Biochar improve plant yields: results of pot experiment on lettuce and tomato

Objectives and Materials and Methods Biochar soil amendment is globally recognized as a strategy to improve soil fertility and to mitigate climate change. However, recently published researches, highlighted as the biochar effects on crops are more dependent by the site characteristics (climate, soil and other environmental parameters), than the intrinsic biochar characteristics, chemical and physical. In this view, the soil fertility could constrain the expected beneficial biochar effects. In our research, we have applied different levels of soil fertility to assess the effects of the biochar amendment on lettuce (Lactuca sativa L.) and tomato (Solanum lycopersicum L.). The experiment was done on pot in a greenhouse during summer 2014. Lettuce plants were grown on poor soil (in term of carbon content and nitrogen content) (PS), poor soil plus biochar (PSB), poor soil plus compost (PSC) and poor soil plus compost and biochar (PSCB). Tomato plants were grown on poor soil (PS), poor soil plus biochar (PSB), rich soil (in term of carbon content and nitrogen content) (RS) and rich soil plus biochar (RSB). Each treatment was replicated 10 times. The biochar was obtained from the carbonization of orchard pruning residues and it was applied at rate of 65 g kg-1 dry weight of soil. The compost used was a commercial product (composted olive mill wastes) and it was applied at rate of 50 g kg-1 dry weight of soil . The lettuce and tomato plants were fully irrigated through the experimentation until harvest, after 9 weeks. Morphological traits of six plants for each treatment were weekly recorded and analyzed by Image J software. In detail, for lettuce the following leaves parameters were taken: number, area, length, width and perimeter; for tomato the measurements were taken on number of leaflets and compound leaves, stem height and branching. At harvest, the following tomato fruits parameters were measured: number, length and diameter. At the end of experiment, stem and root biomass allocation (fresh and dry weights) of lattuce and tomato plants were determined. Leaf water potential, gas exchange and chlorophyll content were measured during the experimentation on five randomly selected plants for each treatment. Results and Conclusion The lettuce experiment demonstrated that the morphological plant traits, both above and below ground, increased in plants grown in PSB, PSC and PSCB, compared to PS. Ecophysiological traits indicated that the transpiration rate, stomatal conductance, leaf assimilation rate potential and water leaf potential were significantly higher in PSB respect to PS, while no significant differences were found between PSC and PSCB. The tomato experiment demonstrated a not so evident biochar effects on morphological and ecophysiological plant traits among substrate treatments. Our results indicated that biochar added to non-fertile soil increase yield of lettuce, thus, biochar could effectively be used to implement low-input cropping systems. On the other hand, biochar shows neutral/negative effects on tomato yield, without adding benefits to high-inputs crops as recently observed in field experiment.