Location: Crop Improvement and Protection ResearchTitle: Evapotranspiration-based irrigation scheduling of lettuce and broccoli Author
Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2015
Publication Date: 7/1/2016
Citation: Johnson, L., Cahn, M., Martin, F.N., Melton, F., Benzen, S.D., Farrara, B., Post, K. 2016. Evapotranspiration-based irrigation scheduling of lettuce and broccoli. HortScience. 51:935-940. Interpretive Summary: This manuscript describes the evaluation of two different irrigation models for predicting irrigation scheduling of lettuce and broccoli in the Salinas Valley of California. The model takes into consideration the size of the plant, environmental conditions and standardized water need coefficients for evaluating when and how much to irrigate to maintain crop productivity. The use of these models reduced the amount of water applied by 21-34% compared to standard grower irrigation scheduling.
Technical Abstract: Estimation of crop evapotranspiration supports efficient irrigation water management, which in turn supports water conservation, mitigation of groundwater depletion/degradation, energy savings, and crop quality maintenance. Past research in California has revealed strong relationships between fraction of the ground covered by photosynthetically active vegetation (Fc), crop coefficients (Kc), and evapotranspiration (ET) of cool-season vegetables and other specialty crops. Replicated irrigation trials for iceberg lettuce and broccoli were performed during 2012 and 2013 at the USDA Agricultural Research Station in Salinas, Calif. The main goal was to compare ET-based irrigation scheduling with the current standard practice used by the industry. Sprinkler irrigation was used to establish the crops, followed by surface drip during the treatment period. Each experiment compared three irrigation scheduling treatments replicated five times in a randomized block design. Two decision-support models were evaluated as follows: 1) an FAO-56 based algorithm embedded in NASA's prototype Satellite Information Management System based on observed Fc, and 2) an on-line database driven irrigation scheduling tool, CropManage, based on modeled Fc. Both methods used daily reference ETo data from the California Irrigation Management Irrigation System (CIMIS) to translate crop coefficients to crop ET. A third treatment followed an irrigation schedule representing grower standard-practice. Cored-trimmed lettuce yields were near 20 tons/ac, and broccoli yields near 8 tons/ac, across treatments, approximately in line with industry averages. Treatments using the decision-support models had 21-34% reductions in applied water as compared to standard practice, with little-to-no impact on marketable yield.