Alternate Furrow Irrigation: A Strategy to Reduce Applied Water without Yield Decrease in California Processing Tomatoes.

Alternate furrow irrigation (AFI) is based on the partial root drying technique, which manages soil moisture around the root zone to reduce applied water and increase crop water use efficiency (yield/water applied; WUE). Past research has shown general crop physiological responses to partial root drying, but strategies for reliable management depend on individual crop responses. Alternate furrow irrigation consists of selectively watering only every other furrow at each irrigation, while the ‘dry’ furrows receive water at the next irrigation. We conducted a field trial in 2010 and 4 on-farm trials in 2011 comparing alternate furrow irrigation to every furrow irrigation. These studies included three soil types: Reiff very fine sandy loam, Yolo silt loam and Sycamore silty clay loam. Total applied water, soil moisture, canopy cover, gas exchange measurements, leaf ¹³C, aboveground biomass, yield and fruit quality were measured. Preliminary results show that alternate furrow irrigation can reduce water applied by at least 25% without yield decrease, or about 30% increase in crop water use efficiency. Photosynthetic rates (P_n) and stomatal conductance (g_s) decreased in 2% and 9% in the AFI treatment, respectively. This resulted in an increase of 8% in intrinsic WUE (P_n/g_s) along with a very slight but significant reduction in ¹³C discrimination in the AFI treatment. In the on-farm trials, soil canopy cover was slightly affected by the AFI treatment especially at later stages of crop development, but yields were similar regardless of soil type.