Grazing management the key to successful dual-purpose crops
GroundCover™ Issue: 127 Mar - Apr 2017 | Author: Bob Freebairn
- Dual-purpose crops, if well-planned and managed, can be considerably more profitable than grain-only crops
- Grazing stubble over the fallow and grazing during the winter period, if managed correctly, cause little damage to soil attributes such water infiltration rates
- Important aspects include sowing times and variety choice, grazing management choice and adhering to basics such as efficient capture and storage of fallow rainfall
Dual-purpose cropping trials for the northern region show that grazing stubbles, and winter crops during their winter growing period, can lead to similar or even better grain yields than farming without livestock.
With buoyant lamb, mutton, wool and beef markets lately, the trials reinforce the increasing uptake of dual-purpose winter crops (cereals and canola) in many parts of the Australian cropping belt. An estimated one million hectares are now sown annually across Australia.
GRDC-funded research frequently shows dual-purpose winter crops can be grazed profitably for 30 to 90 days (with the length depending on factors including sowing time, environment, season and variety) and then yield similar to grain-only crops.
Stubble grazing management
Research has shown that stubble grazing is not detrimental to grain production provided clear rules are followed.
For example, a study by CSIRO, the New South Wales Department of Primary Industries (NSW DPI) and grower groups FarmLink and Central West Farming Systems found: “Sheep grazing on crop residues do not reduce crop yields in no-till, controlled-traffic farming systems in an equi-seasonal rainfall environment.”
The report also noted that careful stubble grazing had no adverse impact on soil water storage, soil quality or crop yields. The study covered the low and medium-rainfall environments of southern central NSW.
This report – authored by James Hunt, Antony Swan, Neil Fettell, Paul Breust, Ian Menz, Mark Peoples and John Kirkegaard – was based on the first four-year period of the project, but the study, now in its ninth season of continuous crop (canola-wheat-wheat rotation), continues to show similar results.
A critical point made by the report is that grazing stubble residue after harvest and during the fallow does pose a weed risk. If weeds get away they consume water and nitrogen. Successful stubble grazing therefore requires a timely herbicide treatment.
Fallow weeds not quickly killed rapidly utilise fallow moisture that is critical for the next crop. Soil moisture differences between fallows in which weeds are controlled with herbicides and those that are controlled by grazing can be about 50 millimetres of rainfall equivalent.
Researchers suggest stubble should not be grazed below 70 per cent ground cover. This is the level at which research shows the best balance between not hindering the next sowing, and soil protection and rainfall infiltration.
One of the surprise findings in these trials has been the retention of nitrogen in the soil during grazing. In one season the soil nitrogen levels were up to 100 kilograms per hectare higher at sowing in well-grazed fallows compared with ungrazed fallows. Researchers suggest stubble under grazing may be immobilising the nitrogen.
The other prime concern for many growers considering grazing cereals and/or canola – soil compaction by livestock – has also been largely allayed by the research. The compaction has proven to be comparatively shallow and not enough to cause any lasting soil structure damage.
Machinery compaction, though, is far more severe and affects the profile more deeply.
Managing dual-purpose crops to optimise profit from grazing and grain has been the focus of considerable GRDC-funded research over the past decade.
For example, a GRDC 2016 Update paper written by Dr Kirkegaard and CSIRO colleagues, ‘Managing dual-purpose crops to optimise profit from grazing and grain yield’, noted that grain yields can commonly be similar for winter crops (cereals, canola) to grain-only crops, provided aspects such as variety choice, sowing time and grazing management (lock-up dates and residual biomass levels) are appropriately managed.
Grazing of the crops had no adverse effects on soil quality.
Dr Kirkegaard says that well-managed, early-sown crops in medium and high-rainfall areas often produce significantly more biomass at flowering than is needed for likely grain yields. This explains why it is possible to use some of this excess biomass with careful and timely grazing and still achieve the flowering biomass required to reach target grain yield.
He says the safe grazing period for cereal and canola crops is from the time the crop is well-anchored until the reproductive parts start to elongate above the ground (Z30 for cereals and bud elongation for canola).
An example is a typical grazing ‘winter habit’ wheat crop sown on 25 March with a target yield of 4.5 tonnes per hectare that would require a critical flowering biomass of about 8 to 9t/ha.
The critical biomass required for a July lock-up is at least 0.5t/ha. Grazing past this point would require a higher grazing height to ensure the reproductive parts that are starting to elongate above the ground are not removed, and even more residual biomass (1 to 1.5t/ha) would be needed if lock-up was delayed to mid-August. This is because there would be less time to reach the biomass required for the 4.5t/ha target yield.
Dr Kirkegaard says that with good management, the grazing period can increase net crop returns by more than $600/ha. (For example, 2000 sheep grazing days/ha – 40 DSE/ha for 50 days at 28 cents a day.)
Dual-purpose varieties with ‘winter habit’ can be sown earlier and have a longer safe vegetative period during which grazing will not damage growing points and emerging heads.
‘Winter habit’ varieties sown relatively early (March) on as close as possible to full soil moisture profiles and with adequate nitrogen are most likely to provide the optimum grazing with minimal if any adverse impact on grain recovery.
Because of their ‘winter habit’, sensible winter grazing results in almost no loss of tillers.
These varieties mainly flower around the same time as non-grazed ‘spring habit’ crops sown at their more traditional later sowing time (May).
The amount of ‘winter habit’ required in a variety depends on environment and sowing time. For many areas, varieties with relatively moderate winter habit levels are sufficient and include varieties such as the recently released, rust-resistant LongReach Kittyhawk winter wheat, Eurabbie oats, Urambie barley and Cartwheel triticale. (It is always advisable to seek professional advice for suitable varieties for different environments.)
Resistance to the diseases stripe, leaf and stem rust is an important requirement for dual-purpose wheat varieties. Susceptible winter wheats are often the first to be infected with stripe rust, which can lead to early epidemics. Highly mobile rust spores can move via wind over vast areas to infect later-sown spring wheats.
GRDC Project Code FLR00005, CWF00013, CSP00111, CSP00174