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

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.