Farmers who increase their profits through flexible cropping systems in the high rainfall zone (HRZ) are also doing their bit for the environment, according to research by the Grains Research and Development Corporation (GRDC).
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Studies carried out on in the HRZ of Victoria show that where farmers maximise their gross margins by applying less fertiliser nitrogen at sowing, they are also likely to be improving their environmental performance.
Dr David Nash, from the Department of Primary Industries Victoria, has been investigating nitrogen and phosphorus runoff from ‘on-the-flat’ cropping.
Although some farmers might wonder why they should care about the quality of the run off from their crops, Dr Nash said that this is going to become increasingly important in the future.
“The export of pollutants from agricultural production systems, especially phosphorus and nitrogen, into our rivers is a major environmental problem,” Dr Nash said.
“The increasing frequency of potentially toxic blue-green algal blooms in our rivers is highly visible evidence of this.
“While all land uses contribute nutrients to our water supplies, agricultural industries are particularly important because they occupy most of the landmass.”
There is growing pressure for agricultural industries to improve their environmental performance, with Catchment Management Authorities developing nutrient management strategies to deal with the issue.
“Our research shows that phosphorus and nitrogen concentrations in cropland drainage can be well in excess of stream targets, and so we need to do what we can to bring these concentrations down,” Dr Nash said.
“While farmers are, understandably, primarily focused on profits rather than environmental benefits, we now know that the two are not necessarily mutually exclusive.
“In fact, our research showed that by focusing on maximising gross margins farmers achieve better environmental outcomes, in terms of lower nitrogen exports, than if they simply aimed to maximise crop yield or apply all of their nitrogen up-front.”
According to Dr Nash, there are four key factors affecting nutrient run off on farms:
- soil structure and infiltration rate;
- the cropping practice in place (e.g. stubble burning vs. stubble retention and direct drilling vs. conventional cultivation);
- the timing of fertiliser application in relation to rainfall (soil wetness); and
- the paddock and farm layout and the ability to retain, detain or clean-up runoff water before it leaves the property.
“While some of these factors may be difficult to address, our studies have shown that changes in farming practices can have a big effect,” he said.
“We investigated the nutrient levels in simulated run off from three different tillage systems typically used in the HRZ: direct drilling with stubble retained; direct drilling with stubble burnt; and conventional cultivation with stubble burnt.
“The results showed that cultivation and stubble burning increases surface runoff volumes compared to direct drilling and stubble burning,” Dr Nash said.
“Most importantly, while greater concentrations of nitrogen and phosphorus were measured in the runoff from the direct drill treatments, the amount of run off was so much less than from conventionally cultivated systems with stubble burning that less nutrients would end up off-site, and hence in our rivers.”
Dr Nash also looked at the effects of different nitrogen fertiliser application strategies and compared not only the likely loss of nutrients in run off, but also potential yields and gross margins.
“Our studies show that matching fertiliser applications to the needs of the crop at strategic times of the year not only reduces potential nutrient loss, it also increases profits,” Dr Nash said.
“We used this information to develop a series of nitrogen fertiliser recommendations for different wheat varieties grown on high medium and low nitrogen soils in the Dunkeld region of south eastern Australia.
“When growing short and medium season wheat varieties on soils with medium to high nitrogen levels, our research shows that only 10 kg nitrogen/ha needs to be applied at sowing. Additional nitrogen fertiliser can then be applied later in the season, taking into account the yield potential of the crop and seasonal conditions, optimising both gross margins and environmental performance.
However on low nitrogen soils our studies show that more than 10 kg of nitrogen/ha is required at sowing, most probably around 60 kg nitrogen/ha.”
Growing long season wheat however requires a different approach, according to Dr Nash.
“These varieties, for example Mackellar, seem to need more nitrogen early in the season, which means it also needs more than 10 kg of nitrogen/ha at sowing, even on medium and high nitrogen soils.
“Most importantly though, our research suggests that flexible cropping systems that maximise crop potential at sowing using the minimum amount of fertiliser nitrogen, optimises economic performance and environmental performance at the same time.”
