Pivot irrigation in Georgia

In Southwest Georgia there are more than 6,000 center pivots used to water peanuts, cotton and corn. Farmers have control over how much water the irrigation nozzles spray as they pass over fields. Small fields can vary in topography and soil types, with some places wetter or drier than other places in the same field.

VRI technology

The concept is simple: apply water when and where crops need it. Don't apply it where they don't. VRI technology uses computer maps, global positioning systems, soil sensors and software to control where and how much water the nozzles on a center pivot spray on crops.

Growers want to irrigate more precisely, but don't have the time or level with higher-tech gadgets. The more time-consuming technology steps have been eliminated to make the system easier for farmers to use.

Instead of having to create computer maps of fields, this system has a simple "push-button" feature. A farmer can start the center pivot over a field. When it gets to a location he doesn't want to apply water, the farmer pushes the button to train the system not to water that area. Once the system passes this area, he pushes the button again to resume watering only the crop. This can be done in as many as 8 locations in the same field.

The water efficiency of VRI has been tested on farms in Georgia and found it can reduce the water use in a field by as much as 15% annually without sacrificing crop yield.

Record yields on rice fields

A production of rice under center-Pivot irrigation systems, located in Missouri (United States) reached record yields. While the majority of fields were well-suited for flood irrigation, one field had sandy loam soils and hilly terrain, which previously made it impossible to produce rice. The kind of soil cannot maintain a flood, so Pivot irrigation is a good alternative. It was the first experience with rice for the producer, but it didn't mean more work than in the corn field. They just ran the center-Pivot more time.

A grower who produces rice with a center pivot can be 5% more profitable than if he had flooded his field. Data collected throughout the years, on traditional and non-traditional rice fields, have recorded cost savings that rice producers have experienced with center pivot irrigation and linear machines versus flood.

Though a rice producer may use more pesticides and herbicides with a center pivot, the fertilizer costs remain the same as with a flooded field. Because a rice field irrigated with a center pivot does not need to be flat, and crop protection products can be applied through the irrigation machine, growers may see a 75 percent or more difference in labor costs, and a 50 percent or more difference in maintenance costs. Compared with a flooded field, fuel costs are also lower for rice produced with a center pivot due to a significantly smaller volume of water that is pumped throughout the growing season.

What's so great about Pivot irrigation?

Benefits to irrigating crops with a center Pivot

Flying across the USA, passengers notice green circles and half-circles, on the ground below. Those circles are created when a farmer waters his crops with Pivot irrigation.

There are two major benefits to a Pivot system. The first is simply that plants receive water on a regular, consistent basis. Pivot irrigation systems allow plants to receive water every 3 days, on average. This allows the water to soak into the ground, promoting deep root growth which in turn encourages healthy plants.

The second benefit to a center pivot is that water loss because of evaporation and drifting in the breeze is minimized. Pivots allow the sprinkler heads to be lowered to just inches above the tops of the plants, thus ensuring that most of the water reaches the crop and doesn't blow away in the wind. Water conservation is a serious concern today. Evaporation and wind drift are a concern also because many farmers are allowed a limited amount of moisture to get their crops to harvest.

Varied Terrain is Okay for Pivot Irrigation

Center pivots offer the ability to irrigate fields that have surface slopes that make it impossible to irrigate with surface methods. Many crops benefit from this type of watering system: alfalfa, corn, soybeans, sunflowers and more do very well with Pivots.

Center-Pivot systems and lateral move irrigation machines

Center pivots are a form of sprinkler irrigation consisting of several spans joined together and supported by trusses, mounted on wheeled towers with sprinklers positioned along its length. The machine is fed with water that comes from the Pivot pad.

Center-Pivots are typically less than 500 metres in length (circle radius). To achieve uniform application, center Pivot systems require a continuously variable emitter flow rate across the radius of the machine. Nozzle sizes are smallest at the inner spans to achieve low flow rates and increase with distance from the pivot point.

Most center pivot systems now have drops hanging from goosenecks attached at the top of the pipe with sprinkler heads that are positioned a few feet above the crop, thus limiting evaporative losses and wind drift. Pressure regulators are typically installed upstream of each nozzle to ensure each is operating at the correct design pressure.

Crops may be planted in straight rows or are sometimes planted in circles to conform to the travel of the center pivot.

Originally, most center pivots were water-powered. These were replaced by hydraulic systems and electric motor-driven systems. Most systems today are driven by an electric motor mounted at each tower.

For center pivot to be used, the terrain needs to be reasonably flat; but one major advantage of center pivots over alternative systems is the ability to function in undulating country. This advantage has resulted in increased irrigated acreage and water use in some areas.

Linear/Lateral Move Irrigation Machines

The above mentioned equipment can also be configured to move in a straight line where it is termed a linear move or lateral move irrigation system. In this case the water is supplied by an irrigation channel running the length of the field and positioned either at one side or midway across the field width.

The motor and pump equipment is mounted on a cart adjacent to the supply channel that travels with the machine. Farmers may opt for linear moves to conform to existing rectangular field designs such as those converting from furrow irrigation.

Lateral moves are far less common, rely on more complex guidance systems and require additional management than compared to centre pivot systems.