Nutrient acquisition and eucalyptus growth affected by humic acid sources and concentrations

Abstract

Humic acid (HA) can increase eucalyptus growth due to its biostimulant effect and improvement in plant nutrient uptake. Magnitude of these stimuli varies according to the source, chemical composition, presence of bioactive fragments, and concentration of HA. The aim of this study was to evaluate the effect of HA sources and concentrations on dry matter, accumulation and uptake efficiency (UpE) of nutrients for eucalyptus seedlings cultivated in nutrient solution. A randomized block experimental design was adopted, with four replications, in a 3x4+1 factorial scheme, in which three sources of HA (HA-L1 and HA-L2, derived from different commercial HA extracted from leonardite with 0.5 mol L -1 NaOH and 0.5 mol L -1 KOH, respectively, and HA-Com, which was extracted from compost with 0.5 mol L -1 KOH) were combined with four concentrations of C-HA (5, 10, 25, and 100 mg L -1 ) as well as a control treatment in which eucalyptus was cultivated without HA. Eucalyptus seedlings were grown for 20 days, maintaining three plants per pot. At the end of the experiment, production of shoot dry matter (SDM), root dry matter (RDM), and total dry matter (TDM); the Root: Shoot dry matter ratio; and the accumulations of N, P, K, Ca, B, Cu, Fe, and Zn in the shoot and root were evaluated as well as the UpE of these nutrients by the seedlings. Maximum production of SDM was reached at the concentrations of 14 and 13.5 mg L -1 of C-HA, for HA-L1 and HA-Com, respectively. The RDM increased with the use of HA-Com, with optimal concentration of 55 mg L -1 of C-HA. Accumulation of Fe in the eucalyptus shoot decreased in HA-treated pots, compromising Fe translocation from the root to the shoot. Regardless of HA source used, Cu accumulation by plants diminishes as C-HA concentration increases. A greater growth of eucalyptus at concentrations lower than 15 mg L -1 of C-HA occurs more through the stimulus to shoot and root growth than due to greater acquisition and UpE of nutrients by plants. Use of high concentrations of C-HA requires greater concentration of some micronutrients in the nutrient solution tested. Key words: Nutrient uptake. Bioactivity of humic fragments. Organic-metallic complexes. Uptake efficiency of nutrients. Humic substances. ResumoO ácido húmico (AH) pode aumentar o crescimento do eucalipto devido a seu efeito bioestimulante e aumento da absorção de nutrientes pelas plantas. A magnitude desses estímulos varia conforme a fonte, composição química, presença de fragmentos bioativos e concentração de AH. Objetivouse, assim, avaliar o efeito de fontes e concentrações de AH na massa seca, aquisição e eficiência de absorção (EAbs) de nutrientes por mudas de eucalipto cultivadas em solução nutritiva. O experimento foi realizado em delineamento de blocos casualizados, com quatro repetições, em esquema fatorial 3x4+1, sendo testadas três fontes de AH (AH-L1 e AH-L2, derivados de diferentes produtos comerciais de AH, tendo como material de extração leonardita, sendo extraídos com NaOH 0,5 mol L -1 e KOH 0,5 mol L -1 , res...

Humic Acid Improves Zn Fertilization in Oxisols Successively Cultivated with Maize–Brachiaria

“…The HA used in the experiment was extracted from Leonardite through a 0.05 mol L −1 KOH solution [ 24 ]. The main HA properties are described as follows: pH: 9.7, E4/E6 ratio: 4.84, C: 354.9 g kg −1 , N: 5.3 g kg −1 , Zn: 76.3 g kg −1 [ 10 , 17 ]. The Zn source was the heptahydrate zinc sulfate (ZnSO 4 ·7H 2 O) pure per analysis reagent [p.a.]).…”

“…Indirect effects of HS are related to the modifications in the growing medium in response to humic fertilization [ 11 , 12 ]. In soil, HA may complex Zn [ 7 ], improving Zn nutrition and plant growth [ 17 ]. Complexation of Zn by organic ligands is relevant to improve Zn uptake by plants, considering that the organometallic complexes increase Zn content in soil solution and Zn diffusion from solution to cell root surface as well [ 4 , 7 , 10 , 14 ].…”

“…Humic acid effects on plants also rely on the properties of HA’s structure-organic functional groups-function [ 15 , 17 ]. The positive effects of humic acid on maize or brachiaria were already reported, as well as the residual effects of humic fertilization on brachiaria after successive cuttings [ 8 , 19 ].…”

Irrigation frequency and vermiculite proportion in substrate for Eucalyptus grandis seedling

“…In 2015, the planted area covered 5.56 million hectares, which stands for 71.9% of the total forestry area (Felippe et al, 2016). It is a forestry species of high economic relevance for Brazil (Morais, Silva, & Rosa, 2018). Among Brazilian states, Mato Grosso do Sul stands out for its flatter terrain, which favors mechanized silviculture, and for having high-permeability soils.…”