Tree nut growers using pressurized irrigation systems in their orchards have the opportunity to fertigate, but may not be maximizing the opportunities it offers. Fertigation—injecting crop nutrients through the irrigation system—enables a more precise fertilizer application, flexibility in timing applications, saves labor, and can reduce production costs.

Advantages of using fertigation are lost if growers or farm managers choose the “one size fits all” approach of standard fertilizer rates and irrigation timing. Water and nutrients are delivered to the trees, but growers won’t achieve maximum nutrient use efficiency.  The four Rs of nutrition still apply in fertigation: right rate, right source, right placement, and right timing. Attention to these factors will provide adequate nutrition for crop production while minimizing the risk of loss of nutrients to the environment.

Optimizing Fertigation Systems

Estimating tree demand, monitoring tree nutrient status, and allowing for orchard variability and environmental conditions will optimize use of a fertigation system. Sebastian Saa, senior manager of agricultural research for Almond Board of California, said about 80 percent of California’s almond growers/orchard managers have micro-irrigation systems that are capable of fertigation. Saa said growers are adopting fertigation for applying nitrogen but may be leaving potential benefits behind by not adopting it properly.

“For the case of nitrogen, I would say there might still be some technological barriers. However, I would say that the limiting factor is not the adoption of this technique, but the proper use of it,” Saa said.

In other cases (i.e. some micro elements such as Zn or macros such as K), fertigation might not be the exclusive way of delivery, giving room to other methods such as foliar sprays of micro elements or direct and concentrated application of K to avoid K immobilization in the soil.

Cory Broad, key grower development manager with Jain Irrigation USA, said one of the biggest fertigation misses in the field is not planning applications around crop need, but rather applying based on irrigation scheduling.  A balance between irrigation scheduling and fertilizer application rates needs to be developed, Broad said.

Fertigation can increase nutrient use efficiency by providing the right amount to the tree for the stage of production. More efficient use of the nutrients provided can allow for a reduction of overall nutrient use over the course of the growing season, Broad said.

Saa added that a common misconception about the practice of fertigation is that it is management of nitrogen to enhance yield, instead of managing nitrogen to support yield.

Nitrogen is not a solution for all production problems, Saa said. If trees are small or do not grow well due to a pathogen issue (i.e. phytopthora) that issue cannot be solved by applying more nitrogen.  Nitrogen is a function of yield, meaning, for instance, that aiming to achieve a yield of 2,000 pounds of kernel, the trees need about 120 pounds of N to support that yield. Applying 120 pounds of N, Saa stressed, will not guarantee that production level. Growers should avoid applying the same amount of nitrogen every year without taking into account expected yields.

In addition, Saa said growers sometimes make the mistake of fertigating too early in the season, before 70 percent leaf out, and applying nitrogen at the beginning of the irrigation set or just before a long irrigation cycle, which can reduce efficiency and lead to leaching beyond the root zone.

Proper Technique to Improve Efficiency

Saa said proper fertigation techniques could improve nitrogen use efficiency if nutrients are positioned in the active root zone and the irrigation system has a good distribution uniformity.

Broad said he also sees growers and managers who opt to apply an average rate of fertilizer across the field for an entire season, not fully recognizing the benefits of implementing fertigation. The ability to match supply with demand not only lowers the risks of volatilization and leaching, it ensures the crop has access to the necessary nutrients it requires during different production stages.

There are also physical reasons that efficiency is lost. Soil types can play a role in fertigation efficiency if applications are not managed. Broad said excess application of water in an orchard with fast draining sandy soils can allow nutrients to leach beyond the root zone. On the other hand, he said, heavy soils can hold water in the soil pores and deny use by trees.

Saa pointed out that most growers have other production operations going on besides fertigation at the beginning of the busy growing season. Managing fertigation at a high level of precision can be difficult due to the time and dedication needed.

The system must also be properly maintained. The same rational used in timely oil changes in vehicles applies to irrigation systems, Saa said. Checking filters, checking distribution uniformity, using the programmer correctly, and proper mixing of fertilizers in the fertigation tanks will assist with maximum efficiency.

Broad said systems need to be set up appropriately for the types of fertilizer and crop stage and not the “set it and forget it” category. He also advised making sure the correct amount of fertilizer is flowing as the system is running and making sure all equipment is maintained throughout the season to prevent plugging or flow rate changes.

Broad said he doesn’t see many growers or managers following specific protocols in regard to fertigation. They may be on point with their fertigation but referencing the many materials online can be helpful in improving efficiency. Broad said he uses the Cal Poly ITRC Fertigation handbook to answer questions.

Fertigation systems, Saa said, are a fantastic tool that if used properly can result in optimal nitrogen use efficiency. Each production unit should be evaluated early in the season and fertigation plans adjusted as the season progresses and ability to predict yield improves.