Enrique Barriuso

Influence of compost addition to soil on the behaviour of herbicides

The transformations of eight herbicides (atrazine, simazine, terbutryn, pendimethalin, carbetamide, 2,4-D, metsulfuron-methyl and dimefuron) in soil after compost addition were monitored during long-term laboratory incubations. The herbicides were applied to soil, compost and soil-compost mixtures. Herbicide sorption, their kinetics of mineralisation and the extractability of residues were compared in the different treatments. Compost addition to soil generally decreased herbicide mineralisation and favoured the stabilisation of herbicide residues. A fraction of the stabilised residues remained extractable and potentially available. However, most of them were unextractable and formed bound residues. Sorption could be at the origin of a kinetically limited biodegradation, mainly for the most highly-sorbed herbicides (atrazine, simazine, terbutryn, pendimethalin and dimefuron). Compost addition had little effects on the less sorbed herbicides (carbetamide, 2,4-D and metsulfuron- methyl).

Rapid meneralization of the s-triazine ring of atrazine in soils in relation to soil management

Abstract Mineralization of the triazine ring of atrazine was studied in soils with similar physicochemical properties, from experimental plots under different crop rotations located in Grignon, France. Rapid mineralization rates were found inplots under continuous maize receiving atrazine every year. On the contrary, low mineralization rates were measured in plots under continuous wheat or permanent grass that had never received atrazine. The rapid mineralization of the atrazine-ring was observed without any previous laboratory microbial enrichment. It was also related to the presence of a chloro-substituent on the ring: rapid mineralization was also observed with simazine, another chloro-s-triazine, but not with terbutry, a thiomethyltriazine. The characterization of the extractable metabolites during the incubation experiments did not allow determination of the degradation pathway. In these soils, two competitive dissipation processes are proposed: (1) rapid dissipation through ring cleavage and mineralization in soil from the plot receiving atrazine every year, (2) more progressive dissipation through formation of bound residues in the other soils. The rate of mineralization of the atrazine-ring varied during the year and was rather sensitive to soil storage conditions.

Soil enzymatic response to addition of municipal solid-waste compost

Modifications of soil microbiological activity by the addition of municipal solid-waste compost were studied in laboratory incubations. Three composts were compared, one lumbricompost and two classical composts with different maturation times. Organic C mineralization and nine enzyme activities (dehydrogenase, peroxidase, cellulase, β-glucosidase, β-galactosidase, N-acetyl-β-glucosaminidase, protease, amidase, and urease) were determined in the composts and the amended soil. Initial enzyme activities varied in the soil according to the sampling date (winter or summer) and were greater in the composts than in the soil, except for urease. Generally, the youngest compost exhibited greater activity than the oldest one. In the amended soil, the composts did not increase enzyme activity in an additive way. Dehydrogenase, the only strictly endocellular enzyme, was the only one for which the activity in the amended soil increased significantly in proportion to the addition of compost. During the incubations, C mineralization and dehydrogenase activity were significantly correlated, indicating that dehydrogenase was a reliable indicator of global microbial activity. Peroxidase activity in the soil remained constant, but increased in the composts and amended soil. Addition of the oldest compost had no effect on the activity of the C cycle enzymes, but the youngest compost increased creased soil activity at the higher application rate. Enzymes of the N cycle were stimulated by all compost amendments, but the increase was only transient for amidase and urease. Lumbricomposting had no marked effect on compost enzyme activity, either before or during the incubation.

Sorption of weak organic acids in soils: clofencet, 2,4-D and salicylic acid

The sorption behaviour of a new wheat hybridising agent (clofencet, 2-4-(chlorophenyl)-3-ethyl-2,5-dihydro-5-oxopyridazine-4-carboxylic acid) was investigated in batch equilibrium experiments and compared to that of two other organic acids (2,4-D and salicylic acid). Sorption coefficients Kd for the three compounds were determined in 18 Cambisols and Ferralsols. Kd values for clofencet were 0.3-9.4 l/kg for Cambisols and 2.1-68 l/kg for Ferralsols. Sorption of clofencet was strongly related statistically to that of salicylic acid. Sorption of clofencet and salicylic acid decreased exponentially with increasing solution pH in Cambisols whereas a bell-shaped curve was obtained for the sorption of salicylic acid in Ferralsols. Sorption of 2,4-D (2,4-dichlorophenoxyacetic acid) was not statistically related to the pH of the different soils. Positively charged oxide surfaces were shown to play a significant role in the sorption of clofencet and salicylic acid. The use of simple correlation and multiple linear regressions suggested that the main sorption mechanisms of clofencet in soils were likely to be ligand exchange on oxide surfaces and, to a lesser extent, cation bridging. Differences in the sorption behaviour of clofencet/salicylic acid and 2,4-D might be attributed to the possibility of the two former compounds forming bidentate complexes with metals.

Tillage management effects on pesticide fate in soils. A review

Reducing tillage intensity through the implementation of conservation practices is a way to reach a more sustainable agriculture. Reducing tillage is indeed an efficient way to control soil erosion and to decrease production costs. Nonetheless, the environmental impact of reduced tillage is not well known because conservation techniques may induce strong changes in soil physicochemical properties and biological activity. Knowledge on the fate of applied pesticides under conservation practices is particularly important from this point of view. We review here the advances in the understanding, quantification and prediction of the effects of tillage on pesticide fate in soils. We found the following major points: (1) for most dissipation processes such as retention, degradation and transfer, results of pesticide behaviour studies in soils are highly variable and sometimes contradictory. This variability is partially explained by the multiplicity of processes and contributive factors, by the variety of their interactions, and by their complex temporal and spatial dynamics. In addition, the lack of a thorough description of tillage systems and sampling strategy in most reports hampers any comprehensive interpretation of this variability. (2) Implementation of conservation tillage induces an increase in organic matter content at the soil surface and its gradual decrease with depth. This, in turn, leads to an increase in pesticide retention in the topsoil layer. (3) Increasing retention of pesticides in the topsoil layer under conservation tillage decreases the availability of the pesticides for biological degradation. This competition between retention and degradation leads to a higher persistence of pesticides in soils, though this persistence can be partially compensated for by a more intensive microbial activity under conservation tillage. (4) Despite strong changes in soil physical properties under conservation tillage, pesticide transfer is more influenced by initial soil conditions and climatic conditions than by tillage. Conservation tillage systems such as no-tillage improve macropore connectivity, which in turn increases pesticide leaching. We conclude that more knowledge is needed to fully understand the temporal and spatial dynamics of pesticide in soil, especially preferential flows, in order to improve the assessment of pesticide risks, and their relation to tillage management.

Stable carbon isotope evidence for the microbial origin of C14C18 n-alkanoic acids in soils

Abstract In order to delineate the origin of soil fatty acids, crop soil samples have been incubated for 21 days in vitro either with unlabelled or 13 C-labelled glucose. Analyses of C 14 C 32 n -alkanoic acids from monocarboxylic acid fractions, as methyl esters, by gas chromatography-combustion-isotope ratio monitoring mass spectrometry (GC—C—IRMS) show that C 14 , C 16 and C 18 n -alkanoic acids are 13 C-labelled, thus demonstrating their derivation from soil microorganisms, e.g. fungi or bacteria, growing during the experiment. Higher n -alkanoic acids, C 16 C 33 n -alkanes, and C 22 C 30 n -alkanols have not been significantly labelled, thus suggesting their derivation from other sources, e.g. higher plants. This short-term tracer experiment using stable carbon isotopes represents a novel and fruitful approach to study organic matter transformations in soils and other systems such as sediments.

Modification of Soil Water Retention and Biological Properties by Municipal Solid Waste Compost

A compost originating from the organic fraction of MSW, separately collected, was added to a loamy soil at different application rates. Modifications of soil physical and biological properties were studied after compost addition. Water retention properties, after compost addition to soil, were monitored. Organic carbon mineralization was followed during a six-month incubation. Enzyme activities were assayed immediately after compost addition, as well as after incubation of soil-compost mixtures. These properties provided information about the modification of overall microbiological activity and specific nutrient cycles in the amended soil. Water retention, carbon mineralization and most enzyme activities after incubation were increased by compost incorporation. The additivity or nonadditivity of compost effects on soil properties was discussed.

Biosorption characterization of herbicides, 2,4-D and atrazine, and two chlorophenols on fungal mycelium

Biosorption of the 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4-dichlorophenol (2,4-DCP), 4-chlorophenol (4-CP) and 2-chloro-ethylamino-6-isopropylamino-1,3,5-triazine (atrazine) has been studied on the mycelium of Emericella nidulans and Penicillium miczynskii, isolated from composted wheat straw and a soil respectively. Results obtained with inactivated fungal biomass showed that a rapid adsorption on fungal cell walls surfaces was the main sorption phenomenon for the more hydrophobic molecules. This sorption was only partially reversible. With active living mycelia, additional phenomena were responsible for an increased sorption of all chemicals. This process was slow and depended on the chemical concentration. For 4-CP, it was attributed to biodegradation as demonstrated by the presence of degradation products in solution. Bioaccumulation inside the mycelium could also partially explained the results observed with living biomass for 4-CP, 2,4-DCP and 2,4-D.

Degradation of formulated and unformulated triticonazole fungicide in soil : effect of application rate

Laboratory incubation studies were conducted to evaluate the influence of commercial formulation adjuvants and application rate over a range of 0.2–80 mg kg−1 on the dissipation of 14C-triticonazole systemic fungicide in a loamy clay soil, at 22 and 28°C, and 80% of water field capacity. Measurement of the balance of the 14C-residues after incubation at 22°C showed an increased resistance to desorption with time, as apparent desorption Kapp increased from 2 to 10 l kg−1 in a 133 d period. Decreased extractability of the residues with incubation time and formation of bound residues up to 20% showed that the overall availability of triticonazole decreased with incubation time. The addition of diluted doses of formulation adjuvants did not significantly affect the degradation and binding of the active ingredient. Mineralization of triticonazole was slow, with a high activation energy of 130 kJ mol−1. The persistence of triticonazole increased with application rate, as the first-order mineralization rates at 28°C decreased from 2×10−3 to 0.7×10−3 d−1 with amount applied increasing from 0.2 to 80 mg kg−1. However, the absolute amount of triticonazole mineralized increased with increasing concentration in the soil solution, and the slow mineralization was attributed to limited availability in the soil solution due to high sorption.

Composting in small laboratory pilots: Performance and reproducibility

Small-scale reactors (<10 l) have been employed in composting research, but few attempts have assessed the performance of composting considering the transformations of organic matter. Moreover, composting at small scales is often performed by imposing a fixed temperature, thus creating artificial conditions, and the reproducibility of composting has rarely been reported. The objectives of this study are to design an innovative small-scale composting device safeguarding self-heating to drive the composting process and to assess the performance and reproducibility of composting in small-scale pilots. The experimental setup included six 4-l reactors used for composting a mixture of sewage sludge and green wastes. The performance of the process was assessed by monitoring the temperature, O(2) consumption and CO(2) emissions, and characterising the biochemical evolution of organic matter. A good reproducibility was found for the six replicates with coefficients of variation for all parameters generally lower than 19%. An intense self-heating ensured the existence of a spontaneous thermophilic phase in all reactors. The average loss of total organic matter (TOM) was 46% of the initial content. Compared to the initial mixture, the hot water soluble fraction decreased by 62%, the hemicellulose-like fraction by 68%, the cellulose-like fraction by 50% and the lignin-like fractions by 12% in the final compost. The TOM losses, compost stabilisation and evolution of the biochemical fractions were similar to observed in large reactors or on-site experiments, excluding the lignin degradation, which was less important than in full-scale systems. The reproducibility of the process and the quality of the final compost make it possible to propose the use of this experimental device for research requiring a mass reduction of the initial composted waste mixtures.