The importance of soils, nutrient supply, and fertilizer application

Soils are crucial to life on Earth, fulfilling many important functions. Healthy and nutritious soils are not only the basis for food and fibre production, but also play a key role in the global carbon, nutrient and water cycle. Over 95% of global food production relies on soils in one way or another [1]. Therefore, proper nutrition is crucial for efficient plant growth to secure global agricultural production. A key challenge is replenishing soils with adequate amounts of nutrients and in doing so, not jeopardise environmental quality. Many soils, particularly in the global south, remain undersupplied by essential nutrients, reducing their productivity. In contrast, soils in industrialised countries often suffer from excess fertilizer application, which can impair surface water quality. The risk is particularly pronounced in areas with intensive animal husbandry and manure application.

Figure 1: Phosphorus deficiencies in rice and maize [2].

For healthy plant development, crops need the right amount of all the essential nutrients. If even one nutrient is deficient, then plant growth and yields will suffer. Nutrients are usually divided in three groups:

  • Macro – or primary nutrients: nitrogen (N), phosphorus (P), potassium (K)
  • Secondary nutrients: calcium (Ca), sulphur (S), magnesium (Mg)
  • Microelements: copper (Cu), iron (Fe), zinc (Zn), nickel (Ni), chlorine (Cl), boron (B), molybdenum (Mo) and others

According to the International Fertilizer Industry Association (IFA), nitrogen, phosphorus, and potassium account for 60%, 23%, and 18% of global fertilizer consumption, respectively.

For millennia, humankind has applied different types of nutrient inputs to improve soil fertility. Today, sustainable management of these nutrients is relevant to food security and ecosystem sustainability. This includes increasing efficiency of nutrient use, assuring fertilizer quality, and improving knowledge on nutrient supply in soils. To apply fertilizers efficiently means achieving a balance between nutrient input and output [3]. For this it is important to know the specific nutrient crop needs and soil characteristics. Such knowledge is essential in preventing nutrient losses, a major environmental concern due to excess run-off that can cause eutrophication. Soil characteristics are determined via periodical soil testing, including for nutrient levels. To understand the water pollution risk, an understanding of erosion risks as well as point in comparison to non-point sources is fundamental.

Efforts towards how to best use fertilizers to the largest total benefit of man and the environment have been ongoing for a long time. Newer approaches to carefully and responsibly manage fertilizers include integrated plant nutrient management practices, precision farming or a cradle-to-cradle approach implying a safe use and handling of fertilizers along all stages of the product lifecycle. Nutrient uptake by crops can be optimized if fertilizers contain the required nutrients and are applied in the right quantities at the appropriate time and place. Such practices are the basis of the 4R Principles of Nutrient Stewardship, which are aimed at an efficient use of nutrients in order to achieve positive economic, social and environmental effects (see Figure 2 and Table 1).

Diagram 2 - 4R Principles of Nutrient Stewardship
Figure 1: The 4R Principles of Nutrient Stewardship [4].

Agricultural producers do not always follow the 4R Principles of Nutrient Stewardship, however, and do not apply the right fertilizers at the right rate in the right time and place. The most serious negative environmental consequences arise from improper use of organic and mineral fertilizers containing phosphorus and nitrogen. The application of acid-forming fertilizers (primarily nitrogen-based fertilizers) changes various properties of soil. Without proper management, soil acidity will eventually stunt plant growth and depress crop yields. Due to high nitrogen mobility, nitrogen-based fertilizers can leach from soil into groundwater and surface water. Nitrogen can also be lost from soil as nitrous oxide, a potent greenhouse gas. Accumulation of phosphate in the soil can increase the risk of P loss through erosion, with negative impacts on nearby surface waters.

Table 1: The 4R Principles of nutrient stewardship [4].
Principle Why do this?

Right source

The source should provide balanced composition of all nutrients required by crop

  • To provide nutrients in accessible form
  • To match fertilizers with chemical and physical properties of soil
  • Identify fertilizer compatibility
  • To identify crop reaction to fertilizer application
  • Impurities content control

Right rate

Providing the crops with the required amount of nutrients

  • To identify microelement reserves in soil
  • To identify available nutrient sources
  • To identify crop nutrient requirement
  • To assess fertilizer efficiency
  • To analyse the changing requirements for nutrients across different seasons
  • To identify the budget

Right time

Applying fertilizers at the right time increases the yield and ensures that all nutrients are assimilated

  • Identify the nutrient assimilation time
  • To analyse soil microelement storage dynamics
  • To identify nutrient assimilation speed
  • To assess the logistics of field work

Right place

Applying fertilizers in the right place nurtures the root system for the whole cultivation period

  • To understand soil movements
  • Identify and control the loss of nutrients
  • To reduce the risk of oversaturation of young crop
  • To provide external nutrition