Item

Growth and regrowth of dual-purpose wheat and canola following different methods of grazing

Brooker, Tim
Date
2015
Type
Dissertation
Fields of Research
ANZSRC::070302 Agronomy , ANZSRC::070304 Crop and Pasture Biomass and Bioproducts
Abstract
A field experiment was conducted to investigate the forage yield and subsequent recovery of dual-purpose wheat and canola crops sown at different times and subjected to differing durations and intensities of grazing. The success of a dual-purpose crop is determined by the combined value of vegetative biomass consumed by livestock and grain yield, and hence maximised when forage yield is greatest and grain yield is unhindered. This experiment investigated the forage yield and crop recovery for wheat and canola sown on two dates, with two grazing methods and three times of closure. When sown on 9 December (TOS 1), canola sheep consumed 5540 kg DM ha⁻¹ over 28 days in March, compared with wheat, where 1905 kg DM ha⁻¹ was consumed. Accumulated biomass for grazing commencement in June was 2270 kg DM ha⁻¹ for 17 February-sown crops (TOS 2) and 1173 kg DM ha⁻¹ for TOS 1 crops, with no difference between crops. Grazing took place between 5 June and 20 July, with greater forage yields of TOS 2 crops. TOS 2 wheat had the greatest rate of recovery, increasing to 2405 kg DM ha⁻¹ after the accumulation of 700 °C d following the termination of grazing. Canola TOS 1 recovered to 1570 kg DM ha-1 over the same period; canola TOS 2 and wheat TOS 1 reached 1135-1165 kg DM ha⁻¹. The canola was infected with a virus due to aphid damage before the winter grazing, which affected the recovery following the grazing period. Duration of grazing was determined to be detrimental to crop recovery, with periods <20 days required for maximum recovery rate. Timing of grazing was not important when biomass was considered on a thermal time accumulation basis, however reduced time from the termination of grazing to flowering for canola defoliated in late July may not allow for sufficient leaf recovery to support grain yield. There is potential for use of dual-purpose crops in New Zealand mixed farming systems, and grazing management is more likely to be determined on stock management factors opposed to specific crop management requirements, however break feeding will result in variable recovery across a paddock.