Investigating the effect of applying different organic amendments on the soil ecosystem.
Identifying potential interrow cover crops and fallow crops and testing their host status for burrowing nematode and Fusarium wilt.
Developing a soil health testing kit from the key indicators that respond to changes in soil management under banana cultivation. The soil health testing kit is a result of the above research activities.
The above research needs to be integrated into farm practices to bring about changes to soil health management of bananas.
Comparing the biological, chemical and physical characteristics of soils from banana plantations with the same soil type in an adjacent undisturbed site lets us make comparisons that identify what changes occur in the soil environment from banana production systems.
In this project we have surveyed in the southeast and north Queensland production regions, on a number of different soil types.
Soil biological, chemical and physical properties have been measured at 4 locations in north Queensland (Table 1).
Table 1. Locations of sites used in a paired sampling survey to determine changes in soil properties due to banana cultivation.
Location
Systems being compared
East Palmerston
Conventional bananas with permanent pasture
Mission Beach
Conventional bananas with rainforest and certified organic bananas
Tully
Conventional bananas with rainforest and permanent pasture
Kennedy
Conventional bananas with rainforest
Comparing the soil ecosystems of banana plantations with undisturbed sites identifies what changes occur in the soil from banana growing
Comparing soil biological characteristics
One method of assessing the biological status of a soil is to look at the numbers and types of different nematodes in the soil. While most growers know of the nematodes that attack plants, there are many other types that feed on bacteria, fungi and other nematodes.
These other types of nematodes play a crucial role in recycling the nutrients carried in the soil microorganisms. The results from our survey of different sites shows significantly more diversity of nematodes in soil from the rainforest sites compared to the conventional banana sampling sites. The pasture and organic banana sites have nematode diversity ratings between the rainforest and conventional banana sites.
These results show that a typical banana production system has less microbial diversity than the other plant systems surveyed.
Figure 2. A cluster analysis of the nematode community feeding groups, at 10 sites from 4 locations in north Queensland
The cluster analysis in Figure 2 is a way of showing how similar the nematode communities are in each plant system.
Our results show that the communities from conventional banana sites were all quite similar. They are characterised by having a large percentage of the nematodes as plant parasites, with much fewer nematodes active in the nutrient recycling pathways.
This indicates that the amount of nutrient recycling in the soil of a banana plantation is reduced compared to the other plant systems. The East Palmerston pasture and Tully rainforest site also shared many of this group’s characteristics.
Another grouping with similar characteristics represents the Mission Beach and Kennedy rainforest sites and the Tully pasture site. At these sites the nematode communities were quite diverse with a significantly lower percentage of plant parasitic nematodes compared to the conventional banana sites.
This indicates a more complex soil food web that is actively recycling many of the nutrients in the soil ecosystem.
The organic banana site was not closely related to either of the other groups. However, the organic banana site had more similarities to the undisturbed group of sites than to conventional banana production.
Soils under conventional banana production systems had a less diverse population of soil microorganisms than most of the rainforest and pasture sites.
Comparing soil physical characteristics
Soil physical measurements were made on soils at the Mission Beach, Kennedy and Tully sites. While not all of the analyses have been completed, the soil physical measurements that have been finalised included:
Bulk density – indicates the degree of compaction of the soil
Total porosity – measures the airspace in a soil
Pore continuity – measures how well connected the soil pores are
Infiltration rate of water – measures the speed at which water can enter a wet soil.
The available results are:
Banana rows
Bulk density under banana rows increased by 4%, 16%, and 18%, in Mission Beach, Tully, and Kennedy soils respectively, compared to the corresponding rainforest sites.
Total porosity under banana rows decreased by 3%, 7%, and 12%, in Mission Beach, Tully, and Kennedy soils respectively, compared to the corresponding rainforest sites.
Pore continuity under banana rows decreased by 4%, 9%, and 15%, in Mission Beach, Tully, and Kennedy soils respectively, compared to the corresponding rainforest sites.
Average infiltration under banana rows decreased by 64%, 93%, and 69%, in Mission Beach, Tully, and Kennedy soils respectively, compared to the corresponding rainforest sites.
Banana interrows
Bulk density in the interrows was significantly higher by 10%, 20%, and 27%, in Mission Beach, Tully, and Kennedy soils respectively, compared to the corresponding rows.
Total porosity in the interrows was less than rows by 13%, 13%, and 21%, in Mission Beach, Tully, and Kennedy soils respectively, compared to the corresponding rows.
Pore continuity in the interrows was less than rows by 16%, 16%, and 24%, in Mission Beach, Tully, and Kennedy soils respectively, compared to the corresponding rows.
Soil in banana plantations is more compacted, and has lower infiltration rates, compared to the rainforest sites. The interrow area is significantly more compacted than the row.
Comparing soil chemical characteristics
The chemical analysis of the soils from the 10 sites is still continuing. The key indicators that we have results for are:
pH – can indicate nitrate leaching
Carbon – a measure of organic matter
Extractable phosphorus – phosphorus can have environmental impacts if it enters waterways
Traditionally carbon has been measured as total carbon, which measures all the forms of carbon in the soil. However, not all carbons are equal because some are more quickly broken down, having a more immediate impact on the soil. This is called labile carbon and it is also being measured in this survey. Another form being measured is called microbial carbon, and it is all the carbon contained in living organisms in the soil. It is being tested for its useful in indicating soil biological activity.
The results so far are:
Total carbon levels are reduced under conventional banana production compared to the rainforest or pasture sites.
Labile carbon levels are reduced under conventional banana production compared with rainforest, pasture and organic bananas (Figure 3)
All the conventional banana sites have higher levels of phosphorus compared with rainforest, pasture and organic bananas. The conventional banana sites at Mission Beach and Tully have very high levels of phosphorus (see Figure 4).
Soil pH is significantly acidified down to 50 cm at the conventional banana site at Kennedy, compared to the adjacent rainforest. At the 20 – 25 cm depth under conventional bananas the pH has dropped to 4.2 compared to 6 in the rainforest.
Figure 3. Comparing levels of labile soil carbon from the survey sites
Figure 4. Comparing levels of soil phosphorus (Colwell) from the survey sites
Conventional banana production reduces total carbon and labile carbon, and acidifies the soil in most cases. Very high soil phosphorus levels indicate more phosphorus fertiliser is being applied than is needed by the banana crop.
When a soil is known or suspected of being degraded then banana producers need some guide to how to improve the soil ecosystem. Remediation of degraded soils may be possible with the use of pre-plant amendments.
While some organic amendments are known to improve banana plant growth and production, there is very little detailed information for tropical soils on the aspects of the soil ecosystem they influence, and how they affect soil interactions.
This is important to know because an understanding of the interaction between the soil properties and soil-borne diseases, such as Fusarium wilt and burrowing nematodes, can determine how farm management practices will influence soil health.
So in this part of the project a series of glasshouse pot trials, followed by field trials, is being carried out to study the effect on banana plant growth and key soil characteristics of a range of different pre-plant organic amendments. The effect of these amendments on populations of burrowing nematodes and Fusarium wilt were part of the assessment.
Effects on nematode populations
Ten different organic amendments were added to 3 different local soils in a glasshouse trial at the DPI&F South Johnstone research facility (Table 2.). Half of the plants were inoculated with burrowing nematode. Similar trials are being conducted for southeast Queensland soils.
Table 2. Amendments and soils used to assess effects of additives on nematode populations and banana growth.
Amendments used
Soil types used
MW Compost – composted green waste Biosolid – treated sewage by-product Grass hay Mill ash – 2 different rates Lucerne hay Mill mud Molasses Paunch material – gut contents from abattoir Banana trash Wollastonite – a calcium silicate product
Kraznozem (Mundoo series) – red clay Innisfail series – alluvial clay Coomb series – alluvial clay, poor internal structure and drainage
A summary of the results for burrowing nematodes is:
Disease suppression
Four amendments were able to suppress nematode numbers in the pot trial – grass hay, lucerne hay, mill mud, and banana trash (Figure 5.).
Plant growth
Three amendments were able to significantly increase the weight of roots of banana plants – mill ash at 120 t/ha, mill mud and banana trash.
Two amendments increased the stem and shoot weight of banana plants – mill mud and banana trash.
Soil biology
The addition of the amendments to the soil significantly changed the composition of the nematode community in the soil. The changes in nematode community structure affected the diversity of nematodes in the soil.
The structure index, a measure of the different layers in the soil food web, was increased in compost, grass hay, mill mud and banana trash treatments.
Soil interactions
A very significant finding is that there is an interaction between the different amendments and the different soil types. This means that the same amendment added to different soil types can have different effects.
Figure 5. Burrowing nematode (R. similis) recovered from the roots of banana plants grown in soil with different amendments.
The addition of some organic amendments suppressed burrowing nematodes, improved plant growth and changed the diversity of the soil microorganisms. Different soils can react differently to the same amendment.
Effects on Fusarium wilt populations
The same amendments were used in a pot trial investigating their ability to suppress the infection of bananas by the Fusarium wilt fungus. The summary of results is:
Wollastonite (calcium silicate) was the only amendment to suppress Fusarium in the glasshouse trial. This is being investigated further with another glasshouse trial currently under way.
Most amendments acted as a food source for the Fusarium to colonise, and then infect the banana plants.
What works in one situation does not necessarily work in another - amendments that suppressed burrowing nematode did not suppress Fusarium wilt.
One of the key soil management principles to encourage a healthy soil ecosystem is to develop a diversity of active root systems in the paddock. In the current banana production system vegetating the interrow area presents an opportunity to achieve this.
The aim of this part of the project is to identify low growing, shade and traffic tolerant plants, and then determine if these plants growing between banana rows can improve soil health, suppress soil borne diseases (burrowing nematode and Fusarium wilt) and reduce the movement of sediment. So far ten shade-tolerant plant species have been tested in glasshouse trials for their resistance to Fusarium wilt (Race 1 and 4) and plant parasitic nematodes (Radopholis similis and Pratylenchus goodeyi).
The most suitable species for interrow cover crops will then be tested in field trials in north Queensland for their ability to persist in the interrow, their effect on soil physical, chemical and biological characteristics, and their ability to suppress soil borne diseases.
Nematode resistance
The results so far are:
Grasses were mostly resistant to burrowing nematode, and the most suitable appear to be carpet grass (Axonopis affinis) and Bahia grass var. ‘Argentine’ (Paspalum notatum).
Most legumes are not resistant. The best performers in the trial, Pinto’s peanut (Arachis pintoi) and Butterfly pea (Clitoria ternatea), are still more susceptible than most of the grasses tested (Table 3 and 4)
Table 3. Resistance of potential interrow legume species to burrowing nematode
Variety
Nematodes recovered (100g of root)
% Resistance relative to banana (‘Williams’ Cavendish
Butterfly pea Pinto peanut Banana (‘Williams’) Shaw vigna Verano stylo Villomix Central bundy Wynn cassia
7 54 314 327 1235 1259 2542 3554
2 a 17 b 100 c 104 c 393 cd 401 cd 809 d 1131 d
Resistance ratings followed by the same letter are not significantly different at the 5 % level.
Table 4. Resistance of potential interrow grass species to burrowing nematode
Variety
Nematodes recovered (100g of root)
% Resistance relative to banana (‘Williams’ Cavendish
0.1 a 0.5 ab 0.5 ab 0.7 ab 0.8 ab 0.8 ab 0.9 b 1.3 b 1.9 b 100 c
Resistance ratings followed by the same letter are not significantly different at the 5 % level.
Fusarium resistance
The results so far are:
No pasture species was able to suppress the Fusarium wilt fungus.
Fusarium appears to be able to live on the roots of interrow pastures like a parasite. However, indications from the trial are that its ability to infect may be lost, highlighting a possible benefit of living roots over straight organic matter. This result is being investigated further.
Interrow cover crops reduce soil erosion and sediment movement in banana plantations. Grasses have the best resistance to burrowing nematode, but no cover crop was resistant to the Fusarium wilt fungus.
One of the major objectives for this project is to identify key indicators for the soil ecosystem that can be used to benchmark and monitor trends in the soil environment. A list of the most likely candidates for key soil indicators is presented in Table 5.
These soil indicators need to be validated and measured over time, and also related to farm management practices. Two levels of indicators are needed – one level for research purposes to understand soil ecosystem functioning, and a second level that are simple, practical tests that would be suitable for use by banana producers or consultants.
Table 5. Key soil indicators for assessing degradation of agricultural soils
Lack of suppressiveness Lack of biodiversity Size and quantity Crop sustainability
Labile carbon, disease incidence/population
Root weight, yields
We are currently testing and modifying a soil health testing kit from the US as a basis for the practical on-farm tests being developed.
The current list of tests is quite large and we hope to be able to focus in to a limited number of key indicators. However, the potential to develop a single test or indicator to cover all the aspects of soil health is not realistic. The soil environment is too complex to expect a single key soil indicator.
No single key indicator can accurately reflect the state of soil health. Regular monitoring over time with a number of key indicators will provide a better idea of changes in the soil ecosystem.
Fitting this into your farm
The major outcome for this project is to give the banana industry the tools and information with which to develop more sustainable use of its soil resources. To achieve this we are developing practical field tests that link to key indicators of soil health and can also be related to detailed laboratory tests.
So how can this help banana producers improve their soil health?
4.1 Monitoring – identifying which practices are best
Using the soil health tests to monitor changes in the key soil health indicators is the main application for banana producers. A system of regular monitoring allows banana producers to check if their soils are being degraded. Having monitoring tools also allows producers to compare the effects of different practices on the soil ecosystem, and from this to identify which practices have a positive effect on the soil environment.
4.2 Application to Environmental Management Systems (EMS)
An EMS is most simply described as any system that helps a business to continuously improve its environmental performance.
For any business that is aiming to improve the sustainable use of the soil environment then the development of the soil health testing kit for key soil indicators, and the identification of beneficial practices for soil health, can play an important role in the development of EMS for farm businesses.
The soil health tests and information being developed in this project will be suitable for use by a business to identify improved soil management practices, and to monitor their impact on the soil environment. As mentioned in the previous section, the ability to monitor and compare the impact of different practices allows a business to make changes and improvements over time. The ability to do this is at the heart of any EMS
The development of key soil health indicators allows any producer to improve the sustainable management of the soil. Monitoring and comparing the impact of different practices is essential for improvement to occur.
Home > Research > BRASH Project > Project Results
