Potential Nitrogen Contributions from Legumes in Pacific Northwest Apple Orchards

Abstract

As costs for nitrogenous fertilizers become increasingly expensive, organic and conventional apple producers recognize the potential to integrate leguminous plants in the orchard agro-ecosystem to contribute to N nutrition. We evaluated alfalfa as a drive row cover and white clover as an under tree living mulch. Both impacted nitrogen dynamics and tree performance. Alfalfa did not adversely affect tree growth and yield while potentially contributing to tree N nutrition. The white clover living mulch, clearly impacted soil nitrate and tree performance. Clover co-location with tree roots enabled N contribution from both tops and roots.

Growing Legumes in Orchard Alleys as an Internal Nitrogen Source

“…With only an estimated 7% of the nitrogen in the added alfalfa residue mineralized and measured in the soil over 21 d, it is difficult to assess the effects of the treatments on long term mineralization. This is considerably lower than a previous estimate of 43% using the same method on another site with white clover (Mullinix and Granatstein, 2011). The clover may have been easier to degrade than the alfalfa because of clover having more leaves and less resistant stems.…”

“…In addition, they typically result in far more light reaching the orchard floor, which creates the opportunity to grow plants on the orchard floor for specific purposes, such as flowering species to support beneficial insects or legumes for nitrogen fixation (Granatstein and Sanchez, 2009). This could occur in the tree row, as a ''living mulch'' or in the drive alley, where the legume biomass could be mowed in place, mowed, and blown on to the tree row, or incorporated into the soil (Mullinix and Granatstein, 2011). In the Pacific Northwest United States, nitrogen is the macronutrient most often needed on a yearly basis to sustain fruit production (Neilsen and Neilsen, 2003).…”

“…Leguminous species can be planted in the drive alley to produce a significant portion of the nitrogen needs of the orchard (Goh and Ridgen, 1995;Sanchez et al, 2006) by mowing the vegetation and blowing it onto the tree row where it mineralizes and releases available N over the tree roots (Marsh et al, 1996). This may be particularly attractive for organic producers who do not have access to low-cost organic nitrogen sources (Mullinix and Granatstein, 2011) as legume nitrogen is normally the least expensive organic N source per dry kilogram N. Biologically fixed nitrogen also has a smaller carbon footprint than synthetic N which is commonly made from natural gas using considerable energy (Camargo et al, 2013). Growers who have used or are currently using legumes in orchards normally till the soil to prepare a seedbed and then mechanically incorporate the legume biomass into the soil later in the season (Proebsting, 1958).…”

Establishing peach trees for organic production in Utah and the Intermountain West

“…Black et al, (2010) showed that root growth of tart cherry in orchards managed with a grass alleyway was primarily constrained to the area below the herbicide strip, confirming the need for weed control in orchards managed with grass alleyways. Locating legumes in the alleyway versus the tree-row, as in this study, may be critical to reducing competition in the alleyway, hence optimizing the benefits of orchard-grown legumes and reducing tree susceptibility to weed pressure (Granatstein and Sánchez, 2009;Mullinix and Granatstein, 2011).…”

“…Stasiak and Rom (1991) indicated that competition effects may be short lived in establishing peach orchards, however. In addition, locating the legumes in the alleyway versus the tree-row may be critical to reducing competition and optimizing benefits (Granatstein and Sánchez, 2009;Mullinix and Granatstein, 2011).…”