How Soil Fertility is Reduced & Possible Solutions

Soil fertility is the ability of the soil to supply essential and adequate nutrients required for plant growth. It is one of the most important factors in agriculture and food production. A soil is said to be fertile if there is an adequate amount of nutrients and at the required proportions.

Fertile soil provides essential nutrients, moisture, and structure to enable plants to grow and yield effectively. Maintaining optimal soil fertility is crucial for meeting global food security needs. Read on to understand ways soil loses nutrients and how soil fertility can be maintained and revived.

soil fertility

How Soil Fertility is Reduced

Soil fertility can be reduced by several factors that degrade the soil and deprive it of nutrients needed for plant growth:

1. Plant removal

A plant feeds directly from the soil through absorbing the nutrients with its roots, these nutrients are what the crop uses to support its vegetative and reproductive activities.

The amount of yield obtained from the plant is directly proportional to the nutrients the plant absorbed or removed from the soil. Grains like maize, absorb more nitrogen than other crops, forage crops like vegetables, coffee, sugarcane, root crops, and fiber crops like cotton, kenaf, etc. absorb a large amount of potassium.

If any grain crop is planted, the amount of nitrogen present in the soil will be reduced by virtue of the affinity grain crops have for nitrogen. Same as forage crops reduce the potassium content of the soil. This is one of the ways soil loses its fertility.

2. Soil erosion

Soil erosion is the washing away of the most fertile part of the soil (the topsoil). It houses more nutrients than the other parts of the soil, if it is not protected by crop cover, it may be slowly washed away by surface runoff. The loss of the topsoil represents high losses of organic matter, minerals solids, and plant nutrients.

Ways to avoid this include: 

  • Planting of cover crops, like cowpea, and pumpkin leaf(Ugwu).
  • Practicing crop rotations. 
  • Terracing.

3. Leaching

Leaching is the process by which soil nutrients are washed down by water from the root zone to the underground water. This is common in the tropics where rainfall is common, it also makes the soil acidic. Leaching can be minimized through:

  • Timely addition of organic manure.
  • Proper timing and placement of fertilizer.

4. Acidification

Acidification is the lowering of soil pH through the accumulation of hydrogen ions. It can result from the use of acid-forming fertilizers, oxidation of sulfur and nitrogen compounds, or leaching of basic cations. Acidic conditions make it difficult for plants to absorb nutrients.

5. Salinization

This is the accumulation of soluble salts like sodium, calcium, magnesium, and chlorides in soil. It most often occurs through improper irrigation practices that deposit salts on the surface or cause a rising water table. High salinity interferes with plants’ ability to take up water.

6. Pollution

Soil pollution from industrial activities, urban runoff, mining, and excessive pesticide use introduces harmful compounds like heavy metals, hydrocarbons, and toxic chemicals. These can directly damage plants or reduce fertility by degrading soil structure and microbiology.

Effects of Reduced Soil Fertility

  • Lower soil fertility leads to lower crop yields.
  • Plants are unable to thrive and produce their maximum potential yields.
  • Farmers may see harvests drop by 25-50% or more compared to fertile soils.
  • Fertilizers are also costly and cut into farm profits.
  • Reduced fertility negatively impacts crop quality. Nutrient deficiencies show up as stunted growth and poor vegetable or fruit quality.
  • Low fertility soils are more prone to erosion from wind and rain.
  • Lack of soil biology also reduces the soil’s natural ability to break down wastes and cycle nutrients.

Testing and Assessing Soil Fertility

Understanding the nutrient levels and composition of your soil is crucial for effective fertility management. There are several methods for testing and analyzing soil fertility:

Soil Testing Methods

– Lab testing: The most accurate way to test soil is to collect samples and send them to a lab for analysis. The lab will measure pH and nutrient levels like nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur and can provide specific recommendations.

– At-home soil test kits: These provide a more affordable, though less accurate, way to test your soil. The soil test kits measure pH and primary macronutrients. Follow kit instructions carefully for collecting samples and interpreting results.

– On-site quick tests: Simple on-site tests can check pH and nitrogen levels. These include litmus paper for pH and at-home titration kits for nitrogen. They provide general guidance but are less precise than lab tests.

Related: 3 Ways To Test Soil pH Without Using The Soil Test Kit

Macronutrients vs Micronutrients

Plants require both macronutrients and micronutrients from the soil.

Macronutrients are needed in larger quantities and include nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S). Deficiencies in these will greatly impact plant growth.

Micronutrients are essential nutrients required in minute quantity. Micronutrients are boron, chlorine, copper, iron, manganese, zinc and molybdenum. Deficiencies can limit plant growth and health. A complete soil test will analyze levels of both macro and micronutrients.

Optimal Levels of Soil Nutrients

Ideal nutrient levels vary based on factors like soil type, crop species, and growth stage. A qualified lab can provide target nutrient ranges tailored to your needs. Here are some general guidelines for key nutrients:

  • pH: 6.0-7.0 for most plants
  • Nitrogen: 25-60 ppm
  • Phosphorus: 10-60 ppm
  • Potassium: 50-250 ppm
  • Calcium: 500-2500 ppm
  • Magnesium: 25-250 ppm

Regular soil testing helps monitor nutrient levels and determine proper amendments and fertilizers to reach optimal fertility. Proper management maximizes crop growth while avoiding excess nutrient runoff.

Soil Fertility Management Strategies

Soil fertility management requires a decisive approach to protect this soil and its nutrients. Some key strategies include:

1. Regular Soil Testing

Routine soil testing every 2-3 years provides important data on nutrient levels and pH. This allows farmers to make informed decisions about fertilizer applications and soil amendments needed to optimize plant growth.

Targeted soil sampling in suspect areas can also identify problem areas. Regular testing tracks changes over time and indicates whether management practices are improving or depleting soil fertility.

2. Balancing Soil Amendments

The goal of soil amendments is to provide a balanced supply of essential macro and micronutrients. Nitrogen, phosphorus, and potassium are critical macronutrients that must be carefully managed. Micronutrients like calcium, magnesium, and sulfur are also vital.

Organic sources like manure, compost, and cover crops can improve nutrient levels and soil structure. Inorganic fertilizers can also be judiciously used to supplement areas of deficiency. Balancing between organic and inorganic soil amendments creates an optimal nutritional supply.

3. Conservation Practices

Promoting soil conservation helps retain topsoil and nutrients. No-till farming leaves crop residue in place to prevent erosion. Windbreaks, terraces, and contour plowing also reduce soil loss. Cover crops and rotating complementary crops help control weeds and pests.

Returning crop waste to the soil replenishes organic matter. Reducing tillage enhances soil biodiversity. Protecting existing soil structure and nutrients is an essential part of fertility management.

Organic Methods to Improve Fertility

There are several organic methods that can help improve soil fertility without relying on chemical fertilizers. These include:

1. Cover Crops

Planting cover crops like soybean, clover, cowpea, groundnut, and alfalfa can help restore nutrients to the soil. As cover crops grow, their root systems help aerate the soil and replenish nitrogen. When the cover crop dies or is tilled under, the decomposition of plant matter releases nutrients back into the topsoil. Cover crops also help prevent soil erosion.

2. Crop Rotation

Crop rotation helps maintain balanced nutrition levels in the soil. Different crops take up and deplete different nutrients. By rotating crop types each season, farmers allow the soil to replenish the nutrients needed by each crop. Common rotation plans alternate between legumes, leafy greens, and root vegetables.

3. Organic Amendments

Adding organic soil amendments like compost, manure, bone meal, kelp meal, and earthworm castings can restore macro and micronutrients. These amendments release nutrients slowly as they break down, providing a steady fertilizing effect over months. Well-aged manure and compost will not burn plants like fresh amendments.

4. Reduced Tillage

Excessive plowing and soil disruption can cause nutrient losses. Reducing tillage preserves the soil structure and allows the build-up of organic matter. Strategies like no-till farming use specialized equipment to plant seeds without turning the soil. The leftover plant matter serves as a natural mulch.

Inorganic Methods to Improve Fertility

A variety of inorganic methods can be used to enhance soil fertility quickly.  These methods involve applying or adding inputs to the soil to supplement what is already there.

1. Synthetic Fertilizers

Synthetic fertilizers are formulations that provide concentrated nutrients to plants in readily available forms like nitrate, ammonium, and urea.

Fertilizers like urea, ammonium nitrate, and ammonium phosphate are rich sources of nitrogen, phosphorus, and potassium which are commonly deficient in soils. They provide a quick nutritional boost to plants and improve yields in fields where soil is poor. However, overuse of synthetic fertilizers can make soils acidic over time.

2. Liming

Adding lime or calcium carbonate to acidic soils can help neutralize acidity and increase soil pH. This makes essential nutrients like calcium, magnesium, and phosphorus more available to plants. Liming also improves soil structure and the activity of beneficial microorganisms.

Most agricultural lime is derived from limestone, ground up finely into a powder. The amount of lime needed depends on the initial soil pH and desired pH level. Liming should be done well before each crop season for best results.

3. Irrigation

Adequate irrigation provides moisture for crops, dissolves nutrients, and allows roots to access them. Drip, sprinkler, and flood irrigation systems supply water directly to crop roots and recharge soil between rainfalls.

Irrigation scheduling should match crop water needs and rainfall patterns. Excess watering can leach nutrients while inadequate irrigation leaves salts behind. Managing irrigation properly maintains soil fertility over multiple growing seasons.

Lastly, maintaining and improving soil fertility is essential for meeting current and future food production needs. By testing soil regularly, and implementing soil fertility management strategies, fertile soils can be preserved for generations to come.

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