Resumo

SADEGHIAN KHALAJABADI, Siavosh. COFFEE CROPS RESPONSE TO NITROGEN ON DIRECT SUNLIGHT AND SEMI-SHADOW AND ITS RELATIONSHIP WITH THE SOIL'S ORGANIC MATTER. Rev. Fac. Nac. Agron. Medellín [online]. 2011, vol.64, n.1, pp.5781-5791. ISSN 0304-2847.

Soil's organic matter (OM) can be an important source of nitrogen (N) for plants. Through the development of this investigation the response of coffee in full sunlight and under light shade to the supply of N and its relationship to OM was evaluated. For this, 20 plantations exposed to direct sunlight and 12 under semi-shade were selected in 25 municipalities in Colombia, with different content of OM (from 4 to 28%). Two treatments were evaluated, one with N, P, K and Mg and the other without N, which was applied in doses of 240 kg ha^-1 yr^-1 as urea. In the sunlight exposed plantations, the effect of N deficiency on production was expressed from the second year and gradually increased. It reached close to 50% reductions in four years. The plantation under semi-shade registered a similar pattern but of lesser magnitude. The relationship between OM and relative yield was adjusted to a quadratic model, whose behaviour was similar for both systems, with an average inflection point of 18%. The supply of N decreased the soil's pH and increased loss of K+ in the two systems. In sunlight-exposed coffee plantations the foliar contents of N, Mg and Mn increased by the effect of N, while the concentrations of P, K, Cu and B decreased. The N fertilization of the semi-shade plantations only increased the leaf content of Mn and reduced the B.

Palavras-chave : Soil fertility; calibration; nitrate; acidity and foliar nutrients.

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