Effect of biofertilisers on the growth and yield of tomato (Lycopersicon esculentum L.) and wheat (Triticum aestivum L.)

Dr Paul Kristiansen Mr Van Toan Nguyen Organic Research Group,
University of New England Armidale

Executive summary

Introduction

Given rising input costs in agriculture, interest in methods of increasing nutrient cycling and availability to crop and pasture plants is growing. The use of a range of biofertiliser products such as simple composts or more elaborate microbial inoculums, have been reported to have a range of benefits to crop growth and quality, although there is often considerable inconsistency in the observed effectiveness of these diverse products.

The aim of the trials reported here were to assess the efficacy of the several biofertilisers (BioBrew® products and ExuRoot®) supplied by Ausmin in comparison to conventional crop fertiliser programs, considering agronomic variables such as crop growth and yield, crop nutrient levels and soil chemical fertility and biological activity.

Materials and methods

Tomato (Lycopersicon esculentum L. cv. Roma) and wheat (Triticum aestivum L. cv. Janz,) were tested in different inorganic and biofertiliser treatments. The experiments were carried out as pot trials in glasshouses at the University of New England, Armidale.

The biofertilisers used were BioBrew Soil, BioBrew Growth, BioBrew Harvest and ExuRoot. The biofertiliser treatment combinations were developed to provide a set of structured comparisons to (a) contrast their performance with typical current fertiliser practices used by vegetable growers, (b) determine the relative performance of the various biofertilisers products in combination and alone, and (c) test the effect of doubling the rates of certain biofertiliser combinations to get a preliminary sense of the dose-response relationships between the biofertilisers and the measured variables. Inorganic fertilisers were also used to provided a reliable, industry-relevant standard response to compare with any new fertilisers treatments. In addition, a high rate of inorganic fertiliser was used to provide a comparative measure of the effect of high-input practices.

Parameters measured in the trials included basic agronomic and physiological variables such as chlorophyll, sap and fruit chemistry (pH, Brix, electrical conductivity), height, flowering and fruiting, biomass production, yield and quality, as well as a range of soil chemical and biological tests.

Results and conclusions

The most obvious finding from the tomato and wheat trials was the three distinct groups of treatments,

(a) The high fertility treatment (High) generally had a significantly more growth,

(b) Treatments receiving the baseline inorganic fertilisers (Base), with or without biofertilisers, had intermediate growth, and

(c) Treatments receiving no inorganic fertilisers (low fertility) showed very poor growth, with or without amendment with biofertilisers.

Where no inorganic fertiliser was applied, growth was very poor. Therefore, when pre-existing soil fertility is low, it is vital to improve the inherent chemical fertility of the soil and not just rely on biofertilisers to stimulate soil biological activity, enhance quantity and quality of microbial substrates, modify the soil physical environment and so on. However, when supplied with a reasonable amount of plant nutrients, the biofertilisers were able to further enhance growth and quality compared with the baseline inorganic treatment alone.

In tomato, several biofertiliser treatments (i.e. BB Mix(x2), BB/ER Mix and BBS+ER) achieved similar or greater heights than High and doubling the biofertiliser mix improved flowering and fruiting significantly compared with Base. Fruit Brix was increased by 0.5 to 1.0% in BBG(x2) and BBH(x2) compared with the other biofertiliser treatments and Base, suggesting a greater ability to manufacture and store sugars.

Another key finding from the tomato trial is the strongly negative effect inorganic fertilisers had on tomato fruit quality in relation to the nutrient deficiency syndrome blossom end rot (BER), but when those inorganic fertiliser were amended with biofertilisers, there was a very significant reduction the level of BER. This indicates that while fruit quantity was increased by the high use of inorganic fertiliser, quality was seriously compromised. The net effect was that production efficiency in the High treatment was the lowest of all, with 27% of ripe fruit having BER compared to an average of 8% BER in the biofertiliser treatments. Tissue analysis of the tomato fruits found few significant differences, suggesting that fruit tissue biochemistry was not strongly influenced by the biofertiliser treatments.

In the wheat trial, the combined effects of the inorganic and biofertilisers on wheat growth was greater than the baseline inorganic fertiliser alone, and the biofertilisers were potentially as effective as the High treatment in some cases. Treatments with BBS had superior height, tillering and flowering in the mid- and later weeks of the trial, BBS(x2) produced significantly more shoot biomass and all biofertiliser treatments (except ER) produced significantly higher root biomass than Base. The potential benefits derived from a greater root mass, e.g. greater water uptake in drier soils, improved nutrient capture in low fertility soils, are not fully explored in a pot trial where nutrients and water tend to be applied regularly and root development is constrained by pot size. Hence, field trials may highlight the practical benefits of greater root biomass not fully investigated in these trials.

In the last weeks of the wheat trial, a number of plants had crown rot (Fusarium pseudograminearum). Although not quantified, informal observations suggested that the most severe infestations were in high and Base, and the least amount of crown rot occurred in the biofertilised and low fertility treatments. Given problems with BER in the tomato trial, the ability of the biofertilisers’ to improve resistance to diseases and physiological disorders requires further research.

The effect of the fertiliser treatments on a wide range of soil chemical and biological parameters was measured. However, few of the variables differed significantly between treatments and changes between the start and end of the trials showed that most soil parameters remained similar. Either differences were not observed (e.g. responses were too variable within treatments), not consistent in terms of gross effects (e.g. High and control with similar responses) or not consistent in terms of expected differences due to the various biofertiliser treatments (e.g. double rates opposite response compared to single rate).

Soil pH in Base and High was significantly lower than the biofertiliser or low fertility treatments, and the inorganic-only treatments had higher soil carbon:nitrogen ratios. These differences have implications for nutrient cycling and availability. In general, fungal and bacterial numbers were higher in the low fertility treatments and the lowest observed active bacterial count occurred in High. Of the biofertiliser treatments, BB/ER Mix (± inorganic fertiliser) had relatively high levels of active bacteria and fungi.

Future research

These trials have highlighted a number of areas for potential further research and development. The main thrusts are to test the findings in the field, as part of functioning agro-ecosystems, and to explore key aspects of plant physiology and soil health. Future work could investigate the effect of the biofertilisers:

• under field conditions, where nutrient availability and crop growth potential is different
• over a longer period of time to determine the effect on short- to medium-term changes in soil physical and nutrient cycling parameters
• across a wider range of fertiliser doses to improve our understanding of the nature of the dose-response relationship between each biofertiliser and specific plant and soil responses
• on the activity of specific taxa or functional groups in the soil biota
• resistance mechanisms against crop diseases and disorders
• physiological responses, e.g. changes in root form and function in response to ExuRoot

For more information on this trial or for information on any of our products contact Mark McNamee or David Hardwick
Ausmin Australia Pty Ltd
Ph +61(0)7 3282 1200
Email reception@ausmin.net.au