Fine roots growth and longevity in a high-density pear orchard on quince C rootstock as affected by nitrogen supply

Root development of quince C (Cydonia oblonga L.) genotype used as a rootstock for pear (Pyrus communis L.), cultivar Abbe Fetel was studied during 2004 and 2005 with the minirhizotron technique. The orchard, located near Bologna (Po Valley, Northern Italy), was planted in February 2003 and spaced 3.8 × 0.9 m. Besides control (unfertilized) trees there were trees fertigated with urea-N and others with an organic soluble N fertilizer. When provided, nitrogen rates amounted to 48 kg N ha-1 year-1. Fine roots were observed with minirhizotrons of 70 cm depth inserted into the soil at 30 cm from tree trunk; root images were taken and analyzed by WinRHIZO Tron MF software. We observed a higher number of new roots in 2004 than in 2005, but in both years root birth mainly occurred in late winter-spring and, with less intensity, in autumn. The distribution of new roots along the soil profile differed in N-fertilized and unfertilized trees. Root longevity was unaffected by N supply but changed over time, being lowest in spring (often less than 20 days) and highest in autumn (often > 100 days). Most (68%) white roots observed at the end of November 2004 were still visible in February 2005 as white roots, a feature that should be favourable for nutrient uptake as soon as spring growth occurs.