SOIL REQUIREMENTS WHEN GROWING CROPS
Soil is a medium for growing plants and is comprised of minerals, organic matter, air and water. For a certified seed to grow, there must be conducive soil environment, light and water. Plants need soil to support growth, avail nutrients and also water through the hydrological system. Soil requirements is an important factor that must be considered when growing crops. It includes; soil physical properties (soil texture, soil depth and structure), soil drainage and permeability and soil chemical properties (soil pH, soil nutrients). All this requirements however vary from one crop to another and at times should be supplemented to suit the crop in place. Also, some of these requirements such as nutrients can be supplemented in case of low levels and also soil pH can be adjusted to suit specific crop. One must therefore attempt to match crop requirements with the soil properties before growing any crop.
When determining the soil requirements when growing crops, the following soil factors must be considered to ensure there is ideal soil environment for the growing crops:
Soil physical properties
It relates to the relative proportion of different size of soil particles in a soil and can be coarse texture or smooth texture. Sandy soils have a coarse texture compared to smooth texture of loam and clay soil. The texture of the soil affects its water holding capacity. This must be considered when growing crops because the coarse nature sandy soil creates very large air spaces when compacted. This thus makes water to drains easily and hence becomes unavailable for the crop. Clay soil on the other hand has a very smooth texture and when compacted it has small air spaces which become water logged. Also, when it dries it damages the plant roots hence the plant is not able to translocate food and transport water and it dies eventually.
Loams and sandy loams are the best for growing crops. For instance onions thrive well in non-crusting soil.
It is the arrangement of soil particles into soil aggregates. The aggregates influence bulk density and porosity and pore size. Pores within an aggregate are small compared to those between single soil particles. For crops to thrive well. Small and large pores should balance to provide good soil aeration, water holding capacity and permeability.
Soil structure influences aeration which inhibits root development, impairs respiration of root system leading to reduction in water and nutrient absorption.
Adequate soil volume is a major requirement for crops root development.one should avoid shallow soil when growing crops. Shallow soil leads to: weak anchorage of roots, low available soil moisture for plants and also low exploitable soil nutrients. E.g. rubber growth and yield decreases with poor soil depth.
Soil water holding capacity/permeability and drainage
- Soil permeability is the ability of soil to retain water before complete percolation. Clay soil has high water holding capacity but is prone to water logging. This leads to rotting and also creates a conducive environment for microorganisms that thrive best in moist conditions.
- Sandy soils on the other hand have low water holding capacity, they drain easily leaving no eater available for plant use. Loam and sandy loams do not retain excess water and thus enough water is available for the crop, they are the best for growing crops.
- Poor drainage leads to high water table which leads to poor anchorage and lodging due to poor root development. It also leads to inadequate soil aeration which hampers root respiration and causes poor nutrient and water uptake.
- For instance, oil palm is less influenced by poor permeability compared to cocoa and rubber.
Soil chemical properties
This is the degree of acidity or alkalinity of soil. pH of 1-6 is acidic, 7 is neutral and 8-14 is alkaline. Too much acid in the soil can lead to scorching of leaves, drying and wilting of the crop. Lime is used to lower acidic level in soils. Different crops thrive under different soil pH, for instance onions thrive well in a pH of 6.0-6.8 while tomatoes thrive well in a pH of 6.0-7.5. Onions do not thrive well in soils below pH of 6.0 because some elements are deficient at that pH and there is also a high chance of aluminium and magnesium toxicity. Also, cocoa trees are more sensitive to soil acidity.
- Nutrients is one of the two limiting factors to crop productivity. It must therefore be correctly assessed to ensure proper fertilizer management properties. The soil has both macronutrients and micronutrients. Macronutrients include; potassium, magnesium, calcium, Nitrogen, Sulphur and Phosphorous. Micronutrients include; Boron, Iron, Cobalt, Nickel, Copper, Zinc, Manganese and Molybdenum.
- Lack of fertilizer or imbalance will lead to poor crop productivity. Inorganic fertilizers and organic manure can be applied in case of low levels of nutrients. Organic manure apart from increasing soil fertility also helps incorporate soil particles together.
- An example is in onions whereby soils with high toxicity of aluminium and magnesium should be prevented. Also in tomatoes, excessive Nitrogen should be avoid as it leads to excessive vegetative growth thus causing poor fruit set, hollow fruits and poor fruit sets. On the other hand inadequate calcium in the soil can lead to blossom end rot disease in tomatoes, this can be prevented by applying calcium fertilizers.
Since soil is a major component for plant growth and development, proper assessment of soil should be done to determine the ideal soil requirements needed for the crop in question. Also, different crops have different soil requirements and one should be careful when selecting the soil requirement for a crop. In conclusion, sandy loams and loam soils are best when growing crops as they have smooth texture and good water holding capacity. In addition, most crops thrive well in a pH of 5.5-7.0.Organic matter supplements provide more fertility to the soil compared to the inorganic supplements.