Soil is a heterogeneous material consisting of three major components: a solid phase, a liquid phase and a gaseous phase. All three phases specifically influence the supply of nutrients to plant roots. The solid phase is the main nutrient reservoir. The inorganic particles of this phase contain cationic nutrients such as K, Na, Ca, Mg, Fe, Mn, Zn, and Cu, whilst the organic particles form the main reserve of N and to a lesser extent also of P and S. The liquid phase of the soil, the soil solution, facilitates nutrient transport in the soil, e.g. for the transport of nutrients from various parts of the bulk soil to plant roots. Nutrients transported in the liquid phase are mainly present in ionic form, but O2 and CO2 are also dissolved in the soil solution. The gaseous phase of the soil mediates the gaseous exchange which occurs between the numerous living organisms of the soil (plant roots, bacteria, fungi, animals) and the atmosphere. This process results in the supply of living soil organisms with O2 and the removal of CO2 produced by respiration from the soil atmosphere. For plant species living symbiotically with N2 fixing bacteria, N2 supply to the root nodules is also mediated by the soil atmosphere.
factors that makes it challenging for plant growth using soil for growing plants:
1) Water Drainage
The soil is exposed to many sediments and particles as it is exposed in the open. A good quality of soil used for the initial stages of planting, which have the ideal water drainage system within the soil. However, with the accumulation of sand and clay particles carried by wind, the water drainage system is affected. Poor water drainage system may result in:
- plants wilting
- Slow growth
- Unhealthy plants (Leaves turn yellow and fall)
- Soil is constantly damp
- roots become spongy and rot
2) pH Levels
This is probably one of the toughest factors to control since your soil is exposed to the elements of the outdoors almost every single day. Areas with air pollutions tend to have acidic rain and areas with dry environment will naturally result in an alkaline soil.
Soil pH is important because it influences several soil factors affecting plant growth, such as (1) soil bacteria, (2) nutrient leaching, (3) nutrient availability, (4) toxic elements, and (5) soil structure. Bacterial activity that releases nitrogen from organic matter and certain fertilizers is particularly affected by soil pH, because bacteria operate best in the pH range of 5.5 to 7.0. Plant nutrients leach out of soils with a pH below 5.0 much more rapidly than from soils with values between 5.0 and 7.5. Plant nutrients are generally most available to plants in the pH range 5.5 to 6.5. Aluminum may become toxic to plant growth in certain soils with a pH below 5.0. The structure of the soil, especially of clay, is affected by pH. In the optimum pH range (5.5 to 7.0) clay soils are granular and are easily worked, whereas if the soil pH is either extremely acid or extremely alkaline, clays tend to become sticky and hard to cultivate.
A pH determination (soil test) will tell whether your soil will produce good plant growth or whether it will need to be treated to adjust the pH level. For most plants, the optimum pH range is from 5.5 to 7.0, but some plants will grow in more acid soil or may require a more alkaline level.
The pH is not an indication of fertility, but it does affect the availability of fertilizer nutrients. A soil may contain adequate nutrients yet growth may be limited by a very unfavorable pH. Likewise, builder’s sand, which is virtually devoid of nutrients, may have an optimum pH for plant growth.
3) Organic Matter
Organic matter contributes to plant growth through its effect on the physical, chemical,
and biological properties of the soil. It has a :
nutritional function in that it serves as a source of N, P for plant growth
biological function in that it profoundly affects the activities of microflora and micro faunal organisms
physical and physico-chemical function in that it promotes good soil structure, thereby improving tilth, aeration and retention of moisture and increasing buffering and exchange capacity of soils.
Humus also plays an indirect role in soil through its effect on the uptake of micronutrients
by plants and the performance of herbicides and other agricultural chemicals. It should be emphasized that the importance of any given factor will vary from one soil to another and will depend upon such environmental conditions as climate and crpping history.
Good horticulture soil contains ideally 50% solid material and 50% pore space. Most soils are dominated by mineral particles while others, organic matter. In order to achieve the ideal conditions for optimal plant growth, it requires lots of monitoring and experimentations to ensure this equilibrium between the minerals and materials within the soil. Beginners will definitely find this a challenge! A healthy soil does not come overnight and is only possible when lots of commitment and time is invested into ensuring the ideal conditions for plant growth.