EFFECTS OF COMMERCIAL ORGANIC AND CYANOBACTERIAL FERTILIZERS ON INSTANTANEOUS WATER USE EFFICIENCY IN DRIP IRRIGATED ORGANIC SWEET CORN

Water and fertilizers are applied to maintain crop growth, yield, and quality. Nitrogen (N) fertilizer plays a crucial role in crop growth and yield development of sweet corn (Zea mays). Organic growers often use commercial organic animalbased fertilizers which vary in nutrient composition, forms of available N (NH4 + N and NO3 - -N), and have high transportation costs. Alternatively, cyanobacteria can be grown on-site as a source of N. Cyanobacteria haves unique dual properties because they can both fix N from the atmosphere and photosynthesize to produce N biofertilizer without fossil fuels. Forms of available N in organic fertilizers may influence photosynthetic enzymes, and therefore photosynthesis (Pn), stomatal conductance (gs), transpiration rate (Tr), and instantaneous water use efficiency (iWUE) were measured to evaluate the effect of different organic fertilizers on sweet corn. A field experiment was conducted during the summer of 2014 at the Horticulture Field Research Center, Colorado State University, Fort Collins, CO. The treatments were solid organic fertilizers,; feather meal and blood meal and liquid organic fertilizers,; fish emulsion and cyanobacteria, applied at 56 and 112 kg N ha -1 . Liquid organic fertilizers were applied every two weeks after planting while the solid organic fertilizers were applied prior to planting. Leaf gas exchange measurements were conducted using a LI- 6400XT portable photosynthesis system at 66 days after planting and Pn, Tr, and gs were automatically recorded. Instantaneous WUE was calculated as a ratio of Pn to Tr and expressed in µmol CO2 ·mol -1 H2O. The feather meal treatment recorded the significantly lowest Pn (19.5 µmol m -2 s -1 ) at 112 kg N ha -1 compared to other fertilizer treatments at 56 and 112 kg N ha -1 . The cyanobacterial treatment recorded the significantly lowest Tr (0.6 mmol H2O m -2 s -1 ) and gs (0.05 mol H2O m -2 s -1 ) at 56 kg N ha -1 compared with other fertilizer treatments at 56 and 112 kg N ha -1 . The cyanobacterial treatment also recorded the significantly highest iWUE (3 µmol CO2 mmol -1 H2O) at 56 kg N ha -1 compared to other fertilizer treatments at 56 and 112 kg N ha -1 . In conclusion, feather meal fertilizer recorded significantly lower Pn at 112 kg N ha -1 and the cyanobacterial biofertilizer application resulted in significantly lower stomatal conductance and transpiration rate, thus recording a higher iWUE at both N rates in drip irrigated sweet corn.