Measure it out

Whether it’s corn, potatoes, alfalfa or other crops, maintaining adequate soil water is critical to maximizing yields, reducing risk, increasing operational efficiency and remaining good stewards of the land.

The No. 1 input for any crop is water. Unfortunately, we can’t always count on Mother Nature to deliver the water our crops need, when and where they need it. While irrigation helps producers overcome many water challenges, applying too much or too little water at the wrong time is a common problem.

For many growers, irrigation scheduling is the most effective approach in order to time and regulate water applications in a way that will satisfy the water requirement of the crop without wasting water, energy and plant nutrients or degrading the soil.

The process of successful irrigation scheduling relies primarily on the ability to make accurate irrigation management decisions based on field-specific data. While the process of collecting and analyzing the necessary data to make irrigation decisions can seem complex, the benefits have been consistently proven in the field through decades of field trials and validation by numerous researchers and commercial growers around the world.

With irrigation scheduling, growers have the ability to improve their operation through the following:

• Provide the exact amount of water a crop needs at the time it needs it and help avoid crop stress, which together can ultimately optimize yield.
• Prevent overirrigation, reducing the amount of energy used for pumping and conserving water.
• Eliminate leaching of fertilizers beyond the root zone, reducing loss of costly inputs.
• Help protect ground and surface water from unnecessary pollution.
• Help prevent yield-reducing disease which can be worsened by overwatering.

Typically, science-based irrigation scheduling in North America is primarily achieved in three ways: using soil moisture sensors, the checkbook method and the automated checkbook method. Let’s compare these three common methods.

Soil moisture sensors

Soil moisture sensors, when coupled with site-specific soil information, can provide insights into water availability in the crop root zone, indicating when crops are at risk for stress, when to irrigate and when to stop. These sensors can be stationary, placed at predetermined locations and depths in the field, or handheld to allow measurement of soil moisture at several locations. Depending on the device, data can be collected manually or transmitted wirelessly.

While soil moisture sensors are typically cost-effective and easy to use, their footprint is limited to the volume immediately surrounding the device. Installing and monitoring multiple sensors can be time- and labor-intensive. Moreover, relying on and making sense of electromagnetic signals for agricultural water management can be a daunting task. Commercial sensors can be subject to soil-specific errors and demonstrate highly variable attributes that mitigate their ease of adoption. In most cases, effective reliance on a soil moisture sensor requires site-specific calibration and frequent, close inspection.

Growers should consider the following when including soil moisture sensors in irrigation decision-making:

• Sampling across the soil profile, monitoring soil moisture across the entire root zone to provide a more comprehensive picture of plant water availability.
• Tracking sensor accuracy, especially if the sensor was installed incorrectly or the field has high levels of clay content or salinity.
• Considering location, placing sensors at a representative spot in the field, out of the way of farm machinery and irrigation systems.
• Comparing wireless versus manual data collection and the cost and convenience associated with each option.
• Looking at the ability to easily and quickly convert collected data to irrigation decisions.

Checkbook method

The checkbook method is a form of soil water accounting that is widely used today in irrigation research. It’s called the checkbook method because it operates just like a bank checking account. Rain and irrigation are deposits while water used by the crops and evaporation from the soil surface are withdrawals. Like a checking account, it’s important to keep a running account of deposits and withdrawals to ensure moisture levels don’t fall below the minimum balance.

To start the checkbook, growers must determine the soil texture, crop type and rooting depth, available water-holding capacity of the soil, minimum allowable balance and an estimate of current soil water balance. During the growing season growers need to monitor and log evaporative demand and measure and log rainfall and irrigation applied to the field. Using a soil water balance spreadsheet, the grower manually enters the data, calculates the new soil water deficit and determines when the next irrigation is needed.

While it is an inexpensive and proven tool for irrigation scheduling, the checkbook method can be very time-consuming, requiring almost daily updates, especially during critical growth periods.

Automated checkbook method

Cloud-based irrigation management technology eliminates the need for complex, manual calculations, delivering continuously updated, science-based irrigation recommendations that are customized for each field.

Using the proven, traditional checkbook method, along with validated crop growth models, as-applied irrigation data and hyper-local, field-specific weather data, the automated checkbook method can very quickly and clearly generate the information needed to help producers decide precisely when, where and how much to irrigate. No special math skills, hardware or agronomic background is required. The calculations are conducted by algorithmic models that produce an irrigation application recommendation the grower can then apply.

After entering the field’s crop type, hybrids and planting dates, the technology will allow growers to

• track the available soil water throughout the field by combining a soil map of the field, proprietary dynamic crop canopy and root growth models, hyper-local weather data and the applied irrigation history.
• forecast the crop’s future water needs and predict when and where, without additional irrigation, the yield will begin to decline due to water stress. It also estimates the amount of yield that would be lost to water stress, which varies based on the crop’s development state and the severity of the stress.
• create a high-resolution map showing the amount of water available to the crop across the entire field.
• automatically generate variable rate irrigation prescriptions, which are continuously updated and optimized to account for actual and forecasted weather, changing crop water requirements and as-applied irrigation.
• integrate into irrigation remote monitoring and control platforms, giving growers the ability to immediately put their irrigation decisions into action and monitor their progress.

Automated irrigation scheduling technology can be combined with remote irrigation management tools in the field, which further enhances the efficiency of this method by allowing the grower to quickly apply the water application recommendations from virtually anywhere. Growers using the automated checkbook method have been able to increase their yields while reducing overwatering and the related input costs and nutrient losses. Growers who implement this method typically find that they are overwatering. Correcting this benefits farm output while also reducing water and energy consumption. While there is an annual subscription cost to using this method, no hardware or sensors are needed to generate the irrigation recommendations, which leads many users to believe the yield boost, combined with time and input savings, more than offsets the cost.

Regardless of the method used, irrigation scheduling is an ongoing best practice that will produce results every season and create a more sustainable future. In fact, the United States Department of Agriculture incentivizes growers to increase sustainability on their farms by offering subsidies for the implementation of water conservation practices and tools, including irrigation scheduling. More information for growers about the Environmental Quality Incentives Program can be found nrcs.usda.gov. The best way a grower can get started exploring this funding for their operation is by directly contacting their local Natural Resource Conservation Service office, which can be located at offices.sc.egov.usda.gov.

Kiran Sharma is associate product manager for digital products at Lindsay Corporation. She holds a M.S. degree in agricultural and biological engineering with a focus on agricultural irrigation.