WithTheGrain: Biologicals need more development for broadacre efficacy
Author: Rachael Oxborrow | Date: 13 Jun 2018
Most biological amendments which aim to address soil health concerns such as biostimulants, humates and beneficial microbes do not provide reliable returns in broadacre agriculture — but some products could have potential.
A GRDC investment investigating biological products commonly utilised in market garden and organic produce operations has found a lack of consistency in outcomes for grain growing areas.
However, CSIRO Agriculture and Food principal research scientist Dr Mark Farrell says the results of his research did not rule out possibilities of some of these amendments being of use to the grains industry with further development.
“It’s fair to say that while we understand the mechanisms behind the conventional fertilisers on the market, the benefits of most of the biological products haven’t had the same scientific evidence,” he says.
“For example, we’ve known for many years that nitrogen and phosphorous are important for plants.
“Using certain methods, we can predict how crops will respond to different fertiliser inputs relatively well, but it doesn’t work perfectly and we get it wrong in some years.
“Even if the mechanism of the benefit is very well understood, it still might not be right every year.
“There is fundamental evidence that some biological amendments can change crop growth, but there has been comparatively little research investigating the 4 Rs – right source, right rate, right time and right placement, particularly in the Australian dry-land grains context.”
Throughout the three-year project, which included a literature review, glasshouse studies and field trials, researchers were looking for crop growth, yield and grain quality increases from treatments with a range of biological amendments.
Dr Farrell says due to the short-term nature of the study, the focus was put on monitoring rapid changes in the soil such as soluble nutrients, microbial biomass and microbial structure.
“Those marketing many biological inputs often suggest that growers can reduce their applications of artificial fertilisers because the amendments increase crop nutrient uptake from the soil,” he says.
“Biological amendments can be costly when compared to conventional fertilisers and our results suggest that the increases in production and dollars per hectare are small.
“Unless you have a real need to use biological amendments or you have a reputable agronomist who can assist you with advising how they might work on a case-by-case basis, they may not be cost effective.”
The research included two years of field trials that spanned eight sites in five states across all three GRDC grain growing regions.
The project used 69 biological inputs for chemical characterisation, consisting of 21 liquid and 48 solid amendments. These were broken down into five classes, and an illustration of magnitude and duration of effects can be seen in figure 1:
1. Alternative fertilisers (8)
2. Active microbials (6)
3. Humates (16)
4. Biostimulants (13)
5. Organic amendments (in turn, consisting of) a. Composts (10)
b. Manures (14)
c. Biochars (1)
d. Biosolids (1)
Potential benefits from the application of biological amendments in agriculture can be associated with direct nutrient contributions, plant physiological responses, and/or modifications in soil physical, chemical or biological components of soil health.
The varied biological amendments were categorised as biostimulants (plant growth stimulants), beneficial microbes, manure and compost, humates (some of which also fit the category of biostimulants), and biochar.
The results were analysed across a number of methods to measure outcomes including plant analysis, soil and amendment chemical analysis and soil biological analysis.
The study demonstrated sporadic effects of biological inputs on soil health, limited impacts at the mechanistic level, such as nitrogen uptake, and very few increases in grain yield.
“Across the eight field trials over two seasons, only one organic amendment led to significant increases in yield at two sites in NSW, with insignificant differences observed between the nil control and other amendments,” Dr Farrell says.
“The soil microbial community was altered at several sites across several classes of amendment, but again there was limited evidence to suggest that after two years this was changing soil function that may lead to greater crop growth.
“The huge variety of biological amendments available makes general recommendations difficult, though some product classes do behave discretely from one another.”
The benefits of organic amendments such as composts, manures and biosolids on soil health and crop production are better understood than the other biologicals, but even these produced varied and small yield responses in the trials.
“These findings indicate that it is unlikely that most other biological inputs will have positive impacts at the broad scale for Australian grain growers, at least in the short-term,” Dr Farrell says.
”This could change in the future as we are observing large companies in America and a large European research effort injecting significant sums of money into the development of beneficial microbes, but reliable scientific evidence of cost-effective responses are not yet available.
“There is an industry shift towards a more systematic research and development based approach, and this needs to be targeted towards testing based upon underlying soil constraints.”
GRDC research code: CSO00044
Mark Farrell, 08 8303 8664, firstname.lastname@example.org
GRDC Project code: CSO00044
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