The objective of this review is to show in a general way how biochar (BC) can be obtained and its effects on the physicochemical properties of soils and physiological behavior of cultivated plants. BC is a product rich in carbon that comes from the pyrolysis of biomass, generally of vegetable origin. BC is obtained by the decomposition of organic matter exposed to temperatures between 200-900 ºC in an atmosphere with low oxygen availability (pyrolysis), which can be slow, intermediate or fast. Depending on the biomass and the temperature used in its production, BC can contain high levels of elements such as carbon, nitrogen, oxygen, hydrogen, sulfur, among others. The main sources to produce biochar are forest, agroindustrial and manure residues. BC quality and physical-chemical characteristics will depend not only on the type of waste or plant material for production, but also on the plant photosynthetic apparatus. The high carbon contents present in organic matter, which are more resistant to biological and chemical decomposition, are stabilized by the pyrolysis process. When incorporated into the soil, BC remains stable for longer periods of time and is not volatilized into the atmosphere; this allows BC to be considered as an important compound for the mitigation of the impacts of polluting substances. Additionally, it has been found that BC application improves the physicochemical characteristics of the soil, including fertility. This improvement generates positive responses in the physiological behavior of cultivated plants such as the increase of germination, accumulation of dry matter, photosynthetic rate, yield and quality of the harvested organ. BC use opens important doors for the sustainable management of agriculture in Colombia. It can be considered in production systems exposed to heavy metals such as vegetables and perennial species, in order to reduce the impact of these substances on human health.

The common bean is susceptible to drought conditions and the evaluation of plant responses to low water availability can be difficult. The quantification of chlorophyll fluorescence as a sensitive trait to environmental stresses is an important alternative in the characterization of drought-susceptible genotypes. The objective of this study was to evaluate mainly the use of chlorophyll α fluorescence (maximum efficiency of PSII (F_v/F_m), photochemical quenching (qP), non-photochemical quenching (NPQ)) and rapid light-response curves (RLCs) (initial slope of the curve (α), minimum saturation irradiance (I_k) and maximum relative electron transport rate (ETR_max)) parameters as tools for the identification of susceptible or tolerant bush bean cultivars to water deficit stress conditions in two different phenological stages. Using a randomized block design in a factorial arrangement, five bush bean cultivars (Cerinza, Bachue, NUA35, Bacata and Bianca) were evaluated under water deficit conditions by the suspension of irrigation for 15 days from 40 to 55 Days after Emergence (DAE) (vegetative stage) or 50 to 65 DAE (reproductive stage). The results showed that F_v/F_m and NPQ recorded the highest variation due to water deficit conditions, especially in the vegetative stage. The greatest reductions in F_v/F_m (0.67) and NPQ (0.71) were evidenced in cultivar NUA35 compared to its control plants (0.78 and 1.07, respectively). The parameters obtained from RLCs showed that cultivar Bacata registered the lowest α (0.17) and I_k (838.19 μmol∙m⁻²∙s⁻¹) values compared to its control plants (α 0.23; I_k 769.99 μmol∙m⁻²∙s⁻¹). Differences were only obtained in ETR_max in the reproductive stage (50–65 DAE) in which cultivar NUA35 reached values of 158.5 in stressed plants compared to control plants (251.22). In conclusion, the parameters derived from RLCs such as α and I_k can be used as tools to identify drought susceptibility in the vegetative stage, whereas ETR_max can be used in the reproductive stage. In addition, PSII photochemistry (F_v/F_m and NPQ) can also help to understand the agronomic responses of common bush bean cultivars to drought conditions.

A field experiment was conducted for 2 years (2019 and 2020) to determine the response to the application of Biochar (BC) obtained from the coffee pulp in combination with chemical fertilization (CF) in coffee trees. The established treatments were the edaphic application of different doses of BC (0, 4, 8, and 16 t ha⁻¹) and levels of CF (0, 33, 66, and 100% of the nutritional requirements) on the physical (bulk density (ρ_a), stable aggregates), chemical (nutrient availability), and biological (respiration) properties of soil from a coffee crop. Regarding the physical properties, it was mainly observed that BC doses of 8 or 16 t ha⁻¹ reduced ρ_a (0.82 and 0.83 g cm⁻³, respectively) and increased the aggregation status (96.5% and 96.84%, respectively) in comparison to 0 t ha⁻¹ in 2020. The chemical properties showed that the application of 16 t ha⁻¹ BC decreased about 60% of the exchangeable acidity (EA) compared to the control (0 t ha⁻¹) whereas the pH (4.96 and 4.92) and organic carbon (OC) (4.41 and 4.59) were higher than in the control soil (EA: 0.58 and 0.54 meq/100 g; pH: 4.63 and 4.55; OC: 4.17 and 4.32% in 2019 and 2020, respectively). Soil respiration (biological property) strongly increased (around 50–60%) with the combination of 66% CF and BC doses between 8 and 16 t ha⁻¹ in both years. Doses between 8 and 16 t ha⁻¹ BC of the coffee pulp can improve the quality of soils for coffee cultivation and provide an alternative and more sustainable amendment that may help reduce chemical fertilization.

Climate change has resulted in an increasing frequency of the phenomenon “La Niña,” generating prolonged periods of waterlogging and low light. The objective of the present study was to evaluate the effects of two abiotic stresses: shading (65%) and waterlogging, and their interaction on fluorescence parameters of chlorophyll a in lulo (Solanum quitoense var. septentrionale) seedlings. A completely randomized design with a factorial arrangement was implemented. The first factor consisted of two levels of light (with and without shading). The second factor were four levels of duration of the waterlogging period (0, 3, 6 and 9 days), for a total of 8 treatments with three replicates. The response variables were recorded at 6, 12 and 18 days after the application of the waterlogging treatments began. Measurements of relative water content (RWC), electrolyte leakage, chlorophyll content and chlorophyll a fluorescence were recorded. The lulo plants appeared to be more susceptible to waterlogging than to shading, with a lower RWC when waterlogged 6 and 9 days, presenting damage at the level of photosystem II from day 3, causing a decrease in the chlorophyll content. The plants flooded under shading had a greater tolerance to this factor than those cultivated in full light. The techniques of quantification of the chlorophyll a fluorescence, especially the maximum quantum efficiency of the PSII, the effective photochemical quantum yield of PS II and the photochemical quenching were useful tools that characterized the lulo seedlings under stress conditions.

Water deficit is one of the main abiotic stressors in crop production. The development of strategies to improve plant tolerance to water deficits has gained importance. Biochar application can be considered an alternative to mitigate abiotic stress. The use of coffee pulp to produce biochar could be a novel strategy for improving drought tolerance in coffee crops. Coffer plants cv. ‘Castillo’ were grown in pots or PVC pipes filled with silt loam soil in two separate experiments to evaluate the effect of coffee pulp biochar application on physiological responses under water deficit conditions. Four different biochar doses (0, 4, 8, and 16 t · ha^-1) were used. A water deficit was imposed through progressive reduction irrigation (25%, 50%, 75%, and 90% of water lost via evapotranspiration). The leaf gas exchange, maximum quantum yield of PSII (F_v/F_m), biomass, and water status were measured. Reduced irrigation negatively affected the F_v/F_m, leaf gas exchange, biomass, and water status. Biochar (8 t ha^-1) increased photosynthesis in both well-irrigated plants (6 µmol m^-2 s^-1) and with reduced irrigation (3.5 µmol m^-2 s^-1) compared to 0 t ha^-1 biochar (reduced irrigation: 1.8 µmol m^-2 s^-1 and well irrigated: 3.9 µmol m^-2 s^-1). In conclusion, 8 t ha^-1 biochar can be a recommended practice for coffee production, not only to capture carbon and reintroduce it to the soil, but also to alleviate the effects of moderate water deficit. In future investigations, biochar application can be evaluated as an alternative to soil management or coffee plant nutrition, and its interaction with drought stress scenarios.

Applying coffee pulp biochar (BC) can be a complementary practice to the application of chemical fertilizers (CF) of crops; however, little evidence of its combined effects on coffee cultivation has been reported. A field trial was carried out during two evaluation years (2019 and 2020) to analyse the effect of the application of different BC doses (0, 4, 8 and 16 t/ha) in combination with four levels of fertilization (0, 33, 66 and 100% of the nutritional requirements) on physiological responses of 3-year-old coffee (Coffea arabica L. var. Castillo) trees. The results indicated that trees with 0 t/ha BC and 0% CF showed the lowest values in all the physiological variables studied (gs = 269.9 and 126.8 mmol/m2/s; Chl = 61.7 and 54.7 At-leaf readings; yield = 0.21 and 0.22 kg of dry parchment coffee (DPC)/tree for 2019 and 2020, respectively). Coffee trees treated with 8 t/ha BC and CF levels of 100% registered the highest results in gs (424.9 and 366.9 mmol/m2/s), Chl (71.1 and 69.8 At-leaf readings), yield (0.41 and 0.57 kg of DPC/tree) in 2019 and 2020, respectively. In conclusion, the application of BC from coffee pulp, especially at a dose of 8 t/ha, generates a positive effect on yield, gs, leaf nutrient concentration and Chl of coffee trees. The use of BC can be an alternative to complement the mineral nutrition of commercial coffee crops to help reduce the application of CF.