The theme of the congress, which was held in Florence, Italy, was “100 Years of Soil Science – Past Achievements and Future Challenges”.
Are we in an era of “carbon mania”?
If you look up the word “mania”, the following description can be found: a mental disorder marked by periods of great excitement or euphoria, delusions and overactivity. In the last 10 years the word “carbon” has enjoyed preferential attention in terms of soil health among researchers and the media. However, the question is: is this just a trend, and what will be the outcome(s) of this trend?
The attention carbon is receiving is backed up by the fact that organic material is the key to healthy soil functioning, but the measurement methods which are commonly used, are still not calibrated with each other. Furthermore, the carbon goals and norms required to assess soil health, still have not been determined. In terms of knowledge transfer, the simplified term “soil-organic carbon” is often used, although it is a much more complex system as organic matter in soil comprises much more than carbon alone.
This year’s International Union of Soil Science (IUSS) centennial celebration and congress were attended by 1 436 guests from 73 countries. Additionally, 1 531 abstracts were accepted and 1 411 presentations were delivered during 82 parallel sessions over three days.
Johan de Jager at the IUSS, Florence, Italy.
During the first main theme, the focus was on global soil management and the effect of humankind on the productivity of soil, as soil is critical to the functioning of the planet. While there is presently a strong worldwide focus on climate change, a similar prioritising of soil has been left behind.
Humankind has had a destructive effect on soil – when the history of soil is considered, more damage has been inflicted than improvements made. This phenomenon is possibly a bigger issue than climate change, because soil security and climate change go hand in hand.
Soil must be placed at the front and centre of the earth’s sustainability. As suggested in Figure 1, soil has an enormous influence on water security, climate change, food security, energy security, human health, biodiversity, the ecosystem and the environment. To prove this statement, ask yourself the question: will soil still play a meaningful role in food production 100 years from now?
FIGURE 1. Global aspects influenced by soil security.
From the presentations which stretched over three days, I would like to highlight and share aspects of the following 10 studies:
Complete abstracts and references are available via the following link: https://drive.google.com/file/d/1mcbITzR1wfY1b4vLAaceHAyg_y_K3vzq/view.
1. Is the organic carbon-to-clay ratio a reliable indicator of soil health?
In the European Union, a proposed soil monitoring law is being implemented to measure soil-carbon losses as an indicator of soil health. The observation points are set out by the LUCAS soil survey in combination with other data sets like soil classes, climate zones and archive carbon data. It was found that when the organic carbon-to-clay ratio is <1:13, it cannot be used successfully as a single indicator to measure soil health.
2. Long-term effects of compost on soil health and yield of winter wheat in a semi-arid environment in Logan, VSA
This long-term study evaluated the long-term effect of a one-time, broadcast large-amount compost application. In 1994, 50 tonnes/ha of compost (consisting of cattle manure and straw) was applied once on an organic wheat farm with sandy soil. The biggest benefit was obtained from the plant-available phosphorus and nitrogen. Carbon content and aggregate stability also improved. Although the rainfall decreased drastically over the past 30 years due to climate change, the yield is still 38% higher. This increase in yield can be attributed to the increase in carbon and increased nutrient availability, as well as improved soil respiration due to microbial change, soil temperature and soil moisture.
3. Inter-laboratory proficiency tests and the reliability of soil laboratory measurements worldwide: the case of GLOSALAN
“Carbon credits” is a buzz term which has been widely used of late, but there is still uncertainty around the accuracy and type of analyses of laboratories worldwide, especially those in developing countries.
In order to monitor the accuracy of soil laboratories worldwide, the Global Soil Laboratory Network (GLOSOLAN) was established in 2017, which forms part of the United Nations’ Food and Agriculture Organisation. This organisation sends the same replicas of soil samples to laboratories and evaluates the results using a Z-score which is determined by a standard deviation, and also offers the laboratory assistance to improve its accuracy. This initiative lends more credibility to carbon credits and helps to set up the use thereof in the industry.
4. A framework for the establishment of soil health targets and threshold values
Soil health is a key effort to reverse soil degradation, but it has to be quantifiable in some way. To determine these targets and threshold values, the soil type, climate, land-use, management, history and other factors must be considered, standardised and then developed into a policy.
Through consultation with stakeholders and considering the available knowledge and theory, the following was determined as a possible framework for the formulation of targets and threshold values:
- Fixed values based on research: certain soils should have certain values.
- Fixed proportions of natural reference values: everyone should choose their own value.
- Values based on the existing ranges: the problem with this approach, is how do you quantify agricultural soil against veld or new soil?
This information can be used to develop a framework for the most suitable target or threshold values for the wine industry.
5. Cover cropping for soil health: does diversity matter? A case study in Reading, UK
Organic matter supports soil health. To accumulate organic material, it is necessary to place organic additions into the soil like animal manure, compost, cover crops, crop residues and root exudates. These additions offer several benefits, like improved water and nutrient retention, soil structure, aggregate stability, microbial biomass and water infiltration.
To establish soil health, the following five principles can be followed:
- Limit disturbance and cover the soil surface.
- Keep living roots in the soil.
- Bring animals into the system.
- Build diversity into the system.
Not all organic matter is the same. Raw organic matter promotes nutrient mineralisation and water retention. Organic matter protects the aggregates and helps with soil structure and aggregate stability. Mineral-associated organic matter assists with the retention of nutrients and carbon storage.
Establishing cover crops is one way to bring organic matter and diversity into the system. In this study, monoculture crops were compared to a mixture of the same combination of monoculture, including sunflower, radish, clover and buckwheat.
After three years there was no difference in soil carbon for mixtures compared to that of the monoculture. Where residues of the mixture were spread or placed on the soil surface, it led to greater microbial assimilation of carbon and mineral-associated carbon. It was also observed that the chemical (sorption) and physical (aggregate) properties of the soil protected the stable carbon (dead microbe network).
6. Seasonality and sensitivity to land use are critical factors for soil health assessment in a Mediterranean climate
A study from a Mediterranean climate in Israel found that environmental factors pose major scientific challenges and in summary showed that, when crops experience stress, it is the ideal time to test for soil health.
7. Spatial patterns of historical crop yields reveal soil health attributes in US Midwest fields
This research shows that yield stability maps provide valuable insights about soil-organic carbon and soil health. Yield maps were used over consecutive seasons to divide blocks into four sections, namely unstable, low to stable, medium to stable and high to stable. Composite samples were taken and each zone was analysed with the use of the Solvita soil health test.
The outcome of the research shows that the differences in yield were influenced by the climate, topography and soil. There was also a direct correlation between higher soil-organic carbon and soil health matrixes in statistically separate regions. The unstable and low-to-stable areas had compact soil layers or shallow soil on steep slopes.
8. SoilBio analysis: a sensitive, calibrated and simple assessment of soil health for Brazil
This study was performed in the Cerrado region in Brazil across approximately 200 million hectares. In line with worldwide concern over soil health, Brazil adopted the SoilBio analysis in July 2020. Together with routine soil samples, two key enzymes are also analysed, namely arylsulfatase and beta-glucosidase.
These analyses can be collected on farm level and have three functions:
- Nutrient cycling (arylsulfatase and beta-glucosidase).
- Nutrient storage (organic matter and CEC).
- Nutrient supply (routine soil analyses).
With 20 years of research data on arylsulfatase and beta-glucosidase, it was observed that these enzymes play a role in soil function and show a correlation with other microbial indicators for soil health. The analyses, which are accurate, consistent and affordable (USD35 per sample), can also be performed on soil which has been air-dried. The protocol is the same as for the routine soil analyses.
The concept is that soil with high arylsulfatase and beta-glucosidase activity stores more water, has a lower phytonematode population, shows better nutrient absorption, as well as fruit quality, and has a higher potential for bioremediation.
9. Isolating the effects of soil-physical properties on fruit composition: a case study in Maryland, USA
This study was performed on Albarino Clone 1 grafted onto 101-14 Mgt which was planted in 2013. The only variation in the block was the topsoil depth, which varied between 0 to 38 cm. The vineyard management was also adjusted to create a balance between the vegetative growth of shallower and deeper soils.
The remarks were as follows (see Figure 2):
- The colour of the juice far left is that of bunches which grew on deeper topsoils, and on the right clusters which grew on thinner topsoil.
- The deeper topsoil produced denser bunches and higher titratable acidity.
- The thinner topsoil produced looser bunches and lower titratable acidity.
- Grapes grown on the thinner topsoil made a better quality wine.
When vineyards are in balance, the titratable acidity and cluster density are more closely correlated to soil differences than to fruit exposure and crop load.
FIGURE 2. Differences in the colour of grape juice correspond with differences in topsoil depth.
10. The effects of soil aeration in combination with a biostimulant in the Tokaj wine region, Hungary
This study was performed to determine the effect of soil aeration with a hydraulic hammer next to the grapevines, after which they were treated with Trichoderma (2 L/ha). The results showed that the leaf area, cane length and cane weight increased. Trichoderma colonised the roots, and this was verified by a serological test. Trunk diseases were also controlled more effectively.
Summary
Soil health refers to the ability of a specific soil to maintain productivity, diversity and the environmental services of a specific ecosystem. Soil health is a key concept in the global effort to reverse soil degradation, but it also serves as an instrument to improve soil and hence must be defined on a policy level and be quantifiable in some way. Soil health is more than just organic carbon and the distribution of microbes in the soil. It also involves the impact of humankind on the soil. When soil is managed in such a way that it can productively maintain the crop established on it, without negatively impacting soil degradation and natural resources, and the soil is regularly monitored, then we are a step closer to protecting soil (and thus also establishing soil health).
The greatest challenge for South African agriculture in general and specifically the wine industry, is to reach a consensus on the indicators for soil health in our context, as well as standardisation of norms and the measurement thereof, following which policy can be formalised for standard application and measurement. The conference was interesting and decisive, an opportunity for me personally to delve deeper into research on soil science, and specifically also soil science from a global perspective.
For more information, contact Johan de Jager at johan@vinpro.co.za.
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