Decomposição in situ de folhas senescentes de pereira (Pyrus communis L. cv. Rocha)

In situ decomposition of pear (Pyrus communis L. cv. Rocha) senescent leaves

C. Neto¹, C. Carranca¹, A. de Varennes², J. Clemente³ & J. Sobreiro⁴

 

RESUMO

Estudou-se a variação da perda de peso e a contribuição das folhas senescentes de pereira (cv. Rocha) para a restituição de azoto (N) ao solo através da técnica dos sacos de decomposição in situ, colocados em Outubro de 2003 à superfície do solo dum pomar situado no Cadaval (Oeste de Portugal). Os sacos contendo folhas senescentes colhidas em pereiras com um ano de plantação e fertilizadas com três níveis de N (0, 10 e 40 kg N/ha), foram recolhidos em Dezembro de 2003, Janeiro, Fevereiro, Maio, Julho e Outubro de 2004 e Março de 2005. No mesmo pomar enterraram-se, em Outubro de 2003, 12 cilindros de PVC, contendo à superfície folhas senescentes de pereiras com três anos de plantação e fertilizadas com 40 kg N/ha de adubo enriquecido com 10% de átomos de ¹⁵N. Os cilindros foram recolhidos em Janeiro, Março, Junho e Novembro de 2004. Determinouse a variação do peso e os teores de N total e enriquecimento em ¹⁵N nos resíduos, e nas amostras de terra avaliaram-se os teores de N “total”, N-inorgânico e carbono (C) orgânico, bem como os nitratos potencialmente lixiviados e adsorvidos em resinas de troca aniónica, em cada data.

A decomposição in situ das folhas senescentes das pereiras ‘Rocha’ jovens variou significativamente com a fertilização azotada após 506 dias. As folhas provenientes da modalidade 0 kg N/ha apresentaram menor peso residual (21% do inicial) e menor teor de N (44% do teor inicial de N) comparativamente com as folhas resultantes das modalidades adubadas com N, no final do período em estudo. Padrão idêntico de comportamento verificou-se na decomposição in situ das folhas das árvores com três anos, colocada à superfície do solo dos cilindros de PVC enterrados. A mineralização do N destas folhas levou à disponibilização do N para as árvores no início do abrolhamento e a partir de Junho, não se tendo observado lixiviação do N mineral produzido.

 

ABSTRACT

The weight loss of one year-old ‘Rocha’ pear senescent leaves and their contribution to nitrogen (N) cycling in the soil, were studied using litter bags. The leaves were collected from trees fertilized with ammonium nitrate, using three N rates (0, 10 and 40 kg N/ha). The litter bags were installed in October 2003, at the surface of the soil, in an orchard located in Cadaval (Western Portugal). Litter bags were removed from the soil in December 2003, January, February, May, July and October 2004, and March 2005. Leaves were also collected from three-year old ‘Rocha’ pear trees fertilized with 40 kg N/ha using ammonium nitrate, double enriched with 10 atom% ¹⁵N. These were placed at the surface of non-disturbed soil cores, from cylinders buried in the same orchard in October 2003. The soil cores were removed from the soil in January, March, June and November 2004, and were analysed for the evolution of leaf weight, leaf N and ¹⁵N enrichment. Inorganic and “total” soil N, ¹⁵N enrichment, and organic carbon (C) in the soil and leached N captured in anion- -exchange resins were also determined at each sampling time.

The decomposition of one-year old ‘Rocha’ pear senescent leaves was affected by N applied to the trees, after 506 days of decomposition in the field. The leaves from the 0 kg N/ha plots had less final weight (21% of the initial) and leaf N content (44% of leaf initial N content) at the end of the studied period, when compared to the leaves from the plots fertilized with N. Decomposition of senescent leaves from three-years-old trees at the soil surface in PVC cylinders showed a similar pattern. N mineralization in these leaves showed the potential availability of inorganic N at the beginning of trees bud break and after June, without nitrate leaching in the soil.

 

 

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¹ Estação Agronómica Nacional, Quinta do Marquês, Av. República, 2784-505 Oeiras, email: claudia.neto@netvisao.pt

²Instituto Superior de Agronomia, Tapada da Ajuda, 1349-017 Lisboa, email: adevarennes@clix.pt

³Central de Frutas do Painho, EN 115 – km 6, Dagorda, 2550-417 Vermelha Cdv, email: tecnico@cfpainho.com

⁴Escola Superior de Biotecnologia - UC, Pólo de Caldas da Rainha, Rª Mestre Mateus Fernandes, 2500-237 Caldas da Rainha, email: justino.sobreiro@netvisao.pt