Factors associated with turnip dry matter yield, metabolisable energy and
crude protein were investigated in 266 turnip forage crops on 142 dairy farms
in south-western Victoria during spring 1999 and summer 2000. Factors measured
were primary cultivation method, secondary cultivation method, soil texture,
soil temperature and moisture at sowing, seedbed preparation, turnip variety,
sowing method, sowing rate, rolling post-sowing, harrowing post-sowing,
seedling establishment, insect damage, water received, phosphorus and nitrogen
application.
The average date for the commencement of seedbed preparation was early
October, although the range was from mid-March until mid-December. Sowing
dates ranged from mid-September to mid-December, with an average of
mid-October. The most common turnip variety sown was Barkant, followed by
Mammoth Purple Top, Vollenda and Rondo. Growing periods ranged from 8 to 23
weeks, with the majority of crops grazed from 8 to 15 weeks. The average dry
matter yield was about 5 t DM/ha, with values ranging from 0.4 to 19.2 t
DM/ha. The average metabolisable energy content of turnips was 13.7
MJ/kg DM with values ranging from 11.3 to 14.6 MJ/kg DM. The
metabolisable energy of roots was on average higher than the leaf component of
the plants (14 v. 13.5 MJ/kg DM). Conversely, crude
protein content of leaves (15.4%) was higher than in the root
fraction (13.9%). The average neutral detergent fibre content of
turnips was 22.5% with values ranging from 16.9 to
30.5%. The water-soluble carbohydrate content of the leaf component
ranged from 1.1 to 26.8% with an average of 14.7%, while
starch content of the root component ranged from 0.3 to 38.8% with
an average content of 16.9%. The average cost of growing a turnip
crop was $485/ha or $133 t DM.
Total, leaf and root dry matter yield as well as metabolisable energy and
crude protein were analysed by a mixed effects model (with factors fixed and
farms and paddocks random). Factors that were associated with total dry matter
yield were total water received, soil temperature and moisture at sowing,
seedling density, method of secondary cultivation, soil type and insect
damage. The application of nitrogen fertiliser had the greatest association
with turnip crude protein content.
In conclusion the findings of this study indicate potential ways to increase
the dry matter yield of turnips grown in south-western Victoria. Given the
current average dry matter yields and cost of growing turnips, purchasing
cereal grain may be a viable alternative. An increase in average dry matter
yield would make the choice of growing turnips as a feed for lactating dairy
cows a more profitable option.
Cocksfoot pasture production in relation to environmental variables
