Agriculture Reference
In-Depth Information
reduce the potential for soil N losses in the autumn. The difference in ef-
fect between systems was likely due to cooler temperatures and slower
decomposition (or cover crop uptake) after late-broccoli. In comparison
to previous laboratory research, it was demonstrated that wheat straw in-
corporated with broccoli crop residue could signifi cantly lower SMN via
N immobilization, (relative to incorporating crop residue alone) after 8
weeks of incubation [11]. Previously, cereal straw immobilized 35 kg N
ha
-1
within the fi rst month after incorporation with caulifl ower crop resi-
dues in the fi eld [12]. It has been estimated that straw incorporation can
result in the net N immobilization of 64 kg N ha
-1
after two months [45],
or 39 to 44 kg N ha
-1
after one year [20], and reduce the amount of NO
3
-
-N leached by 27% after a year [45]. The current study has suggested that
the OCA-straw treatment after the early-broccoli system can reduce SMN
concentrations by 57 to 96 kg N ha
-1
, which could otherwise be lost during
autumn.
The OCA-oil treatment appeared to result in consistent N immobiliza-
tion after both early- or late-broccoli systems (Figure 1). Compared to
the typical grower practice (CR-control), the OCA-oil treatment had 53
to 112 kg ha
-1
less SMN, thus 30% to 50% less SMN could be available
for losses from the top 30 cm soil layer during the autumn after broccoli
harvest. This fi nding was consistent with previous fi eld research, which
found that oily food waste application in autumn reduced soil NO
3
-
-N
by immobilization and lowered the potential for N losses by 47 to 56 kg
N ha
-1
in the top 60 cm of soil [26]. Furthermore, a previous laboratory
study suggested that OCA-oil immobilized more SMN than OCA-straw
or OCA-yard, when incorporated with broccoli crop residue [11]. The rate
of used cooking oil decomposition was synchronous with that of broccoli
crop residue, whereas yard waste or wheat straw decomposed slower than
broccoli crop residue or used cooking oil [11]. Because decomposition of
more recalcitrant substances is more limited at low temperatures than that
of easily decomposed material [43], the OCA-oil is likely the most prom-
ising material to reduce the potential for soil N losses due to its readily
decomposable and labile matter. Thus, OCA-oil may be the most suitable
amendment tested, because broccoli can be harvested anytime from early
August to late October in southern Ontario.
