UC Research: Irrigation management boosts yields

Issue Date: April 22, 2009

By Mike Cahn, University of California Cooperative Extension farm advisor, Monterey County

When growing crops like Romaine lettuce, good water management is needed to keep the nitrogen in the root zone; if you don't look at water management your chances of having success with nitrogen management tools are greatly reduced.

In 2008 we began commercial field trials in the Salinas Valley to evaluate how to grow lettuce with less water and nitrogen fertilizer using CIMIS evapotranspiration data.

The ET data is available for free on the CIMIS Web site. We developed a spreadsheet calculator that converts the CIMIS ET data into an irrigation schedule for lettuce.

The spreadsheet bases the crop coefficient for lettuce on the canopy size. The canopy cover for lettuce is almost zero for the first 20 days. For days 20 to 60 it rises to around 80 percent. A lot of the excess water in our 2007 study was being applied when the crops were young, and the ET requirement was low.

We also did a detailed analysis of the water holding capacity of different Salinas Valley soils so that the irrigation schedule was based on soil moisture tension. Lettuce growth slows at soil moisture tensions above 30 centibars.

At this stage we're just seeing if this complex irrigation management system works, and if it can save money on water and fertilizer.

We tried our system in large-scale trials of 15 to 27 acres on three lettuce farms in different areas of the Salinas Valley.

On average we were able to reduce water use by almost 25 percent over the course of the season using our system. This water use also translated into an average savings of 65 pounds of nitrogen per acre because we lost less to leaching of nitrate.

In a Salinas-area Romaine field, the grower was already using detailed irrigation management strategies, applying only 10 inches of water per acre, but we were still able to reduce water use on the summer crop by 12 percent. Even this modest increase in irrigation efficiency allowed us to save $10 an acre in nitrogen fertilizer. And there was no difference in yield.

Our greatest success came in a sprinkler-irrigated head-lettuce field planted in late June near King City. We reduced water use by 17 percent. This allowed a savings of more than $100 an acre in nitrogen fertilizer, and there was no loss in yield.

We ran into irrigation system problems in a Romaine field planted in August in San Ardo. We were able to reduce irrigation by nearly 40 percent, and that helped with a large savings in water and fertilizer. But one section of this field did not yield well, and we think the problem was with the irrigation system.

The total yield loss at this site was 14 percent, but the crop quality was better in the plots where we used our system.

Permission for use is granted, however, credit must be made to the California Farm Bureau Federation when reprinting this item. Top