Agriculture Reference
In-Depth Information
3.3.3 SOIL MINERAL NITROGEN IN THE SUBSEQUENT
SPRING AND SUMMER
The 0-90 cm profile was investigated to assess the quantity of SMN in the
soil depth accessible for the crop, at spring wheat pre-plant and harvest.
Prior to spring wheat planting, the SMN concentrations were generally
not affected by the post-broccoli-treatments (Figure 1). Because the 2011
spring had a one and a half times higher precipitation (512 mm from Feb-
ruary to May) compared to 2010 (343 mm from February to May), it is
possible that SMN was subjected to different mechanisms of concentra-
tion reduction depending on the year. In the CR-control, NO
3
-
-N leaching
may have occurred to a greater extent in 2011, thereby lowering spring
SMN concentrations. Although NO
3
-
-N leaching could have also occurred
in the OCA treatments, the amendments may have immobilized N in the
spring, also lowering SMN concentrations. Additionally, the condition of
high soil water content combined with the presence of a readily decompos-
able C source and SMN, denitrification could have been favored. Given
the possibility of different mechanisms of SMN concentration reduction
across treatments, further investigation is required. Future research should
focus on 15N labeled crop residue to investigate the infl uence of the OCA
treatments on the fate of the crop residue-derived N.
At spring wheat harvest, 0-90 cm SMN results indicated that the post-
broccoli-harvest treatments did not lower SMN, compared to the CR-con-
trol (Figure 1). However, the application of N fertilizer at spring wheat
pre-plant (CRN-control) left a larger quantity of SMN at harvest compared
to most other treatments (Figure 1).
3.3.4 SPRING WHEAT PRODUCTION
Overall, the 2011 spring wheat grain contained 49 kg N ha
-1
less N and had 1.6
Mg ha
-1
less yield than 2010 (Figures 2 and 3). Early- and late-broccoli sys-
tems did not have different spring wheat yield or N contents. The yield ranged
from 0.9 to 3.4 Mg ha
-1
(Figure 3), similar to the average Ontario spring wheat
yields of 3.5 Mg ha
-1
in 2010 and 2011 [46]. The N harvest indices ranged
from 55% to 90%, and did not vary by treatment (data not shown).
