Figure 1: Grain yield (t/ha, bars) and water use efficiency (kg/ha/mm, line) for 2014 wheat.
Further work in 2015 and 2016 will consider the cost versus the benefit to achieve the higher yields of the high-input scenarios.
“With no decrease to wheat yields over seven years, the trial has proven that sheep don’t negatively impact on any component of the cropping system, including water use efficiency, soil quality, soil nutrients (nitrogen, organic carbon and phosphorous), pests or diseases in the cropping phase as a result of sheep grazing. But further to that, we’ve found a number of benefits that come along with grazing sheep in break years,” Ms Crettenden said.
A major benefit is improved weed control. Grassy weeds including ryegrass, brome and barley grass are a significant issue on the Eyre Peninsula, with dormancy and herbicide resistance development reducing control options (see ‘Controlling barley grass on the Eyre Peninsula’).
“While some growers might be concerned the grazing will increase weed problems, we have seen a visual reduction in summer weed populations where grazing is used, with yield results showing improved water use efficiency in the following crop. By grazing pastures in break years, the animals can keep down the size of the weeds, delaying seed set,” Ms Crettenden said.
“The sheep are making use of what would otherwise be a waste product, the weed biomass, while keeping their size down so they can be adequately controlled.”
A second benefit was in pest control. Reduced populations of both mice and snails have been observed in the grazed paddocks, with 50% reduction of live snails recorded in the summer of 2013.
“Snails are effected by stubble grazing, because the sheep knockdown the stubbles, so the snails cannot retreat up the stubble in high temperatures and they die. Grazing over summer also eliminates the feed and habitat source for mice,” she said.
Sheep grazing medic pasture at the Minnipa Agricultural Centre in August 2012. Source: Jessica Crettenden
Soil health factors were also monitored, with no change seen in organic carbon levels, or erosion. An increase in nitrogen cycling was observed in the grazed areas, with an average increase of total mineral nitrogen of 52 per cent and 37 per cent in the low-input and high-input areas respectively, though the exact cause is not yet fully understood. Groundcover was not significantly affected, with a 5 percent and 1 percent reduction from grazing for the low input and high input systems respectively in 2014.
“We are thinking that the grazing is increasing nitrogen cycling and somehow making the nitrogen more available to the plant, however further research is in progress to get to the bottom of this effect,” she said.
The trial will investigate the risk of compaction from grazing in 2015, however Ms Crettenden believes if there is any impact it will be minor.
“Seven years is quite a long time, so to see no negative response over that period, we expect that there won’t be a significant impact on crop and pasture production from compaction, but we’ll be testing over the next two seasons to see if there is any effect.”
The grazing trial will continue at least through 2015 and 2016, for a total of nine years. In addition, two other GRDC-funded Grain and Graze trials are underway at the MAC.
“The first is a study into soil rhizobia, the bacteria in soil that fixes nitrogen to the plant roots. We know a good medic stand increases rhizobia populations, so what we’re looking at now is twelve different treatments to look at the best options for increasing rhizobia through improved medic production,” Ms Crettenden said.
The treatments include volunteer compared to sown medic, and seed and soil applied inoculation, with each treatment assessed with and without grazing, with the team expecting that grazing will increase fixation.
The second trial will investigate dual-purpose crops, grazing up to GS30 and then assessing the nitrogen requirements to achieve the same yield as not grazing.
A winning combination
Including sheep into a cropping system on the Eyre Peninsula can benefit the whole farming system with no negative influence on wheat yields, but Ms Crettenden says the decision to graze sheep should also be about risk.
“In a low rainfall area, sheep can help growers better manage their risk and the effects of seasonal variability. Just like with any diversification, grazing can limit exposure to risks posed by diseases and pests, while also providing another source of income in years when yields or grain prices are low,” she said.
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