Achieving Greater Uniformity, Overall Effectiveness

Tips for better watering

Published in the March 2009 Issue Published online: Mar 30, 2009 Irrigation

It would be impossible to discuss high-yield western agriculture without considering irrigation to be the most significant contributor to increased production. In Idaho a variety of irrigation systems are used to deliver water to thirsty fields.

Over the years, furrow and flood irrigation have been largely replaced by sprinkler and center pivot irrigation. In recent history, drip irrigation systems have been gaining popularity in more permanent cropping systems such as fruit and nut trees and vine crops.

Some research has been done with drip systems in potatoes, with encouraging results as far as yield and quality. Although, challenges continue to exist for large-scale application and maintenance of drip systems especially with multiple rotational crops grown over a 3-4 year cycle.

Regardless of the particular irrigation system used, there are some important points to consider as time is drawing close to begin another irrigation season.

UNIFORMITY

When your local fertilizer dealer pulls into your field to apply pre-plant fertilizer, it is expected that they will uniformly apply the pre-determined amount across the whole field. Stripping a field or mis-applying any fertilizer or chemical is not accepted very well.

In extreme cases, words like "law suit" or "using a competitor" enter into the discussion. While we should expect accurate and precise application of fertilizer or chemicals, do we hold water application to the same high standard?

Irrigation problems are often times very difficult to see with the naked eye-initially. Later in the season, after it is too late to do anything it becomes very evident where the problems were. The primary culprits that decrease uniformity are worn nozzles and sprinkler heads on lateral move systems and bad pressure regulators and packages on pivots.

If you are pumping a lot of sand through your system, you will need to check for wear and replace worn parts more frequently.

Often times our test of an irrigation system is to drive by and if all the sprinklers are turning, then we assume all is well. As a sprinkler head wears out, it doesn't do it uniformly. Often times you will see it moving very slowly for part of the pattern and quicker through the rest of the pattern.

On lateral-move systems, later in the season it may appear drier on one side of the line and you may assume it is a wind skip, while that is possible, it may well be sprinkler heads not rotating properly.

Bottom line: if you can't remember the last time heads and nozzle were replaced, it is probably time to do it.

Some problems with pivot packages are easy to see. If a regulator is blown or a resistor motor is worn out on rotators, it is usually easy to see. If the plates are worn, your pattern may still appear to be okay until later and you start to see dry rings in the pivot. If your pivot package is more than five years old, you may want to do some testing with rain gauges to see if the pattern is still uniform.

While this sounds simple, you may want to seek additional advice on how to properly carry out a rain gauge test. It takes quite a few rain gauges spaced correctly to test uniformity.

It is very important to be sure that all leaks in main line and pipe are fixed. Not only are you wasting water and causing erosion, you are robbing pressure and decreasing uniformity of the whole system.

It is also a good idea to check the pressure on the end of the system to make sure there is adequate pressure throughout the system. Again, by the time low pressure problems are discovered it is too late to recover lost yield. You can purchase a pressure gauge and a pieto tube from your irrigation dealer for less than $30.

This simple tool can help you detect a number of problems early in the season.

Another major consideration in irrigation uniformity should be the amount of slope you have in a given field. On steeper fields it is not uncommon to see lakes in the low ground or water running across roads and into neighboring fields.

Not only do you have crop loss on the hill and in the valley, but the runoff water is carrying top soil loaded with nutrients and organic matter away from an area of the field that is probably already low on those two things. If that runoff water is either returning to a canal system or a stream there are substantial environmental concerns a grower may have to deal with.

Fortunately there are many options available to help minimize water runoff. The primary tool used by the majority of growers is some form of reservoir tillage. While this has proven to be effective, at reducing runoff, it often times doesn't provide season-long runoff control.

One of the biggest contributors to runoff is soil compaction. While we usually think of compaction in terms of implement traffic through the field, one of the greatest contributors to compaction is sprinkler irrigation.

PRODUCTS

In addition to tillage, there are some products that can significantly improve water infiltration and reduce runoff. There are two main types of products that are used. The most common type of product used would fall into the surfactant/detergent class of product, whose primary function is to condition the water.

These products break the surface tension of water which in turn helps with water movement into soil micro-pores. The other type of product used is called polyacrylamide or PAM products. PAM products can significantly improve infiltration rates and water retention in the soil. They can also improve soil structure and help reduce crust formation.

PAM products can also be very useful tools in helping to move salts out of the root zone.

The important thing to remember in using these tools is to start using them before you have a problem. If you wait till the problem is obvious, either product will at best be less effective at solving the problem at worst, it will be a waste of your money.

Water conditioning/surfactant products are generally less expensive, but need to be applied throughout the year. PAM products are often applied at the beginning of the season and last throughout the irrigation season. It is important to note that all tillage should be done before applying a PAM product. Tillage will significantly reduce the effectiveness of PAM and surfactant-type products.

Considering the cost, it would be reasonable to make an application of a surfactant-type product before a reservoir tillage pass, then again after, but with PAM, wait till after dammer diking to apply. When considering what type of product to use and how to apply it, consult with your crop advisor. In my experience, positive results can be achieved with both products, but the appropriateness of the product will need to be determined on a field-by-field basis.

When designing a new system or improving an older system one of the most important considerations is the amount of water the system can deliver over the field for which it is designed. All too often, new pivots are adjusted too low for the application.

For me, a properly adjusted pivot would be around 8 gallons/acre/minute, higher in some circumstances. A pivot can always be turned off for a day if it gets too wet, but it is hard to get more than 7 days of continuous operation/week out of a system.

Anything less than 7 gallons/acre/minute will lead to reduced yield. If you have higher soluble salt content in the field, it will be very difficult to flush salts out of the root zone.

Irrigation is absolutely essential to successful operation of your farm. Additional attention to older systems can significantly improve yield and quality. Making wise decisions on new systems will save you headaches and frustration down the road and will positively affect your bottom line.

There are plenty of good resources available to help you make the best possible irrigation decisions for your farm.

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