Getting On Top of Soil Fertility

Careful management of farmland maintains soil fertility and maximizes sustainable crop yield and quality.

July 10, 2023
8 mins

We talk of the Fertile Crescent as being the birthplace of agriculture and we emphasize the importance of ‘fertility’ in our soils. But what exactly is fertility, why is it important, and how do we measure it?

Back to basics: soil fertility is best described as soil’s ability to provide the essential nutrients required for plant growth and optimum crop yield. At its heart, this is about soil productivity – and while some soils are inherently more fertile or productive than others – because of geography or soil chemistry – all soil used for agriculture will need fertilizers to maintain soil nutrients. This is because the nutrients taken up by plant roots as the crops grow are removed when the crops are harvested. This nutrient mining will gradually deplete the soil’s nutrient reserves. These nutrients must, therefore, be replenished through fertilization to replace the nutrients removed at each harvest.

All soil used for agriculture need fertilizers to maintain soil nutrients, replacing those removed at harvest

Essential Plant Nutrients

In this article, we are particularly interested in the soil nutrients from the plant’s perspective. Plants require 17 essential nutrients for growth: carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and zinc (Zn).

Carbon, hydrogen, and oxygen are supplied by air and water. Out of the remaining nutrients, we refer to the six that plants require in the largest quantities as macronutrients – nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. The remaining elements are required in trace amounts and are known as micronutrients.

All these nutrients are essential for healthy plant growth, and for plants to complete their life cycle, i.e., for seeds to germinate and for the development of roots, stems, leaves, flowers, fruit, and seeds.

Macronutrients are essential for basic functions of plant life, including photosynthesis, enzyme synthesis, cell wall formation, and manufacture of proteins, but so too are the micronutrients or trace elements. For example, molybdenum is essential for nitrogen fixation and uptake, while boron is essential for pollination and seed set.

Deficiency of any single nutrient, macro or micro, will act as a limiting factor on crop development or performance. What’s more, humans also rely on many of these trace elements for our own dietary needs, so nutrient deficiencies in crops can also lead to significant issues in human health.

While entire scientific papers are written on every aspect of soil fertility, we’re going to take a simpler approach: what are the crucial elements in managing soil fertility to optimize crop yield?

Physical Factors

Some soils will always be better than others. That’s because the physical nature of soil affects its fertility. When we talk of this physical nature, we refer to the soil texture – the proportion of sand, silt, and clay in the soil – and the soil structure – the way the individual particles of sand, silt, and clay combine to create pore spaces within the soil. Both these factors affect soil fertility by determining how water and nutrients move through the soil, as well as impacting root penetration and soil waterlogging.

There’s little that farmers can do to change their soil type, but they can improve its physical performance by focusing on the soil health. It is important to pay attention to the soil structure when engaging in farming operations. For example, using heavy machinery when there is a high moisture content in the soil can lead to soil compaction, which can reduce water infiltration and lead to surface run-off.

Chemical Factors

Many chemical factors can influence the availability of soil nutrients, including soil pH, cation exchange capacity, salinity, and soil buffer capacity. As an example, soil pH, the acidity or alkalinity of the soil, influences the soil’s ability to ‘give up’ nutrients for uptake by the crop’s roots. The solubility of most nutrients that plants require is higher in slightly acidic soils, although strongly acidic soil can reduce the availability of nutrients such as potassium, phosphorus, and calcium. Some nutrients, including iron and manganese, are more readily available in soils with low pH, i.e., higher acidity. It’s worth pointing out that increased availability of nutrients isn’t always welcome; iron and manganese can be toxic to plants if levels are too high.

Biological Factors

Healthy soil is not only made up of physical particles and nutrients. There are biological factors that can also impact soil fertility. Many of these factors involve organisms that live in the soil and play a role in moving and recycling nutrients. For example, earthworms and insects may eat crop residues, such as old roots from previous crops, which they then excrete as they move through the soil. And as they pass through the soil, they may also create tunnels that improve drainage and the movement of water and nutrients.

Smaller organisms, such as fungi and bacteria, are the most abundant and play critical roles in recycling nutrients in the soil

But when it comes to the number of life forms in the soil, the smaller organisms, such as fungi and bacteria, are the most abundant and play critical roles in recycling nutrients. A single gram of soil can contain several billion bacteria of thousands of different species. While some of these organisms may feed on organic matter, there is another well-known bacterium, Rhizobium, which are soil microorganisms that are in symbiosis with leguminous plants to form root nodules, where it carries out the essential role of fixing nitrogen from the atmosphere and making it available to leguminous plants. But it is not just nitrogen that bacteria recycle; all nutrients have a cycle that involves soil microorganisms.

One approach to improve soils’ biological health is to incorporate organic matter. While organic matter, such as manure, contains small amounts of N, P, and K, it cannot supply all the nutrients crops needed in modern farming systems. But the application of organic manure in balanced fertilization is still valuable due to micronutrient supply and improvement of the soil quality by enhancing microbiological activity and physical properties, including improving soil structure, water-holding, and aeration. The best results are obtained when commercial fertilizers are applied in combination with organic manures in a process called Integrated Nutrient Management (INM).

Managing and Measuring Soil Fertility

Despite the role of natural biological processes in recycling nutrients in the soil, productive farmland needs careful management to maximize crop yield and quality.

Plants require adequate nutrients in an optimum ratio, known as “Balanced Fertilization”

It is not just a question of providing a few key nutrients at high doses. Instead, plants require adequate nutrients in an optimum ratio, known as “Balanced Fertilization”. Continuously imbalanced fertilization (i.e., too much nitrogen and no potassium) causes depletion in soil fertility, a decrease in crop yields, poor crop quality, and diminishing profits.

As a leading fertilizer producer, ICL encourages farmers to engage in more precise, judicious, and balanced fertilizer use to increase the quality of their produce and boost economic profitability while keeping the environment safe.

To achieve this optimum nutrition, the most productive farmers will typically use soil and water tests, leaf tissue tests, and adviser recommendations to understand the characteristics of their soils and the nutritional status of their crops. It’s an invaluable part of an integrated soil fertility approach.

And armed with details of the crop’s needs and the fertility that is in the soil, it is then a case of identifying and applying the right plant nutrition solutions to ensure any nutrient gaps are met, as well as ensuring nutrient removal by the crops does not leave the soil depleted and unable to support future crops.

Within ICL’s portfolio of plant nutrition solutions, we have fertilizers designed for every crop, growing condition, and growing system.

Within ICL’s portfolio of plant nutrition solutions, we have fertilizers designed for every crop, growing condition, and growing system.

Nutrition Solutions to Improve Crop Productivity

With over 40 fertilizer brands globally and multiple product formulas in each brand, ICL has the right fertilizer for every crop, growing system, and soil fertility status.

For example, we have conventional granular fertilizers and fertilizers designed for fertigation systems (both liquid and water-soluble fertilizers), which can include a balanced nutrient formula or formula with increased levels of particular nutrients.

With over 40 fertilizer brands globally and multiple formulas in each brand, ICL has the right fertilizer for every situation

Our controlled-release fertilizers, like Agrocote, ensure that nutrients are available for crops throughout their entire growing season by managing the release of the nutrients according to the crop’s needs for up to 18 months. This controlled release has multiple benefits, including potentially applying the crop’s total nutrient needs in a single application and, by matching the release rate to the crop’s needs, reducing nutrient losses to the environment and increasing nutrient use efficiency. In fact, trials indicate that growers can often reduce the total nutrients applied while maintaining the same crop yield.

For growers who engage in organic growing systems, we have our natural granular, multi-nutrient, prolonged-release fertilizer, Polysulphate.

ICL also has a range of biostimulants in our BIOZ brand. Biostimulants are substances or microorganisms that promote plant growth and increase yield. Stress caused by heat, drought, or disease can limit the nutrient uptake from the roots to the plant. BIOZ, the ICL biostimulants line, delivers an effective approach for achieving sustainable agriculture since they stimulate soil activity, resulting in better availability of nutritional elements for the plant, reducing stress and improving nutrient uptake. They have become a vital constituent in integrated crop and soil management for many growers worldwide.

Making a Commitment to Sustainability

It’s not just about providing innovative products that meet the technical needs of crops and soil. At ICL, we recognize the necessity of supporting a global population with plentiful, healthy, sustainably grown food.

It’s essential that we respect our environment and do as much as we can to preserve natural resources.

As a leading crop nutrition manufacturer, we’ve invested heavily in developing new technologies, such as our controlled-release, fertigation, granular, foliar, and organic fertilizers, and our biostimulants. But technology’s no good without application. That’s why we also invest heavily in our customer support capabilities: our worldwide team of expert agronomists, soil scientists, and plant nutritionists are all involved in efforts to train farmers, advisers, and distributors in the correct use of crop nutrition products: optimizing crop yield, maximizing nutrient use efficiency, and preserving soil health.