Agriculture Reference
In-Depth Information
more sustainable agricultural practices, which are focused on soil N man-
agement after vegetable harvest, is necessary.
Cole crop (
Brassica
vegetables), in particular, produce optimal yields
with high N applications, ranging from 270 to 550 kg N ha
-1
for broccoli
(Brassica olecerea
var
italica
L.) [4,6-9]. Cole crop residues may leave
≈100 to 330 kg N ha
-1
in the fi eld at harvest [2,3], and post-harvest mineral
N losses are more related to crop residue N rather than N fertilizer remain-
ing in the soil [3]. Considering that 35 to 60% of broccoli crop residue
N has been found to mineralize in controlled incubation studies [10,11],
and that the crop residue may contain up to 330 kg N ha
-1
[1], then up to
198 kg N ha
-1
would be mineralized in the fi eld after harvest from broc-
coli crop residue [11]. Thus, cole crop residue poses a signifi cant risk for
N losses due to the large quantity of mineralizable N in the post-harvest
season.
Amending the soil with organic C material has the potential to reduce
soil mineral N (SMN) concentrations through N immobilization [11,12].
By redirecting organic C materials from waste streams, a new sustain-
able method of utilizing these materials could be developed. Some high
C materials, which are expected to be readily available for vegetable pro-
ducers in Ontario, are wheat straw, yard waste, or used cooking oil. For
example, winter wheat typically has 1.4 Mg ha
-1
of straw residue [13]. Up
to 326,000 ha
-1
of winter wheat was harvested in Ontario in 2010 [14].
Also, 400,000 Mg yr
-1
of leaf and yard waste has been estimated from
Ontario residential collection [15], and approximately 450,000 Mg of oily
food waste is produced annually in Ontario [16,17]. Considering that the
estimated total production of broccoli, cabbage, and caulifl ower in Ontario
was on 4147 and 4247 ha
-1
in 2010 and 2011 [18], respectively, there is
potential for incorporating the organic C waste materials as amendments
for N management after cole crop production.
Research has demonstrated that SMN concentrations may be reduced
via N immobilization by the applications of wheat straw [19-21], yard
waste [22-24], and oily food waste [16,25,26]. In the aforementioned stud-
ies, immobilized N was derived from fertilizers or indigenous SMN. The
synchrony of cole crop and organic C material decomposition is crucial for
the immobilization of N derived from crop residue. In an incubation study,
N derived from broccoli crop residue was immobilized by the addition of
