Leaching and volatilization of N from urea, and precipitation and fixing of Zn by commercial fertilizers, has led to excessive costs for farmers and problems for the environment. Incorporating fertilizers in a porous material such as diatomite can prevent these losses by slowing the nutrient release. A new fertilizer formulation, based on the urea-zinc (UZn) complex in the eutectic solution of salt-urea was prepared. In the following, UZn was incorporated into diatomite and nano-diatomite by using hydroxypropyl methylcellulose (HPMC) as a binder. The treatments included the following: U: urea; UZn: urea-Zn; UZn-D: urea-Zn-diatomite; UZn-ND: urea-Zn-nano-diatomite; UZn-D-B: urea-Zn-diatomite-binder; and UZn-ND-B: urea-Zn-nano-diatomite-binder. The slow-release urea fertilizers (SRUFs) were characterized using FESEM/EDS, FTIR, CHN, XRD, DLS, and zeta potential techniques. Urea slow-release behavior, kinetics in water, and available Zn and N-forms leaching in the soil column were evaluated compared with conventional urea and zinc fertilizers. The pattern of release of urea in water was sigmoidal and after 12 h, only 20% of urea was released from fertilizers containing diatomite and HPMC. The NO3– release pattern in the soil started with a 12-day delay, and after that, the rate of NO3– leaching decreased by two to three times in the application of fertilizers containing HPMC compared with urea. The Zn concentration in the leachates of columns supplied with SRUFs was 35% less than for those supplied with ZnSO4. The results showed that the SRUFs make N and Zn available in the soil and but reduce the rate of their release.

Sets of replicate hydraulic conductivity tests were conducted using 100 mM KCl and 20 and 40 mM CaCl2 solutions to evaluate how changes in hydraulic conductivity are related to changes in the exchange complex and physical properties (water content and free swell) of prehydrated and non-prehydrated bentonite used for geosynthetic clay liners (GCLs). Essentially no change in hydraulic conductivity and water content (or void ratio) occurred during tests with the 100 mM KCl solution even though K+ was replacing Na+ on the exchange complex. In contrast, for the CaCl2 solutions (20 mM and 40 mM), the hydraulic conductivity increased and the free swell and water content decreased as exchange of Ca2+ for Na+ occurred. Faster changes in hydraulic conductivity and the exchange complex occurred in the tests with the 40 mM CaCl2 solution and the non-prehydrated bentonite (i.e. the hydraulic conductivity changed more rapidly when exchange occurred more rapidly). Even though exchange of Ca2+ for Na+ was essentially complete at the end of testing, the hydraulic conductivity obtained with the 20 mM CaCl2 solution was less and the water content greater than obtained with the 40 mM CaCl2 solution (2.6 × 10−8 cm/s vs. 6.7 × 10−8 cm/s, 122% vs. 111%, and 3.2 vs. 2.9). Similarly, the prehydrated bentonite had lower hydraulic conductivity (1.9 × 10−8 cm/s vs. 6.7 × 10−8 cm/s) and greater water content (167% vs. 111%) than the non-prehydrated bentonite at the end of testing, even though Ca-for-Na exchange was essentially complete.

Organic matter water extract, or so-called ‘tea’, may be used to correct nutrient deficiencies in crops or enhance their defense systems. Such tea mixtures are prepared locally by Mediterranean farmers to offset a multitude of constraints, particularly a scarcity of organic manure or high synthetic input costs. However, the diverse range of tea production and usage practices and farmers' underlying rationales have yet to be thoroughly studied. Yet locally they constitute real alternatives that allow farmers to maintain their income levels while reducing reliance on chemical inputs. The main objective of this study was to gain insight into farmers' rationale and practices regarding the production of homemade dry manure tea (HMT) in North Africa, while also highlighting the benefits perceived by farmers. Nearly 50 interviews with farmers were thus conducted in three irrigated cropping areas in Morocco, Algeria and Tunisia. Our results showed that HMT is widely used in intensified family horticultural cropping systems that usually rely on drip irrigation and chemical fertilization. The analysis of farmers' practices revealed that HMT was generally made from aged manure that was pure or consisted of a mixture of sheep, cow or poultry dung. The production protocol varied in terms of drenching techniques, maceration time, container volume and type, and filtration techniques. Farmers applied the derived tea via the drip irrigation system, regularly or with a limited number of applications. The analysis of farmers' rationales and perceptions regarding HMT clearly highlighted that they felt that these practices played a positive role. HMT was considered to improve vegetative growth, yield and, to a lesser extent, soil properties. These benefits could in turn lead to decreased use of synthetic fertilizers by farmers, while boosting their income. The increased understanding of HMT and the underlying rationales showcased in this study could help scientists better analyze and assess these practices in the future. The findings could also facilitate improvement and wider dissemination of these practices to achieve more sustainable irrigation systems in the intensified irrigated cropping areas that abound in North Africa.

The percolation of water through waste landfill sites produces leachates with large amounts of pollutants. Clay barriers are often used to limit soil and underground water pollution. A better understanding of the interaction between ammonium smectite and carboxylic acids would contribute significantly to our understanding of such systems. The SWy-2 (Wyoming smectite) was exchanged with NH4+ and then batched with carboxylic acids (acetic, formic, chloroacetic and oxalic) in concentrations between 0.01 M and 1 M. The solid phases obtained were analysed chemically and characterized by infrared absorption spectroscopy (IR) and powder X-ray diffraction (XRD). Ionic chromatography was used for the quantitative measurement of ammonium ions in the solution after the interaction. For the four acids, the interaction was characterized by a cationic exchange of NH4+ to H3O+. A partial exchange to Al3+ due to a partial dissolution of the sample in strong acidic medium was observed with chloroacetic and oxalic acids for which adsorption of molecules on the clay sample occurs, mainly through H-bonding with the cation. Moreover, the intercalation of oxalic acid in the interlayer space was highlighted.

Routine monitoring of landfill leachates has been extended to include characterization of suspended solids recovered by filtration. Calcite is consistently identified as a suspended solid, with less frequent reports of quartz and clays (kaolinite, illite, chlorite). Morphologically, calcite occurs as discrete grains, coatings on quartz sand and as microconcretions. Preliminary stable isotope data for seven samples generally show positive δ13C values (relative to PDB) up to +3.5‰ and δ18O values between −5 and −8‰, consistent with an origin through precipitation from leachate. Geochemical modelling of leachate compositions for the same samples indicates that the leachates are saturated with respect to calcite, and that the degree of supersaturation decreases for older samples. Mass balance considerations show that the proportions of methane and carbon dioxide observed for landfill gas do not reflect the amount of bicarbonate that is potentially available from the anaerobic decomposition of putrescible waste. Overall, putrescible waste has the potential to form a maximum of 1.9 g of calcite for every gram of waste, although values less than this are likely to be achieved in practice. From these differing lines of evidence, there can be no doubt that calcite precipitation should be expected to take place within landfill systems as an essential part of the waste degradation and stabilization process, and should be considered in modelling both gas evolution and carbon emissions.

Pendimethalin dissipation was studied following annual 1.7 kg ai ha–1 applications to 3-yr-old Kentucky bluegrass turf growing on a Sharpsburg silty clay loam soil and an 85/15 by volume sand/Sharpsburg soil mixture in 150-cm-deep rhizotron containers. Plant tissue, thatch, and soil were sampled periodically between application and 168 days after treatment (DAT). Soil and leachate were collected to monitor pendimethalin movement. Most of the herbicide appeared to remain within the turfgrass system. Pendimethalin concentration was highest in plant tissue and thatch. The 4-hydroxymethyl pendimethalin metabolite was detected in turfgrass tissue up to 42 DAT. No pendimethalin was detected at the 30-, 60-, or 120-cm depths in the rhizotron containers. Traces (≤0.003 mg kg–1) of pendimethalin detected in rhizotron leachate collected between 6 and 14 days after heavy rainfall (88 and 95 DAT, respectively) were attributed to gravitational displacement of soil colloids containing adsorbed herbicide. Pendimethalin application to established turfgrass would not appear to pose a high risk of groundwater contamination.

Experiments were conducted in 1990 and 1991 to determine bioavailability of PRE herbicides at three soil profile depths and two soil types in established common bermudagrass sods. Prodiamine and oryzalin reduced ‘Tifgreen’ bermudagrass root growth in the 5- to 7.5-cm layer of a Bosket very fine sandy loam soil at 2 and 4 wk after treatment in 1991. These herbicides decreased bermudagrass root weight in both the Bosket and Marietta sandy clay loam both years in samples taken from the 2.5- to 5-cm depth layer. In the 0- to 2.5-cm soil layer, all herbicides reduced root weight in 1990. In a bioassay, prodiamine caused decreased Tifgreen bermudagrass root growth at concentrations as low as 4 ppb by wt in the very fine sandy loam soil, while 8 ppb was necessary in the sandy clay loam soil. Prodiamine was detected in the very fine sandy loam at 4 wk after treatment at all depths in 1991 (65, 45, and 39 ppb in the 0- to 2.5-, 2.5- to 5-, and 5- to 7.5-cm soil layers, respectively). Oryzalin was also detected at all depths in 1991 when sampled at 2 and 4 wk after treatment in the very fine sandy loam. Pendimethalin was present in concentrations of 38, 39, and 37 ppb in the sandy clay loam at 2 wk after treatment in the 0- to 2.5-, 2.5- to 5-, and the 5- to 7.5-cm soil layers, respectively. Pendimethalin was also detected in the very fine sandy loam at 2 wk after treatment at concentrations of 55, 69, and 36 ppb in the 0- to 2.5-, 2.5- to 5-, and 5- to 7.5-cm soil layers, respectively.

The application of a simple, fast and reliable volumetric microrespirometric method to assess respiration of bivalve larvae is discussed. As a model, C. gigas larvae of various sizes were used. Metabolic activity of veliger larvae was assessed by measuring respiratory rate for use in ecophysiological modelling. As an example of the application of this approach, additional measurements of veliger respiratory rates were carried out to assess the effect on larval metabolism of different concentrations of leachate from wood treated with chromated copper-arsenate (CCA).Veligers of Crassostrea gigas (length from 95 to 331 µm) were fed with a mixture of Isochrysis galbana and Chaetoceros pumilum cells. Experiments were performed in a 20 °C constant seawater temperature. The wet and dry weight of four length (L, in µm) classes of larvae were obtained from which the relationship between total dry weight and veliger length was derived {DW = e (3.27+L×0.0154)} (R 2 = 99%). Moreover, tissue dry weight (TDW; in ng) was calculated according to Gerdes (1983). Since the mathematical model between larval length and respiratory rate explained 88% of the total variability, a more conservative approach using oyster larval dry meat weight (in ng) and respiratory rate (in µl O2 h−1) was developed to establish a linear model explaining 94.5% of the variability: Resp. = -3.849 × 10-4 + 5.211 × 10-6 × TDW. These experiments provided updated figures of C. gigas larval respiratory rates for use in ecophysiological models. The relationship between tissue dry weight and respiratory rate was close to previous estimates obtained by Gerdes (1983) and Hoegh-Guldberg and Manahan (1995) at 25 °C and 20 °C respectively. Our experiments demonstrate that volumetric microrespirometry is suitable for assessing larval respiratory rate and therefore can be used to assess impacts of pollutants on an early larval stage. Oysters exposed to leachates from chromated copper arsenate (CCA) treated timber at 5 kg m−3 showed initially highly variable respiratory rates while those rates decreased drastically for a 15 kg m−3 CCA treatment exposure. Among bioindicators using physiological response to assess pollutant effects, swimming activity and respiratory rates can be compared, the later showing a significant response at a lower pollutant concentration.