Pó de rocha, biocarvão e inoculação microbiana na produção de mudas de açaizeiro em solo de baixa fertilidade.

Abstract

The association between rock dust, biochar from açaí (Euterpe oleracea Mart.) seeds, and inoculants with native microorganisms may have the potential to improve the quality of low-fertility soils in the Amazon. Thus, the objectives of this study were to: i) determine the nutrient contents in metabasalt rock dust produced in the Carajás Mineral Province, as well as in biochar from açaí seeds; ii) understand the changes in the chemical attributes of low-fertility soil with the application of metabasalt dust, açaí seed biochar, and microbial inoculant; and iii) evaluate the growth, gas exchange, and nutrient uptake in açaí seedlings in soils subjected to the application of these products. The experiment consisted of eight treatments: 1) natural soil; 2) soil + rock dust; 3) soil + biochar; 4) soil + inoculant; 5) soil + biochar + inoculant; 6) soil + rock dust + biochar; 7) soil + rock dust + inoculant; and 8) soil + rock dust + biochar + inoculant. After the experiment, the substrates were evaluated in terms of fertility, and the plants were assessed for growth (120 days), nutrient content in plant tissue, and gas exchange. Rock dust contained several nutrients in levels above those required by Brazilian legislation, including bases (Ca, Mg, and K) and micronutrients such as Fe and Mn. The biochar presented nutrient contents ranging from 0.3 mg kg−1 to 9.4 g kg−1, following the sequence Mo < S < Ni < B < Cu < Zn < Fe < Mn < Mg < Ca < P < K. The experimental results indicated changes in soil fertility, particularly in treatments with rock dust, which increased pH, sum of bases, and base saturation to values of up to 7.5, 8.3 cmolc kg−1, and 91.9%, respectively. In general, plant growth was not favored by the application of rock dust, except when combined with biochar and microbial inoculant, which resulted in height, diameter, and root dry mass increases of up to 54%, 136%, and 45% compared to the control treatment, respectively. Moreover, except for internal CO2 content, all physiological variables showed a reduction, particularly leaf transpiration, which decreased with the application of all treatments. Several treatments promoted higher nutrient levels in plant tissue, including Ca and K, with the application of rock dust and biochar, respectively. The results of this study indicate the potential of the evaluated products for soil acidity correction and increased nutrient availability, but they also suggest adverse effects on plant growth and physiology. Further research is recommended to promote the use of mining by-products and agro-industrial residues for soil improvement in the Amazon.