On our last Wednesday Wisdom [we have since been interrupted by lockdown #2 and KC has been in Darjeeling] we pondered a number of key questions - one particularly peaked the readers interest :
Pondering 1 : Should the way soil is managed be more transparent to consumers? What impact would that have on our purchasing decisions?
I have long been interested in how we can bring soil, approaches to soil and the quality of the soil to the forefront on consumers minds - I would say I ponder it weekly - and I feel I am moving towards an answer - slowly! Returning to this pondering led KC and I to discuss - 'what checklist could apply to soil if we were looking to evaluate its health'. Of course says KC 'this is something that has to be felt not measured' - I could not agree with him more - for those working in tea the indicators of a healthy soil are sensual in nature rather than a list in a textbook. Todays Wednesday wisdom is therefore centred around the senses of smell, touch and sight. As we all live so far from the tea fields we thought it would be interesting to explore what these indicators may be - as your tea merchant we look for these on our tea trips
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When researching our book wonderful Sonia from Nuxalbari sent me a comprehensive list of answers to some questions I had and while this particular story did not make it into the final book it is a brilliant introduction to this first indicator :-
'Soil is fascinating. We know this as children, but lose our love for it as we grow older. My great grandfather, the Nawab of Jalpaiguri had a legendary nose for soil. There's an apocryphal story about the way he would choose planting areas. In the late 19th and early 20th c. there was no question of getting soil tests from those remote areas. He would smell the soil and know whether it was conducive or not. Apart from the humus, I guess he could tell acidic from alkaline soil, because the tea plant prefers acidic to alkaline' Sonia is an incredible woman who makes incredible tea : check out her first flush here
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Factor 1 : The Smell of Soil :
So what is it about the smell of soil? Well KC explains ‘A soil should smell good. If it has a bad or foul smell then this indicates the presence of pathogens' As the soil association say on their website : Get in your garden after a spring rain, dig up some soil and give it a big sniff. Can you smell an “earthy” distinctive and refreshing aroma? If you can, that’s good! It means that your soil is fertile and hosts an abundance of microorganisms' Maybe we will pause here to enable you to step outside and take a sniff.....
IF the soil smells good :
Well you you may be surprised to learn that it is not actually the 'soil' you are smelling. It is in fact the compound Geosmin [Geosmin is a colourless liquid, a member of a large family of Terpenoid oils. Terpenoids have aromatic characteristics, which means they give out a smell] This article gives a beautiful introduction so I'll quote directly from here and you can read more through this article and also here and here. I've chosen to share these words because this is more than just 'science' - this description evokes something deeper and shows the deep connection that exists between human and land - I encourage you to think about this yourself and I would place a bet that you have a memory of the smell of soil - let me know!
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[....]You speak like the very spirit of earth, imbued with a scent of freshly turned soil’ : The Hall of Fantasy by Nathaniel Hawthorne
‘And scent of earth, sweet with the evening rain…’ : All Round the Year by Edith and Saretta Nesbit
'Just what is the scent that inspires such celebratory descriptions? The chemical responsible has been given the name ‘geosmin’. In the last few decades we have learnt not only its molecular structure, but also its microbial and biochemical origins. It has turned out that geosmin must have perfumed the soil that first began to cover the land half a billion years ago, thanks to the activity of the earliest Streptomyces bacteria' [....]'
'[.....] By the time that geosmin was chemically characterised it was well established that its major source in soil was bacteria of the genus Streptomyces. These abundant and complex bacteria grow like fungal moulds as a mycelium of branching thread-like hyphae, playing a very important part in the recycling of vegetable matter. Echoing fungal moulds, they reproduce by sending up aerial hyphal branches that bear spores. Geosmin is associated with Streptomyces spores, which are present in huge numbers in many soils. We can safely assume that the time-traveller visiting the planet as it was about 440,000,000 years ago would recognise the familiar smell of soil, as the earliest land plants collaborated with the first streptomycetes to generate protocompost'
BUT WHAT IF the soil smells bad :
If you are still with us at this point of the journey then you will be aware that microbes in the soil are directly tied to nutrient recycling especially carbon, nitrogen, phosphorus and sulphur. Bacteria are a major class of microorganisms that keep soils healthy and productiveSo pretty important! They are gram-positive aerobic bacteria. Aerobic bacteria [most bacteria fit into this category] prefer well-oxygenated soils and use oxygen. to decompose most carbon compounds. As outlined here in contrast 'Anaerobic bacteria are generally found in compacted soil, deep inside soil particles (microsites), and hydric soils where oxygen is limiting. Many pathogenic bacteria prefer anaerobic soil conditions and are known to outcompete or kill off aerobic bacteria in the soil' This provides us with nice link to the questions of bad or 'rotten' smelling soil. Whats causing it?
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>> A smell of Sulphur or 'rotting eggs' : indicates that there is an anaerobic environment, operating without oxygen. This could be as a result of water logging [where water is taking the place of air] and/or compaction [where there is no space for air] As stated above this environment does not suit the 'good' bacteria that will enrich the soil but instead the the anaerobic microorganisms which produce hydrogen sulfide as a by-product and that's what you can smell.
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>> What about the smell of ammonia? This can be related to too much "green" material. 'Green' material is nitrogen rich so disrupts the carbon [which comes from organic matter] : nitrogen ratio and the result is that the soil will start giving off the excess nitrogen (N) in the form of ammonia (NH3). A healthy soil should roughly have twice the amount of carbon rich [organic] to nitrogen rich [green]
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Factor 2 : The Touch of Soil :.
These next two sections are linked to what we have described above and also to some of the previous blogs I have written as part of Wednesday Wisdom. Lets head back to our soil and take another handful - instead of taking a sniff this time lets 'touch' & look at its structure..
Soil should crumble easily in your hands : Crumbly soil is also referred to as Friable soil : soil that has the crumbly texture ideal for the underground activity that is the foundation of success with most plants. A Friable soil drains well, retaining enough moisture for plants to grow, and provides space for roots to grow and thrive. So as this paper outlines soil must have the correct friability as this is crucial for optimal plant growth. The following interesting information is from this paper also :-
>> Soil with an ideal friability will crumble of its own into suitable fragment sizes called aggregates. To maintain a good friability the soil has to contain sufficient organic matter
>> It can take a long time to restore a soil to good friability and it is something that must be worked on continually : a continual flow of organic material into the soil is necessary to stimulate biological activity,
>> Poor friability creates problems : if the soil is not very friable, it will quickly form a crust and be difficult to penetrate when it is dry, and will more readily become elastic – like modelling clay – when wet
>> If the farmer undertakes methods to loosen a soil with poor friability then even when loose the soil will have poor structural stability. This means that it will easily collapse and is very sensitive to compaction.
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When faced with problems in the soil it is not always straightforward to correct them. Let look at compact soils : compact soils prevent water from being appropriately used throughout the plant system and as this article references the care that must be taken in dealing with compact or waterlogged soils :
>> Simply tilling a compact will not help and can actually cause more damage : because it exposes organic material to air, speeding up mineralization and erosion. As previously reference working organic matter into the soil is a better method which allows roots to penetrate and the water to drain.
>> Working with wet soils is also not advisable. The article explains that this can destroy the structure, of the soil [how the individual particles of sand, silt, and clay are arranged] which can then actually increase compaction
From wider reading it is apparent that there is much modelling ongoing around the optimum friability of soil - organic matter is central : very simply ensure that the soil is regularly replenished with organic material, either in the form of animal manure, straw incorporation or the use of cover crops
So why share all this? Well, educating ourselves around the topic of soil and soil management changes the way we look at a tea farm or the questions we ask when travelling to source tea. And as soil is so important to tea from both an environmental and also 'profile' perspective we believe that a good amount of our time with our partners should be spent discussing this topic.
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Factor 3 : The Sight of Soil :.
Of course 'sight' can also be applied the the section above. You can observe the structure of a soil as well as touch it. The main subject we will look at as we refer to 'sight' is colour. What can the colour of the soil tell us? When we think about how we can bring soil to the forefront of consumers minds the colour of soil and determining what that means could present interesting possibilities for starting meaningful discussions. Lets start with the basics :- as this paper states 'Soil colour never lies'
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'Colour is a physical property of soils that allows us to know some of its most important characteristics, such as mineral composition, age and soil processes (chemical alteration, carbonate accumulation, the presence of humified organic matter, etc.). The presence of water in the soil profile during long periods of time also affects soil colour as a result of changes in the oxidation rate'
So the colour of soil reveals a lot if we take the time to look and notice. Before we dive in deeper it is important to highlight a couple of things : firstly soil is made of a number of layers referred to as 'horizons' - these 'horizons' combined form a soil profile. For the purposes of this blog we are going to refer to 'soil' colour but with an awareness that soil scientists are not looking at 'soil colour' in one block but rather at the colour of the soil 'horizons'. Secondly I want to remind us of organic matter in soil as we will refer to this 'soil organic matter is the fraction of the soil that consists of plant or animal tissue in various stages of breakdown (decomposition). Most of our productive agricultural soils have between 3 and 6% organic matter and soil organic matter contributes to soil productivity in many different ways'. In general a darker colour means the soil has organic matter in it
As outlined in this paper : Soil colour is related to soil processes, and is used as a diagnostic criteria for soil classification. The substances resulting from decomposition of the organic matter are oxidized and acquire a dark coloration...[....] some of these substances can be combined with mineral substances present in the soil as a consequence of mineralization of organic materials or chemical alteration of clays (such as iron oxides). After physical and chemical alterations, organic and inorganic materials contribute to soil colour in different ways and proportions and, as a result, colour is a product of co-working soil processes and environmental conditions.
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You will remember form one of our previous blog that we talked about the fact that 'organic soils contain much more humus' and it is this humus fraction that also contributes to the soils darkening. As outline in the statement above as well as the organic matter the presence of other minerals can also affect soil colour. The statement below is taken from the book wine science from the section that looks at site selection : there are many parallels between wine and tea making this a good overview as we ponder soil types in tea regions :-
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'Soil colour is influenced by the moisture content, mineral composition, and organic content. For example, soils high in calcium tend to be white, those high in iron are reddish, and those high in humus are dark brown to black. [.......] Soil colour is also a reflection of its age, and the temperature and moisture characteristics of the climate. Thus, cooler regions tend to have topsoils grayish to black, due to the accumulation of humus. In moist, warm regions, the soils tend to be more yellowish-brown to red, depending on the hydration of ferric oxide and extensive weathering of the parental mineral content. Rapid mineralization of the organic material in warm moist regions means that insufficient humus accumulates to influence soil colour : arid soils tend to be light in colour (little staining from the low-organic content) and primarily show the colour of its parental mineral content. In some soils, manganese oxidation may significantly stain the inorganic component of the soil'
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This book goes on to explain how addition to providing an indication of a soils moisture, mineral and organic content colour 'also influences the rate of soil warming in the spring and cooling in the fall' which of course also determine the microbial activity in the soil. As you can imagine there is a huge rabbit hole you can go down and a lifetime of learning : the text at the very bottom of this blog are from this paper and build on the above. They are perhaps a good entry point if you wish to know more and certainly will feature in future work from us around soils in the countries we travel to to find the teas we are proud to serve at Comins
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Until next time we hope you have have enjoyed this blog and [in a positive way] never smell, touch or look at soil in the same away again! I'd like to end with these two quote I found when researching this blog :
“Land, then, is not merely soil; it is a fountain of energy flowing through a circuit of soils, plants, and animals”. Aldo Leopold, A Sand County Almanac, 1949.
Soil…..”the Latin name for man, homo, derived from humus, the stuff of life in the soil.” Dr. Daniel Hillel
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The below is all taken from this paper
Dark or black : Dark colors are usually due to the presence of organic matter, so that the darker the surface horizon more organic matter content is assumed [At other times, the dark color is due to the presence of compounds of reduced iron and manganese (as in Vertisols, black poorly drained soils), the presence of charcoal in soils]
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Clear or white : Usually due to the presence of calcium and magnesium carbonates, gypsum or other more soluble salts.
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Red : usually a result of alteration of clay minerals [...] Weathered clay minerals release aluminium and iron oxides such as hematite (Fe2O3). [....] Reddish colours indicate good drainage and aeration of the soil
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Yellowish brown/orange : Yellowish or orange colours may be due to the presence of goethite, FeO(OH), and bound to the clay and organic matter. Therefore, although composition is similar to some red soils, we know that these soils were formed under conditions of increased moisture availability red soil
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Gleyic color pattern : The Russian word “gley” is used for mucky soil mass or clay. This color pattern is due to the presence of ferrous and ferric compounds. This property appears in soils or horizons that are waterlogged for at least one part of the year.
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Green : The green colour in the soil may be due to the presence of minerals such as glauconite, an iron potassium phyllosilicate mineral (mica group) or melanterite, a hydrated iron sulphate mineral.
