Avaliação da libertação de azoto a partir de correctivos orgânicos utilizando membranas de troca aniónica e um medidor de clorofila SPAD-502

Nitrogen release from organic amendments assessed by using anion exchange membranes and the SPAD-502 chlorophyll meter

A. Pereira¹, M. A. Rodrigues & M. Arrobas

 

RESUMO

Neste trabalho divulgam-se resultados de experiências em vasos em que membranas de troca aniónica (MTA) foram inseridas directamente no solo para monitorar o teor de nitratos ao longo do tempo, e em que o estado nutritivo dasplantas foi avaliado através de um medidor de clorofila SPAD-502. Na estação quente foi cultivado milho e no período outono-inverno nabiça e centeio. O milho foi semeado a 5 de Junho de 2004 e a nabiça e o centeio a 23 de Setembro de 2004. As plantas foram sujeitas aos seguintes tratamentos fertilizantes: Nutrisoil (Nut); Beiraadubo (Bei); Phenix (Phe); e Vegethumus (Veg), quatro correctivos orgânicos comerciais; estrume de bovino (EB); casca de castanha (CC); nitrato de amónio (NA); e um tratamento sem azoto (T). Os resultados das MTA e os valores SPAD foram relacionados com a matéria seca produzida e o N exportado. Em Junho, na primeira amostragem, a concentração média de nitratos nos extractos das MTA variou entre 18,3 e 239,4 mg L^-1, nos tratamentos CC e NA. Na primeira semana de Agosto, foram registados valores médios de nitratos no solo de 12,9 a 52,3 mg L^-1 nos tratamentos CC e Bei. Na última amostragem, em Setembro, os valores médios de nitratos no solo variaram entre 9,7 e 67,9 mg L^-1 nos tratamentos CC e Nut. As MTA revelaram boa capacidade para discriminar a forma como os diferentes fertilizantes libertaram o azoto ao longo do tempo e como este aspecto condicionou a absorção do nutriente e o desenvolvimento das plantas. Os valores SPAD revelaram-se bons indicadores do estado nutritivo azotado do milho, em condições em que foi possível controlar grande parte da variabilidade experimental. Os valores SPAD estiveram linearmente relacionados com a produção de matéria seca e o N exportado. Nas condições deste ensaio, em que a lixiviação e a desnitrificação foram controladas, as culturas intercalares centeio e nabiça recuperaram o N residual da cultura anterior até próximo do limite da sua senescência por falta de azoto.

 

ABSTRACT

Results from pot experiments where anion exchange membranes (MTA) were inserted into the soil to monitor soil nitrate levels over time, and the plant N nutritional status assessed with a SPAD-502 chlorophyll meter, are reported in this work. Maize was grown in the summer season and turnip and rye in the winter period. Maize was sown on June 5, 2004, and turnip and rye on September 23, 2004. The plants were subjected to the following treatments: Nutrisoil (Nut); Beiraadubo (Bei); Phenix (Phe); Vegethumus (Veg); cow manure (EB); chestnut fruit bark (CC); ammonium nitrate (NA); and control treatment, without N fertilization (T). Two weeks after the maize was sown, soil nitrate levels extracted by MTA ranged between 18.9 and 239.0 mg _L-1 in the CC and Bei treatments, respectively. In the first week of August mean soil nitrate values ranged between 12.9 and 52.3 mg L^-1 in the CC and Bei treatments. In September, the last sampling date, mean soil nitrate levels were found to be in the range of 9.7 and 67.9 mg L^-1 in the CC and Nut treatments. Relationships between MTA and SPAD results with dry matter yield and N uptake were established. The MTA were able to differentiate well as the organic amendments released their N during the season and this aspect influenced N uptake and plant growth. SPAD readings were also a good index of plant N nutritional status. SPAD values were linearly related with dry matter yield and N uptake. In this study, where the pots were managed to avoid nitrate leaching and denitrification, winter grown species recovered the residual N of maize fertilization. At the end of experiment the plants showed senescent leaves with deep N deficiency symptoms.

 

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¹ CIMO – E. S. Agrária, 5301-855 Bragança, Email: angelor@ipb.pt;