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


01 Apr 2014

Project Description

The primary goal of this project is to identify the environmental optimum rate of fertilizer N (i.e., the rate that provides the greatest yield increase with the lowest FIE) for irrigated crops.

The specific objectives are to:
    1. Evaluate 4R-based BMPs for irrigated canola;
    2. Identify and demonstrate the environmental optimum fertilizer N rate
    3. Assesss the occurrence and importance of diurnal variations in N2O emissions on seasonal estimates of total GHG emissions;

Global food demand is increasing rapidly and irrigated agriculture is poised to play a prominent role in meeting these demands. This is especially true in the western Canadian prairie region where there is the potential to see large increases in the number of irrigated hectares—provided that existing water supplies are proven reliable (as in the Lake Diefenbaker Development Area) and the economic and environmental sustainability of irrigated cropping systems can be assured. Indeed, sustainable development of the Province’s land resources is the foundation on which agricultural production is based, and is key to ensuring future food security. Moreover, establishing the environmental sustainability of crop production practices has become a critical aspect of market access (e.g., the European Union Renewable Energy Directive) and, for crop production practices on the Canadian prairies, N2O emissions constitute a key sustainability indicator.

Nitrous oxide is an important greenhouse and ozone-depleting gas that is emitted from both terrestrial and aquatic ecosystems as a natural consequence of microbial activities. However, the amount of N2O being generated has increased dramatically as a result of human activities—with agricultural activities comprising the largest source (60–70%) of these emissions (Desjardins et al. 2005). Not surprisingly therefore, reducing N fertilizer application rates has been proposed as one strategy for reducing greenhouse gas emissions associated with crop production (Climate Action Reserve, 2013).

The magnitude of soil-emitted nitrous oxide is strongly governed by prevailing soil-water regimes, and in the Canadian semi-arid prairies direct emissions of N2O tend respond to increasing levels of N fertilizer in a linear but frequently non-significant fashion (Rochette et al. 2008). However, relative emissions have been reported to increase rapidly at fertilizer rates in excess of crop requirements for portions of the landscape where water stress is minimal (Izaurralde et al. 2004). This implies that fertilizer-induced emissions (FIE) on irrigated land—where moisture stress is minimized by the application of water—in the semiarid prairies may be a disproportionately high contributor of FIEs of nitrous oxide. On the other hand, yields are substantially higher on irrigated compared to non-irrigated fields, which could result in greenhouse gas intensity values that are similar or even lower for irrigated compared to non-irrigated crops produced on the Canadian prairies. However, data from irrigated land in the semiarid prairies is extremely limited and though we are closing some of the gaps in our knowledge of FIEs in irrigated cropping systems, information regarding how these emissions respond to fertilizer application rate and estimates of the agri-environmental optimum rate for fertilizer N for irrigated crops in the semiarid prairies is entirely lacking.

Climate Action Reserve. 2013. Nitrogen Management Project Protocol, Ver. 1.1. Climate Action Reserve, Los Angeles, CA.
Desjardins, R. L., Verge´ , X., Hutchinson, J., Smith, W., Grant, B., McConkey, B. and Worth, D. 2005. Greenhouse gases. Pages 142-149 in A. Lefebvre, W. Eilers, and B. Chunn, eds. Environmental sustainability of Canadian agriculture: Agrienvironmental indicator report series Report #2, Agriculture & Agri-Food Canada, Ottawa, ON.
Izaurralde, R.C., Lemke, R.L., Goddard, T.W., McConkey, B.G., and Zhang, Z. N2O emissions from agricultural toposequences in Alberta and Saskatchewan. 2004. Soil Sci. Soc. Am. J. 68:1285-1294.
Rochette, P., Worth, D., Lemke, R.L., McConkey, B.G., Pennock, D.J. and Desjardins, R.L. 2008. Emissions of N2O from Canadian Agricultural soils using an IPCC Tier II approach: 1 – Methodology. Can. J. Soil Sci. 88:641-654.

Irrigation is a key component of the continuing development and intensification of crop (and animal) production on the prairies—with a related benefit to agricultural manufacturing and processing—and the Lake Diefenbaker Development Area has great potential for irrigation expansion and development. Indeed, in 2012 the Irrigation Branch of the Saskatchewan Ministry of Agriculture indicated that there was potential for a 500% increase in the number of irrigated acres in Saskatchewan.

Opportunities for incresed nitrogen use efficiency under irrigated conditions clearly exist; however, inappropriate management of nitrogen fertilizers can result in greatly increased N2O emissions—signaling reduced nitrogen use efficiencies. Thus, although irrigation and nitrogen management can be complementary, there is little information available regarding 4R-based BMPs that address irrigated cropping systems of the type common to Saskatchewan and the western Canadian prairies.

The proposed research will address this knowledge gap by determining whether it is possible to synchronize the agronomic (yield) and environmental (N2O emission minimization) optimum N rate for irrigated canola. In addition, this project will provide critical data regarding both the timing (single vs. split application) and placement (broadcast & incorporated vs. side-banded) of fertilizer N in an irrigated cropping system. Results from this study will assist producers in making informed decisions about N fertilization, help reduce their “carbon footprint” and take advantage of environmental marketing opportunities to improve on-farm profitability by contributing to agri-food marketing strategies that promote environmental quality and sustainability.

Research Plan:
Field plots will be established at the Canada-Saskatchewan Irrigation Diversification Centre (CSIDC) near Outlook, SK. The plots will be set up in a randomized complete block design with five (5) nitrogen treatments replicated four (4) times. The nitrogen treatments will be: 0, 55, 110, 165, and 220 kg N/ha. Nitrogen fertilizer source (urea) and the choice of timing and placement will be guided by results from an ongoing study at CSIDC by Dr. Tomasiewicz. For example, results from the first (2012) season showed that a split application which is broadcast and incorporated lowered the N2O emissions – with no difference in yield. Other nutrients (P and K) will be supplied following recomendations based on the results of a spring soil test. The test crop is canola, and to avoid confounding effects associated with the previous crop, the canola will always be seeded into wheat stubble (i.e., plot location will change from year to year).

Greenhouse gas (N2O, CO2, CH4) fluxes will be monitored on a semi-continuous basis using the FTIR-AFC system developed at the U of S. The system consists of a Fourier Transform InfraRed (FTIR) gas analyzer interfaced to a series (n = 20) of automated flux measurement chambers (AFC). The number of measurements that can be made in a single day depends on both the time required to obtain an accurate flux measurement (ca. 12–15 min) and the number of chambers interfaced to the gas analyzer. Thus, to increase temporal resolution, two FTIR-AFC systems will be depolyed – with each interfaced to 10 chambers. Consequently, each chamber will be sampled 8 to 10 times per day, resulting in excellent temporal resolution of the daily and seasonal greenhouse gas flux estimates. [Note: system 1 will be deployed in blocks 1 and 2 while system 2 will be deployed in blocks 3 and 4.] Each system will be calibrated against a standard gas three times daily to account for any measurement bias associated with the analyzers. Each automated chamber is also connected to temperature and moisture probes, the data from which are recorded during each flux measurement period.

In addition, at two of the N rate levels (110 and 220 kg N/ha), both timing (all the N applied pre-seeding vs. 1/2 applied pre-seed + 1/2 before bolting) and the placement (broadcast & incorporated vs. side-band) of the fertilizer N will be varied. The GHG fluxes associated with these treatments (n = 28) will be measured using traditional vented, non-flow through, non-steady state chambers that are manually sampled throughout the season. Gas samples will be collected and stored in pre-evacuated 12-mL Exetainer vials and shipped to Saskatoon for analysis using gas chromatography. Manual sampling will be conducted 2-3 times weekly when emission potentials are high (i.e., following fertilizer applications, irrigation and/or high rainfall events, and during spring thaw), and with reduced frequency through the balance of the season until the soils freeze. [Note: placing manually sampled chambers in the plots with the automated chambers will allow us compare the effect of sampling intensity on the seasonal flux estimates used to calculate fertilizer-induced emissions (FIE).] Headspace gas samples will be collected at only one time point (15 to 30 min after the chamber is placed on the base—depending on logistical constraints) during chamber deployment.

In addition to a basic soil chacterization (textural analysis; soil pH, EC, and organic C & N), ancillary measurements will include: above ground biomass; grain yield, grain & residue N; spring and fall soil profile mineral N (nitrate & ammonium; 0–120 cm); and nitrate concentration in the drainage water.