IRRIGATION & WATER MANAGEMENT


Back to Basics

By Tamara Scully




The R64 Briggs four-wheel boom from Cadman is adaptable to a wide range of applications.
Photos court esy of Cadman Power Equipment.

Irrigation is so much more than simply delivering water to plants. A properly designed irrigation system doesn't happen by chance, and there are many factors to consider before investing in a system for your farm or orchard.

According to Dr. Eric Simonne, northeast district extension director, University of Florida, irrigation is first and foremost a vital component of a farm business plan. The irrigation system must be cost-effective in the long run, and also make sense for your crops and acreage.

Once the decision to invest in an irrigation system is made, determining the water source is critical. Whether the water is from a well, farm pond, river, potable water system or water utility, the costs of using and moving the water need to be determined. Permitting or water usage fees may also be a concern.

Finally, there's the design of the system. Any irrigation system, Simonne said, needs to be designed by a qualified engineer. Irrigation equipment supply companies typically have consultants available to help assess the needs of the farm and design an appropriate system.

Watering basics

"The key to getting the right irrigation equipment in place is to understand what problems the farmer needs to solve. Besides getting water onto the field, there are other issues that need to be understood in order to recommend a solution that will accurately meet the grower's requirements," said Scott Black of Cadman Power Equipment (http://www.cadmanpower.com). Specializing in overhead irrigation systems, Cadman offers irrigation booms, hard hose reels, center pivots, sprinkler designs, traveling guns and pumps.

"The basics of irrigation are the same, regardless of the system: a water source, such as a well, pond or stream; a pump - be it diesel, electric or natural gas-powered; a means of moving water from the pump to the irrigation equipment, either through soft hose or above or belowground pipe; and the irrigation equipment itself," Black stated.

Drip irrigation and overhead watering systems are two ways to deliver water to crops. Within these categories are various operating configurations. Micro irrigation systems consist of drip, or trickle, systems and micro sprinklers. These provide low-pressure, low-volume water distribution to the root zone. Overhead systems include center pivot, linear move, traveling gun, and solid set or permanent set pipe sprinkler systems. Since irrigation is sometimes needed for frost protection, dust suppression, or to irrigate fields before planting, these concerns also factor into the final product selection.

Drip or overhead?

"Not every field is well-suited for every type of irrigation," Black stated. Field shape, obstacles, the volume of water needed, the amount of wind typically seen, and even the elevation of the field factor into the proper components of the system and its design. "With crop input and labor costs rising, ease of operation and simplicity are key," Black said.

While images of large booms traveling across massive fields may accurately depict the needs of some farms, small farms also have options that make these systems feasible. For example, Valley Irrigation (http://www.valleyirrigation.com) offers a single-span center pivot system for small fields up to 5.4 acres. The gas-driven system uses low-pressure watering, can use a variety of sprinkler packages, and can be used on 10 percent slopes.



Cadman Travellers are available in several models with a number of options.

Cadman's Mini Travellers similarly offer a labor-reducing system for smaller applications. Here, the machine is towed via a small tractor to the end of the field, the hose is pulled out, the system is engaged, and the hose retrieval rate is set. The machine irrigates the field at the desired rate, reeling the hose back in until irrigation is completed.

According to the Valley Irrigation website, mechanized overhead irrigation systems have a longer life span, can be less expensive to install, and are preferred where salinity or water quality is an issue, or where foliar chemical application and crop cooling are needed. While drip may offer more energy efficiency, overhead systems using low-energy precision applications are almost as efficient.

Drip systems are beneficial in many small farm applications. When growers use plastic mulch, rainwater or overhead irrigation is blocked from reaching the root zone; drip irrigation delivers water to the root zone. Drip irrigation products are available from John Deere, Toro, Agriculture Solutions, Rain-Flo Irrigation, Berry Hill Drip Irrigation and other companies.

"You get more production on a square-foot basis with drip than you would with overhead," Simonne said. "There is no money in growing - only in selling - vegetables. Grow in a way that you make money." While the initial cost of a drip irrigation system may be higher, the potential gain for the crop, and in water efficiency, may make it the better choice.

"Systems that keep the leaves dry are more desirable than overhead," Simonne said. Wet leaves lead to fungal and bacterial diseases. "Drip systems allow you to control how much water you put [down] and allow you to inject fertilizer," he added.

According to a section on the Penn State Extension website (http://extension.psu.edu/busi ness/ag-alternatives/horticultural-production-op tions/drip-irrigation-for-vegetable-production), drip irrigation "may require less than half of the water needed for sprinkler irrigation."

Efficient application of fertilizers is a factor, and drip irrigation can be implemented over a wide range of field conditions. However, frost protection is not readily available via drip systems, and drip tape is prone to damage from freeze events, rodents, equipment and other factors. Both drip tubes and drip tape can be reused, but commercial vegetable growers rarely reuse tubes, and it is costly to retrieve, store and repair tape. Management requirements are somewhat higher in drip irrigation than with overhead systems.

If a grower is considering an irrigation system for frost protection, Simonne cautions that all of the crops' needs should be considered when making the final decision. While frost protection needs are important, the probability of crop loss needs to be realistically considered from all angles.

"If you have a mild frost, overhead frost protection will work, [but] it is not a magic shield," Simonne stated. The system only works to a certain point; if temperatures drop more than a few degrees below freezing, it may not provide enough protection to matter. This type of frost protection requires large amounts of ongoing water application, he explained.

Whether or not to invest in irrigation for frost protection depends upon the value of the crop and the risk being taken. Growing under cover may be a more cost-effective option for some growers.

Micro sprinklers can be used successfully, particularly in orchards, for some degree of frost protection. They rely on the fog method, saturating the air with water in areas where low dew points are rare, and typically protect up to 4 feet of tree height. This may be a consideration for some orchard growers, depending on climate and other factors.

Measuring success

Putting water on the crops isn't simple. Even with a well-designed system in place, using the system properly and understanding the science of water application is necessary.

"If you want to have healthy plants, manage your water first," Simonne said.

If a grower feels that a crop is not growing optimally, often the first instinct is to increase the amount of water going to the crop. That, Simonne said, may be the wrong move.

"Typically, growers put on too much water, and that tends to push the soluble nutrients below the root zone," he said. "The key is to put the water on slowly, use drip tape with a low flow rate, and put it on in split intervals."

Simonne likens this to filling a glass from a gallon jug of water. If you pour the gallon into the glass all at once, it will overflow. The overflow represents the leaching of nutrients that will occur with an overabundance of water. However, if you fill the glass, drink it, then fill it again and continue until the gallon jug is empty, all of the water will be utilized without waste.

The type of soil determines the amount of water that can be stored in the root zone. The amount is limited in sandy soils. The soil moisture content should be maintained to eliminate plant stress, and irrigation should be timed accordingly. Irrigating at the wrong times, or in the wrong amounts, can reduce crop yield, as well as waste water and nutrients, no matter what type of irrigation system is in use.

Sprinkler systems tend to promote weed growth, since the space between rows, where the weeds can grow, is also watered. With drip systems, only the crop row itself is watered. The rate of watering is crucial with any system, as too fast an application causes puddling and crusting. Too much water and the nutrients will leach; too little and the plants will be stressed.

For vegetable crops, the effective root zone is from 12 to 20 inches below soil level, and the water needs to be available for these roots. Water moves through soil at different rates, based on soil composition. The available water capacity (AWC) is an important number; it is the difference between the total amount of water the soil can hold up to saturation and the permanent wilting point, where plants can no longer access residual moisture. About 50 percent of the AWC can be depleted without plant harm.

"Measuring is the key to check that plant status is good," Simonne said. The role of extension, he adds, is "to help growers design their irrigation schedule" so crops receive enough water and nutrients to meet their needs, as opposed to simply being watered. "The recipe is the irrigation schedule and the fertility plan."



Assessing your farm's irrigation needs requires an understanding of your goals, crop needs, the growing system, soil characteristics, your market, and your current and long-term budgets.

Bottom line

Assessing your farm's irrigation needs requires an understanding of your goals, crop needs, the growing system, soil characteristics, your market, and your current and long-term budgets.

"No one application is going to fit every scenario, so flexibility, labor, energy costs and water sources all need to be considered before making a recommendation," Black said. "When making a decision, more than just the price of the equipment needs to be considered. The cost per acre needs to be determined, and understood, in order for a farmer to make a choice of equipment that makes the most sense for their business."

"It's all about the money," Simonne stated. Any irrigation decision has to be cost-effective, designed for the needs of the crops and the farm, and used properly.

"The price of equipment is not the total cost," Black said. "Sometimes the initial investment of one system over another is higher, but the lower operating costs pay back the higher investment in less than a season. Irrigation is more than just slinging water: fuel costs, water source, crop type, wind, evaporation, field setup, pipelines, elevation, soil types, drainage, labor costs and system efficiency all need to be considered." l

The author is a freelance contributor based in New Jersey. Comment or question? Visit http://www.farmingforumsite.com and join in the discussions.