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From Dirt to Data: Scientific Method of Soil Sampling for Better Sustainable Farming

07 April 2025

What is Soil Composed Of?

Soil is a perfect blend of essential components that support plant growth. It consists of 45% minerals that form its structure, 25% water that hydrates plants, and 25% air that provides oxygen for roots and microbes. The remaining 5% of soil composition is organic matter, consisting of both living and non-living components; like soil- dwelling microbes, flora and fauna, decomposed plants and animals, as well as organic residues that enrich the soil with essential nutrients, improving its fertility and structure. This balanced composition ensures fertility, proper drainage, and a healthy environment for crops.

India’s soil diversity is as vast and rich as its culture! Alluvial soil in river plains sustains wheat and rice, while black soil in the Deccan is perfect for cotton. Red and yellow soils support millets, and laterite soil aids tea and coffee growth. Mountain soil nourishes fruits, while arid soil supports crops like millets and wheat. With this diversity, soil nutrition also varies, influencing the type of crops that thrive in each region.

Soil type and structure, including texture and compaction, affect nutrient movement and plant root access. Soil testing helps manage these factors to optimize nutrient availability and enhance soil health.

Why is Soil Testing Important?

  • Soil plays a vital role in plant growth and directly affects crop productivity. Since soil conditions vary, testing helps assess soil health and nutrient levels
  • A soil test determines the availability of essential nutrients, soil pH, organic matter content, and electrical conductivity. These insights help in recommending fertilizers, ensuring balanced nutrition for crops
  • Soil sampling increases farmers’ profit by decreasing unnecessary input costs while ensuring better returns on investment
  • It improves overall soil health by identifying and correcting nutrient imbalances, leading to long-term soil fertility
  • Soil testing helps farmers make smart, data-based decisions, leading to better crop management
  • Soil testing reduces environmental damage by preventing excess nutrient runoff

Soil Sampling

Soil sampling is crucial for effective soil testing and ensures accurate results. A precise sampling method is essential, as even advanced testing can't make up for poor practices. Proper soil testing reveals nutrient levels and soil health, helping farmers make informed decisions to improve crop yields.

Materials Required for soil sampling

Clean spade
Core sampler
Specially designed Multiplex sampling bags
Plastic tray or bucket
Permanent marker
A record sheet for data entry

Soil Sampling Depth Recommendations

When conducting soil sampling, it's essential to consider the root depth of the crops in question. For shallow-rooted crops, such as herbs and leafy greens, samples should be collected from the top 0-15 cm of soil, where these plants primarily absorb nutrients and water.

For deep-rooted crops like potatoes and corn, it's crucial to sample down to at least 30 cm, as these plants extend their roots deeper into the soil to access moisture and nutrients.

In the case of horticultural crops, sampling depth can vary significantly based on the specific root penetration of each plant species. It is advisable to assess the individual root structures to determine the most effective depths for sampling, ensuring accurate and representative soil analysis for optimal growth.

Frequency of Soil Sampling

  • Annually for Agricultural crops, high-value or sensitive crops, such as horticultural crops, greenhouses, and precision farming.
  • Soil sampling can be done 6 months after soil amendments
  • Soil sampling can be taken Immediately when visible signs of nutrient deficiency, poor plant growth, or pH imbalance.

Optimal Timing for Soil Sampling

  • The recommended period for soil sampling is from November to April.
  • It is advisable to conduct sampling 2 to 3 months prior to sowing or planting.
  • Soil sampling should take place following the harvest of crops.
  • The soil should be in a moist state, yet not excessively wet; ideally, sampling should be conducted during dry conditions, avoiding periods immediately after rainfall or irrigation.

When and where to avoid soil sampling?

Soil sampling should be avoided under the following circumstances:

  • Within nine months following the application of rock phosphate.
  • Within ninety days after the application of organic manure or phosphorus fertilizers.
  • Within thirty days after the application of nitrogen or potassium fertilizers.
  • Immediately following periods of heavy rainfall or irrigation or During wet conditions
  • In unusual areas, including but not limited to: road margins, undulating terrain, highly sloped lands, labor line sites, areas in proximity to cattle sheds, damp locations, and regions adjacent to shade trees, compost piles, bunds, and channels.
  • These precautions will help ensure the accuracy and reliability of soil sampling
Compost piles
Road margins
Bunds
Cattle shed

Procedure of soil sampling

  • Select a flat, undisturbed site in the field, at least 20 feet away from field borders. The starting point is one corner of the field, moving diagonally to the opposite end, then back in the other direction, forming a Z shape. Take 8-10 subsamples at evenly spaced points along the Z-line.
  • Scrape to remove litter, stones, plant residues, or any foreign material before sampling.
  • Use a spade to cut a V-shaped section and take a uniform slice from both sides of the cut.
  • Transfer the collected soil onto a plastic sheet/tarpaulin and mix it thoroughly. Follow the quartering technique.
  • The soil should be divided into four equal parts.
  • Two opposite quarters should be discarded, and the remaining two should be mixed again.
  • The process should be repeated until about 500 grams to 1 kg of soil is obtained.

Where Should You Get Your Soil Tested?

After sampling, the final sample should be placed in a specially designed Multiplex soil sampling bag. The sample bag should be labeled with essential details, including:

  • Farmer’s name
  • Farm location and survey number
  • Previous crop grown
  • Current and upcoming crop
  • Date of sampling
  • Sampler’s name

The best place for soil testing is Multiplex NABL Accredited Laboratory. NABL (National Accreditation Board for Testing and Calibration Laboratories) accreditation ensures that the testing process follows stringent quality standards, providing accurate and reliable results. Our state-of-the-art facility is equipped with advanced technology to deliver precise soil health assessments. After completing the soil sampling process, securely seal the bag and courier it to our Multiplex Soil Lab.

Why Choose Multiplex for Soil Testing?

At Multiplex, we provide a comprehensive soil analysis report that includes:

  • pH and Electrical Conductivity (EC) – Determines soil acidity/alkalinity and salt levels.
  • Organic Carbon (OC) – Indicates soil fertility and microbial activity.
  • Macronutrients (NPK - Nitrogen, Phosphorus, Potassium) – Essential for plant growth.
  • Secondary Nutrients (Calcium, Magnesium, Sulphur) – Helps in nutrient balance and soil structure.
  • Micronutrients (Iron, Manganese, Zinc, Copper, Boron, Chlorine) – Ensures optimal plant nutrition and prevents deficiencies.

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