Boron, copper and zinc levels in the nutrient solution and in two soils for maize

Realizaram-se experimentos em casa-de-vegetação, em condições de solução nutritiva e em dois solos (Areia Quartzosa e Podzólico Vermelho-Amarelo), utilizando-se cultivar de milho AG-303, com 2 plantas por vaso. O experimento em solo foi instalado em blocos ao acaso com 4 níveis de cada nutriente, B:0, 0,35; 0,70 e 1,40; Cu: 0; 0,5; 1,0 e 2,0 e Zn: 0; 0,7; 1,4 e 2,8 (mg ´dm POT.-3´ de terra) e 4 repetições. Cada unidade constituiu-se de um vaso de plástico com 3,2 ´dm POT.3´ de terra. Antes da calagem, ao final do período de incubação e após a colheita das plantas, Cu, Zn, Fe e Mn foram extraídos do solo com DTPA-TEA e, somente após a colheita, com DTPA-TEA, HCl 01M, Mehlich 1 e Mehlich3; o B foi extraído com água quente nas 3fases. O experimento em solução nutritiva foi instalado em delineamento inteiramente casualisado com 5 níveis de cada nutriente, B: 0; 0,25; 0,5; 1,0 e 2,0; Cu: 0; 0,015; 0,020; 0,025 e 0,030 e, Zn; 0;0,05; 0,10; 0,20 e 0,30 (mg L-1) e 4 repetições. Em ambos os experimentos, os nutrientes foram fornecidos como: ácido bórico, sulfato de cobre e sulfato de zinco, para B, Cu e Zn, respectivamente. Avaliou-se o efeito desses nutrientes, através dos parâmetros: produção de material vegetal seco (MVS), concentração e nutrientes absorvidos pela parte aérea das plantas de milho. A adição de B, Cu e Zn proporcionou aumentos nos teores desses nutrientes no solo e na planta, entretanto, apenas o Zn influenciou significativamente a produção de MVS. No experimento em solução nutritiva, a dose 0,1 mg L-1 de Zn foi suficiente para se obter uma produção de MVS estatisticamente semelhante à dose máxima. No experimento em solo, a dose 2,8 mg dm-3 de Zn foi a que propiciou a maior produção de MVS. O extrator que melhor se correlacionou com o Cu aplicado aos solos foi o DTPA-TEA. Nenhum dos extratores estudados se correlacionou com o Cu absorvido pelo milho. O extrator que melhor se correlacionou com o Zn aplicado aos solos foi o HCl 0,1MMaize is traditionally the most planted cereal, being cultivated in practically all the regions of Brazil. Although the country is one of the world biggest producers of maize, the national productivity is still one of the lowest of the continent. The culture productivity is intimately related with an adequate plant nutrition and the micronutrients have high importance, since they have less studies than the macronutrients. The dry matter production of and the nutrients absorption by the plants can be different in function of the nutrient levels in the nutrient solution and in each soil type. Based on this, the experiments took place at greenhouse conditions in nutrients solution and in two soil types (Sand soil and Red-yellow Podzol), using maize (AG-303), with two plants per pot and evaluating levels of each of the micronutrient: boron, copper and zinc. The experiment in soil had a statistical design of randomized blocks with four replications. Each experimental unit was constituted by plastic containers with 3.2 dm3 of soil The blocks were constituted by four levels of each micronutriente, in mg dm-3 of soil, being for B: 0, 0.35, 0.70 and 1.40; for Cu: 0, 0.5, 1.0 and 2.0 and for Zn: 0, 0.7; 1.4 and 2.8. The experiment in nutrient solution was installed in entirely randomized design with four replications. Five levels of each nutrient were used, in mg L-1, being for B: 0, 0.25. 0.5, 1.0 and 2.0, for Cu: 0, 0.015; 0.020, 0.025 and 0.030 and for Zn: 0, 0.05, 0.10, 0.20 and 0.30. The nutrients form used were: boric acid (H3BO3), copper sulfate (CuSO4.5H2O) and zinc sulfate (ZnSO4.7H2O), for B, Cu and Zn, respectively. Before liming, at the end of the incubation period and after harvest of maize, the nutrients Cu, Zn, Fe and Mn were extracted from the soil with DTPA-TEA and only after the harvest, the nutrients were extracted by: DTPA-TEA, HCI O.IM, Mehlich1 and Mehlich3. Boron was extracted with hot water, before the liming, at the end of the incubation period and after harvest. The results of the experiment in nutrients solution, and of the experiment in soils as wall, were evaluated with the parameters: dry matter production of above ground part of maize plants, nutrient concentration and the amount of absorbed nutrients. The boron, copper and zinc addition provided increases in the nutrient contents in soil and in plant, but, only zinc influenced significantly the dry matter production. ln the nutrient solution experiment, the level 0.1 mg L-1 of Zn was enough to obtain dry matter production statistically the sarne to the maximum levei. ln the soil experiment, the level 2.8 mg dm-3 of Zn had the highest dry matter production. The extractant which better correlated with the applied copper to the soils was DTPA-TEA. None of the tested extractants correlated with the copper absorbed by maize. The extractant which better correlated with the zinc applied to the soils was HCl 0,1M. The zinc extracted from the AQ soil with Mehlich1 extractant correlated better with the zinc absorbed by maize. ln the PV soil that correlation was better for the HCI O.IM and DTPA-TEA extractant. The DTPA-TEA extractant only had a good correlation in the PV soi