Soils

Healthy soils

Healthy soils are essential for plants, animals and humans to live. Soils help sustain life by fulfilling our needs for food, feed and fiber plus a number of critical ecological services. They provide the essential macronutrients needed by plants to grow, nitrogen (N), phosphorus (P), potassium (K), sulphur (S), calcium (Ca) and magnesium (Mg), along with several micronutrients, such as zinc (Zn), iron (Fe) and many more. In addition, soils constitute the largest terrestrial pool of carbon : they can store up to 50-300 tons of carbon per hectare, which is equivalent to 180-1100 tons of CO2. In healthy crops, for every two to three tons of carbon above ground, there will generally be one or more tons of carbon below ground in roots or root exudates.

Fertilizers play an incredibly important role for soil health. The purpose of fertilizers are to supplement the natural supply of soil nutrient, build up soil fertility in order to satisfy the demand of crops with a high yield potential and to compensate for the nutrients taken by harvested products or lost by unavoidable leakages to the environment, in order to maintain good soil conditions for cropping.

Optimized fertilizer management leads to maximized biomass production, which maximizes the carbon uptake by plants, and resulting in higher Soil Organic Matter (SOM). SOM has a strong influence on the overall health of soils. By introducing soil organic carbon to soils that help build up SOM, fertilizers stimulate microbial activity, improve soil structure, and increase their water holding and cation exchange capacity. This can reduce soil erosion, degradation, improve nutrient retention, and act as a buffer against acidification.

Integrated soil fertility management

Most agronomists agree that optimal nutrient management entails starting with on-farm organic sources of nutrients and then supplementing them with manufactured fertilizers to achieve the farmer’s yield goal , contrary to some beliefs that supporting the use of manufacture fertilizers implies opposing the use of organic sources of nutrients.

It should be noted that organic sources of nutrients, like mineral fertilizers, can gave negative environmental impacts if not properly managed, for instance in case of excessive application rates, or in case of wrong timing or placement of manure application.

The integration of organic and mineral sources of nutrients should be seen in the context of overall crop production, which includes the selection of crop varieties, pest control, efficient use of water, soil management and other aspects of integrated farm management.

Manufactured fertilizers and organic sources of nutrients can, and should, be used in a complementary fashion.

Integrated use of organic and mineral nutrient sources can improve soil fertility, enhance soil organic matter content and improve physical, chemical and biological soil properties. This integrated approach is an appropriate strategy for effective and responsible plant nutrition.

IFA therefore advocates for:

  • Sound science as the basis for food and environmental safety standards, applied equally to all nutrient sources used for food production;
  • Uniform descriptions of available nutrient content for all commercial fertilizer products, whether of organic or mineral origin.

Integrated Plant Nutrient Management

Using organic and mineral fertilizers combined, known as integrated plant nutrient management, is the best solution for maximizing plants yields and sustaining healthy soils with the greatest ability to sequester carbon.

Soils and Water

Soils however need more than nutrients to be healthy and to sustain plant growth, they also need water. Water is fast becoming a scarce resource in certain regions of the world, and farmers need to be very careful in managing inputs (water and nutrients) to ensure high yields while reducing adverse effects of this management on the environment. Soil fertility management must take water into consideration in order to be effective. Indeed, the accumulation or depletion of nutrients in soils is directly affected by the movement of water in soils.

Here are what the three main considerations that govern the relation between water and nutrients in soil fertility management:

  • Soil water stress will limit soil nutrient use at the plant level;
  • Soil-supplied nutrients can be taken up by plants only when sufficient soil solution allows mass flow and diffusion of nutrients to roots;
  • Soil water content is the single most important factor controlling the rate of many chemical and biological processes, that influence nutrient availability.

Soil degradation and desertification

Most soils lack some plant nutrients at some point, as growing crops and harvests remove them over time. Soil nutrients therefore must be replaced when removed and supplied when deficient.

Deficient soils, i.e. soils that lack one or several essential nutrients, pose serious risks for people’s food and nutrition security, and also raise environmental problems. Continuous soil depletion leads to low yield potential and conversion of natural habitats to cropping. In extreme cases, it can trigger desertification.

Desertification is the degradation of land in arid, semi-arid and dry sub-humid areas, primarily caused by human activities and climatic variations. Although other regions, mostly in Asia and Latin America, are also concerned, the most dramatic examples of desertification are found in Africa, where declining soil fertility is linked to declining agricultural productivity. Restoration of degraded soils through soil conservation practices and the widespread adoption of fertilizer best management practices that include both organic and mineral nutrient management, can reverse the historic losses of soil carbon worldwide and increase soil carbon sequestration. Optimized fertilizer management leads to maximized biomass production, which maximizes carbon uptake by plants and increases soil carbon storage when non-harvested biomass (e.g. roots and stems) returns to the ground. Improved agricultural practices will lead to higher Soil Organic Matter (SOM), which improves not only soil health and productivity but results in more CO2 sequestration.

IFA Publications

Integrated
Plant Nutrient Management
The Role of Fertilizers in Integrated Plant Nutrient Management
Managing Fertilizers to Enhance Soil Health