See more from this Session: Organic Farming Impacts: Environmental, Social, Soil Quality, Soil Management, and Cultivar Selection
Monday, November 1, 2010: 9:00 AM
Long Beach Convention Center, Room 203A, Second Floor
The applicability of traditional N monitoring approaches has not been fully demonstrated within organic vegetable cropping systems. Over 4-yr, we monitored crop N status within on-farm and experiment station trials in western Oregon, USA. Indicators included: preplant, in-season, and postharvest soil nitrate-N; potentially mineralizable soil N (Nmin, aerobic incubation at 22 oC), crop N uptake without current season N addition, and petiole nitrate-N. Early-season soil nitrate tests were the simplest and most useful of the indices. Early season soil nitrate-N values above the PSNT threshold (25 to 30 mg kg-1; 0-30 cm depth) indicated N sufficiency. Aboveground crop N uptake on unfertilized plots on established organic farms was typically 150 to 200 kg N ha-1. Potential Nmin (aerobic incubation) was 2 to 3x greater in soils with 5+ yr. organic history vs. soils from nearby fields under transitional or conventional management. We recommend in-season monitoring of soil nitrate-N to adjust organic N fertility management practices to meet site-specific need.