The Stars in Our Soil: The Science Behind Soil Testing
Having acquired some basic understanding of soil health in our first article, Understanding Soil, we will now delve into the science behind soil testing.
In the lush fields of rural Zambia, a dedicated farmer named Choolwe noticed his once-thriving crops were wilting. He heard about soil testing, a method to analyze soil’s nutrient content and pH levels, and decided to give it a try. Choolwe collected samples and sent them to a lab. The results revealed his soil was deficient in nitrogen and too acidic. Armed with this knowledge, Choolwe applied the right fertilizers and amendments. Gradually, his crops flourished again, turning his farm into a green oasis. Soil testing didn’t just save his harvests; it empowered Choolwe to cultivate healthier, more productive land, securing a brighter future for his family and community.
Soil testing in agriculture is a process of analyzing soil samples to determine their nutrient content, pH levels, and other vital characteristics with a view to identifying nutrient deficiencies or excesses, ensuring proper soil pH balance, and detecting contaminants. This knowledge allows farmers to make informed decisions on fertilization, crop selection, and soil management, ultimately leading to healthier crops and higher yields. The process of soil testing involves collecting soil samples, sending them to a lab (mobile or station) for analysis, interpreting the results, and applying the recommended amendments and fertilizers.
Soil testing equipment ranges from basic tools to sophisticated devices used at research stations and higher learning institutions. Basic tools may include vinegar and baking soda found at home, soil augers and probes for collecting samples, and simple pH meters for measuring soil acidity. More advanced equipment comprises soil sieves and hydrometers for particle size analysis, and compaction testers - like the Proctor compaction apparatus - to determine optimal moisture content for soil compaction. At research stations, sophisticated devices such as triaxial shear strength testers, consolidation test apparatus, and California Bearing Ratio (CBR) equipment provide comprehensive analysis of soil properties. Additionally, the Krishi Rastaa mobile tester, a portable device using IoT technology, can conduct 12 key soil parameter tests and provide results directly to farmers' mobile devices in just 30 minutes. These tools help researchers and farmers understand soil health, leading to better crop management and the adoption of sustainable agricultural practices.
Some characteristics can be examined physically on one's farm, all soil health enthusiasts and soil managers must have this basic knowledge at their fingertips.
Have a look at the examples below:
Soil Texture
Query: Is soil loamy, sandy, silt or clay?
Equipment: Water, soil sample
Method: Ribbon test
Process: Moisten the soil and try to form a ribbon by squeezing it; the ease with which it forms can indicate its texture.
Interpretation: If the soil sample does not form any ribbon, the texture of your soil sample is sandy. The more clay there is in your sample, the longer your ribbon will last.
Some Possible Interventions:
Sandy: minimum tillage, retaining crop residues, zero burning
Clay: encourage earthworms, raised beds, add organic matter
Loamy: crop rotation, hedgerows, cover crops or green manures
Reference: https://www.youtube.com/watch?v=fufeaLBLGlk
Porosity
Query: How much space is between soil particles?
Equipment: Good eyesight, water, timer, soil sample
Method: Percolation test
Process: Observe how quickly water drains out of a soil sample
Interpretation: A quick drain indicates ease of water and air movement
Some Possible Interventions: Maximum protective cover, incorporate compost, minimize water stress
Reference: https://www.youtube.com/watch?v=5nLOLEgJd3A
Soil pH
Query: Is the soil acidic or alkaline?
Equipment: Baking soda, vinegar, distilled water, bowl, soil samples.
Method: Baking soda and vinegar Test
Process: Mix two tablespoons of soil with distilled water in a bowl then add half a cup of baking soda or half a cup of vinegar.
Interpretation: If the mixture fizzes, the soil is acidic, if not, the soil is neutral.
Some Possible Interventions:
Acidic soil can be neutralised by adding agricultural lime or ash.
Alkaline soil can be neutralised by adding sulphur-based materials.
Soil Colour
Query: How much soil organic matter can be found in soil of this colour? What are its drainage conditions?
Equipment: Munsell colour chart
Method: Comparison of soil sample to munsell chart
Process: Collect soil sample, compare it to it's equivalent on munsell chart, read about the soil type and interventions to keep it healthy
Interpretation: Common soil colours include brown, which indicates the presence of dead and living organisms; red, often due to iron oxides; yellow, which can indicate the presence of hydrated iron oxides; black, rich in dead and living microorganisms and often found in fertile soils; and gray or white, which may indicate poor drainage or the presence of salts. More details are here!
Some Possible Interventions:
Pale brown/yellow: Mulch/ add organic matter
Red: Use manure and lime as fertilizer and conditioner respectively
Black: Multi-cropping, shelter forests, conservation tillage
White or gray: Religiously follow a recommended fertilisation plan, physical replacement or removal
A Munsell Colour Chart in action
These tests help manage soil health, ensuring optimal conditions for plant growth and sustainable farming. However, soil managers must endeavour to engage experts and extension service providers in order to receive comprehensive support in determining results and reinforcing recommendations for the health of their soil. There must be deliberate efforts to foster the smooth sharing of information between professionals, entrepreneurs and farmers among other stakeholders regarding soil health and its relevance for climate resilience and agriculture productivity.
Soil Health is “the ability of the soil to sustain the productivity, diversity, and environmental services of terrestrial ecosystems” (IPTS, 2020). This includes maintaining its structure, nutrient cycling, biodiversity, and water regulation. Healthy soil supports robust plant growth, resists erosion, retains water, and filters pollutants, making it essential for sustainable agriculture and environmental balance.
Source: Pittaki, Ateku, Weullow, Winowiecki (2024) Available at: https://www.fao.org/global-soil-partnership/resources/events/detail/en/c/1679538/
This definition weighs in on the needs of soil that we ought to pay attention to in order for soil to function to the best of its ability for the benefit of the greater ecosystem. Soil testing must therefore be prioritised in order for those particular soil needs to be met. A soil sample should be taken for comprehensive analysis at least once every 3 years, when there is a change in crops to be grown or if a problem occurs during the growing season. Some of these problems include; dying or struggling plants, poor root development, poor drainage, foul odour, mold growth and pest infestation. Other signs that your soil needs to be tested include the absence of worms and other microorganisms in soil, the absence of birds and animals that flocked the area previously, and plants’ performance on that land.
There are several soil testing initiatives that have achieved great strides in promoting soil health among farmers.
In Zambia, The Ntaka Hyperlocal Soil Analysis and Advisory Services established in 2018 sought to make soil testing and advisory services affordable, accessible and relevant to small-scale farmers in Zambia. They used state-of-the-art analytical equipment to provide a technology platform and training that enabled local micro-entrepreneurs to deliver soil analysis and decision-making services to their community and networks.
The services achieved much in a short time by measuring over 17000 soil properties within 6 months of operations, creating jobs for professionals and income-generating activities for entrepreneurs. The recommendations for this operation translated into reduced cost of expensive agriculture inputs, increased yields of cereal, legume, vegetable and fodder crops, improved long-term sustainability of farmers' fields and identified valuable local crop varieties that would thrive in particular soils to combat household malnutrition.
A more recent initiative was by the lndaba Agricultural Policy Research Institute (IAPRI). IAPRI held a national launch of a knowledge-sharing and awareness-raising campaign dubbed “Farmer Know Your Soil: The Path Towards Increased Productivity and Profitability” on August 29, 2023. The main objective of the campaign is to share best practices in soil management with smallholder farmers in order to improve crop productivity and farm profitability. This is motivated by the realization that the foundation for efficient fertilizer use is determining the status of the soil and its needs.
Soil managers can maintain soil health by applying sustainable agriculture practices such as crop rotation, cover cropping, green manuring, adding organic matter, ensuring efficient use of fertilizers, maximizing biodiversity and practicing agroforestry among others. Soil managers must also endeavour to test their soil, not just for NPK but for microbial activity and micronutrients. Having this knowledge offers great insight into the nutrient-cycling capacities of one's soil. Tracking that throughout a cropping season gives valuable information on practices to prioritise in order to improve soil and crop health.
The science behind soil testing presents a lot of opportunities for young professionals, students and entrepreneurs with regard to green jobs. Those interested in agriculture but don't know where to start can look further into this array of the agri-food system and become a champion for soil health through their work while earning a living. In China, black soil is so important that there is a law to protect it, that's the level of importance and opportunity with which we must regard our soils.
Have you ever benefited from the benefits of soil analysis recommendations?
What are the barriers to soil testing around you?
After this article, we hope to have more people enjoy the benefits of soil testing like Choolwe did in the introduction of this article.
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About the Author
Sussana Phiri is an alumnus of the Global Change Makers School, where she pursued Project Management for Change Makers (2020). She is also an alumnus of the Global Leadership Fellows Programme (GLFP ‘19), which focuses on imparting Strategic Management and Science Communication skills. Her most recent achievement is becoming the Young Professionals in Agriculture Development (YPARD) Zambia country representative.
Sussana carries a wealth of experience in fostering meaningful youth engagements in youth-led projects and women-focused interventions as a developer and project lead of the Future Fields and Orange Fleshed Sweet Potato Projects respectively. She is a certified aquaculture and fish farming professional and holds a certificate in agriculture mechanics and machinery. She possesses a Bachelor’s Degree in Education and is currently studying for a Master of Education in Curriculum Studies from the University of Zambia. Most recently, she acquired a Diploma in Agroecology from the Kasisi Agricultural Training Centre.
Sussana has developed and implemented assignments with partners such as the Zambia Youth Environmental Network, Women Who Farm Africa, Zambia Agriculture Research Institute, Access Agriculture, CAADP Youth Network, Grand Challenges Canada, Chedic Associates, Ministry of Health- Mother and Child Health Department and the Chilanga District Agriculture Department.
Sussana is currently working with CA4SH as a Communications and Coordination intern through CIFOR-ICRAF, and is a member of the #Youth4Soil Initiative. The Stars in Our Soil is a 6-part series highlighting the scientific and social elements of the soil that are synonymous with the stars; each of them unique but when they are together, they light up the universe.
