Soil Test: Baselining Soil Health

As a part of our initial phase of showcasing a profitable regenerative agriculture in three demo farms, we started by examining the soil health of each farm. The soil was sent to a soil testing laboratory so that we have baseline measures to compare by repeating the same test after a year.

However, it is not mandatory to do a lab test for soil to get started with regenerative farming practices. Many parameters such as the soil structure and pH can be measured by simple DIY tests such as the jar test and a litmus paper test. Overall soil health can be assessed by visually examining the soil and by finding out the recent history of the land use.

To learn more about soil, including simple tests and ways to improve your soil health, check out The Tropical Permaculture Guidebook’s Soil chapter (downloadable pdf).

The key to regenerative agriculture is a healthy soil via a closed loop system where all the biomass, crop residues and farm animal dung and urine go back to the soil as nutrients. This along with a good design that incorporates a biodiverse mix of crops, shrubs and trees with various functions will go a long way in stepping up soil health.

Having said all that, here is what the soil test of the six demo farms have revealed.

Soil pH

Soil pH level is the measure of acidity or alkalinity in the soil. A healthy soil should have a neutral pH level that is neither overtly acidic nor alkaline. If the soil is acidic, nutrients are easily leached out of the soil. On the other hand, if the soil is alkaline then nutrients get locked and are not easily available for the plants. Therefore, in both situations very few plants can grow and be healthy.

In a pH chart 7 is neutral. A healthy soil pH is in the range of 6 to 7.5.

Soil pH

The soil test results from the demo farms indicate an overall borderline high alkalinity.

To lower the pH we need to increase the organic matter (OM) in the soils. This can be achieved by adding dry leaves and crop residue to the soil and turning it in, growing green manure crops and incorporating it back into the soil, and heavy mulching of all crops. Over time, this will make the soil pH neutral, the soil itself visibly rich and supple, thereby allowing more nutrients to be readily available for the plants.

Moisture

Moisture is naturally retained in the soil in undisturbed places like a forest. The forest floor is always covered with fallen leaves and other plant residues. This makes the top soil rich in humus, visibly dark and crumbly, and a suitable cool environment for soil microorganisms and soil life to thrive. All these conditions will give a sponge like characteristic to the soil enabling it to absorb and retain moisture. Greater moisture retention means healthier plant growth, increase in groundwater levels, and less (soil, water and nutrient) erosion.

Moisture

All the demo farms were visibly bare and the soil was exposed. Therefore, the soil tests also showed an overall low moisture content.

The best way to retain moisture is to always keep the soil covered, either with live mulch (i.e. with something growing on it like ground cover crops such as sweet potato, even weeds, leguminous crops like velvet bean) or just about anything that covers the soil. Dry ground cover or mulch such as fallen leaves, crop residue also helps retain moisture by acting as a sponge.

Nitrogen

Vital for plant growth. A deficiency will mean pale leaves, not much new growth, early maturing and small sized fruit or flower.

Nitrogen

The soil test results from the farms reveal that one has soil that is richer in nitrogen (comparatively!) than the others.

We can increase or make available nitrogen in the soil by adding cow dung and urine, which we intend doing as a part of our soil rejuvenation method. We can also ensure we rotate or border crop nitrogen fixing plants such as legumes, and trees or fence plants like Gliricidia, and Vegetable Hummingbird Tree. We can also do some green manuring with nitrogen fixing crops like Indigo, Sun hemp and Legumes.

Phosphorus

Vital for good fruiting. Deficiency will lead to poor fruiting and small fruit size.

Phosphorus

The test results show some amounts of phosphorus present in the soils in varying amounts in different demo farms.

Bird manure and bone meal (powdered ground animal bones) are good sources of phosphorus. A natural system will ensure that there is a steady availability of phosphorus by attracting birds and animals whose excreta will contain phosphorus. On the other hand, a chemical farming system will deter many fauna and hence the need to add nutrients such as phosphorus externally in the form of laboratory made fertilisers.

Total Organic Carbon

Carbon is the measurable component of soil organic matter. Total Organic Carbon (TOC) in soil is the amount of carbon stored in soil organic matter. It comes into the soil through the process of decomposition of plant and animal residues, root excudates, and soil microorganisms. It constitutes a healthy top soil, important for the healthy growth of plant and soil microorganisms.

Organic Carbon has multiple advantages. It is the main source of energy for soil microorganisms. It makes nutrients easily available for the plants growing on it (nutrient mineralisation). It also gives top soil a sponge like structure (humus) that helps retain moisture and nutrients. Conversely, in chemical farming, higher application of synthetic fertilizers result in the disappearance of carbon residues in the soil.

Organic Carbon

A visual observation is enough to know whether there is enough organic matter — the top soil will be dark, crumbly and slightly moist. The soil tests reveal low organic matter content in all the soils. This is one area where we are hoping to have the maximum impact since it is such a critical component of an alive and healthy soil.

Organic Carbon in the soil can be improved by simply adding biomass to the soil and by always keeping the soil covered by mulching. Sweeping or clearing of dry fallen leaves should be avoided. Regenerative agricultural practices and the resultant OM and OC have the capacity to reduce temperatures and reverse climate change. It acts like a sink by taking the excess CO2 from the air and storing it in the soil as OM.

Other Soil Nutrients

Potassium: A deficiency will lead to small leaves, yellow leaves, slow plant growth. Ash can be added to the soil from kitchen fires and banana leaves and stems can be dropped back into the soil as mulch and biomass.

Magnesium: Deficiency leads to yellow leaves, brown spots on leaves, early leaf drop. Animal manures are a good source of magnesium.

Sulphur: A lack of it deters new shoots from developing properly and leaves become dull. Organic matter and animal manure will ensure a healthy sulphur content.

Other Micronutrients: There are several other soil micronutrients that are key for healthy plant growth. A full list is below.

Soil Test Results — All Parameters

The Foundation: Soil Health

Overall, we can maintain good soil health by incorporating carbon (dry leaves and crop residues) into the soil, keeping the soil covered always by mulching, not ploughing the soil too much, by adding back all crop residue into the soil and adding animal dung and urine from time to time. This will ensure a wholesome increase in all soil nutrients.

Soil health is the foundation of Krishi Janani’s objective which is to showcase profitable regenerative agriculture in smallholder farms. With this baseline in hand, we plan to conduct a test periodically (probably once a year) to identify what regenerative agriculture practices are doing to the soil. Stay tuned!