Effect of rates of boron and of zinc, in different acidity condition of cerrado soil, on soybean crop (Glycine max. (L.) Merrill)

No presente trabalho procurou-se verificar o efeito de doses de boro e de zinco, em diferentes condições de acidez do solo, sobre alguns parâmetros da cultura da soja, tentando estabelecer os níveis críticos e adequados, internos e externos. Para tal conduziu-se dois experimentos em que foram testadas cinco doses de boro (0; 0,2; 0,4; 0,6 e 0,8 ppm B) ou cinco doses de zinco (0; 1,0; 2,0; 3,0 e 4,0 ppm Zn), em três níveis de correção de acidez correspondente a 0; 2,0 e 3,2 t de calcário/ha (PRNT =100%), em um Latossolo Vermelho-Escuro, textura argilosa, originalmente recoberto por vegetação de cerrado, e em condições de casa-de-vegetação. Dentre outros resultados verificou-se que as doses de boro influenciaram a produção de matéria seca da parte aérea e de grãos, nos tratamentos que não receberam corretivo e nos que receberam a dose correspondente a 2,0 t de calcário/ha. Para o zinco houve efeito das doses, nos tratamentos que receberam corretivo. As doses aplicadas que propiciaram a máxima produção de matéria seca da parte aérea e de grãos estiveram entre 0,33 a 0,42 ppm de B e de 1,9 a 2,3 ppm de Zn. Os níveis críticos internos estiveram entre 34 a 56 ppm de B e 36 a 53 ppm de Zn e os níveis críticos externos entre 0,11 a 0,23 ppm de B e 0,27 a 0,37 ppm de Zn; nos níveis de corretivo em que houve efeito das doses de B ou de Zn.The objective of this research was to investigate the effect of rate of boron and zinc, under different soil acidity condition, on some parameters of soybean crop in order to establish the critical and adequate levels (internal and external) of these nutrients. Two experiments were conducted in green-house with five rates of boron (0, 0.2, 0.4, 0.6 and 0.8 ppm B) and of zinc (0, 1.0, 2.0, 3.0 and 4.0 ppm Zn), in three levels of soil acidity amendment corresponding of the 0, 2.0 and 3.2 t lime/ha, using a clay textured Dark- Red-latosol, originally under cerrado vegetation. The rate of boron affected the dry matter and grain yields, in the treatments without liming and in the rate corresponding of the 2.0 t/ha. For the zinc, there was effect of rates in the treatments with addition of lime. The rates of boron affected the dry matter and grain yields in the treatments without lime and with lime equivalent to 2.0 t/ha. As for the zinc, its rate effect was observed in the treatments with addition of lime. The rates of B and Zn, which promoted maximum aboveground dry matter and grain yield, ranged from 0.33 to 0.42 ppm and from 1.9 to 2.3 ppm, respectively. The internal critical levels of B and of Zn varied from 34 to 56 ppm and from 36 to 53 ppm, respectively, and the external critical levels of B and of Zn varied from 0.11 to 0.23 ppm and from 0.27 to 0.37 ppm, respectively; in the treatments with soil acidity amendment in which there was rate effect of B or Zn