Resumo

SALVAGIOTTI, Fernando; CASTELLARIN, Julio Manuel; FERRAGUTI, Facundo Javier  e  PEDROL, Hugo Miguel. Economic optimal nitrogen rate as affected by yield potential and nitrogen supply in the northern pampas. Cienc. suelo [online]. 2011, vol.29, n.2, pp.199-212. ISSN 1850-2067.

Maize is the most important summer cereal in the Northern Pampas of Argentina where soils present severe nitrogen (N) deficiency. N fertilization in maize must optimize available N at planting (Nds=Nds_inic+fertilizer) in order to assure maximum profitability and avoid excessive applications that may harm the environment. The objectives of the present study were to: i) test the capability of the quadratic-plateau (CP) and spherical (Esf) models for estimating crop yield response to N fertilization; ii) determine critical thresholds of Nds (UCNds) in crops that showed high (AR) and low (BR) grain yield. Finally, in these situations, economical optimal N rate (DOE) and N use efficiency at DOE (EA_DOE) were calculated at different Nds. The analysis of 39 N fertilization experiments (site-year-SA) showed that CP and Esf, accurately fitted the relationship between fertilizer N and grain yield analyzing the whole network. However, CP showed some limitations for representing the asymptotic shape of the response curve in some particular SA. UCNds were 137 and 161 kg N ha^-1 for BR and AR, respectively. Using a 10:1 maize:N price ratio, DOE was 99 and 78 kg N ha^-1 and EADOE was 28 and 17 kg grain kg N^-1 in AR when Ndsinic was 40 and 80 kg N ha^-1. On the other hand, in BR, for the same Nds_inic, DOE was 71 and 49 kg N ha^-1 while EADOE was 15 and 8 kg grain kg N^-1. When maize: price ratios were more unfavorable, DOE and EA_DOE decreased, but with a greater magnitude in BR. The results of this study highlight the importance of defining crop potential productivity in maize for diagnosing crop N fertilization in addition to soil analysis for achieving larger profitability with greater fertilizer use efficiency.

Palavras-chave : Spherical model; Quadratic-plateau model; Response thresholds; Nitrogen use efficiency.

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