Whether it is farmland or a garden, the most important thing for crops to grow and bloom beautifully is soil. Knowing our soil conditions can better help us decide what kind of plants to grow. Treating the soil is important not only for agricultural production but also for successful gardening. Check soil fertility to guide you in preparing and maintaining garden beds.
What is soil fertility and why does it matter?
Soil fertility is a soil’s capacity to support plant growth by providing essential nutrients, moisture, and air in a favorable physical, chemical, and biological environment. Fertile soil supplies essential macro- and micronutrients that keep crops strong throughout their development.
Mineral nutrients are not food for plants—plants create their own food through photosynthesis. Instead, these nutrients act as supplements. They boost growth, improve resistance to pests and diseases, and increase crop yields.
A fertile soil holds and delivers nutrients efficiently, supporting healthy roots and steady development. For farmers, soil fertility is one of the first priorities when planning fieldwork, because it directly affects productivity and long-term sustainability.
Components of soil fertility
1. Physical fertility
This is the “framework” of the soil, which determines the storage and circulation of water and air.
Soil texture: Refers to the relative proportion of sand, silt, and clay particles. It influences aeration, water retention, and nutrient-holding capacity. For example, clay soil has strong water and nutrient retention but poor aeration, while sandy soil is the opposite.
Soil structure: Describes how soil particles are arranged and aggregated into clumps (aggregates). A well-developed granular structure—such as those formed by earthworm casts—is a hallmark of fertile soil. It ensures that roots can access both water and sufficient oxygen.
Porosity: The proportion of pore spaces in the soil, which determines its capacity to hold water and air.
2. Chemical fertility
This is the soil’s “nutrient reservoir,” which supplies plants with essential elements.
Soil pH: Directly affects the availability of nutrients. Most plants thrive in slightly acidic to neutral soils with a pH of 6.0–7.5. Excessive acidity or alkalinity can “lock” nutrients, making them unavailable for plant uptake.
Cation exchange capacity (CEC): An important indicator of the soil’s ability to adsorb and exchange cationic nutrients such as calcium, magnesium, and potassium. The higher the CEC, the greater the soil’s capacity to retain nutrients—like a “temporary storage bank.”
Nutrient Content:
- Macronutrients: Nitrogen (N), Phosphorus (P), Potassium (K).
- Secondary nutrients: Calcium (Ca), Magnesium (Mg), Sulfur (S).
- Micronutrients: Iron (Fe), Manganese (Mn), Copper (Cu), Zinc (Zn), Boron (B), Molybdenum (Mo), and others.
Soil organic matter (SOM): The core of soil fertility. SOM improves soil structure, enhances water and nutrient retention, provides energy for microorganisms, and releases nutrients gradually over time.
3. Biological fertility
This represents the “living activity” of the soil and serves as the bridge between physical and chemical fertility.
Soil microorganisms: Bacteria, fungi, actinomycetes, and others act as “conversion factories.” They decompose plant and animal residues, transform organic matter into inorganic nutrients that plants can absorb (mineralization), and play key roles in nutrient cycles such as the nitrogen cycle.
Soil fauna: Earthworms, nematodes, protozoa, and more. Earthworms in particular improve soil structure, enhance aeration and water infiltration through their burrowing, and their casts provide high-quality organic fertilizer.
Biodiversity: A healthy and diverse soil community suppresses harmful pathogens, strengthens ecosystem stability, and improves resilience against environmental stresses.
How to judge soil fertility?
Physical status
- The depth of soil color is positively correlated with humus content; fertile soils usually appear dark brown to black.
- A cultivated layer thicker than 60 cm is a characteristic of high fertility.
- A loose, well-aerated granular structure keeps infiltration speed at 5–8 cm per minute.
- After irrigation, the formation of fine, spider-web-like cracks on the surface is a sign of good soil quality.
Chemical characteristics
- An organic matter content of more than 3% can form a stable aggregate structure.
- Cation exchange capacity reflects the soil’s ability to retain nutrients.
- A pH range of 6.5–7.5 provides optimal nutrient availability.
- Available nitrogen, phosphorus, and potassium should be maintained above 120 mg/kg, 15 mg/kg, and 100 mg/kg, respectively.
Biological activity
- More than 10 earthworms per cubic meter of soil indicates high fertility.
- Actinomycetes accounting for more than 50% of the microbial community reflects strong fertility.
- Weed communities dominated by fertility-loving plants such as Amaranthus retroflexus and Chloris virgata are indicators of fertile soil.
How to measure soil fertility?
1. Experimental detection method
Sampling soils in different regions, and then measuring the soil nitrogen, phosphorus, potassium, and moisture content through experiments. Generally, a sampling shovel is used to collect multiple soil samples in the same field (specifically, grid dot method, plum blossom dot method, serpentine dot method, random sampling method, etc.), and soil of 1-20 cm can be collected in the tillage layer and loaded separately In a self-sealing plastic bag, bring it back to the laboratory for air drying, grinding, sieving, and then mixing evenly to determine its content. Nitrogen is determined by the Kjeldahl method, phosphorus is determined by the molybdenum antimony colorimetric method, and potassium is determined by flame photometry. And measure the soil moisture content by weighing method.
This detection method is usually suitable for researchers. For gardeners, this measurement method is not only time-consuming but also costly. This measurement process is cumbersome. If your garden is large, you need to sample from multiple locations, and you cannot obtain data in real-time. If you need to measure soil fertility frequently, this method is undesirable.
There are various soil sensors on the market, such as soil moisture sensor, soil NPK sensor, soil pH sensor, and so on. After the sensor is installed, insert the detection end into the soil and log on to the platform to get the reading. This measurement method is simpler and more convenient than the first one, but the current sensor brands in the market are uneven, which will test your professionalism very much.
With 15 years of dedicated R&D and manufacturing experience, Renke stands out in the field of soil monitoring. Its soil sensors are not only diverse in types but also highly accurate and cost-effective. The product range includes single-parameter devices(such as soil water potential sensor, multi-depth soil moisture sensor and soil heat flux plate), soil analyzer, as well as integrated 4 in 1 sensors that measure soil temperature, moisture, pH, and conductivity. These solutions enable users to easily monitor critical parameters such as soil moisture, nutrients, and acidity.
3. Soil nutrient testing equipment
Soil nutrient testing equipment is a device that uses the principle of photoelectric colorimetry to measure soil nutrients. When a certain extractant is used to extract soil, fertilizer, or crop plants, effective nutrients enter the solution, and the nutrients in the solution can react with the specific color developer to generate colored substances to make the solution appear color. The depth of the color of the solution is related to the nutrients. The content is positively correlated and obeys Lambert-Beer law. That is E = K×C×L where E: extinction degree, K: extinction coefficient, C: solution concentration, L: solution thickness.
The soil nutrient testing equipment is a portable instrument for quickly testing soil nutrients. However, the accuracy and precision of soil nutrient test results are difficult to guarantee. Secondly, the result of the soil nutrient test is a relative value. It is necessary to have a matching fertilizer field test to establish a recommended fertilization index system. At present, most soil nutrient testing equipment has not yet established a complete recommended fertilization index.
4. Professional agency testing
At present, there are many professional testing agencies on the market that provide soil fertility testing services. You can provide your soil samples to the testing agencies and pay a certain fee, and then you can get the test results of the soil samples. This detection method is suitable for accurate measurement of soil fertility in a small area and is not suitable for long-term or large-scale soil fertility detection.
How to improve soil fertility?
1. Apply organic fertilizer
Organic fertilizer is the first choice for increasing soil fertility, including animal manure and green manure. For example, cow manure is rich in nitrogen, phosphorus, potassium, and organic matter, which can significantly enhance the soil’s water and nutrient retention capacity. It should be fully decomposed before use (generally composted for 3–6 months) to avoid root burn and the spread of pests and diseases. Studies show that farmland receiving organic fertilizer continuously for three years can increase soil organic matter content by 0.5%–1% and enhance microbial activity by over 30%.
2. Return crop residues to the field
After being shredded, plant residues are directly incorporated into the soil (to a depth of 20–30 cm), which not only supplies nutrients but also improves soil aeration. For example, adding rice straw to the soil can increase potassium content by approximately 120 kg per hectare.
3. Add microbial agents
Beneficial microbial inoculants, such as Bacillus subtilis and rhizobia, can decompose organic matter and suppress soil-borne diseases. They should be applied avoiding periods of strong sunlight and high temperatures, and are more effective when used together with organic fertilizers. Trials have shown that combining microbial inoculants with humic acid can increase potato yield by 15%–20% and reduce the incidence of scab disease by 50%.
4. Supplement mineral fertilizers
For nutrient-deficient soils, phosphate rock (to supply phosphorus), potassium feldspar (to supply potassium), or silicate-calcium fertilizers can be added. Silicon fertilizers can enhance rice lodging resistance, increasing stem silicon content by 20%–40%. Fertilizer application should be based on soil testing to ensure proper ratios and avoid blind application.
5. Biochar amendment
Biochar produced from crop residues or nutshells through high-temperature pyrolysis has well-developed pores and strong stability. Applying 15–30 tons per hectare can increase soil cation exchange capacity (CEC) by 10%–15% and improve heavy metal adsorption by 30%–50%.
