The growth of any crop is greatly influenced by the conditions surrounding the soil, this is called soil factor. The soil develops as a result of various biological processes over a long period. these processes, in turn, lead to saline and alkaline soil. These are the major types of soil across the globe. Knowing that saline soil and alkaline soil exist makes soil testing imperative prior to any cultivation.
Saline and alkaline soil have an implication on the choice of crop grown on such land. Crops have an individual preference, not all crops can be grown on any type of soil. Some crops are acid tolerant while others are tolerant to alkaline soil; these are the rudiments every farmer must know before cultivation. This is part of pre-planting operations every farmer must consider before cultivation.
The economic importance of Saline and Alkaline soil
Saline soil and alkaline soil can be determined by testing the pH the soil; there are several ways to test the soil pH; you can test directly on the farm or in the laboratory. The latter is more reliable but expensive. A typical soil pH ranges from 1 – 14. Values between 6.5 and 7.5 are most suitable for all crops; they are commonly termed the neutral value. Below 6.5 means soil acidity and above 7.5 means soil alkalinity.
After testing the pH of your soil; the value must fall within the range of 1 and 14; you are left to determine the precise status of the soil by matching the value to the appropriate range it falls. Either acidic or alkaline, they can be modified to plant any crop.
Salinity and Plant growth: Management of Saline soil and plant growth
Saline soil is a salt-affected soil; it is any soil that contains a high level of soluble salts that can is capable of adversely affecting the growth and yield of crops. Not all crops are vulnerable to this condition; some crops are tolerant and can thrive well in saline soil.
Saline soil can be identified physically; saline soil characteristics are scanty or spotty growth of crops and the presence of white salt crusts on the surface. management of saline soil is crucial to allow it to fit for cultivation of crops that are not tolerant.
What causes salinization of soil?
Salts are naturally present in soils and water in different concentration. Accumulation of salt through water sourced from rain and the once present in the soil can increase the soil salinity.
Decomposition of different minerals in the soil can also result in the formation of saline soil; as soil mineral decomposes, they release salt which in turn accumulate for a very a long time and leaches out of the soil via drainage or rain. Salinization is a natural phenomenon.
How saline soil affect crop growth
Salt salinity makes it difficult for plants to absorb water from the soil, hence causing water stress and leading to poor and scanty growth of most crops. soil salinity and plant growth have an inverse relationship; as salinity increases, the growth rate reduces.
Soil salinity problems are:
It makes less water available to the plant to use; this is because the osmotic pressure of the soil increases as salt concentration increases. Excess concentration becomes toxic to plants and may reduce the absorption of other nutrients available in the soil for the plant uptake.
There are saline soil plants; these plants are tolerant to saline soil.
Examples of crops grown in saline soil are: Sunflower, tomato, broccoli, apple, sweet corn, potatoes, cabbage; etc.; crop tolerant to salinity are called saline soil crops or halophytes.
Reclamation of saline soil: how to reduce salinity in soil
As said earlier, salinity can be treated and make fit again for planting any crop; this is called soil reclamation. Saline soil can only be reclaimed by removing salts from the plant root zone. Reclamation of saline soil can be done in three ways. soil salinity solutions are:
- Artificial leaching of soil: Leaching is the downward movement of liquid below the root zone of plants. It is a natural phenomenon that occurs under certain conditions such as heavy rainfall. In this case, more water, above the plant requirement, is supplied to the plant. This method drives in the water below the plant root zone.
- Leaching with Artificial drainage: Artificial leaching is effective but care must be taken where places where the water table is shallow. This must be considered to avoid water-logging situation which makes the soil anaerobic, thus, killing the beneficial microbes in the soil. To make it more effective, it is better to supplement with drainage as a prophylactic measure against water-logging situation. Artificial drainage is needed where water table limits the use of leaching. Drainage ditches may be constructed below the water level to allow salt leaching out of the soil.
- Managed accumulation: This is a sophisticated method of controlling soil salinity. It involves the movement of the salts away from the root zones to another region aside from the root zone, where they are not harmful. It is a way of partitioning the saline salt in the soil away from the root zone of the plants.
Soluble salts in soil with salinity are Gypsum, sodium and chlorides and nitrates. soil salinity management is important to reduce the threat of water stress and poor yield
Alkaline soil and plant growth
Alkaline soil is a soil with high pH value; alkaline soil pH is usually above 8. characteristics of alkaline soil are poor soil structure, hard calciferous layer, and low infiltration rate. They are usually clay soils.
Alkalinity in soil results as a result of high content of calcium carbonate which causes the soil to swell and difficult to settle; these are common alkaline soil problems. Because alkaline soils are less soluble, it leads to several effects of alkaline soil on plants such as: reduced availability of essential nutrients which results to stunted growth and deficiency of minerals in the soil.
A common problem in alkaline soil is iron chlorosis caused by inadequate iron; hence, soil alkalinity test must be carried out to ensure smooth production.
Causes of soil alkalinity
There are several causes of soil alkalinity; the most prominent ones are:
- Over-liming: At times, over-liming an acidic soil can result in alkalinity.
- Using alkaline irrigation water: Because acidity and alkalinity occur in both soil and water, it is very possible the source of irrigation is alkaline in nature.
Reclamation of alkaline soil: how to correct alkaline soil
Just like saline soil, alkaline soil treatment can as well be done. These are ways of correcting alkaline soil:
- Application of fertilizer to the alkaline soil: fertilizer for alkaline soil can greatly increase the productivity of the soil. Application of fertilizer to the soil increases the concentration of plant nutrients. Care must be taken when applying fertilizers to the soil. Do not add phosphate fertilizer alone; this will further reduce the availability of nutrients in the soil.
- Lowering the pH of the soil: When the pH of the soil is high, it can be reduced by adding elemental Sulphur to the soil or other substances to acidify the soil.
- Addition of organic matter: Organic matter helps to neutralize the soil; they can as well acidify the soil as microbes decomposed material in the soil leading to the release of carbon-dioxide which then forms carbolic acid to acidify the soil.
- Application of acidify fertilizers: There are some fertilizers that are naturally acidic in nature; they are the best fertilizer for alkaline soil. Examples of acidifying fertilizer are ammonium sulphate. It supplies nitrogen and also helps lower the soil pH. Ammonium is nitrified by soil bacteria into nitrate and hydrogen ions.
- Adding Gypsum to the soil: gypsum is used for the improvement of alkaline soil; it is a soluble saline salt that can lower soil pH
There are some crops that grow in alkaline soil; they are tolerant to alkaline soil. alkaline soil plants are: cabbage, carrot, lettuce, spinach etc. these alkaline soil crops can thrive in this soil without any adjustment of the soil status.
Adequate control of the soil salinity or alkalinity status is very important and imperative to having a good yield. An improved seed may not perform up to its genetic potential if the soil condition does not facilitate its growth.
Reclamation of saline and alkaline soil is important; increase in crop yield can only be achieved if the medium, soil, is in good condition.