Soil Microbiology Consultancy as to Eveleigh Hills Report

Executive Summary

This report provides an analysis and assessment of the biological properties of the soils under the dominant land use of cultivation found on Eveleigh Hills. Methods of analysis included terminal restriction fragment length polymorphism (T-RFLP), Solvita soil respiration tests, baiting, physical and chemical tests as well as inoculation assays.

Recommendations for the client include:

• Sandy soil should be inoculated with microbial populations to enhance the resistance of crops to nematodes.
• Irrigation should be done to provide the optimum moisture levels for the growth of legumes and other crops due to the low soil moisture content.
• More legume plants should be cultivated to boost soil health.
• The low biological activity of the soil warrants the application of stable organic matter.

Acknowledged report limitations include drawbacks of T-RFLP that make it semi-quantitative due to disparities in the number of 16S rRNA gene copies and low limits of detection in a mixture of PCR products. Another shortcoming is the Solvita soil respiration method that disregards anaerobic microorganisms in its analysis.

Introduction

The purpose of this report is to analyse and evaluate the biological properties of Eveleigh Hills soil for use in land cultivation. The main issues addressed are indicated as shown below.

Suitability of Land for the Growth of Crops with a Focus on Legumes

This decision was made considering the microbial function of the soil under cultivation together with the physical and chemical properties as provided by the client. A detailed analysis of these factors provides information regarding the suitability of the soil for large scale cropping of legumes.

Differences in Microbial Diversity following Previous Land Uses

Microbial diversity was assessed by amplifying the 16S rRNA gene bacteria that is usually conserved in bacteria. Total microbial DNA was extracted from soil samples and amplified followed by restriction digestion using a four-cutter enzyme. Terminal-Restricted Fragment Length Polymorphism (T-RFLP) was then conducted by separating the restriction fragments via electrophoresis and detecting the terminal fragments.

The Microbial Functions of the Soils

This aspect was determined using the Solvita soil respiration test to ascertain the biological activity of soil by measuring the amount of carbon dioxide produced. Specifically, soil, plants, microbes and plant roots are responsible for the production of carbon dioxide.¹ This test is the most accurate and widely used diagnostic method for the measurement of soil carbon dioxide levels because of its high sensitivity to low levels of the gas. The outcomes of this test indicate the soil’s capacity to support plant growth. Approximately 30cm³ of soil samples oven-dried at 40^oC were put in beakers together with 9 cm³ of water. Jars containing soil and test paddles were sealed tightly and incubated for 24 hours. The resultant colour changes measured in a digital colour reader to determine the concentrations of carbon dioxide.

The Presence and Diversity of Nematodes in the Soil and Their Potential to Damage Crops Grown in These Soils

The presence of nematodes in the soil was determined through plant soil feedback and inoculation studies by measuring root and shoot length of plants growing in sterilised, unsterilized and sand soil. Studies show that soil infestation by nematodes, particularly the sting nematode, results in a reduction in shoot and root length.

The Presence and Abundance of Phytophthora in the Soils

Soil baiting was done on oat seedlings to identify the presence of Phytophthora cinnamomi in soil. Baiting was chosen because it only permits the permeation of the plant under investigation. The process relies on the ability of the pathogen to detect plant roots.²

Analysis of the Findings

For the sake of clarity when reading, the findings of this report have been separated into the cultivated land use on Eveleigh Hills. These outcomes have also been separated based on the five main objectives.

Suitability of Land for the Growth of Legumes

The cultivated soils were classified as Tenosol based on the Australian soil classification system. The proportion of clay was 17%, which fell within the range of 10 to 20% that is usual for sandy loam soils. The bulk density was 1.18g/cm³, whereas the moisture content was 13.9%w/w. The ideal moisture content for cropping soil should be at least 25%. In this case, the soils had lower than expected moisture levels. The soil pH was 6, which fell within the ideal pH range of between 5.5 and 7.5 for the cultivation of legumes.³ The concentrations of organic carbon, nitrogen, phosphorous and potassium were 1.56 %w/w, 1.4 g/kg, 22 mg/kg and 273 mg/kg, respectively. Legumes improve soil fertility through nitrogen fixation, increasing microbial diversity and increasing the organic content of the soil. The current soil state can support the growth of legumes and improve its physical and chemical properties.

Differences in Microbial Diversity Following Previous Land Uses

There was no strong amplification of soil DNA apart from sample 13. The T-RFLP output (plot) generated a species count (S) of 30 for soil and 9 for plated bacteria, a Shannon Diversity Index of 3.5657 and species evenness (J) of 1.048 and 1.622 for soil and plated bacteria. The Shannon Diversity Index of 3.5657 showed a low diversity of microbial populations in cultivated soils. This observation was in line with other investigations on monoculture cropping because this practice selects for microbes that thrive following their interactions with the cultivated crop.

The Microbial Functions of the Soils

The average concentration of soil carbon dioxide as determined by the Solvita soil respiration test for cropping soils was 31.22 mg/kg or parts per million (ppm). These findings showed moderate nitrogen-mineralisation potential of the oil, which corresponded to biomass of less than 1200 ppm. There was a need to apply stable organic matter to enhance the health of the soils.

The Presence and Diversity of Nematodes in the Soil and their Potential to Damage Crops Grown in These Soils

For the cropping soil, plants growing in uninoculated unsterilised and sterilised soils had greater shoot length than those planted in inoculated soil. On the other hand, plants grown in inoculated sand had greater shoot length than those planted in uninoculated soil. Reductions in shoot and root length showed that the soils contained nematodes that could damage crops.⁴ However, the higher shoot and root lengths in uninoculated soils showed that the soil had the potential to counter the harmful effects of nematodes in the soil. Nonetheless, the sandy parts of the soil could benefit from inoculation with microbial populations.

The Presence and Abundance of Phytophthora in the Soils

The baiting test did not show any signs of infestation by P. cinnamomi.

Recommendations

From the above observations, PPAT3003 Microbiology Services recommends that the following actions should be taken in Eveleigh Hills to maintain the biological diversity of the soil and its functionality. Other benefits that will be achieved from implementing these recommendations include enhancement of the quality of degraded soils and promoting biological resilience.

• Parts of the farm with sandy soil should be inoculated with an array of microbial populations to enhance the resistance of crops to nematodes.
• The soils should be irrigated to provide the optimum moisture levels for the growth of legumes and other crops given the low moisture content.
• Plant legumes to improve the physical and chemical properties of the soil such as the reduction of pH, which means that more legumes should be planted.
• The low biological activity of the soil necessitates the application of stable organic matter.

Conclusion

This report uses various tests to draw different conclusions regarding the biological health of Eveleigh Hills soil under cultivation. The analytical scope included soil function, microbial activity, diversity, soil’s suppression ability of the root-knot nematode and possible infestation by Phytophthora. The report finds that the suitability for cropping is moderate on cultivated soil. The key recommendations include inoculation of sandy soils with microbes to improve resistance to soil nematodes, irrigating and applying stable organic matter. PPAT3003 Microbiology Services accepts the limitations of the analysis and admits that the views presented herein may differ from those given by other consultant agencies.

Footnotes

1. Thoumazeau, A, Gay, F, Alonso, P, Suvannang, N, Phongjinda, A, Panklang, P, Chevallier, T, Bessou, C & Brauman, A 2017, ‘SituResp®: A time-and cost-effective method to assess basal soil respiration in the field’, Applied Soil Ecology, vol. 121, pp. 223-230.
2. Redondo, MA, Boberg, J, Stenlid, J & Oliva, J 2018, ‘Functional traits associated with the establishment of introduced Phytophthora spp. in Swedish forests’, Journal of Applied Ecology, vol. 55, no. 3, pp. 1538-1552.
3. Moir, J, Jordan, P, Moot, D & Lucas, R 2016, ‘Phosphorus response and optimum pH ranges of twelve pasture legumes grown in an acid upland New Zealand soil under glasshouse conditions’, Journal of Soil Science and Plant Nutrition, vol. 16, no. 2, pp. 438-460.
4. Zhao, D, Zhao, H, Zhao, D, Zhu, X, Wang, Y, Duan, Y, Xuan, Y & Chen, L 2018, ‘Isolation and identification of bacteria from rhizosphere soil and their effect on plant growth promotion and root-knot nematode disease’, Biological Control, vol. 119, pp. 12-19.