How is corn field irrigation done?
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Almost all 400 thousand hectares of agricultural land under corn cultivation in Iran is irrigated. Therefore, improving irrigation management can have a significant impact on the quantity and quality of water, which is known as the most important resource of the country. Proper management of irrigation in corn fields can bring factors such as economic production, saving water resources and maintaining or increasing water quality. For this purpose, it is necessary to use estimation of evaporation and transpiration of corn and accurate measurement of water in the soil profile to determine the time and amount of irrigation.
In this article, the following are proposed:
What is the relationship between water, soil and plants?
What are the characteristics of water consumption for corn?
How is the water requirement of the plant matched with irrigation?
What are the growth stages of a corn plant?
When is it appropriate to water corn?
How is farm irrigation managed?
What is the texture of the soil?
How is the corn field irrigation systems?
In the rest of this section, the answers and explanations related to the above questions will be examined in full.
What is the relationship between water, soil and plants?
For effective irrigation management, understanding the relationships between plants and their environment is essential. In the case of a corn field, important plant characteristics for water management include total water use per season, daily water use by the plant, plant growth rate, and root growth depth. Also, the characteristics of the soil are also very important, which include the capacity to hold water, the ability to absorb water, and the presence of restrictive soil layers that may prevent the penetration of root growth. Also, the quantity and quality of water resources should be considered. The main goal in water management in corn fields is to provide additional plant water needs and to maximize the value of using water resources.
What are the characteristics of water consumption for corn?
Evaporation and transpiration (ETc) is defined as the water that leaves the soil as a result of evaporation from the soil and plant transpiration. In the case of corn, up to 30% of ETc evaporates from the soil during the growing season. The last stage of transpiration is to move water from the soil to the roots of the plant, through the stems and finally from the leaves to the air. About 70 to 80 percent of the water used in crops is caused by plant transpiration. Corn's daily water consumption varies depending on weather conditions.
The amount of water consumption during the seasons is determined according to weather conditions, corn variety, soil fertility and water availability. In addition, different factors also affect the amount of corn water consumption. However, the seasonal trend of corn water consumption in each region will be shaped by the climate and plant growth needs. In Figure 1, the smooth black curve represents the long-term average pattern of corn water consumption. This pattern refers to the average daily temperature based on daily transpiration evaporation over a 10-year period. The jagged green curve in Figure 1(b) shows the updated 12-month temperature. Therefore, farmers should be familiar with the long-term trend and at the same time, have the ability to determine the amount of daily evaporation and transpiration in the short term. Having knowledge of the long-term trend and the actual amount of daily water consumption of the plant is crucial for determining when and how much to water.
According to the climatic conditions and the variety of corn, the water requirement depends on two factors: the relative ripeness of the variety and the length of its growth. Corn hybrids with longer maturity require more water. But if the right temperature and water source are available, longer hybrids can produce more seeds. If both cultivars are able to mature fully, the amount of grain produced per millimeter of evaporation and transpiration will be almost equal in both cultivars. The difference in seasonal water consumption may also be different due to the number of days of water consumption and the amount of daily water consumption.
Figure 1) Average long-term water consumption of corn (a) and daily water consumption of corn in a certain year (b)
Due to climate changes throughout the year and from year to year, the average water consumption for long-term irrigation and daily consumption of corn (A and B) can have a statistical standard deviation of up to 50 mm per day. Therefore, in advanced corn fields, it is recommended to use soil water sensors and access to estimate the daily water consumption of plants based on weather conditions during the growing season. Also, the duration of each stage of growth may differ by up to 2 days from the long-term average value in Table 1. Each millimeter of water is equivalent to 0.001 meters of water per hectare (100 meters x 100 meters x 0.001 meters), which is equivalent to 10 cubic meters.
Figure 2) Soil water extraction area by roots and plant root development patterns
Maize does not extract water uniformly throughout the depth of its roots. In general, more water is extracted from shallower (higher) soil depths. When water enters the soil, the pattern of extracting water needs from different root zones is usually according to the 4-3-2-1 rule, meaning that 40% of water is extracted from the top quarter of the root zone, 30% from the second quarter. and less in order. This pattern is shown in Figure 2. The water that is applied using subsurface drip irrigation systems causes water to be collected from a deeper depth than the location of the irrigation lines in the corn field.
Additionally, although corn roots can reach 150-180 cm deep into the soil, a conservative assumption is that the first 100 cm of soil is considered the effective root zone by late in the growing season. At the end of the season, when predicting the time and amount of the last irrigation, the effective depth of the root extends up to 120 cm.
How is the water requirement of the plant matched with irrigation?
In general, irrigation water refers to the amount of water in the soil and any beneficial rainfall that occurs during the growing season. Therefore, one method to estimate irrigation needs is to add useful rainfall to the amount of water available in the soil
Ten and subtract from that the amount of evaporation and transpiration of the plant or the water requirement. For corn planting land in stony soil, the average irrigation amount for a long time is about 15 to 35 mm per year. These values may vary in different regions and years due to meteorological conditions (rainfall, solar radiation, temperature, wind speed and humidity) that affect evaporation and transpiration.
When designing an irrigation system, we must make sure that the system is able to supply the water needed by the plant. But the simple conversion of the plant's water requirement to the required capacity of the system may lead to the addition of unnecessary components of the irrigation system. Therefore, to determine the irrigation requirement and the capacity of the irrigation system, the amount of water in the soil and the rainfall during the plant's growing season should be taken into account.
The goal of irrigation management should be to provide sufficient water for the plant, taking into account the economic and environmental effects. Because corn yield decreases near the maximum yield due to a decrease in response to irrigation water. However, irrigation systems cannot transfer 100% of water to the plant, and this causes that all the water does not lead to the plant's performance. Therefore, in choosing the time of irrigation, it is necessary to consider the cost and the ability to increase the yield.
Using excess water may reduce plant performance and increase water pumping costs. For this reason, limited irrigation or low irrigation may lead to increased yield.
Table 1) Average corn water consumption (ETc*) based on growth stage for 113-day-old corn
Corn growth stages Number of days for each stage of growth Water required to reach each stage (mm) **Total water required in each stage (mm) Average water consumption (mm per day)
Seedling emergence (VE) 0-10 20.32 20.32 2.032
4 leaves (V4) 29-11 45.72 66.04 2.54
8 leaves (V8) 30-46 73.66 139.7 4.572
12 leaves (V12) 47-55 45.72 185.42 6.604
Beginning of tasseling (R1) 56-68 96.52 281.94 8.128
silking (R2) 69-81 96.52 378.46 8.128
Milk seed (R3) 82-88 48.26 426.72 8.128
The beginning of seed depression (R4) 89-104 96.52 525.78 6.096
Full seed indentation (R5) 105-125 96.52 622.3 5.08
Complete treatment (R6) 126-140 35.56 657.86 2.54
*: ETc is the evaporation rate of plant transpiration, which is obtained by multiplying the base evaporation and transpiration (ET0) in the plant coefficients of corn.
**: The amount of water is calculated as a net water requirement without considering the efficiency of water use in the farm.
However, using less water than the plant needs usually leads to a decrease in yield compared to water corn. But in times of severe water limitation, for optimal use of water, it is necessary that the available water be allocated to the vital stages of plant growth, such as the time interval between the pollination stage and the initial seed pulp stage.
What are the growth stages of a corn plant?
Immediately after planting, plant water consumption consists almost entirely of evaporation from the soil surface. Estimated plant evapotranspiration is usually less than 2.5 mm per day, unless the soil surface is moistened by irrigation or rain. Following rainfall, the amount of soil evaporation can be more than 5 mm per day, which depends on the texture of the soil and remaining plant remains and the amount of rainfall. Irrigation during this period is not recommended because the use of water through irrigation systems can cause sloughing on the soil surface, which reduces water penetration and in some cases prevents the emergence of plants. Maintaining the remaining suitable vegetation cover by absorbing the energy of the water drop hitting the soil limits the water and by reflecting a part of the incoming solar radiation, it minimizes the evaporation of the soil.
In about two weeks after the emergence of the seedling, the corn plant grows to a height of about 15 cm (4-leaf stage). During this period, the permanent root system starts to grow from nodes and crown. At the height of about 25 to 30 cm of the plant (6-8 leaf stage), crown flower (tassel) and ears start to form inside the stem. The number of rows and the number of seeds per row are determined in this step. The leaf area index (LAI), which ranges from 0 to 5, increases to 2.0 for corn under full irrigation. Daily water consumption of corn is on average between 4 and 6 mm per day. If there are no soil limiting factors such as compaction, impermeable layer or gravel, plant roots are concentrated in 50 cm above the soil surface. Assuming an effective root depth of 50 cm, the usable water of the plant is 8 mm in silty loam soil and 4 mm in sandy soil. In the depth of the first irrigation, it is necessary to take into account the amount of rainfall and it should be light in order to limit the loss of deep penetration of water.
Between the 8-leaf stage and tassel appearance in maize, leaf area and water use grow rapidly and reach the maximum daily water consumption during pollination. During this period, the root depth increases from 50 cm to 120 cm and doubles the amount of water in the soil for plant growth. The leaf area of blue corn increases to more than 5 with plant population above 60 thousand plants per hectare. The average water usage rate increases to 8 mm per day in a period of three to five days. With the increase in air temperature, decrease in humidity and wind, the amount of daily water consumption can reach more than 10 mm per day.
At this stage, preventing water stress is very important because water stress causes silk and pollen grains to dry, which causes poor pollination. The depth of irrigation should be proportional to the evaporation and transpiration of the corn minus the rain. Also, determining the right time to stop irrigation is an important economic decision.
When is it appropriate to water corn?
In response to this article, it should be said that when the soil moisture is limited, it is better to start watering the corn field. But it is usually observed that in the absence of irrigation, despite the sufficient moisture in the soil and d
Above 26°C, corn leaves begin to curl or wilt. Therefore, leaf wilting alone cannot be a definitive sign of drought stress. Therefore, to determine the water requirements of corn, we must evaluate the soil moisture throughout the root zone, and ultimately determine whether the crop needs more moisture to increase crop yield. It should also be noted that too much premature and unnecessary watering can slow down the growth of corn roots. In addition, excessive field irrigation or rain and soil saturation can lead to reduced plant growth, reduced corn yield, and nitrogen loss. Therefore, to provide the water needed by corn in all the vegetative stages, we must irrigate with conservatism and vigilance.
Figure 3) The effect of drought stress on yield reduction in different stages of corn growth
In the natural state, the growth period of corn requires a large amount of water, and it must be continuously supplied with water. Although maize is susceptible to wilting in the early stages of growth, its tolerance to water deficit is high until the 9-leaf stage. Therefore, it is less justified to expect a decrease in yield at these stages, especially if the soil moisture is at a suitable level. Consequently, irrigation should be planned carefully and conservatively until the tillering stage.
How is farm irrigation managed?
Irrigation management is a vital issue that includes various actions and decisions, including the time of irrigation and the amount of water consumption. These decisions must be made based on the water resources available for irrigation, the water holding capacity of the soil, and the water needs of the corn plants. Timely irrigation leads to sufficient water supply to prevent stress in corn plants, at the same time, with maximum use of rainwater and soil moisture. Therefore, in irrigation planning, all water resources are considered to achieve economic efficiency. For this purpose, the use of soil water condition measurement sensors is suitable for irrigation management. These sensors provide information about the amount of water in the soil or the amount of water that is drained.
The management of corn field irrigation includes the assessment of the economic and environmental consequences of each irrigation. For example, if 50 mm of irrigation last time increases the production of 320 kg of seeds per hectare and the price of imported corn is 19,500 Rials per kg, it can increase the income from water use up to 6,240,000 Rials per hectare. But for the purpose of environmental management, irrigation should also be examined; Because if the plant does not consume all the irrigation water, this excess water can lead to negative environmental effects.
At other times, some farmers cut off irrigation early to allow the corn to grow faster. But this method may lead to not achieving the full potential of the product. Stopping irrigation in the depression stage can cause a 15-20% decrease in corn growth performance. Therefore, irrigation decisions should be made according to the life cycle of the corn plant, soil moisture in the field, and how water resources are used.
In general, the right time to ripen corn is 60-75 days after silking. At this stage, the water requirement of the plants is minimized. Depending on weather conditions and soil moisture, a decision should be made whether to continue watering or not. Maintaining soil moisture until corn ripening can help reduce stress and increase yield.
Figure 4) Installing the irrigation sensor in the soil, the red arrow indicates the location of the sensor relative to the corn row.
By examining the signs of maturity, it is possible to determine the right time to stop watering. Observing and monitoring the milk line can help to determine when it is due. When the milky line (the boundary between soft and hard starch) moves towards the end of the grain, it indicates an increase in grain weight. In the ripening stage (R6), the milky line reaches the end of the seed and a black spot is formed. At this time, the seed reaches its maximum dry weight and has a moisture content of 28-35%. Therefore, irrigation after this time will not affect the yield or weight of corn seeds.
What is the texture of the soil?
Soils classified as coarse-textured soils include fine sand, sandy loam, and fine loamy sand. These types of soils generally have less than 120 mm/m water holding capacity available to plants. In the upper 90 cm of these soils, the available water can be between 40 and 70 mm. Some of these soils have root-limiting layers at shallow depths that can limit root growth. By combining the low water capacity of the soil and the shallow root depth, a relatively small water and soil reservoir is formed, which can lead to water management challenges. Watering more than 20 mm can lead to plant stress in case of unexpected system failure. On the other hand, frequent irrigation of less than 10 mm can reduce the efficiency of water consumption. The logical solution is to use relatively frequent irrigation programs (between 10 and 20 mm of irrigation). However, in soils with medium and fine texture, the available water capacity is more than 150 mm/m and due to less storage, they have more flexibility in irrigation planning. If no leaching or surface runoff occurs, 19 to 33 mm of irrigation is suitable for these soils.
How is the corn field irrigation systems?
In Iran, about 70% of surface irrigation systems and almost 30% are done through pressurized irrigation. To determine the amount of water that should be pumped in each season, we need to estimate the irrigation efficiency. Atmospheric and ridge irrigation is usually done with an efficiency of about 50%. This means that if there is a need for 10 mm of net irrigation, 20 mm of water should be pumped. With
Using the reuse system, the maximum efficiency increases to nearly 70% and the amount of pumped water decreases to 14 mm.
In farrow irrigation, quick irrigation of the entire field is important. If water is applied to the field once in a while in a certain period of time, the water reaches more areas and produces a better yield than that obtained by irrigating all the farrows. In addition to saving irrigation time, it is possible to reduce the depth of water consumption to between 20 and 30% by implementing farrow irrigation once in a while. Without the reuse system, one-in-one Faroe irrigation efficiency is approximately 60%. With a reuse system, the maximum efficiency increases to nearly 75%.
Rainwater irrigation systems, with proper design and proper maintenance, can be 85 to 90 percent efficient. A rain irrigation system that is 90% efficient requires 11 mm of water to provide 10 mm of net irrigation. If cropping practices are changed to increase water efficiency and sprinkler spacing is less than 2.30 meters, system efficiency can be improved by moving the sprinkler closer to the soil surface. Also, center-centered rain irrigation systems provide the possibility of irrigation with a more precise depth and time than Faro irrigation systems. The ability to use the depth of water required for a center-driven rain irrigation system allows it to make full use of rainfall and minimize the potential for plant stress.
What are the important points in corn irrigation?
The best indicator for determining when to irrigate a corn field is soil moisture in the soil profile. At the beginning of growth, it is observed that corn resistance to water deficit is much higher than expected. If the soil moisture reserves are sufficient at the time of planting, the initial irrigations can be limited. The only necessary condition for this issue is that the lack of water is compensated before tasseling and in all reproductive stages.
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