The art of irrigation scheduling is a tricky business. However, done the right way, it can lead to a very successful season not to mention a profitable one. The term irrigation scheduling simply means you have a system in place for when and how much water to apply to your crops. There are many different factors to consider when planning an irrigation schedule. For example, the type of soil will determine how much moisture storage capacity there is. Also, crop water use depletes the amount of available water which will affect how much water to apply.
Since various points in the field are not all the same, irrigation scheduling will need to differ accordingly. A great way to stay organized and ensure long-term success is by implementing an irrigation scheduling checklist. There are five main points to keep track of. They are soil texture, crop root zone, available water, minimum balance, and current soil water balance.
First, we’ve established that different soils will impact irrigation scheduling. Soil types are categorized by their texture. Soils that are fine in texture can hold more available water than soil that is coarse. For instance, silt or clay has a fine texture and therefore will hold more available water than something more coarse in texture like sand. If your fields have soil that is coarse, irrigation will be needed much more frequently. Sometimes, soil texture may be unknown but there are resources available to figure it out. Each field will have its own unique soil composition, with contrasting soil types throughout.
Crop Root Zone
Next, another factor that will affect irrigation scheduling is the crop root zone. The active root zone for crops planted annually will increase in depth during growing season. The type of crop and the stage of growth determines what the root zone depth is, along with conditions in the soil profile. Check the root zone depth for your specific crop. Keep in mind that adjustments may need to be made depending on if there are any restrictive layers.
When talking about available water, you have the soil water balance and the soil water deficit. The soil water balance means the available water left in the soil. By the same token, soil water deficit means the amount of water that’s already been used. So, if your soil water deficit was at 30 percent, that would mean available water is 70 percent.
The minimum balance means the driest that soil will be allowed to get. Most people try to set this just above the level where plants experience water stress. Most of the time, the minimum balance lands around 50 percent of the available water. However, a healthy range is anywhere from 40 to 60 percent. Anything lower than this and you run the risk of water stress.
Current Soil Water Balance
In order to properly schedule irrigation, you need a starting point. Figure out what the current soil water balance is, either by using special sensors or the hand-feel method. Record the soil water balance every few weeks and update your irrigation schedule accordingly.