Estudos sobre a nutrição mineral do milho: II - deficiências de macronutrientes na variedade Piranão

Corn plants, Piranão variety, were grown in nutrient solution, complete and with omission of one macronutrient each time, in order to gain information on the effects of treatments on growth, symptoms of deficiency, and mineral composition of the leaves. The following symptoms of deficiency were obtained: Nitrogen -- plants underdeveloped; "V" shaped chlorosis beginning in the older leaves followed by drying and necrosis; Phosphorus - older leaves dark green with a purple hve; Potassium - plants underdeveloped; marginal chlorisis and necrosis in the older leaves; iron induced chlorosis in the younger leaves; Calcium - plants very underdeveloped due to death of apical merystem; younger leaves showing tip and marginal chlorosis and afterwards necrosis and break down of the tissue; wide whitish areas in the younger leaves; Magnesium - plants very underdeveloped; internerval chlorosis in older leaves first, proceeding to the young ones; Sulfur - absence of marked symptoms, except for a slight chlorosis in the younger leaves. Dry matter production obeyed the following decreasing order: Complete, minus S, minus P, minus K, minus Mg, minus N and minus Ca. Ears were obtained only in treatments complete and minus S. Top/root ratio decreased according to this order: minus S, complete, minus K, minus Mg, minus N, minus P and minus Ca. The macronutrient content for the treatment complete was the following respectively for lower and upper, leaves: N - 2.76 and 2.52%; P - 0.59 and 0.53%; K - 2.25 and 2.26%;Ca - 2.17 and 1.85;Mg - 0.82 and0.66;S - 0.38 and 0.32. The values of the element corresponding to each treatment were: N - 1.84 and 1.22 (that is: lower leaves in the minus N plants had 1 84% N, whereas the upper leaves in same treatment had 1.22% N; P - 0.14 and 0.17%; K - 0.29 and 0.78%; Ca - 0.29 and 0.05; Mg -0.09 and 0.05%; S- 0.31 and 0.26%.Foram induzidos sintomas de carência de macronutrientes no milho, var. Piranão, exceto no caso do enxofre. Os níveis foliares de N, P, K, Ca, Mg e S foram determinados nas plantas sujeitos à nutrição completa e às deficiências de macronutrientes