Understanding soil texture is a key factor for successful crop production. Soil texture is crucial when determining what crops grow best in a field and how farmers should manage their land.
It’s particularly important if crops need irrigation.
Soil and water compatibility is extremely important to irrigated land. Water that is not applied at a rate and intensity compatible with a farm’s soil texture will have adverse effects on the chemical and physical properties of the soil.
That is why putting the focus on soil is key to irrigation management and selecting the right equipment for the job. While there are various considerations to take when selecting a sprinkler system, there are two big reasons to put priority on soil texture: it will let you know what flow rate (application rate) you need and how much water you can drop on your soil without damaging it.
Understanding Infiltration Rates
A good understanding of a field’s soil texture will help irrigators determine the length and frequency of irrigation events.
Water infiltrates soil’s pores at varying rates depending on texture. For example, water infiltrates through dense, clay soils around 1 to 5 mm/hr while sandy soils can absorb water at 30 mm/hr. This means that a water layer of 30mm on the soil surface will take one hour to infiltrate sandy soil.
However, this amount of water will take much longer to infiltrate clay soils. With more than 5mm/hr, runoff, soil sealing and salinity issues are likely to occur due to poor drainage and pooling on the soil surface.
As a rule of thumb, farmers irrigating sandy soils need to irrigate more often for shorter intervals. Irrigating sandy soil for too long will waste water due to deep percolations and wash nutrients beneath the root zone. Clay soils require long and infrequent irrigation while loam soils are somewhere in between.
Focus on Application Rate
The application rate of a sprinkler system must match the intake rate of the least porous soil in a field. If the application rate exceeds the soil intake rate, water will run off the field or relocate within the field, resulting in over and under watered areas.
Matching sprinkler application rates to the soil intake rate can be difficult though. The rate at which water infiltrates into soil is complex. First, the intake rate varies with time, being higher when water is first applied and decreasing as the soil obtains more moisture.
Application rate also varies depending on the crop growing.
For example, corn may need 7.0 mm (0.27 inches) of water per day during ear formation no matter the soil type. Gowers irrigating sandy soils will probably need to apply 1499 L/hr (6.6 GPM) for every acre irrigated to keep the crop healthy. In contrast, growers irrigating silt-loam soil may only need to apply 1113 L/hr (4.9 GPM) for every acre.
If the corn is rotated with dry beans later on though, then growers will need sprinklers than can be adjusted to apply 1612 L/hr (7.1 GPM) for every acre irrigated over sandy soils.
Irrigating just taking into account crop needs alone is risky and could result in lesser yields or poor crop development.
Don’t Forget Application Intensity
Before choosing a sprinkler system based on flow rate alone, it is important to think about the sprinkler’s wetted pattern and how the water is applied over the soil surface.
As water droplets are distributed onto the soil, the structure and infiltration rate of the soil becomes altered. To keep soil close to its pre-irrigation state, growers need to distribute water over largest area of instantaneous coverage possible and with low application intensity.
Although larger droplets are desirable to combat wind-drift, droplets that are too large have a higher kinetic energy. This can cause surface sealing and lead to erosion or inefficient irrigation on tighter soils. In general, tighter soils benefit from smaller droplets while looser soils can accept larger droplets.
Sprinklers with customizable deflectors and a wide range of nozzles, like the Senninger® i-Wob®2, are well suited for various soil textures due to the variety of droplet sizes available. The droplet size can be tailored to the needs of the soil and the flow rate can be adjusted for specific crop and climatic needs.