Agriculture Reference
In-Depth Information
occurred on August 3, 2010 and August 23, 2011. Soil was sampled, as
described above, for mineral N analysis from depths of 0-30, 30-60, and
60-90 cm at spring wheat planting and harvest.
3.2.1 NITROGEN MEASUREMENTS
Plant N content (broccoli and spring wheat) was determined by dry com-
bustion method [34] using a LECO CN analyzer (Leco Corporation, St.
Joseph, MI, USA), following grinding with a 2 mm diameter mesh screen
opening on a Wiley Mill (Thomas Scientific, Swedesboro, NJ, USA). Soil
NO
3
-
-N and NH4 +-N concentrations were quantified by the KCl extrac-
tion method [35]. Briefly, 5 g of soil was extracted with 25 mL of 2 M
KCl, shaken for 30 min, filtered and analyzed colorimetrically on an Au-
toAnalyzer3 (SEAL Analytical Inc., Mequon, WI, USA) with high resolu-
tion digital colorimeter to quantify NH4 +-N (method G-102) and NO
3
-
-N
(method G-200). Soil mineral N was the sum of NO
3
-
-N and NH
4
+
-N and
expressed as kg N ha
-1
based on soil bulk density.
3.2.2 ECONOMIC ANALYSIS
The economic analysis was conducted through a comparison of spring
wheat profit margins for each treatment. Profit margins were calculated
by subtracting costs that varied across post-harvest treatments from rev-
enues. Revenues were calculated based on spring wheat yields from each
treatment and the average spring wheat price in Ontario between 2010 and
2011, as reported by the Ontario Ministry of Agriculture Food and Rural
Affairs [36]. Costs that varied included those associated with mulching
residue (all treatments except the CR-removal treatment), residue remov-
al, pre-plant N fertilizer for spring wheat crop, seeding cover crop, and
applying the OCA as listed in the OMAFRA's Custom Rate Survey [37].
Costs associated with the OCA included transportation and application as
well as baling wheat straw. Some assumptions were made regarding the
equipment and the associated rates that would be used to conduct the re-
quired activities on a large field scale. For example, application costs were
