Nitrogen source effects on soil nitrous oxide emissions from strip-till corn

Nitrogen (N) application to crops generally results in increased nitrous oxide (NO) emissions. Commercially available, enhanced-efficiency N fertilizers were evaluated for their potential to reduce NO emissions from a clay loam soil compared with conventionally used granular urea and urea-ammonium nitrate (UAN) fertilizers in an irrigated strip-till (ST) corn ( L.) production system. Enhanced-efficiency N fertilizers evaluated were a controlled-release, polymer-coated urea (ESN), stabilized urea, and UAN products containing nitrification and urease inhibitors (SuperU and UAN+AgrotainPlus), and UAN containing a slow-release N source (Nfusion). Each N source was surface-band applied (202 kg N ha) at corn emergence and watered into the soil the next day. A subsurface-band ESN treatment was included. Nitrous oxide fluxes were measured during two growing seasons using static, vented chambers and a gas chromatograph analyzer. All N sources had significantly lower growing season NO emissions than granular urea, with UAN+AgrotainPlus and UAN+Nfusion having lower emissions than UAN. Similar trends were observed when expressing NO emissions on a grain yield and N uptake basis. Loss of NO-N per kilogram of N applied was <0.8% for all N sources. Corn grain yields were not different among N sources but greater than treatments with no N applied. Selection of N fertilizer source can be a mitigation practice for reducing NO emissions in strip-till, irrigated corn in semiarid areas.     

A regional-scale study on the crop uptake of cadmium from sandy soils: measurement and modeling

Plant uptake is one of the major pathways by which cadmium (Cd) in soils enters the human food chain. This study was conducted to investigate the uptake of Cd by crops from soils within the wastewater irrigation area (WIA) of Braunschweig (Germany) and to develop a simple process-oriented model that is suited to predict Cd uptake at the regional scale. The sandy soils within the WIA (4300 ha) have received considerable loads of heavy metals by irrigation using municipal wastewater for up to 40 years. In 1998 and 1999, we sampled soil and plant material at 40 potato (Solanum tuberosum L.), 40 sugar beet (Beta vulgaris L.), and 32 winter wheat (Triticum aestivum L.) fields. In both years and for all three crops, we found close linear relationships between the Cd content of plant material and the Cd concentration in soil solution. For all three crops, we observed a trend of relatively increased Cd uptake in the year with the higher saturation deficit of the atmosphere. We interpret this to indicate that transpiration plays an important role in the Cd uptake of crops under the conditions of the WIA. In modeling the uptake of Cd by crops, we assume that uptake is proportional to mass flow, that is, the product of water transpired, Cd concentration in soil solution, and a plant-specific empirical parameter. The simulations agreed well with the observed Cd contents in crops. Our model explained between 66 and 87% of the observed variance.     

Elevated cadmium concentrations in potato tubers due to irrigation with river water contaminated by mining in Potosí, Bolivia

Risk of cadmium (Cd) in the human food chain in Cd-contaminated areas is often limited by phytotoxicity from zinc (Zn) that is associated with the Cd contamination. A semiarid area, 60 km downstream of a tin mine in Bolivia, was surveyed where irrigation with Cd-contaminated river water (65-240 microg Cd L(-1)) has increased median soil Cd to 20 mg kg(-1) while median soil Zn was only about 260 mg kg(-1). Cadmium concentrations in potato tubers increased from background values (0.05 mg kg(-1) dry wt.) in soils irrigated with spring water to a median value of 1.2 mg kg(-1) dry wt. in the affected area. Median concentration of Cd in soil solutions was 27 microg L(-1) and exceeded the corresponding value of Zn almost twofold. Soil-extractable chloride ranged from 40 to 1600 mg Cl(-) kg(-1) and was positively correlated with soil total Cd. Increasing soil solution Cl(-) decreased the solid-liquid distribution coefficient of Cd in soil. Soil total Cd explained 64% of the variation of tuber Cd concentration while only 3% of the variation was explained by soil extractable Cl(-) (n = 49). The estimated dietary Cd intake from potato consumption by the local population is about 100 microg d(-1) which exceeds the WHO recommended total daily intake. It is concluded that the food chain risk of Cd in the irrigation water of the semiarid area is aggravated by the association with Cl(-) and, potentially, by the relatively large Cd/Zn ratio.     

Arsenic, cadmium, and lead in California cropland soils: role of phosphate and micronutrient fertilizers

Phosphate and micronutrient fertilizers contain potentially harmful trace elements, such as arsenic (As), cadmium (Cd), and lead (Pb). We investigated if application of these fertilizer increases the As, Cd, and Pb concentrations of the receiving soils. More than 1000 soil samples were collected in seven major vegetable production regions across California. Benchmark soils (no or low fertilizer input) sampled in 1967 and re-sampled in 2001 served as a baseline. Soils were analyzed for total concentrations of As, Cd, Pb, P, and Zn. The P and Zn concentrations of the soils were indicators of P fertilizer and micronutrient inputs, respectively. Results showed that the concentrations of these elements in the vegetable production fields in some production areas of California had been shifted upward. Principal component analysis and cluster analysis showed that the seven production areas could be sorted into three categories: (i) enrichment of As, Cd, and Pb, which was associated with the enrichment of P and Zn in one of the seven areas surveyed; (ii) enrichment of As, which was associated with enrichment of Zn in two of the seven areas surveyed; and (iii) no remarkable correlation between enrichment of As, Cd, and Pb and enrichment of P and Zn in the other four areas surveyed.     

Food safety assessment of planting patterns of four vegetable-type crops grown in soil contaminated by electronic waste activities

A field experiment was conducted to assess the effect of crop and planting pattern on levels of cadmium (Cd), lead (Pb), and copper (Cu) in crops grown in soil contaminated by electronic waste. The crops were maize (Zea mays L. var. Shentian-1), tomato (Solanum lycopersicum L. var. Zhongshu-4), cabbage (Brassica oleracea L. var. Jingfeng-1), and pakchoi (Brassica chinensis (L.) Makino. var. Youdonger-Hangzhou). The planting patterns were crop monoculture, crop co-planted with a legume, and crop co-planted with another crop. Metal concentrations in the edible parts of the crops varied with types of metals and crops. Pb concentration was higher in leafy vegetables (cabbage and pakchoi) than in maize or tomato, Cd concentration was higher in tomato and pakchoi than in maize or cabbage, and Cu concentration was higher in maize and pakchoi than in tomato or cabbage. Metal concentrations in the edible part were also influenced by planting pattern. Relative to monoculture, co-planting and especially co-planting with Japanese clover tended to decrease Pb accumulation and increase Cd accumulation. According to the maximum permissible concentration (MPC) standard of the National Standard Agency in China, only maize (under all planting patterns) could be safely consumed. Because co-planting tended to increase Cd accumulation even in maize, however, the results suggest that maize monoculture is the optimal crop and planting pattern for this kind of contaminated soil.     

Nitrogen and phosphorus status of soils and trophic state of lakes associated with forage-based beef cattle operations in Florida

Forage-based livestock systems have been implicated as major contributors to deteriorating water quality, particularly for phosphorus (P) from commercial fertilizers and manures affecting surface and ground water quality. Little information exists regarding possible magnitudes of nutrient losses from pastures that are managed for both grazing and hay production and how these might impact adjacent bodies of water. We examined the changes that have occurred in soil fertility levels of rhizoma peanut (Arachis glabrata Benth.)-based beef cattle pastures (n = 4) in Florida from 1988 to 2002. These pastures were managed for grazing in spring followed by haying in late summer and were fertilized annually with P (39 kg P2O5 ha(-1)) and K (68 kg K2O ha(-1)). Additionally, we investigated trends in water quality parameters and trophic state index (TSI) of lakes (n = 3) associated with beef cattle operations from 1993 to 2002. Overall, there was no spatial or temporal buildup of soil P and other crop nutrients despite the annual application of fertilizers and daily in-field loading of animal waste. In fact, soil fertility levels showed a declining trend for crop nutrient levels, especially soil P (y = 146.57 - 8.14 x year; r2= 0.75), even though the fields had a history of P fertilization and the cattle were rotated into the legume fields. Our results indicate that when nutrients are not applied in excess, cow-calf systems are slight exporters of P, K, Ca, and Mg through removal of cut hay. Water quality in lakes associated with cattle production was "good" (30-46 TSI) based on the Florida Water Quality Standard. These findings indicate that properly managed livestock operations may not be major contributors to excess loads of nutrients (especially P) in surface water.     

Mapping the probability of exceeding critical thresholds for cadmium concentrations in soils in The Netherlands

The probability of exceeding critical thresholds of Cd concentrations in the soil was mapped at a national scale. The critical thresholds in soil were based on food quality criteria for Cd in crops or in organs of cattle (Bos taurus), and were calculated by inverting a regression model for the Cd concentration in the crop, with the Cd concentration in soil, soil organic matter (SOM) content, clay content, and pH as predictors. The probability of exceeding the critical threshold for Cd in soil per node of a 500- x 500-m grid was approximated by Monte Carlo simulation, using the estimated cumulative distribution functions (cdf) of SOM, clay, pH, and Cd as input. The cdfs were estimated by simple indicator kriging with local prior means. For SOM, clay, and pH, detailed maps of soil type and land use were used to define subregions with assumed constant local means of the indicators (a priori distributions). The cdfs were sampled by Latin hypercube sampling. We accounted for correlation between the actual and critical Cd concentrations in soil by drawing Cd values from cdfs conditional on SOM and clay. The estimated probability for grassland is negligible, even in areas with high Cd concentrations in soil, and for maize (Zea mays L.) land the probability is almost everywhere smaller than 5%. For arable soils, however, these probabilities commonly are larger than 5% when sugar beet (Beta vulgaris L.) or wheat (Triticum aestivum L.) is taken as a reference crop, and locally exceed 50%.     

Binding of heavy metal contaminants onto chitosans--an evaluation for remediation of metal contaminated soil and water

The binding efficiency of chitosan samples for Ag(+), Cd(2+), Cu(2+), Pb(2+) and Zn(2+) has been evaluated in order to consider their application to remediate metal contaminated soil and water. The sorption behaviour of metal ions was assessed using a batch technique at different contact time and initial metal concentration with different background electrolytes. The kinetics followed a pseudo-second-order model, while the equilibrium data correlated well with the Freundlich and Langmuir isotherm models. For example, the maximum sorption capacity (Q) for chitosan was estimated as 1.93 mmol/g for Ag(+), 1.61 mmol/g for Cu(2+), 0.94 mmol/g for Zn(2+), 0.72 mmol/g for Cd(2+) and 0.64 mmol/g for Pb(2+). Covalent interaction between metal ions and functional groups (amino and hydroxyl) of the chitosans was the main binding mechanism. Ion exchange is not an important process. Chitosan and cross-linked chitosans were able to bind metal ions in the presence of K(+), Cl(-) and NO(3)(-). The nature of Cl(-) and NO(3)(-) ions did not affect Zn(2+) binding by the chitosans. Even at 11x dilution, the chitosans were able to retain metal ions on their surfaces.     

Effect of chloride in soil solution on the plant availability of biosolid-borne cadmium

Increasing chloride (Cl) concentration in soil solution has been shown to increase cadmium (Cd) concentration in soil solution and Cd uptake by plants, when grown in phosphate fertilizer- or biosolid-amended soils. However, previous experiments did not distinguish between the effect of Cl on biosolid-borne Cd compared with soil-borne Cd inherited from previous fertilizer history. A factorial pot experiment was conducted with biosolid application rates of 0, 20, 40, and 80 g biosolids kg(-1) and Cl concentration in soil solution ranging from 1 to 160 mM Cl. The Cd uptake of wheat (Triticum aestivum L. cv. Halberd) was measured and major cations and anions in soil solution were determined. Cadmium speciation in soil solution was calculated using GEOCHEM-PC. The Cd concentration in plant shoots and soil solution increased with biosolid application rates up to 40 g kg(-1), but decreased slightly in the 80 g kg(-1) biosolid treatment. Across biosolid application rates, the Cd concentration in soil solution and plant shoots was positively correlated with the Cl concentration in soil solution. This suggests that biosolid-borne Cd is also mobilized by chloride ligands in soil solution. The soil solution CdCl+ activity correlated best with the Cd uptake of plants, although little of the variation in plant Cd concentrations was explained by activity of CdCl+ in higher sludge treatments. It was concluded that chlorocomplexation of Cd increased the phytoavailability of biosolid-borne Cd to a similar degree as soil (fertilizer) Cd. There was a nonlinear increase in plant uptake and solubility of Cd in biosolid-amended soils, with highest plant Cd found at the 40 g kg(-1) rate of biosolid application, and higher rates (80 g kg(-1)) producing lower plant Cd uptake and lower Cd solubility in soil. This is postulated to be a result of Cd retention by CaCO3 formed as a result of the high alkalinity induced by biosolid application.     

Nitrogen source effects on nitrous oxide emissions from irrigated no-till corn

Nitrogen fertilization is essential for optimizing crop yields; however, it may potentially increase nitrous oxide (N2O) emissions. The study objective was to assess the ability of commercially available enhanced-efficiency N fertilizers to reduce N2O emissions following their application in comparison with conventional dry granular urea and liquid urea-ammonium nitrate (UAN) fertilizers in an irrigated no-till (NT) corn (Zea mays L.) production system. Four enhanced-efficiency fertilizers were evaluated: two polymer-coated urea products (ESN and Duration III) and two fertilizers containing nitrification and urease inhibitors (SuperU and UAN+AgrotainPlus). Nitrous oxide fluxes were measured during two growing seasons using static, vented chambers and a gas chromatograph analyzer. Enhanced-efficiency fertilizers significantly reduced growing-season N2O-N emissions in comparison with urea, including UAN. SuperU and UAN+AgrotainPlus had significantly lower N2O-N emissions than UAN. Compared with urea, SuperU reduced N2O-N emissions 48%, ESN 34%, Duration III 31%, UAN 27%, and UAN+AgrotainPlus 53% averaged over 2 yr. Compared with UAN, UAN+AgrotainPlus reduced N2O emissions 35% and SuperU 29% averaged over 2 yr. The N2O-N loss as a percentage of N applied was 0.3% for urea, with all other N sources having significantly lower losses. Grain production was not reduced by the use of alternative N sources. This work shows that enhanced-efficiency N fertilizers can potentially reduce N2O-N emissions without affecting yields from irrigated NT corn systems in the semiarid central Great Plains.     

Leachability and phytoavailability of nitrogen, phosphorus, and potassium from different bio-composts under chloride- and sulfate-dominated irrigation water

Concerns over increased phosphorus (P) application with nitrogen (N)-based compost application have shifted the trend to P-based composed application, but focusing on one or two nutritional elements does not serve the goals of sustainable agriculture. The need to understand the nutrient release and uptake from different composts has been further aggravated by the use of saline irrigation water in the recent scenario of fresh water shortage. Therefore, we evaluated the leachability and phytoavailability of P, N, and K from a sandy loam soil amended with animal, poultry, and sludge composts when applied on a total P-equivalent basis (200 kg ha(-1)) under Cl(-) (NaCl)- and SO4(2-) (Na2SO4)-dominated irrigation water. Our results showed that the concentration of dissolved reactive P (DRP) was higher in leachates under SO(4)(2-) than Cl(-) treatments. Compost amendments differed for DRP leaching in the following pattern: sludge > animal > poultry > control. Maize (Zea mays L.) growth and P uptake were severely suppressed under Cl(-) irrigation compared with SO4(2-) and non-saline treatments. All composts were applied on a total P-equivalent basis, but maximum plant (shoot + root) P uptake was observed under sludge compost amendment (73.4 mg DW(-1)), followed by poultry (39.3 mg DW(-1)), animal (15.0 mg DW(-1)), and control (1.2 mg DW(-1)) treatment. Results of this study reveal that irrigation water dominated by SO4(2-) has greater ability to replace/leach P, other anions (NO3(-)), and cations (K+). Variability in P release from different bio-composts applied on a total P-equivalent basis suggested that P availability is highly dependent on compost source.     

Preceding crop affects grain cadmium and zinc of wheat grown in saline soils of central Iran

Enhanced Cd concentrations in wheat (Triticum aestivum L.) grain produced on saline soils of central Iran have been recently reported. Because wheat bread is a major dietary component for the Iranian people, practical approaches to decrease Cd concentration in wheat grain were investigated. This study investigated the influence of sunflower-wheat vs. cotton-wheat rotations on extractable Cd and on Cd uptake by wheat in these salt-affected soils. Two fields with different levels of Cd contamination (1.5 and 3.2 mg total Cd kg(-1) dry soil) were cropped with different rotations (cotton-wheat and sunflower-wheat) in Qom province, central Iran. Seeds of cotton (Gossypium L.) or sunflower (Helianthus annuus L. cv. Record) were planted in plots. After harvesting of the plants and removal of crop residues, wheat (cv. Rushan) was seeded in all plots. For both studied soils, the concentrations of Cd extracted by 0.04 M EDTA and 1 M CaCl(2) were significantly (P < or = 0.05) greater after cotton than after sunflower. Accordingly, the total amount of Cd in sunflower shoot was significantly (P < or = 0.05) greater than in the cotton shoot. Shoot Cd content in wheat plants grown after cotton and sunflower were significantly different; wheat shoots after cotton accumulated more Cd (two to four times) than after sunflower. Wheat grain Cd concentration after sunflower was much lower (more than seven times) than after cotton. The results of this study showed that sunflower in rotation with wheat in salt-affected soils of central Iran significantly reduced the risk of Cd transfer to wheat grain.     

浙江省主要优势农产品产地土壤-农作物镉含量空间分布及相关性研究

针对目前土壤-农作物镉污染问题,以浙江省40个县（市、区）主要优势农产品产区为研究对象,在粮食、油菜、蔬菜种植地以及茶园和果园土壤中共采集898个单元土壤样品及相对应的五大类农作物,并对其镉含量进行分析评价;同时采用富集系数比较不同农作物对土壤重金属镉的吸收差异。结果表明,研究区产地土壤和农作物的镉含量存在一定程度超标,土壤超标率为10.69%,农作物超标率为4.57%。不同农作物对土壤镉的富集系数差异较大,变化范围在0.002～0.257之间。土壤-农作物镉含量的相关性并不显著。     

Leaching and crop uptake of nitrogen from nitrogen-15-labeled green manures and ammonium nitrate

Green manures can be used as an N source for agricultural crops as a substitute for inorganic N fertilizers. The effects of using green manures on leaching and uptake of N by spring barley (Hordeum vulgare L.) were evaluated in a 2-yr lysimeter study. Ryegrass (Lolium perenne L.) and red clover (Trifolium pratense L.) labeled with (15)N were applied in May of the first year at 160 kg total N ha(-1). Simultaneously, (15)NH(4)(15)NO(3) was applied at 80 kg N ha(-1) to additional lysimeters and others were left without N additions (control). During the second year, all lysimeters, except the control, received 80 kg N ha(-1) as unlabeled NH(4)NO(3). The cumulative, average loads of total N leached during the two years were: 37 (control), 62 (NH(4)NO(3)), 50 (ryegrass manure), and 73 (red clover manure) kg ha(-1). The differences among the treatments were not significant (P > 0.05), but the control had significantly smaller (P < 0.05) leaching loads than the treatments. About 24% of ryegrass- and red clover-derived N and 43% of NH(4)NO(3) were removed through spring barley grain and stover during the two growing seasons. Thus, the N use efficiency in barley was substantially larger when grown with inorganic N fertilizer than when grown with green manure. Viewed in combination with the tendency for larger N leaching loads under red clover manure, claims about water quality benefits of legume-based green manures should be evaluated with regard to the timing of N release and demand for N by the plant.     

Cadmium, copper, nickel, and zinc availability in a biosolids-amended piedmont soil years after application

Concerns over the possible increase in phytoavailability of biosolids-applied trace metals to plants have been raised based on the assumption that decomposition of applied organic matter would increase phytoavailability. The objectives of this study were to assess the effect of time on chemical extractability and concentration of Cd, Cu, Ni, and Zn in plants on plots established by a single application of biosolids with high trace metals content in 1984. Biosolids were applied to 1.5 by 2.3 m confined plots of a Davidson clay loam (clayey, kaolinitic, thermic Rhodic Kandiudults) at 0, 42, 84, 126, 168, and 210 Mg ha(-1). The highest biosolids application supplied 4.5, 760, 43, and 620 kg ha(-1) of Cd, Cu, Ni, and Zn, respectively. Radish (Raphanus sativus L.), romaine lettuce (Lactuca sativa L. var. longifolia), and barley (Hordeum vulgare L.) were planted at the site for 3 consecutive years, 17 to 19 yr after biosolids application. Extractable Cd, Cu, Ni, and Zn (as measured by DTPA, CaCl(2,) and Mehlich-1) were determined on 15-cm depth samples from each plot. The DTPA-extractable Cu and Zn decreased by 58 and 42%, respectively, 17 yr after application despite a significant reduction in organic matter content. Biosolids treatments had no significant effect on crop yield. Plant tissue metal concentrations increased with biosolids rate but were within the normal range of these crops. Trace metal concentrations in plants generally correlated well with the concentrations extracted from soil with DTPA, CaCl(2), and Mehlich-1. Metal concentrations in plant tissue exhibited a plateau response in most cases. The uptake coefficient values generated for the different crops were in agreement with the values set by the Part 503 Rule.     

Predicting cadmium concentrations in wheat and barley grain using soil properties

The entry of Cd into the food chain is of concern as it can cause chronic health problems. To investigate the relationship between soil properties and the concentration of Cd in wheat (Triticum aestivum L.) and harley (Hordeum vulgare L.) grain, we analyzed 162 wheat and 215 barley grain samples collected from paired soil and crop surveys in Britain, and wheat and barley samples from two long-term sewage sludge experiments. Cadmium concentrations were much lower in barley grain than in wheat grain under comparable soil conditions. Multiple regression analysis showed that soil total Cd and pH were the significant factors influencing grain Cd concentrations. Significant cultivar differences in Cd uptake were observed for both wheat and barley. Wheat grain Cd concentrations could be predicted reasonably well from soil total Cd and pH using the following model: log(grain Cd) = a + b log(soil Cd) - c(soil pH), with 53% of the variance being accounted for. The coefficients obtained from the data sets of the paired soil and crop surveys and from long-term sewage sludge experiments were similar, suggesting similar controlling factors of Cd bioavailability in sludge-amended or unamended soils. For barley, the model was less satisfactory for predicting grain Cd concentration (22% of variance accounted for). The model can be used to predict the likelihood of wheat grain Cd exceeding the new European Union (EU) foodstuff regulations on the maximum permissible concentration of Cd under different soil conditions, particularly in relation to the existing Directive and the proposed new Directive on land applications of sewage sludge.     

Drying of granulated wood ash by flue gas from saw dust and natural gas combustion

At the district heating plant of Kalmar, Sweden an on-line unit for production of granulated wood ash for nutrient recycling on forest soils is being applied. Currently, the granules are dried by hot air from an oil-fired burner. The objective of this work was to investigate how drying by flue gas affects the hardening of granules, or impacts their chemical composition and properties. Ninety-six granule samples were treated by flue gas from natural gas combustion in a laboratory pilot scale flue gas generator. CO₂, CO, O₂, C₃H₈ and NO concentrations were varied during the experiment. Additionally, some samples were treated by flue gas from combustion of sawdust at the heating plant in Kalmar. Drying by flue gases did not affect the chemical composition of granules, but minor effects were seen in their mineralogy. The carbonate content was slightly higher in granules treated with flue gas from natural gas combustion compared to the granules dried by hot air only, when measured by wet chemical methods. Results from XRD analysis imply that the calcite content is higher and the portlandite and arcanite content slightly less in granules treated with flue gas from sawdust combustion compared to the granules dried by hot air only. The results from this investigation showed no negative effects on ash granule composition or physical structure by the use of a flue as a drying medium.     

Vegetation as an Indicator of Soil Properties and Water Quality in the Akarçay Stream (Turkey)

In this study, the relationship among water quality, soil properties, and plant coverage in the region of the Akarçay stream was examined. Correlation analyses were carried out between soil samples taken from each of four plant communities in the Akarçay basin and water in the Akarçay stream. The four plant communities in the study area are as follows: Limonium lilacinum (Boiss. et Bal.) Wag., Alhagi pseudalhagi (M. Bieb.) Desv. Peganum harmala L., and Hordeum marinum Huds. subsp. marinum. B, Cl, EC, K, Mg, Na, pH, and SO₄ data from both soil and water samples were subjected to statistical analysis, and significant correlations were obtained (p < 0.05). These correlations indicated that the chemical features of the soil had a major effect on water quality. The important parameters were B, Cl, EC, K, Mg, Na, pH, and SO₄ for Limonium lilacinum communities; Ca, K, and pV for Peganum harmala; and B, Cl, Mg, pH, and pV for Alhagi pseudalhagi. There were also statistically significant relationships (p < 0.05) among the parameters examined. These findings strongly suggested that these plant communities can be used as indicators for soil chemistry and water quality.     

Uncertainty and sensitivity analysis of spatial predictions of heavy metals in wheat

Heavy metals seriously threaten the health of human beings when they enter the food chain. Therefore, policymakers require precise predictions of heavy metal concentrations in agricultural crops. In this paper we quantify the uncertainty of regression predictions of Cd and Pb in wheat (Triticum aestivum L.) and the contributions to the uncertainties in these predictions associated with inputs to the regression model. For each node of the 500- x 500-m grid covering the arable soils in The Netherlands, a latin hypercube sample size of 1000 is constructed from the uncertainty distributions of the explanatory variables (pH, soil organic matter [SOM], and heavy metal concentration in soil), the regression coefficients, and the random term of the regression model. This sample is used as input for the regression model to obtain 1000 values from the uncertainty distributions of the log(Cd) and log(Pb) concentration in wheat. There were no nodes where the recent EU quality standards for Cd and Pb (0.2 mg kg(-1) fresh wt.) in wheat were almost certain to be exceeded. For most nodes with clay soils, the quality standard for Cd in wheat almost certainly will not be exceeded; for Pb this is much less certain. The uncertainty in the Cd concentration in soil contributes most to the uncertainty in the predicted Cd concentrations in wheat (36% on the average), followed by the random term of the regression model (23%). For Pb the contribution of the random term is by far the largest (52%).     

Nonpoint source of nutrients and herbicides associated with sugarcane production and its impact on Louisiana coastal water quality

A watershed analysis of nonpoint-source pollution associated with sugarcane (Saccharum officinarum L.) production was conducted. Runoff water samples following major rainfall events from two representative sugarcane fields (SC1 and SC2) were collected and analyzed. The impact of runoff on two receiving water bodies, St. James canal (SJC) and Bayou Chevreuil (BC) in a drainage basin (Baratarian Basin), was studied. Results show that runoff flow/rainfall ratios at the SC1 were significantly higher (P < 0.0001, n = 14) than at the SC2, probably mainly due to higher sand content and higher infiltration rate of surface soil at the SC2. In runoff water samples, total suspended solids (TSS) showed a significant correlation with the concentrations of N and P. Sugarcane runoff showed a direct impact on the SJC and BC locations where seasonal variations of pollutant concentrations in the waters followed the patterns of runoff loadings. Swamp forest runoff (SFR) location showed a buffering effect of forested wetlands on water quality with the lowest measured pollutant concentrations. The ratios in total N/total P and in inorganic N/organic N in runoff waters indicated that fertilization in spring greatly contributed to the temporal increase of N loadings, especially in forms of inorganic N. Isotope signature of (15)N-nitrate in the water samples verified that the nitrate was derived from fertilizers and was consumed during transportation. Both N and P concentrations in the receiving water bodies were above the eutrophic level. During the study period, herbicide concentrations in the receiving water bodies rarely exceeded the drinking water standards.