182 Ferrini et al.: Effect of Fertilization and Backfill Amendment on Oak EFFECT OF FERTILIZATION AND BACKFILL AMENDMENTS ON SOIL CHARACTERISTICS, GROWTH, AND LEAF GAS EXCHANGE OF ENGLISH OAK (QUERCUS ROBUR L.) By F. Ferrini1 , A. Giuntoli2 , F.P. Nicese3 , S. Pellegrini4 Abstract. The influence of fertilization and soil amendments on plant growth and leaf gas exchange was monitored on English oak trees (Quercus robur L.) over a 3-year period after planting. The results indicate that shoot growth, leaf area, chlorophyll content, and leaf gas exchange were higher in fertilized plants, especially during the second and third years after planting. However, compost and leonardite were rarely better than the control. Soil physical characteristics were positively influenced by soil amendments, which promoted a better structure and lowered penetration resistance compared to control and fertilization. Key Words. Chlorophyll; compost; humate; photosynthesis; soil characteristics. , and N. Vignozzi4 results. While some authors found an increase in aggregate stability, a shift in pore distribution, or a decrease in bulk density, others found no changes in soil physical properties (Vetterlein and Hüttl 1999). The reason for this discrepancy might be the difference among soil types, and the results might also be affected by the type of organic matter applied. Research on the effects of these products is mostly reported for vegetable and fruit species (Obreza and Biggs 1989; Duval et al. 1998), and their efficacy on woody species in urban environments has not been determined. As to fertilization, there is still a heated debate among Various practices increase root growth by improving soil characteristics and are essential for a successful planting outcome in a stressful urban environment. The most common practices are incorporation of top soil, inorganic soil amendments, or organic soil amendments, such as composted materials. Positive effects from compost as a soil amendment at planting are often found in disturbed areas, where composted materials have demonstrated a certain efficacy, at least in the short term, in improving water retention capacity, organic matter content, soil density, and plant growth (Rakow 1992; Watson 1993; Day and Bassuk 1994; Smalley and Wood 1995; Kelting 1997; Watson and Himelick 1997). Some attention has also been directed toward humic acids and their commercial forms, such as leonardite. The importance of humic substances lies in their ability to contribute to cation exchange capacity (Vetterlein and Hüttl 1999) and to establish nutrients regimes more similar to those of natural ecosystems in ways that cannot easily be mimicked by the use of mineral fertilizers (Greenly and Rakow 1995; Vetterlein and Hüttl 1999). Greater resistance to drought and winter injury has been documented, and accumulation of dry matter has also been attributed to humic acid application. However, results obtained by the addition of humic substances and compost on soil physical properties are contradictory and don’t always result in clearly positive ©2005 International Society of Arboriculture arborists revolving around if, what, when, and how much fertilization is appropriate (Miller 1998, 2003; Marion 2003). At present, because of many contrasting results, there is no consensus on whether fertilizers should be applied to landscape trees (Marion 2003). The aim of the present study was, therefore, to evaluate the effects of backfill organic amendment and fertilization on post- transplant growth and physiological characteristics of Quercus robur L. trees and on soil physical characteristics in an urban park. MATERIALS AND METHODS Plant Material Before budbreak, 48 uniform, 5-year-old, 4 to 4.5 m (13 to 15 ft) tall, 12 to 14 cm (5 to 6 in.) in circumference (mea- sured at 1.3 m [4.3 ft] height), balled-and-burlapped (B&B), grafted English oak (Quercus robur L.) trees were planted in a public park in Florence, Italy. All trees with identical size characteristics were obtained from the same nursery and planted at the same time. Until the late 1970s, the park was used as a rubble dump to fill some drained ponds. The rubble was covered with a 80 to 100 cm (approximately 3 ft) layer of clayey soil. Planting holes were two times the width and one and a half times the depth of the root ball (size of the root ball was 40 to 45 cm [16 to 18 in.] in diameter). Trees were placed in the holes and backfilled with one of the following: 1. excavated soil with 50% composted yard waste obtained through aerobic biostabilization of selected organic residues;
July 2005
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