Whole almond orchard recycling and the effect on second generation tree growth, soil carbon, and fertility
The grinding and incorporating into soil of whole almond trees, during orchard removal, may provide a sustainable practice that could enhance air and soil quality. Removed orchards are typically either pushed out and burned or ground up and removed. Stored carbon is lost from the orchard site. Woody 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 the grinding up of whole trees with burning as a means of orchard removal. Twenty-two rows of an experimental orchard were used in a randomized blocked experiment with two main treatments, whole tree grinding and incorporation into the soil versus tree pushing and burning. The whole tree grinding did not stunt replanted tree growth. Sampling from plots showed elevated levels of fungal and bacterial feeding nematodes (Tylenchidae) along with associated woody soil aggregates in the grind treatment. Fungal mycelium was readily observed colonizing woody aggregates and significantly more basidiomycetes (mushrooms) were observed in the grind plots. No difference in yield was observed in 2011, however, in 2012 and 2013 (P=0.08) greater yields were observed in the grind treatment when compared to the burn. In 2010, more carbon, organic matter, and a greater cation exchange capacity were initially observed in the burned plots, but by 2012 and 2013 the grind plots had significantly more calcium, manganese, iron, magnesium, boron, nitrate, copper, as well as higher electrical conductivity, organic matter, total carbon, and organic carbon. Soil pH was significantly lower in the grind treatment plots. Leaf petiole analysis in 2013 showed significantly greater levels of nitrogen, potassium, phosphorus, manganese, and iron from trees growing in the grind treatment, while magnesium and sodium levels were significantly less.
Holtz, B.A., Doll, D. and Browne, G. (2016). Whole almond orchard recycling and the effect on second generation tree growth, soil carbon, and fertility. Acta Hortic. 1112, 315-320
carbon sequestration, carbon recycling, plant nutrition