Biochar e carvão ativado do endocarpo do coco utilizados como condicionadores de um solo cultivado com alface (Lactuce sativa)

Abstract

Soil fertility for being one of the factors that can limit crop acting, makes farmers to periodically apply synthetic fertilizers to the soil to maintain adequate levels of plant essential nutrients. However, this practice increases production costs and can promote contamination of soil and groundwater by excess doses of fertilizers. To minimize this problem, it is indicated to increase the capacity of the soil to retain and available these nutrients to the plants for a longer period, incorporating organic matter into the soil. However, depending on the chemical and physical properties of this organic matter, this material is rapidly decomposed thus losing its effect on the soil over time. Thus, it is indicated the use of materials that are resistant to oxidation, as biochar and activated carbon. These biocarbons (biochar and activated carbon), by exhibit a very slow decomposition, have a very high porosity and surface area and because they have functional group on their surfaces, can act in the increase of the carbon stock and the cation exchange capacity of the soil for many years, increasing the fertility of the soil over time, which may result in the reduction of the need for synthetic fertilization. And yet, through its pores, it can provide shelter and protection to soil microorganism. Based on this, the objective of this research was to evaluate the changes in fertility, soil microbiological indicators and plant productivity after the incorporation of biochar and activated carbon in the soil. For this, were apply six doses of biochar and activated carbon in the soil, leaving it at rest for 245 days and maintaining soil moisture at field capacity. After this period, lettuce seedlings of the cultivar '' Elba '' were planted. The experimental design was in randomized blocks, in a 2 x 6 factorial scheme, with two types of biocarbons (biochar and activated carbon) and 6 doses (0 Mg ha-1, 15 Mg ha-1, 30 Mg ha-1, 45 Mg ha-1, 60 Mg ha-1and 75 Mg ha-1) of biocarbons, using 5 replicates, totaling 60 experimental units. Of the 71 days after transplanting of lettuce seedlings, was perform hasvest plant, assessing height plant (ALT), number of leaves (NF), fresh shoot mass (MFPA), fresh root mass (MFR), dry shoot mass (MSPA) and root mass (MSR). Were also determined the leaf contents of calcium (Ca), magnesium (Mg), potassium (K) and phosphorus (P). In relation to the soil, samples of soil were collected from each treatment to perform the following chemical and microbiological analyzes: pH, Ca, Mg, P, K, exchangeable aluminum (Al+3) and potential acidity (H + Al); total soil organic carbon (TOC), microbial biomass carbon (CBM) and microbial respiration (C-CO2). With the result of this data were get the values of the effective cation exchange capacity (CTCef), cation exchange capacity at pH7 (CTCpH7), base sum (SB), base saturation (V), microbial quotient (qMic) and metabolic quotient (qCO2). It was verified in the soil that the values of K, Ca, P, COT, CBM and qMic had significant interaction (source x dose). All these variables increased their values according to the increase in doses, being that, among the biocarbons used, the activated charcoal promoted higher changes in Ca, P and TOC contents and biochar in K, CBM and qMic values. For the isolated source factor, it was observed that H + Al and CTCpH7 were higher in the treatment with biochar and V was higher in the soil with activated carbon, indicating that the activated carbon was more efficient in reducing the potential acidity of the soil and, consequently promoted better soil fertility. The dose factor was significant for pH, Mg, H + Al, CTCpH7, SB and V, showing a tendency of increase in the pH, Mg, SB and V variables with the elevation of the biochar and the values of CTCpH7 and H + Al with increasing doses. In relation to the lettuce plants, interaction (dose x source) was observed for leaf contents of K and P, indicating higher values of P in the plants treated with activated carbon and higher K content in those cultivated with biochar in the soil. Activated carbon was responsible for the higher leaf yield and MFPA, reflecting the greater changes in the fertility of the soil treated with this biocarbon. The increase of the biocarbon doses promoted an increase in ALT, NF and MFPA values, relating this growth and production to the changes that occurred in the soil. These results showed that both biochar and activated carbon have the potential to improve soil properties, resulting in higher plant productivity. Since activated carbon promoted a larger production of lettuce plants, probably due to the greater changes in soil fertility.