Agriculture Reference
In-Depth Information
(Figure 1). A reason may be that little or no NO
3
-
-N leaching occurred in
the CR-control treatment; the soil textures with 24% to 25% clay (loam or
sandy clay loam) (Table 1) would support a slower rate of NO
3
-
-N leach-
ing than sandier soils. Alternatively, the soil may have provided substan-
tial quantities of plant available N regardless of the treatment, as suggested
earlier. Thus, future experiments should investigate the fate of broccoli
crop residue-derived N as infl uenced by the used cooking oil in N limited
soil, sandy soil, or trace the crop residue-derived N into the subsequent
crop via
15
N studies.
A pattern of N immobilization followed by re-mineralization with used
cooking oil or “fat oil grease” amendments has been found in previous lab-
oratory [11] and fi eld [26] research. In the present study, N immobilized
in the OCA-oil after broccoli harvest in autumn could have re-mineralized
for the subsequent spring wheat plant uptake. Net N mineralization has
also been observed in the spring following an autumn application of oily
food waste [26]. Previous research has found corn yields to be similar be-
tween un-amended treatments and autumn amendments of “fat oil grease”
[16]. Based on the maximum economic rate of N applied to the corn crop,
it was found that N availability to corn was not affected by autumn appli-
cation of “fat oil grease” [16]. The authors suggested that suffi cient time
was probably available for decomposition of the C material when it was
applied in autumn [16]. Also, researchers have found little concern for det-
rimental accumulations of oily food waste and observed that the waste can
promote water stable aggregation [25]. However, the spring application of
“fat oil grease” prior to corn production resulted in net N immobilization
during the spring [26], reduced corn yields up to 23%, and the additional
requirement of 60 kg N ha
-1
to offset corn yield declines [16]. Thus, “fat
oil grease” or OCA-oil applied in the autumn did affect the following corn
yield [26] or spring wheat yield.
3.3.5 ECONOMIC ANALYSIS
The potential environmental benefit of reduced N losses must be consid-
ered in combination with economic outcomes. Although the OCA-straw
and CR-removal treatments showed some potential for reducing autumn
