Factors affecting S- methyl cysteine sulphoxide (SMCO) content
in Maris Kestrel kale were studied in field and glasshouse trials.
SMCO is responsible for kale anaemia in ruminants.
Higher plant populations reduced whole plant and stem SMCO in
six trials, especially at harvests after October. Increasing plant
density from 10 to 80 plants /m2 reduced whole plant SMCO in November
or December by approximately 25 %.
Nitrogen (N) fertiliser increased SMCO and dry matter (DM)
yields in six out of seven trials, with SMCO increases ranging from 8
to 68% depending on soil fertility.
There was a high correlation between SMCO (Y) and N (x) levels
in mature kale from different sites (r = 0.92, n =26) . Using the
relationship Y = 7.53x - 3.20, plant N could be measured as an estimate
of the SMCO level.
On free draining soils low in available sulphate at sowing (<12 ppm)
applied sulphur (S) increased SMCO in two out of six trials, although
only at early autumn harvests. On a soil with impeded drainage
(sulphate = 12.5 ppm), S tended to increase (P <0.10) SMCO at a
December harvest.
As the crop aged, SMCO increased especially in leaves. This
was not caused by frosting, but may have been affected by floral
initiation, as stems with small inflorescences had higher (P <0.05)
SMCO levels than non -flowering stems.
July sown kale had less SMCO than June sown kale in September,
but tended to have more SMCO in November, especially at higher
populations and particularly in stems.
SMCO was not affected by varying growing temperature ( -6 to
15°C) , moisture availability, chopping or wilting for 96 hours.
Chrysol (13.1 g /kg DM) tended to have a higher SMCO content
than Canson, Maris Kestrel, Merlin, Vulcan or Bittern (mean = 9.2 g /kg
DM) . The lower yielding cultivars, Chrysol and Canson, contained
most of their SMCO in leaf tissue. SMCO varied in different plant
components, with SMCO in petioles having the highest correlation with
whole plant SMCO (r = 0.73, n =8 and 18) .
Near infrared reflectance (NIR) analysis accurately predicted N
and moisture contents in different kale tissue types, with correlation
coefficients (r) >0.95 between NIR predicted and Kjeldahl N or oven - dried moisture values. SMCO was only predicted satisfactorily by NIR
for plant breeding purposes in entire leaves and young leaves, which
had average standard errors of 2.3 and 1.7 respectively and correlations
between SMCO values predicted by NIR and the autoanalysis method of
r = 0.87 to 0.91. In stems and whole plants, which had average standard
errors of 2.9 and 3.9 respectively and correlations (r) ranging from
0.69 to 0.84, NIR could only be used to separate low and high SMCO
samples.
