Water Management

Water management can reduce the use of irrigation systems and also save money and may improve crop quality and yield. The section will discuss irrigation scheduling so water is applied when needed and soil moisture sensors that can provide information on how accurately the irrigation scheduling is working.

 

Irrigation Scheduling

The goal of irrigation scheduling is to maximize use of stored soil water and precipitation to minimize pumping. [4-9] Demonstration projects in central Nebraska have indicated that 1.5-2.0 inches of water can be saved by monitoring soil water and estimating crop water use rates. Thus, deciding when to irrigate and how much water to apply can have a great impact on energy and water use. In many cases, good irrigation management can improve crop yield and quality. Table 2 presents a summary of the methods used to decide when to irrigate as a percentage of the total number of farms irrigated in the U.S. (NASS, 2008) [1]. The results include replies from individuals who employ multiple methods depending on the field conditions. Figure 12 indicates that evapotranspiration- (ET) based irrigation scheduling and soil water sensors are used by less than 30% of the irrigators in the region. Consequently, millions of dollars are spent on energy to distribute water that may not be needed by the crop.

 

What practices are available to help producers identify the time when water is needed? The simplest way is to keep track of the water applied to the soil, the amount the plants use, and the water available in the soil by calculating a water balance using a checkbook approach. Rainfall and irrigation events are additions or deposits to the soil water bank and plant water use (called evapotranspiration or ETc), and deep percolation are removals or debits to the soil water bank.

Figure 1: Atmometer. Source: Scott Sanford

Figure 1: Atmometer. Source: Scott Sanford

The checkbook method does require some daily record keeping, but it can help the irrigation manager be more precise about the amount of water available in the soil for plant growth. The ETc value is estimated by universities and water districts and published or emailed to growers.

Growers can also purchase an atmometer (Figure 1) to estimate ETc in the area around their fields. Worksheets and computer programs are available to aid with the calculations and record keeping tasks (see links to various websites in Additional Links and Resources.)

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