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ISHS Acta Horticulturae 1219: VII International Symposium on Almonds and Pistachios

Whole almond orchard recycling and the effect on second generation tree growth, yield, light interception, and soil fertility

Authors:   B. Holtz, G.T. Browne, D. Doll, M. Culumber, M.A. Yaghmour, E. Jahanzad, B. Lampinen, A. Gaudin
Keywords:   carbon sequestration, carbon recycling, plant nutrition
DOI:   10.17660/ActaHortic.2018.1219.41
The grinding and incorporating into soil of whole almond trees, during orchard removal, could provide a sustainable practice that enhances both air and soil quality. We hypothesize that wood debris incorporated into soils could increase organic matter, enhance carbon sequestration, and improve soil quality and tree yield. The objective of this project was to compare on-site grinding up and soil incorporation of whole trees with on-site burning and ash incorporation as a means of orchard removal. In 2008, each treatment was applied to seven replicate plots of an old stone fruit orchard in a randomized block design. An “Iron Wolf,” a 45,454 kg rock-crusher, was used to grind up and incorporate the standing tree rows of the old orchard to a soil depth of up to 30 cm. The grinding incorporated an estimated 67,000 kg of woody biomass ha-1. For the burn treatment, trees were pushed into a pile, burned, and the ash was spread evenly throughout the plot. All replicate plots were re-planted with “bare-root” almond trees in 2009. Significantly greater increase in tree circumference was observed in the grind treatment from 2014-2016 when compared to the burn. Also, in 2016, significantly greater photosynthetically active light interception was observed in the grind treatment. Yields were determined from 2011-2017 and the grind treatment cumulative yield was greater by 1,778.49 kg ha-1 in the ‘Butte’ cultivar. Yields were also determined in ‘Nonpareil’ in 2014, 2016, and 2017 and the grind treatment cumulative yield was 1,120 kg ha-1 greater than the burn yield. Significantly more soil nutrients (calcium, manganese, iron, magnesium, boron, nitrate, potassium, copper), higher electrical conductivity, organic matter, total and organic carbon were measured in the grind treatment soils when compared to the burn treatment. Soil pH was significantly lower in the grind treatment plots. Leaf petiole analysis also revealed higher nutrients (nitrogen, potassium, phosphorus, manganese, and iron) and less sodium and magnesium levels in trees growing in the grind treatment. Bud failure severity was lower on the ‘Carmel’ trees in the grind treatment when compared to the burn treatment. This project demonstrated whole orchard recycling as an alternative to burning in the field or in a co-generation facility. We estimate that over 8,000 ha in California have been ground and incorporated in the last three years.

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