SOILS are mostly formed from the breakdown and decomposition of parent materials such as rocks, minerals, and organic materials.
However, the properties or characteristics of soils are generally controlled by type of parent materials, climate, organisms, topographic, and time. In general, soils which are formed from minerals and rocks are called mineral soils whereas those whose formation is dominated by organic materials are referred to as organic soils (Tanah Gambut).
However, regardless of their type, soils as one of nature’s most versatile valuables had and will continue to play tremendous role in the human civilization.
Provided their resilience is not overstretched or compromised (particularly in poorly managed agricultural systems), they can be very ‘forgiving’ because they support for example, the growth, development, and productivity of inestimable or countless organisms including plants and animals.
In spite of being forgiving in nature, these naturally occurring soils should not be misused as their counter reaction could be devastating if no catastrophic.
Moreover, mismanaged or degraded soils are extremely difficult to mitigate or rehabilitate.
The possibility of their devastating responses to continued misuse, particularly in farming activities which significantly negate the benefits of conservation agriculture could be avoided through in-depth understanding of the meaning and concept of soil fertility.
Thus, the concept of soil fertility in relation to the impact of fertile soils on crop productivity and the economic livelihood of farmers and related professions should not be relegated to the periphery, rather it should feature prominently in most farming systems and related programmes, especially for resource poor land or challenging soils.
In this regard, this write-up discusses the synergy of some physical, chemical, and biological properties of soils in relation to how good management of these properties could profoundly boost farming systems and the like.
Soil fertility can be simply defined as the physical, chemical, and biological properties of soils but what is more important in agriculture is how these properties interact or are managed to support sustainable crop productivity.
In other words, good comprehension of the synergistic effects of these factors in farms is imperative if not crucial. That being the case, balanced interactions among soil properties or how well the properties are managed, especially by farmers including plantations could determine how fertile or infertile a soil is or will be.
In a simple language, soil physical properties are the characteristics of any soil which can be generally seen and felt by anyone including farmers, although some properties are confirmed in laboratory analysis.
Some of the examples of soil physical properties are soil texture, soil structure, soil colour, and so on.
Soil texture is the proportion of sand, silt, and clay. On the other hand, the arrangement of sand, silt, and clay to ensure some degree of the stability of these particles to prevent for instance, soils from collapsing is referred to as soil structure.
Soil texture can easily indicate how sandy or clayey soils are or it could suggest how challenging it will be to manage such soils.
On the other hand, how loose or dense (compact) such soils are is partly controlled by soil structure.
Therefore, the nature of the composition of soil particles and their aggregation (soil texture and structure) play essential role in determining for example, how well water is distributed in soils, how much water and nutrients soils can hold, how fast or slow water and air can move in soils, how fast water can penetrate (infiltrate) soils during and after rain fail or irrigation, how much water runs through and out of soils (leaching), and how water can run on and from soils’ surface (runoff).
Soil physical properties can also control plant root respiration (breathing of plants), movement of roots, uptake, transmission, and distribution of water and nutrients by roots.
They also influence the living conditions/environment of organisms which are not seen with naked human eyes (example, nematodes, bacteria, fungi, viruses, and so on) or can be seen with naked human eyes (termites, earthworms, rodents, and so on).
Although soil physical properties are important in agriculture, their role vis a vis soil fertility is not exclusive from other categories of soil characteristics because as an example, aggregation of soil particles to form good soil structure to enable good plant growth and development needs literally, a ‘special glue’ called soil organic matter which holds/cements sand, silt, and clay together such that such a soil has good spaces for crops and organisms to thrive.
It must be noted that soil organic matter comes from decomposition or breakdown of dead plants materials, animals, and other living and non-living organisms.
How fast or slow soil organic matter forms in soils is partly controlled by soil physical properties such as texture and the activities of very tiny organisms such as bacteria and fungi and also bigger organisms such as earthworms, insects, root exudates, and so forth.
The involvement of organisms to positively or negatively impact soil quality or health is known as soil biological properties and this is shown in the picture below where organisms interact with the soil.
Among the positive interactions is borrowing soils by rodents (rats, mice) and earthworms to create channels (holes) for water, air, and nutrients transmission and one of the negative interactions is plant root destruction by nematodes and fungi.
Note that soil organic matter is one of examples of soil chemical properties.
This means that good soils should have some reasonable amount of organic matter to ensure such soils are less compact to some extent that good amount of water can be held and supplied to plants for use.
This soil water should also be able to transport nutrients (food of plants) timely without the nutrients being lost from the soil or locked up in the soil.
The organic matter also facilitates the inflow and outflow of oxygen in soils to ensure that plants and other organisms have adequate amount of oxygen for their daily activities just as in human beings.
The right amount of organic matter also ensures good soil temperature to avoid excessive heat which could kill or destroy plant roots and other organisms in soils.
Certainly, soils with good organic matter makes such soils reasonably loose to boost the activities of living organisms.
For such soils, rain water as an example, can easily penetrate or infiltrate them to avoid too much of water being lost from their surfaces to cause flooding or washing away of seeds, fertilizers, pesticides, weedicides, and herbicides.
Water distribution in soils with reasonable organic matter is good because soil organic matter literally acts like a sponge to timely absorb and release water.
Moreover, soil organic matter significantly improves the amount of nutrients soils can hold from for example, fertilizers.
From economic point of view, sufficient amount of soil organic matter will not only save farmers from losing fertilizers but it will also enable farmers to make good money from good harvest because efficient use of fertilizers and related farm inputs are guaranteed to increase crop yield and profit margin.
Furthermore, the soil organic matter itself is rich in plant nutrients such as nitrogen, potassium, phosphorus, calcium, magnesium, and so on, thus it could compliment nutrients from chemical fertilizers.
Additionally, because soil organic matter are made up of negative charges, they are very good in attracting and storing positively charges nutrients such as potassium, ammonium, calcium, magnesium, copper, and zinc fertilizers or limes from being lost from farms.
The ability of soils to hold or store and release positive nutrients for plants to use is called cation exchange capacity (CEC). Soil clays are also able to attract and hold positive charges just like soil organic matter although soil organic matter holds more positive charges than clays.
Based on the negative charges which are contributed by both the physical and chemical aspects of soils, we can now appreciate that both soil physical and chemical properties interaction to control the use nutrients by plants, therefore one can say that both soil physical and chemical properties contribute to soil fertility.
With the basic understanding of what soil fertility is, part two of this article discusses how soils could be managed for optimum crop yield with good economic returns.