Agriculture Reference
In-Depth Information
The lower spring wheat grain yield compared to the CR- or CRN-
control in 2011 after the OCA-straw or CC-oat treatment (Figure 3) may
have been an allelopathic result, because straw mulch often reduces sub-
sequent wheat yields [47]. Considering that wheat seed in the OCA-straw
treatment germinated and established a cover crop after broccoli harvest,
the continuous cereal cropping from autumn to the subsequent summer
may have accumulated phytotoxins or pathogens in the soil [47], which
lowered the grain yield in 2011. Variation in environmental conditions be-
tween years likely contributed to the severity of phytotoxic or pathogenic
factors. It is also possible that plant available N concentrations were not
suffi cient for optimal spring wheat yield in the OCA-straw and CC-oat
treatments. In a previous study, which incorporated cereal straw with cau-
lifl ower crop residues, a pattern of autumn N immobilization was followed
by N re-mineralization in the following spring [12]. However, a different
study found no apparent re-mineralization even one year after straw incor-
poration in the fi eld [20].
The lack of effect on spring wheat harvest parameters from the OCA-
yard treatment (Figures 2 and 3) may be related to the limited effect on
SMN after broccoli harvest in autumn (Figure 1). Similarly, limited autumn
N immobilization and no consistent N re-mineralization were found fol-
lowing the autumn incorporation of green waste compost or sawdust with
caulifl ower or leek crop residues [12,44]. It was suggested that rye, leek,
or lettuce production may not be negatively affected following autumn
caulifl ower crop residue incorporation with compost or straw amendment
because plant N uptake or dry matter accumulation were generally similar
between amendment and crop residue alone treatments [12], which was
similar to the present OCA-yard results.
Considering that autumn N immobilization occurred in the OCA-oil
treatment (Figure 1), yet spring wheat harvest parameters were generally
not affected (Figures 2 and 3), it is possible that N losses may be reduced
during a period of high risk for losses, without negatively affecting the
subsequent crop. It is therefore suggested that the OCA-oil after broccoli
harvest may be a better N management practice than the typical practice of
the CR- or CRN-control. Although N was immobilized during the autumn
after broccoli harvest, it appeared that OCA-oil did not conserve more N
in the soil compared to the CR-control for subsequent spring wheat use
