Irrigation is the application of water to ensure the sufficient amount of soil moisture is available for good plant growth throughout the entire growing season. For irrigation planning purposes, the average precipitation rate during the growing season could be a better yardstick for determining the need for irrigation. The timing and amount of rainfall during the season, the soil’s capacity to hold water, and the crop’s water requirements all influence the need for irrigation.
Soil and water compatibility are essential for irrigation, and this can be very well determined with soil mapping in the USA. If they are not compatible, the applied irrigation water could harm the soil’s chemical and physical properties. Determining the suitability of the plot of land for irrigation requires a thorough assessment of the soil properties, the topography of the land in the field, and irrigation management.
Soil Permeability and Infiltration:
The measure of the ability of air and water to pass through or move through soil is its permeability. It is influenced by the pore spaces’ size, shape and continuity, which in turn depend on the soil’s bulk density, structure and texture.
Soil density or depth refers to the thickness of the soil materials that give structural support, nutrients and water for plants. While soil structure refers to the grouping of particles of sand, silt and clay into larger aggregates of various sizes and shapes. Again, soil texture is determined by the size and variety of solid particles that make up the soil. Soil series is the Earth’s layer that has been altered by physical or biological processes. The five prominent soil-forming factors that control the process of this change are the parent material, topography, climate, biota – plants and animals, and time.
Soils are grouped into different categories according to their observed properties. In most cases, soil layers with a slow, very slow, rapid and very rapid permeability classification are considered very poor for irrigation.
Table 1. Soil permeability classes
Soil Infiltration:
Infiltration is the downward percolation of water from the surface through the soil. The infiltration rate (sometimes also called intake rate) of soil measures its ability to absorb an amount of rainfall or irrigation water during a particular time. It is commonly expressed in inches per hour. The infiltration rate is dependent on the permeability of the surface soil, moisture content, and surface conditions like roughness (tillage and plant residue), slope, and plant cover.
Coarse-textured soils, such as sand and gravel, usually have high infiltration rates. The infiltration rate of medium and fine-textured soils, like loams, silts, and clays, is lower than that of coarse-textured soils and is influenced by the stability of the soil aggregates.
Water and plant nutrient losses may be more significant on coarser-textured soils. Thus, the timing and quantity of the chemical and irrigation water applications are particularly critical on these soils.
Lay of the land:
Topography significantly impacts whether a field can be irrigated. Relief is that component of topography that refers to the stark difference in height between the hills and valleys or depressions in the field. The topographic relief will impact the type of irrigation system used, the water conveyance system, drainage requirements, and water erosion control practices.
The shape and arrangement of the topographic landforms and the type of surface waterway network will also influence irrigation management.
With some crops like potatoes, a wet low spot could become a source of disease.
Irrigation Water:
Some water sources are unsuitable for irrigating croplands. Irrigation water must be compatible with crops and soils on which it will be applied. Before a recommendation can be made, a water analysis and legal description of the land that is proposed for irrigation are typically required.
The quality of water for irrigation is determined by its total dissolved salt content. An irrigation water analysis should include the cations such as calcium, magnesium, and sodium and the anions (bicarbonate, carbonate, sulphate, and chloride). As some crops are sensitive to boron, it is often included in the analysis.
The two most vital factors to look for in an irrigation water quality analysis are total dissolved solids (TDS) and sodium adsorption ratio (SAR). The TDS of a water sample measures the concentration of soluble salts in the water and is commonly referred to as the salinity of the water.
A water sample’s electrical conductivity (EC) is often used as a proxy for TDS. EC can also be expressed in many different units, which usually needs clarification.
Crop Water Use:
Crop water use, also known as evapotranspiration, or ET, is often the daily estimate of the blend of the amount of water transpired by plants and evaporation from the soil surface around them. A plant’s water usage changes with a predictable pattern from its germination stage to maturity.
All agronomic crops follow a similar water use pattern. However, total crop water use will vary from every growing season to growing season due to climatic variables of air temperature, amount of sunlight, humidity, wind and soil differences among fields like root depth, soil’s water holding capacities, texture, structure, etc.
The knowledge of the water use patterns during the different growth stages greatly influences how an irrigation system is designed and managed. Recognizing a crop’s water use patterns may result in better managed water applications. The crop water stress, fertilizer and pesticide leaching, and increased pumping costs are just a few of the results of very poor irrigation water management.
Irrigation Water Management:
One of the most challenging parts of irrigation water management is deciding when to start the irrigation supply and how much to apply. Good irrigation management often begins with accurately measuring the rain received on each irrigated field. Ideally, every irrigated field should have at least one and two rain gauges of at least 2 inches in diameter mounted atop posts next to the field.
Estimating soil moisture is the most common irrigation water management method; however, it must be done regularly throughout the growing season.
If you are looking for expert advice to determine the right irrigation management for your cropland this growing season, contact our experts at SoilOptix®. They can analyze your soil to give you accurate information on soil-water compatibility. Visit https://soiloptix.com/ now!
