Managing Water Infiltration Problems
Over the past few weeks, there have been several farm visits discussing water infiltration issues. In many of these cases, chemical sealing of the surface soil has occurred. This creates a crust that reduces the movement of the water into the soil. In subsequent irrigation, when water is applied faster than the rate of infiltration, puddling occurs, leading to an increase in evaporation as well as saturated soil conditions. This impacts water use efficiency and tree health. A season of irrigation can require between 36 and 52 inches of applied water per acre. This is often applied to a limited area of an orchard, which is defined as the wetting pattern. Each irrigation system has a different wetting pattern, with micro-sprinklers somewhere around 30-60% of the orchard area, and drip around 20%. This means that, dependent on the system, the wetted area may receive 2-5 times more water than the targeted season’s application per acre. In other words, if four acre feet/acre were applied using a drip system that wets around 20% of the orchard floor, the soil in that wetting profile has nearly 20 acre feet of water that must pass through in order to infiltrate the soil. This is a tremendous volume of water to pass through the soil, and it can leach away beneficial elements which leads to chemical sealing and infiltration problems. When infiltration rates slow, it is important to know the causes as not all infiltration issues are the same. Taking an analysis of the water and soil is a good place to start. Unlike soil sampling conducted in the fall, soil sampling of the top 2-3″ of soil should occur to identify the chemical imbalance. Analyzing the soil and water will give an idea of salt load, SAR, pH, as well as other elements. This will help identify
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