How to Get What You Need from Fertigation
During the last few decades, the acres of drip-irrigated vegetables have greatly increased in California. Research studies have shown that drip can increase the efficiency of water and nutrient applications.
But in practice, many farming operations may not be reaping all the benefits of drip. Perhaps because the shift from sprinklers and furrow irrigation to drip requires giving up some old habits.
Shorten Timing Between Irrigation for Drip
Waiting seven or more days between irrigations is one common practice for irrigating by furrow and sprinklers in order to dry out furrows so tractors can access fields. Or in the case of sprinklers, it avoids frequently soaking leaves and promoting foliar diseases.
Studies we have conducted in California’s coastal valleys show many growers drip irrigate vegetable crops at an interval commonly used with sprinklers.
Irrigating at this longer interval limits the water and nutrient use efficiency benefits that drip irrigation provides. At these longer irrigation intervals, a vegetable crop is more likely to experience water stress, slowing growth. Plus, more water must be applied with each irrigation, potentially causing nitrate to leach below the root zone.
There’s No Need for Side-Dress Applications
Another custom practice that has persisted is to fertilize drip irrigated fields in the same way you would in sprinkler and furrow irrigated fields: using a tractor-side-dress applicator.
When you use the side-dress applicator, you’re generally limited to two applications before a vegetable crop is too large for fertilizer to be knifed into the bed. So fertilizer side-dressed early on may exceed the crops’ needs and increase the risk of nitrogen deficiency developing later.
Fertigating through drip has a couple advantages over side-dress applications:
- It allows you to spoon feed fertilizer to match crop nutrient needs.
- You can place nutrients where roots are most concentrated.
Take Advantage of Fertigation’s Timing Flexibility
Though most of us are familiar with fertigation’s benefits, many vegetable operations fertigate drip-irrigated crops in two split-applications, similar to side-dressing with a tractor.
And although drip provides flexibility to finely adjust fertilizer rates, many vegetable operations fertigate more nitrogen than the plants can utilize early in the crop cycle.
What’s Limiting Fertigation’s Widespread Use?
There may be several reasons why many growers have not fully transitioned their management to maximize the water and nutrient efficiency benefits of drip.
The labor shortage can thwart plans. In California, labor has become more expensive, and skilled irrigators are hard to find. Every irrigation and fertigation activity on a farm requires labor. At the start of a drip irrigation, an irrigator needs to monitor the pressure and check and fix leaks in the tape. Fertigation requires the added steps of setting up a pump and a fertilizer tank by a field, as well as someone to monitor that the fertilizer is properly injected.
Drip irrigation doesn’t always apply evenly. You may be uncertain if the fertilizer applied through the drip lines is distributed evenly. The uniformity of many drip systems we have evaluated in vegetables is less than optimal. Leaks can stem from reusing tape for eight to 12 crop cycles. Clogged emitters make the drip system operate below the recommended pressure.
Improperly injecting fertilizer limits fertigation’s payoff. Injecting too quickly or not completely flushing it before the end of the irrigation cycle will reduce application uniformity.
Tips to Get More from Your Fertigation System
Drip fertigation can be a valuable tool for efficiently using water and nutrients to produce vegetables, but all tools must be used correctly to achieve the best results. A prerequisite for optimizing water and fertilizer in drip is to assure that the system has a high application uniformity. Well designed and properly managed drip systems should have an application uniformity greater than 85% (where 100% represents perfect uniformity).
Fertilizer applications often can be skipped or greatly reduced by identifying fields with sufficient soil nitrogen. This strategy allows fertilizer programs to be flexible so they can be adjusted for the site-specific conditions of each field.
Fertigation allows growers to fine-tune fertilizer rates. In contrast, most side-dress applicators can only coarsely adjust fertilizer rates, often in increments of more than 5 gallons per acre.
Evaluate the distribution uniformity on a subset of fields can determine if the drip systems are operating as designed.
Provide proper training and equipment to irrigators helps improve the uniformity of irrigation and fertigation applications. Irrigators should know how to use calibrated gauges and make adjustments so drip systems are operating at the pressure (usually between 8 and 12 psi) required for maximizing application uniformity. Training on the best practices for fertigation also will improve fertilizer application uniformity.
In western states like California, water-quality regulations continue to become more restrictive and will require that growers manage water and nitrogen fertilizer as efficiently as possible to prevent nitrate contamination of underground aquifers and surface waters.
The flexibility to adjust fertilizer rates midstream based on soil nitrate readings is an advantage of fertigation that is difficult to match using a side-dress approach to fertilizing.