A survey on the effect of establishment techniques, crop management, moisture availability and soil type on turnip dry matter yields and nutritive characteristics in western Victoria

Abstract

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.