Determining the Environmental Optimum Rate of Fertilizer N for Irrigated Crops in the Semiarid Prairies

IPNI-2014-CAN-SK45

29 Apr 2016

2015 Annual Interpretive Summary


Nitrous oxide (N2O) emissions from soils are known to be significantly affected by the timing and intensity of precipitation/irrigation events. Indeed, emission intensity generally follows what has been described as an event-based/background pattern wherein the most intense emissions are associated with some sort of triggering event. The primary triggering events are: snow melt accompanying an increase in temperature during the spring thaw; precipitation events following the application of N fertilizer; and large, early- to mid-season rainfall events that can trigger denitrification of inorganic N in the soil. In general, late-season precipitation events do not trigger large N2O emissions as, by then, the available N pool has been largely depleted by the growing crop.

Field plots were established at the Canada-Saskatchewan Irrigation Diversification Centre (CSIDC) near Outlook, Saskatchewan in 2014. The main treatment consists of a split application of urea applied at rates of 0, 55, 110, 165, or 220 kg N/ha, with half the fertilizer applied prior to seeding (broadcast and incorporated) and the remainder applied as a topdressing just prior to bolting. Additional treatments included (i) side-banded applications of urea applied at planting at rates of 110 and 220 kg/ha; and (ii) broadcast applications of urea applied and incorporated prior to seeding at rates of 110 and 220 kg/ha. Cumulative (seasonal) N2O emissions were calculated by performing an area-under-the-curve analysis of the daily flux versus time, expressed as day of the year data.

In general, N2O fluxes measured during the 2015 growing season were generally smaller than they were in 2014, but still followed an event-based and background pattern as being typical of the semi-arid prairies. Cumulative N2O emissions were significantly impacted by fertilizer placement in both 2014 and 2015, though the effect was inconsistent (i.e., whereas emissions were lower for the broadcast application compared to the concentrated side-band application in 2014, the reverse was true in 2015. This suggests that wetter conditions (such as existed in spring 2014) are required to induce and maintain denitrification activity in the sub-surface band. Cumulative N2O emissions were significantly impacted by the timing of the fertilizer application — with emissions being lower for the split N application compared to a single application at seeding in both years. Likewise, N2O emissions in both years were significantly and positively affected by N application rate. This research study will continue for a third year during 2016.