Nutrição mineral e crescimento de mudas de pupunheira (Bactris gasipaes H.B,K), em solução nutritiva, em função do balanço de nutrientes e níveis de salinidade.

Abstract

The optimum growth of plants is reached when the best conditions are proportionated ibr uptake and distribution of nutrients and observed their adjusted proportions. On the other hand, excess of a specific ion as it happens with the Na the and Cl in saline environment can conduct to extreme relationships between such elements and the nutrients, causing reductions in the yield of crops. With the objective of identifying the K/Ca and P/Cl relationships that provide the largest growth of the peach palm {Bactris gasipaes H.B.K.), as well as to evaluate their behavior when submitted to salinity, three experiments were developed in nutrient solution, under greenhouse conditions at the Soil Science Departament — Federal University of Lavras, Minas Gerais state. The experimental design was in randomized blocks, with 9 treatments and 4 replications, for the K/Ca and P/Cl relationships and 7 treatments and 4 replications for the salinity one. In the first experiment the treatments consieed of the following K/Ca relationships: 0.0/ .0; 1.0/2.5; 2.0/2.0; 3.0/1.5; 4.0/1.0; 5.0/0.5 and 6.0/0.0 in mmol L", and two additional treatments with variation in the concentration of Na, constituting the K/Na relationships of 2.0/0.0 and 1.0/2.0. In this last one, part of the potassium was substituted by sodium. In the second experiment, the treatments related to P/Cl relationships were: 0.00/1.50; 0.25/1.25; 0.50/1.00; 0.75/0.75; 1.00/0.50; 1.25/0.25; 1.50/0.00; 1.00/1.00 and 2.00/1.00 in mmol L‘ 1. The 1.00/1.00 and 2.00/1.00 ratios were defined as additional treatments. In the third experiment, the doses of NaCl consisted of: 0.0 Na the and 0.5 Cl; 1 Na and 0.5 Cl (control); 5.0; 15.0; 30.0; 60.0 and 120.0 mmol L". The experimental units were constituted by one vase containing one plant. The height, perimeter at the stem level, leaf area and dry matter of leaves, stipes and roots contents and total accumulation of nutrients were evaluated. The K/Ca ratio of 2.0/2.0 and 3.0/1.5, were the ones that provided larger medium values for leaf area and dry matter of parts of the plant, and this last one was the one that favored more the growth of the plants. In the treatments in which the Na concentration varied, all of the studied variables were negatively affected. The appropriate contents of K corresponded to 14.74 s kS" in the leaves, 19.03 g k3" in the stem and 24.09 g kg" in the roots, while the ones of Ca were 9.91, 9.48 and 7.65 g kg”', in the leaves, stipes and roots, respectively. The largest nutrients accumulation happened in the K/Ca relationship of 3.0/1.5 mmol L". The relationships among the nutrients in the leaves considered appropriate were: KfN = 0.45; K/P = 5.50; K/Ca = 1.50; K/Mg = 4.15; K/S = 5.39; K/Na = 10.35; Ca/P = 3.66; Ca/Mg = 2.78; and Ca/Na = 6.94. The P/Cl relationships with P concentrations starting from 1.0 mmol L", independent of the Cl concentration, presented the largest medium values for the variables of growth, perimeter of the stern, leaf area and dry matter of leaves, stipes and total. The content of P increased, while the one of Cl decreased, with the elevation of the P/Cl relationship. Significant réductions in all of variables were observed when the salinity level was increased, jurtified by negative correlations with the electric conductivité of the growth solution. The addition of Na at 1.0 mmol L”' in the solution provided significant increases in all variables of yowth, while the addition of 5 mmol L", although having reduced the growth in relation to the treatment comrol, was superior than in that é was omitted Na. The contents of the macronutrients varied in function of the salüfity, it P and K in the roots, Ca in the leaves and S in the different parts reduced, while Na and Cl increased in the different parts ofthe plant, and provided increases in the relationships among Na/K, Na/Ca, Na/M3, CI/N, CI/P and CI/S. The accumulation of Na and Cl increased even having happened a drastic reduaion of dry matter production, while the uptake ofthe macronutrients reduced.