Abstract. Bacterial contamination of water is a problem worldwide and is often acute in developing countries where human and animal waste is disposed of on land for use as fertilizer or because of poorly developed sanitation systems. Studying leaching risk through soils is difficult when no suitable microbiological laboratory is available. A method using the movement of ZnO particles through soils as a surrogate for studying bacteria directly was tested. ZnO particles with a similar size to bacteria can readily be detected by chemical analysis. For a range of nine different soil textures, leaching rates of ZnO particles under near saturated conditions were significantly correlated with leaching rates of Escherichia coli cells ( P =0.013). For both ZnO and E. coli , leaching was generally greatest through fine textured soils. 相似文献
Summary Field-moist soil and glass beads mixtures were packed in glass tubes and leached with 100 ml of 5 mM CaCl2 and incubated at 20 or 30°C. The leaching procedure was repeated every 2 weeks for 14 weeks. The leachates were analysed for SO
inf4sup2–
and NO3–. The S uptake by three successive croppings of corn (Zea mays L.) or soybean [Glycine max (L.) Merr.] at 40- or 60-day intervals, respectively, or three cuttings of ryegrass (Lolium multiflorum L.) at 30-day intervals were studied under greenhouse conditions. Results showed that significantly greater amounts of S were mineralized at 30°C than at 20°C in each of 13 Iowa and 7 Chilean surface soils. Expressed as percentages of organic S in soils, the amounts of S mineralized in the Iowa surface soils in 14 weeks at 20 and 30°C ranged from 1.2% to 9.8% and from 2.4% to 17.5%, respectively. The corresponding values for the Chilean soils ranged from 0.9% to 7.2%6 and from 1.4% to 12.1%. The Q10 values of S mineralization ranged from 1.7 to 4.4 (average 2.5) for the Iowa soils and from 1.7 to 3.1 (average 2.1) for the Chilean soils. The cumulative S mineralized at 20°C in 14 weeks was significantly correlated with the cumulative N mineralized (linear model, r=0.72**; quadratic model, r=0.84***). Similarly, the cumulative S mineralized at 30°C was significantly correlated with the cumulative N mineralized at this temperature (linear model, r=0.81***; quadratic model, r = 0.82***). The potentially mineralizable S pool (S0), calculated by using an exponential equation for the S mineralized at 20°C, ranged from 5 to 44 mg kg–1 for the Iowa soils and from 10 to 25 mg kg–1 for the Chilean soils. The corresponding values obtained by using a reciprocal-plot technique ranged from 6 to 48 mg kg–1 and from 12 to 26 mg kg–1, respectively. The S0 values calculated for S mineralized at 30°C, in general, were higher than those obtained at 20°C. The S mineralization rate constant (k) and the time required to mineralize 50% of S0 (Kt), calculated by using the cumulative SO
inf4sup2–
released during 14 weeks of incubation, varied considerably among the soils. Up take of S by corn and soybean (tops+roots) were, in general, lower than the total SO
inf4sup2–
mineralized in 14 weeks at 20°C. 相似文献
Summary
Oniscus asellus produced changes in the nutrients leached from Oie and Oa horizons of a hardwood forest soil. Soil with isopods lost more K+ (54%) from the Oie horizon and more Ca2+ (25%), Mg2+ (40%), and water-extractable S (23%) from the Oa horizon than soil without isopods. In contrast, soils with isopods lost less Ca2+ (39076) from the Oie horizon and less dissolved C-bonded S (33%) from the Oa horizon than soil without isopods. In addition, the Oia and Oa horizons exhibited different nutrient dynamics. When isopods were present, the Oa horizon leachates accumulated more Na+ K+, Ca2+, Mg2+, NO3– , water-soluble SO42–, and dissolved C-bonded S, and the Oie horizon retained more of these nutrients. The type of leaching solution also had a major effect on nutrients. Leaching with a simulated soil solution resulted in smaller nutrient losses for K+ and Mg2+ in both horizons and for Na+, Ca2+, and NO3– in the Oa horizon than leaching with distilled water. 相似文献
Herbicides are key products in sustaining agricultural production and, to minimize agro-environmental concerns regarding their use, continued assessment of their behavior under different management practices is required. Leaching and runoff losses of four herbicides applied preplant-incorporated (PPI) were evaluated in two tillage systems over a 3-year period (1989–1991). Scant leaching during the droughty 1991 growing season limited treatment evaluations to 2 years. Herbicides were applied at recommended rates (1.7 and 2.2 kg active ingredient (a.i.) ha−1) to conventional tillage (CT) and mulch tillage (MT) corn (Zea mays L.) fields on Hagerstown silty clay loam (fine, mixed, mesic Typic Hapludalf). Tillage treatments were defined as moldboard plow-disk-harrow (CT) and single-disking (MT). During this study, CT followed 5 years of corn production in a comparable CT system on this site and, similarly, MT followed a 5-year no-tillage (NT) system. Herbicides were applied preemergence (PRE) to CT and NT in the 5-year study and preplant-incorporated (PPI) in this study. Herbicide mobility in subsurface drainage was evaluated from herbicide mass transported to pan lysimeters installed 1.2 m deep. Surface drainage losses of these chemicals were determined from residues in runoff collected with automated sampling and recording equipment.
Leachate volumes were greater from MT than CT in 1989 and 1990 and exceeded all seasonal losses during the previous 5 years under NT management. Comparisons of total seasonal leachate discharged to pan lysimeters within and among studies and herbicide mass leached showed that timing of leachate-inducing precipitation relative to herbicide application was the key factor in regulating herbicide translocation. Herbicide mass transported through the root zone averaged from less than 0.1% to 0.9% of applied rates in CT and from 1.4% to 5.1% in MT.
Leachate-availability of herbicide residues and extent of herbicide longevity in this soil under MT conditions were similar to previous findings under NT management. Despite these behavioral similarities for herbicides among tillages, herbicide mass discharged per unit of percolate was most often lower for MT compared with NT, particularly in early growing seasons of comparable precipitation. Thus, the PPI treatment in MT appeared to reduce leaching of these chemicals compared with PRE application in NT.
Runoff losses of PPI herbicides ranged from 0.35% to 0.77% of applied rates in CT and from 0.13% to 0.28% in MT. Losses of PRE-applied herbicides from NT averaged less than 0.1% of applied rates; maximum yearly losses ranged from 0.06% to 0.18%. Thus, the character of the disked, minimally tilled surface provided a level of impedance to runoff that was greater than achieved with the tilled surface on this 3 to 5% slope, but less than previously obtained with an untilled, mulch-covered surface. 相似文献
Availability and leaching of dissolved inorganic N (DIN = NH4+ + NO3-) in soil were measured in a periodically flooded forest of the Central Amazon floodplain (várzea) during one terrestrial phase. Special emphasis was on the effects of a legume and a non-legume tree species. NH4+-N accounted for more than 85% of DIN even at the end of the terrestrial phase although it decreased throughout the experimental period. While extractable NO3–-N was always low in the soil (less than 15% of DIN), the amount of leached NO3–-N was in the same range as NH4+-N. Under the legume trees mean DIN contents of the topsoil were higher than under the non-legume trees. DIN leaching from the topsoil (0–20 cm) was significantly higher under the legume trees than at the other sites, also indicating a higher N availability. Therefore, despite considerable leaching legume trees may be an important source of N supporting a high biomass production of the várzea forest. 相似文献