The Effect of Intensification on Nitrogen Losses from Diversified Vegetable Farms

The effect of nitrogen fertilizer use on the environment via greenhouse gas emissions and leaching losses has been broadly characterized in agronomic crop production.  However, it has been less well studied in horticultural systems, be they conventional or organic.  This work, initiated in 2014, seeks to quantify nitrogen leaching, emission and plant uptake in conventional, organic and pasture-based rotational vegetable farms along a gradient of production intensity. The three systems presented in this work are 1) conventional, 2) medium-scale organic, and 3) organic high tunnel.  The data presented here are from the first 1.5 y of a 3-y study of a vegetable rotation, consisting of bell pepper and table beet, to date.   Each system was replicated three times. Nitrogen leaching (ammonium and nitrate) was measured using ion exchange resin lysimeters installed at 60 cm depth, replaced every 3 months.  Greenhouse gas emissions (N₂O, NH₃, CO₂, and CH₄) were measured every 2 weeks using a FTIR-based field gas analyzer (Gasmet Technologies, Finland).  Additionally, N mineralization was measured using ion-exchange resin bags placed at 7.5 cm and 22.5 cm deep, replaced monthly, as well as monthly soil sampling at 0-15 cm, 15-30, and 30-50 cm depths.  To date, we find that N fluxes in each system are seasonally dependent.  The findings from this research will helpful in minimizing nitrogen loss from the soil and minimizing the negative impact to the environment.