A comprehensive review of published literature and overall research data, found limited positive response from a large range of biological products promoted for use in cropping.
CSIRO scientist Dr Mark Farrell and colleagues, (Macdonald LM, Jenkins SN, Webb MJ, Wong MTF, Abbott LK) led the major study. Full results are published in a 68-page final report.
Biological inputs (broad definition) investigated included alternative fertilisers, bio-stimulants, microbial inocula (mycorrhizal fungi/rhizobia), humates, composts, manures and biochars. Their value-added products, including pelletised forms and extracts such as compost teas, were also included.
A number of alternative fertilisers assessed included products that are advocated to increase nutrient use efficiency, or reducing losses to the environment or impacts on the biological health and function of soil.
Data was sourced from local reports, international peer reviewed literature, as well as collating an inventory of Australian sourced biological inputs.
Despite a wide variability in biological inputs, both within and between product classes, few significant results were found either in the glasshouse, or in a series of eight field experiments across two growing seasons and five states. Further research found no positive effect of bio-stimulants or humates on wheat capture of nitrogen, either from soil or from legume residue.
The study noted that while there are positive results observed in scientifically rigorous studies, these can often be very context specific. Many of the positive results either came from laboratory or glasshouse experiments, and usually on higher value (higher input) crops, such as vegetables and fruit. Very limited reporting of consistent results of any class of biological input was found in dry-land broad acre context.
As part of the three-year study, more than 60 amendments were chemically analysed, 38 of these were in-field experiments. Eight field experiments were established for consecutive years across Australian grain growing regions, including Rankins Springs and Parkes.
The review of nationally and internationally data found there was a general lack of evidence for the efficacy of biological inputs within the broad-acre dry-land grains context, both in Australia and abroad.
Laboratory testing and glasshouse screening quantified chemical variability of biological inputs, both within and between product classes; examined wheat growth responses in a controlled environment; and probed key mechanisms underlying input modes of action. Testing and screening revealed that although there is huge diversity in chemical composition, there were very limited responses to the more than 50 amendments glasshouse tested.
As part of the three-year study, more than 60 amendments were chemically analysed, 38 of these included in field experiments.
Over a two year period, 38 biological inputs were field tested at eight sites (five states), only four significant results in terms of wheat yield were observed. Two significant yield reductions occurred after application of one bio-stimulant and one humate treatment at the Paskeville site (SA). A chicken litter treatment had a significantly positive effect on grain yield at two NSW sites, possibly related to high nitrogen availability. In these trials increased yield well exceeded that of a double district practice of conventional fertiliser.
More in-depth analysis of soils from several of the treatments at each site revealed only sporadic and generally minor responses in terms of various soil health and fertility indicators, including microbial community structure. In a glasshouse experiment designed to test impacts of bio-stimulants on capture of soil and legume derived nitrogen by wheat, despite optimum growth conditions, the researchers saw no positive but some negative effects.
Generally, only the more nutrient rich composts and manures enhanced soil nutrient availability relative to unamended control treatment. Further knowledge of the chemistry of biological inputs is required to make informed predictions about the impact of them on soil nutrient cycling in the short term.
This project is the largest controlled examination of a wide variety of biological amendments in the Australian grain growing context. Further long-term research is required to identify whether amendments may have cumulative effects in the medium term. The authors do not discount biological input may have effects beyond one season if reapplied annually.
Next week: Passing of pioneer farmer who led the way in weed control and light soil upgrading.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email email@example.com or call 0428 752 149.