Potential of fluorescent tracers to appraise biochar amendment strategies for pesticide mitigation - insights from comparative sorption.

Mitigation of pesticide dispersion in soil and water is required to protect ecosystem health and the anthropic uses of water bodies. Biochar amendments have been suggested to reduce pesticide dispersion due to their high sorption potentials. Nevertheless, appraisals at different scales have been limited by the costs of pesticide analyses. The aim of this study was to evaluate the potential of two fluorescent tracers, uranine (UR) and sulforhodamine B (SRB), for use as pesticide proxies in the context of biochar amendments used for mitigation purposes. Therefore, we compared the sorption processes of both fluorescent tracers and those of three pesticides, glyphosate, 2,4-D, and difenoconazole for soils; three wood biochars (pine, oak, and beech/charm blend); and soil/biochar mixtures representing agricultural usages. The results showed that the sorption of glyphosate by soil was unaffected by amendment with the tested pine, oak, and wood blend biochars. In contrast, the sorption coefficients of UR, SRB, 2,4-D, and difenoconazole were significantly increased with these biochar amendments. SRB, in particular, exhibited sorption behavior similar to that of the hydrophobic fungicide difenoconazole. This indicates promise for the use of SRB as a proxy for hydrophobic pesticides, in testing biochar amendments.

Effect of salinity on the fate of pesticides in irrigated systems: a first overview.

This review investigates the impact of salinity on the fate of the active compounds of pesticides in a cultivated environment. Due to the over-exploitation of water resources and intensification of agriculture, salinity outbreaks are being observed more often in cultivated fields under pesticide treatments. Nevertheless, there is a poor understanding of the incidence of varying water salt loads on the behavior of pesticides' active ingredients in soil and water bodies. The present review established that water salinity can affect the diffusion of pesticides' active ingredients through numerous processes. Firstly, by increasing the vapor pressure and decreasing the solubility of the compounds, which is known as the salting-out effect, salinity can change the colligative properties of water towards molecules and the modification of exchange capacity and sorption onto the chemicals. It has also been established that the osmotic stress induced by salinity could inhibit the biodegradation process by reducing the activity of sensitive microorganisms. Moreover, soil properties like dissolved organic matter, organic carbon, clay content, and soil texture control the fate and availability of chemicals in different processes of persistence in water and soil matrix. In the same line, salinity promotes the formation of different complexes, such as between humic acid and the studied active compounds. Furthermore, salinity can modify the water flux due to soil clogging because of the coagulation and dispersion of clay particle cycles, especially when the change in salinity ranges is severe.

Impact of coffee biochar on carbon, microbial biomass and enzyme activities of a sandy soil cultivated with bean.

Biochar has been used to reuse the agro-industrial wastes and improve soil quality. Several studies have been carried out to show the impact of biochar on physical and chemical soil attributes. However, there are still gaps regarding the effects on as microbial biomass and enzymatic activities that are important to determine sensitive indicators to evaluate changes in management practices. The objective of this study was to assess the effect of two biochars on the chemical, microbial biomass carbon, and the enzymatic activities in an Entisol cultivated with bean. We evaluate two types of coffee biochar: ground and husks, four doses (4, 8, 12, and 16 Mg ha-1) and control. All treatments received organic fertilization with cow manure. Husks biochar increase the soil pH, Ca, and K, also contributing to the reduction of toxic aluminum contents and raising the concentrations of P labile. The treatments that received ground biochar showed higher soil organic carbon, microbial biomass, ß-glucosidase, and fluorescein diacetate. Biochar produced from coffee residues increased sandy soil quality. We showed the first report on the beneficial impact of coffee biochar on enzymatic and microbiological quality of sandy soil cultivated with the bean.

A simple framework to analyze water constraints on seasonal transpiration in rubber tree (Hevea brasiliensis) plantations.

Climate change and fast extension in climatically suboptimal areas threaten the sustainability of rubber tree cultivation. A simple framework based on reduction factors of potential transpiration was tested to evaluate the water constraints on seasonal transpiration in tropical sub-humid climates, according pedoclimatic conditions. We selected a representative, mature stand in a drought-prone area. Tree transpiration, evaporative demand and soil water availability were measured every day over 15 months. The results showed that basic relationships with evaporative demand, leaf area index and soil water availability were globally supported. However, the implementation of a regulation of transpiration at high evaporative demand whatever soil water availability was necessary to avoid large overestimates of transpiration. The details of regulation were confirmed by the analysis of canopy conductance response to vapor pressure deficit. The final objective of providing hierarchy between the main regulation factors of seasonal and annual transpiration was achieved. In the tested environmental conditions, the impact of atmospheric drought appeared larger importance than soil drought contrary to expectations. Our results support the interest in simple models to provide a first diagnosis of water constraints on transpiration with limited data, and to help decision making toward more sustainable rubber plantations.