Fertilizing a Nectarine Orchard
Scientific evidence on the impact of organic fertilizer on the dynamics of root production and lifespan in commercially-grown nectarine trees has been published by researchers at the Dipartimento di Colture Arboree, Bologna, Italy and the Department of Horticulture at The Pennsylvania State University. Published in the academic journal Tree Physiology, the paper reports results from the fertilizer trials carried out between 2003 and 2006 in a commercial Prunus persica L. (nectarine) orchard, planted in 2001 and located in the Po valley, northeastern Italy.
The research provides evidence that shifting from mineral fertilizers to organic fertilizers may improve soil properties and nutrient availability, leading to changes in both root production and lifespan of the fruit trees bearing smooth-skinned nectarines. Why is this important to commercial growers? What does it mean for the backyard orchard enthusiast?
The Po Valley Nectarine Orchard Research
The nectarine orchard trial authors, Baldi, Tosellis, Eissenstat and Marangoni (2010), identified that while many studies have examined forest trees and the effects of nitrogen (N) fertilizers, there have been few studies on the impact of soil nitrate on fruit trees within production horticulture and tree physiology. The horticultural scientists hypothesized that the organic fertilizers affected root dynamics differently to mineral fertilizers. Four replicates of three treatments, unfertilized, mineral fertilized and composted with municipal waste, formed a completely randomized black design.
Planting and aftercare of nectarine trees involves a regime of top dressing and deep soil fertilization. In the nectarine orchard research, the mineral fertilizers included phosphorous (P) and potassium (K) applied only at planting and nitrogen (N) split into two applications, one at 40 days after full bloom and the other in September each year. The compost fertilization constituents of P, K and N were split similarly to the mineral fertilization applications.
Comparisons of the root growth and survival of the commercial nectarine trees were made at 20-day intervals during the growing seasons using the horticultural scientific method of minirhizotron. The minirhizotron technique involved the scientists inserting a clear Plexiglas tube into the soil next to each tree that allows digital video data of the root dynamics to be collected. While data about root production was being captured, measurements of the amount of tree fruit yields at the nectarine harvest were measured. Each winter, the diameters of the tree trunks and fresh weight of pruning wood were also measured.
Baldi and colleagues (2010) found that new roots production was increased by applications of compost and that the root lifespan was longer in compost-treated trees compared to the control of no fertilizer applied and the other experimental condition of application of mineral fertilizer. Analysis of across the annual growing seasons in the commercial nectarine orchard in Italy found that average root life span was positively associated with soil nitrate concentration.
Relevance of Tree Physiology Research for Commercial Orchards
The authors concluded, "this work helps to clarify the complex ways the shifts in fertilization practices may affect fruit tree root function and dynamics" (p.1380). The take home messages from the science for commercial fruit growers with a nectarine orchard is that compost can stimulate root production and this is independent from the effects of increasing soil nitrate. Lifespan of nectarine trees is related to soil nitrate concentration.
Soil organic matter or SOM has been decreasing in most growing regions. Recycling and composting of municipal solid waste and organic materials from agri-food industries has contributed to rebuilding the SOM pools and is also replacing chemical fertilizers.
Importance of Soil Organic Matter for Backyard Orchard Growers
In The Royal Horticultural Society Vegetable and Fruit A Definitive Guide to Successful Growing (2008), the advice on container grown nectarine trees is to use a liquid feed or a slow release fertilizer during the growing season. Once the tree has reached its expected maximum size, repot and replace the growing medium with compost, cutting away any pot-bound roots. Larger nectarine trees grown in the ground are recommended to be mulched annually and during the growing season to benefit from a high-potash fertilizer, such as tomato fertilizer, every fortnight until fruits are of full size.
SOM is equally important for gardeners with backyard nectarine trees, both the compact varieties in containers and those planted directly into the ground. Hessayon (1990) covers the cultivars of Early Rivers, Humboldt, Lord Napier and for under cover growing Pine Apple. The availability of compost from municipal waste facilities or home garden composting can both reduce landfill waste and offer a cost-effective 'living' fertilizer that can be applied to nectarines in place of chemical fertilizers and with an increased root production to mineral fertilizers.
References
E. Baldi., M. Toselli., D.M. Eissenstat and B. Marangoni. Organic fertilization leads to increased peach root production and lifespan. Tree Physiology, 30, 1373-1382. 2010.
D.G. Hessayon. The Fruit Expert. 1990. England: pbi Publications
M. Pollock (Ed.). The Royal Horticultural Society Vegetable and Fruit Gardening. The Definitive Guide to Successful Growing. 2008. London: Dorling Kindersley Limited.
Susan Morris - Susan Morris, Scottish food and drink business manager, organic gardener, author and editor
