Resumo

SEVILLA, G.H  e  AGNUSDEI, M.G. Efecto del agregado de fósforo y nitrógeno en el crecimiento de cultivos de alfalfa en rebrotes de primavera y verano en un suelo vertisol de Entre Ríos. RIA. Rev. investig. agropecu. [online]. 2016, vol.42, n.1, pp.93-101. ISSN 1669-2314.

The effect of soil P and N availability on the spring-summer (spr06 - sum07) biomass accumulation (BA) of alfalfa (dormancy group 6) in a Vertisol soil was evaluated. In a complete randomized block design (n = 2) dressings of 0 or 100 kg P ha-1 each autumn and 0 or 150 kg N ha-1 were applied at the beginning of spr06 and sum07, resulting in the combinations: 0P0N (natural condition), 100P0N (P non-limiting) y 100P150N (P-N non-limiting). Aerial BA and leaf - stem composition in successive harvests on independent plots, % intercepted photosynthetically active radiation (PARi) were determined. Lineal fits were performed for radiation use efficiency (RUE) estimation. Curvilineal functions were adjusted to describe the associations between the following variables BA and thermal time (TT), % PARi and TT, leaves and stems BA. Data were processed by ANOVA and Tukey (a= 0.05) using SAS. The water balance was generally negative and lower in sum07. BA ceiling was reached ~500 °Cd in 100P0N-100P150N, with maximum growth rates (GR) of 0.42-0.45 g DM m-2 ºCd-1 during spr06, respectively. Average spr06 GR almost doubled those of sum07. The RUE for 100P0N-100P150N (0.60 g DM MJ-1) averaged one-third of the expected potential for the species. The %leaf of 100P0N-100P150N decreased to a plateau of ~50% at “early bud stage” (~500 °Cd, 13-14 nodes, or maximum %PARi) during spr06, whereas stayed relatively stable at ~50% in the rest of the treatments. The BA of leaves did not increase above 90 g stem DM m-2. Regardless of the level of nutrients, 500 °Cd would be the maximum grazing interval recommended to prevent senescence losses and favor pasture physiology during spring-summer. Locally original ecophysiological parameters applicable for management decisions and modeling purposes, as well as to better understand the productive potential of alfalfa in the region are provided.

Palavras-chave : Medicago sativa; Biomass accumulation; RUE; Nutrients.

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