni, Pb and Zn had been significantly enhanced by all sludge application rates to a soil depth of 30 cm. Below the 30-cm depth, total soil Cd was increased to 75 cm, total Zn to 45 cm (T2 and T3 only), total Cr to 60 cm (T2 and T3 only), but total Cu, Pb, and Ni were not increased at depth. Despite the lack of significant increases in subsoil concentrations for some metals, mass balance calculations showed a relatively high proportion of all the above sludge-borne heavy metals to be unaccounted for in the soil profile for each application rate. Mass balance calculations of losses ranged from a high of 60% for Ni to a low of 36% for Cu and Pb. Similar losses were calculated from metal concentrations measured in soil samples taken at the time the sludge was applied. In soil surface samples (0-15 cm) from maximum sludge-treated plots, percentages of total metal concentration extracted with 4.0 M HNO3 ranged from a low of 31 for Zn to a high of 75 for Cu. Efficiency of metal extraction by HNO3 was inconsistent, depending on the soil horizon and sludge treatment, so that evaluation of HNO3-extractable metals is not a reliable method of estimating total metal retention in the profiles. In soil surface samples from maximum sludge-treated plots, the percentage of total metal contents extracted with DTPA ranged from a low of 0.03 for Cr to a high of 59 for Cd. The DTPA extractable levels of Cu, Ni, and Pb were higher in the subsoils of the sludge-treated soils, indicating that these metals had been redistributed from the surface layer to deeper zones in the profile of sludge-amended soil, despite the absence of elevated total concentrations of these three metals in the deeper subsoil.

Apparent deposition velocity and compensation point of ammonia inferred from gradient measurements above and through alfalfa

Abstract Understanding the cycling of ammonia between croplands and the atmosphere is of importance to agriculturalists and atmospheric scientists. Flux densities of gaseous ammonia (NH3), particulate ammonium (NH4+), and total ammoniacal nitrogen (AN) were measured using an aerodynamic method above an alfalfa (Medicago sativa, L.) canopy between April and July 1981 at a rural location in central New York State. In air not influenced by local sources, NH3 and NH4+ averaged 1.5 and 3.0 ppb, respectively, at 1 m above the crop. Ambient NH4+ varied consistently with synoptic air masses, being lowest (2.3 ppb) for NW and highest (6.4 ppb) for SW flows. Concentrations and gradients of both species were higher during periods of hay harvest. Gradients of NH3 were much steeper than those of NH4+ within the alfalfa canopy, but NH4+ contributed appreciably (36% on average) to above-canopy AN gradients. Alfalfas NH3 compensation point was estimated by combining concentration and gradient data with transport resistances. Gaseous gradients indicated a compensation point of 2 ppb, lower than previously published estimates. Conversion of NH3 to NH4+ within the canopy air could have reduced NH3 gradients and caused a low estimate of the compensation point. Acidic aerosols, by keeping NH3 levels low, may compete with plants for NH3. Future studies of ammonia exchange should distinguish between NH3 and NH4+ if flux densities are to be related to ambient conditions. Total AN level is a poor predictor of soil-plant-atmosphere ammonia exchange since high AN was frequently associated with low NH3, and NH3 is more surface reactive than NH4+.

Modeling cropping strategies to improve human nutrition in Uganda

This paper contrasts two Ugandan cropping systems, a banana-based (Musa AAA) and a grain-based (Zea mays and Sorghum bicolor), and focuses on the potential of each to provide food in suAcient quantity to meet household nutritional requirements. The objectives of this study were to estimate the amount of energy, protein, vitamin A, Ca, Fe and Zn furnished by these two systems; and to model cropping strategies capable of improving nutritional output given the same land area and location. Results show that both systems currently fail to satisfy a range of nutritional needs with Zn and Ca deficits being the most extreme. Modifications in cropping strategies explored through modeling showed that improved nutrition in both systems was possible given the same resource base. Improved nutrition in the banana-cropping system requires major changes in the allocation of land: e.g. a two-thirds reduction in the proportion of land devoted to banana. Adequate nutrition given the same resource base would require the incorporation of several species (e.g. Amaranthus lividus and Glycine max), which though present are uncommon. Though we suggest changes in extant cropping systems, this paper acknowledges that such changes would occur in the context of practices embedded in cultural norms. # 2001 Elsevier Science Ltd. All rights reserved.

Total and labile zinc concentrations in water extracts of rhizosphere and bulk soils of oats and rice

Abstract A greenhouse experiment using three soils of different pH levels (4.37, 5.78, 6.44) was conducted to determine the effects of rhizosphere on pH, total Zn and labile Zn in water extracts of soils grown to oats and rice. Zn concentrations were determined using a linear sweep cathodic stripping voltammetry technique. In oats, the pH and labile Zn in water extracts were lower in the rhizosphere than the bulk soil and there was no difference in total Zn in water extracts between these two soil zones. Consistently, rhizosphere pH was lower than bulk soil pH with rice but total and labile Zn in water extracts were not statistically different. Zn concentrations (both total and labile forms) in water extracts varied inversely with pH; however, rhizosphere pH changes did not always explain observed differences in extractable Zn

Cation accumulation by winter wheat forage: II. Correlation with multi‐ion model

Abstract The effects of three ratios of Ca/(Ca + K) and three rates of NO3‐N on ion ratios in plants grown in soil and nutrient culture are reported. Plant uptake parameters, based on nutrient culture studies, together with soil chemical parameters, were used in a multiple‐ion uptake model to calculate the cumulative, uptake of individual ions. These calculated uptakes were then used to derive relevant ratios for comparison with those measured in plants grown in soil in a growth chamber. The results illustrate that the ionic ratios based on the model are well correlated with the measured plant ratios. Regressions of plant ratios on model ratios were calculated; the intercepts were not zero and the slopes were not one. The discrepancies between measured and model ratios were probably a consequence of deficiencies in the model and unmeasured plant uptake parameters. The results illustrate that the model is a useful way to summarize data and to generate hypotheses.

Lime response of tanier in an Ultisol of Costa Rica

Abstract Root crops constitute an important part in the diet of millions of people throughout the Tropics. These crops are produced by subsistence farmers in poor soils where acidity is the most common problem and liming materials, such as limestone, are scarce and expensive. Few experimental data are available on the fertility requirements and liming response of tanier (Xanthosoma sagittifolium). This study was conducted to determine the effect on yield of limestone application. Rates of 0, 1, 2, 3, and 4 t/ha of calcitic and dolomitic limestome, respectively, were applied in an Ultisol. Tanier shows tolerance to soil acidity with yields 58% a of maximum with 64% aluminum (Al) saturation. The limestone additions of 4 t/ha resulted in a pH of 4.38 and 4.68 with calcitic and dolomitic limestone, respectively, which produced the highest yield.

A cathodic stripping voltammetric method for nanomolar concentrations of labile and total iron and zinc in soil solutions 1

Abstract Linear sweep cathodic stripping voltammetric methods were modified to measure labile and total concentrations of Fe3+ and Zn2+ in the nanomolar range in soil solutions. Labile concentrations of Fe (25–220 nmol/L) and Zn (37–208 nmol/L) were measured in 0.5 mL aliquots of filtered (0.4 μm) distilled water extracts (solution:soil ratio= 1) of four agricultural soils. After decomposition of complexed forms of the metals by evaporation of the solutions in HNO3, total soluble Fe and Zn were measured. Labile Fe comprised approximately 1% of total soluble Fe, while labile Zn comprised 13–43% of total Zn in the four soil solutions. The methods provide a linear range of 5 ‐100 nmol/L and sufficient precision to detect concentrations of labile and total Fe and Zn likely to occur in soil solutions.

Calibration of the time‐domain reflectometer and determination of the volumetric water content of the soil profile in an ultisol of Costa Rica

Abstract An experiment was conducted to determine if time‐domain reflectometry (TDR) could be used to measure the water content at different depths in the O‐to‐75 cm soil layer. Probes of three wires (1/8 inch diameter and 30 cm exposed length) were installed in field plots differing in current crop‐fertilization history. Measurements of volumetric water content using bulk density and gravimetric water content were made to calibrate the TDR method. Comparison of water contents determined by TDR with those from gravimetric samples showed that there is a linear relationship (small offset but same slope) of water content with depth, indicating that there is little difference in volumetric water content from the 0 to 75 depth. However, the TDR method gives consistently lower water content values as compared with values obtained by gravimetric determination. Continuous measurements of profile soil water content with TDR in wet and dry periods during the year indicated that the mayor differences in volumetric w...