Nitrogen Dynamics in Organic Processing Potato Production

The increased demand for organically produced potatoes suitable for the processing market, and availability of approved soil amendments, may change the intensity of nutrient use in organic potato production.

Potato yield benefits from compost application have also been linked to improved soil moisture retention. A study conducted in 2003 and 2004 at Brookside, NS and Kentdale Farms, PEI, examined crop response and nitrogen dynamics under organic potato production as affected by contrasting organic amendments.

A commercial compost and a pelletized dehydrated poultry manure product were applied at 300 and 600 kg total N ha-1 to potato variety Shepody and selection A90586-11 (from McCain Produce Inc). Soil N dynamics were monitored using standard soil and petiole sampling techniques, recovery of whole plant samples at topkill, and N sorbed on anion/cation exchange Plant Root Simulator (PRS™) probes (www.westernag.ca) placed in situ in root exclusion cores until hilling. Soil mineral N (ammonium and nitrate) was also measured at harvest.

Crop yields and crop N recovery was not affected by potato variety. In un-amended plots, relatively high tuber yields (26.5 ± 5.3 t ha-1) and crop N recovery (120.3 ± 28.2 kg N ha-1) was reflective of the long rotations (4-yr +) characteristic of organic potato production.

Poultry manure, at the lower rate only, consistently increased yields (+ 4.9 t ha-1 avg.) in both years. These yield gains were matched by the high rate of compost applied in 2004. Poultry manure increased tuber N concentration and decreased tuber specific gravity. Crop recovery of N applied in compost and manure ranged from -1.3% to 1.2% (compost) and 18.2 to 25.4% (manure).

Nitrate remaining in soil after harvest was below regional averages (~60 kg N ha-1) for residual soil nitrate following potatoes, except for manure applied at 600 kg total N ha-1. At all sites, mineral N sorbed on PRS™ probes reflected N released by organic amendments, and was strongly related to seasonal crop N uptake, whether buried for 3 or 30 days after planting (R2 = 0.96 and 0.99, respectively).

Given current premiums for certified organic potatoes, enhancing yields through application of organic amendments appears warranted. PRS™ probes may be an effective tool to address the uncertainty associated with N availability from soil and amendments, and avoid the risks to crop quality and the environment associated with excessive N supply.

Researchers
Derek Lynch, OACC, Department of Plant and Animal Sciences, NSAC
Bernie Zebarth, Agriculture and Agri-Food Canada, Fredericton, NB

Collaborators
Ken Greer, Western Ag Innovations, Saskatoon, SK

Funding Sources
Funding for this project was provided by the PEI Department of Agriculture and Forestry and the NB Department of Agriculture, Fisheries and Aquaculture.