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Journal of soil science and plant nutrition

versão On-line ISSN 0718-9516

Resumo

LOBOS ORTEGA, I; ALFARO, M  e  MARTINEZ-LAGOS, J. Soil nitrogen contribution to grasslands and its implication for nitrogen use efficiency. J. Soil Sci. Plant Nutr. [online]. 2016, vol.16, n.2, pp.310-322.  Epub 04-Maio-2016. ISSN 0718-9516.  http://dx.doi.org/10.4067/S0718-95162016005000027.

In pasture systems of southern Chile, nitrogen (N) fertilization is mostly carried out without considering soil N supply, while seasonal N plant uptake is partially accounted for. These aspects are fundamental to correctly decide N fertilization. The aim of this work was to determine soil N contribution to grasslands yield in southern Chile and its implication for N use efficiency. Three treatments were distributed in a completely randomized block design with four replicates. A negative control treatment without N application and a positive control without N deficiency (450 kg N ha-1) were considered. An optimized treatment was also used, so that the total amount of mineral N applied as fertilizer was only that necessary to account for the arithmetic difference among plant uptake and N soil supply, resulting in the application of 171 kg N ha-1 only. Soil mineralization was high (241-934 kg N ha-1) and strongly affected by soil available N (VIP > 0.8). The 450 kg N ha-1 treatment produced 1,726 kg DM more than the 171 kg N ha-1 treatment. Nevertheless, this increase was associated to the application of an extra 279 kg N ha-1, so that the extra yield was produced at a 6 kg DM kg-1N efficiency. This value was one third of that showed by the optimized treatment, which was1.8times more efficient in the use of N than the 450 kg N ha-1 treatment, on average. Results suggest that it is possible to adjust pasture’s N fertilization considering soil N contribution via mineralization, and that this improves resources efficiency while maintaining pasture productivity.

Palavras-chave : Soil available nitrogen; fertilization; mineralization; soil budget.

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