Uso do biochar e de resíduos de caulim na mitigação dos efeitos do déficit hídrico em mudas de Jurema-preta (Mimosa tenuiflora (Willd.) Poir).

Abstract

The semi-arid region is characterized by the potential of natural resources, such as wood for energy purposes, commonly used in the production of charcoal, but generating waste (charcoal dust) that is often not used. The wealth of minerals also stands out, including kaolin, the exploitation of which causes diverse environmental impacts, with the accumulation of piles of waste. Alternatives that mitigate these aforementioned impacts can be adopted, such as making use of waste from both production processes. In this context, this work aimed to evaluate the potential use of kaolin residue and biochar in substrate composition, and their effects on gas exchange, growth and quality of black jurema (Mimosa tenuiflora) seedlings, under both water deficit and non-deficit. The materials used in the production of the substrates were soil (S), cattle manure (CM), kaolin residue (KR), and biochar (B). The experiment was conducted in a shaded environment at the Forest Nursery of the Center for Health and Rural Technology (CSTR/UFCG), and was arranged in a completely randomized design (CRD), 4 x 2 factorial scheme, corresponding to four substrates [S1: S (75%) + CM (25%); S2: S (60%) + KR (15%) + CM (25%); S3: S (60%) + KR (15%) + B (25%); S4: S (45%) + KR (30%) + CM (15%) + B (10%)] and two water regimes [(without water deficit (80% cv) and with water deficit (40% cv)], with four replicates, totaling 32 plots. At 120 days after the start of treatments, were evaluated: stomatal conductance (gs), transpiration rate (E), photosynthesis rate (A), internal CO2 concentration (Ci), water use efficiency (WUE), carboxylation efficiency (A/Ci), relative water content (RWC), leaf water potential ( w), seedling height, absolute growth rate (AGR), stem diameter, height/diameter ratio (HDR), biomass production and seedling quality index (SQ/). It was found that, regardless of the substrate used, water deficit negatively affected gas exchange, growth, biomass production and seedling quality. However, the substrate containing soil, cattle manure and biochar favored gas exchange, while the compound composed of soil, cattle manure and kaolin residue provided greater growth and biomass production, regardless of the imposed water condition. The addition of kaolin residue to the soil and cattle manure enabled greater biomass production of seedlings subjected to both water conditions (water deficit or non-deficit). It is recommended to use substrate S4, as it contains a higher concentration of kaolin residue (30%) to replace soil, combined with cattle manure and biochar.