Nitrogen Uptake and Fate of Organic Fertilizers Applied to Drip-Irrigated Lettuce (Lactuca sativa).

In order to maximize the beneficial effects of fertilizers to crops, and minimize environmental impacts due to N fertilizer, it is critical to optimize fertilizer selection and application method, timing, and rate.  Little research has been done in this regard on organic N fertilizers.  In this study, we evaluated two application rates (28 and 56 kg N/ha) of four organic fertilizers, 2 solid fertilizers banded pre-plant (feather meal and blood meal) and 2 liquid fertilizers applied through drip irrigation throughout the growing season (fish emulsion and cyano-fertilizer).  Lettuce (variety ‘Summer Crisp’) was grown on a Nunn clay loam (Aridic Argiustoll) on certified organic land at the Colorado State University Horticulture Farm.  Although there was no significant difference in fresh yield (kg/ha) among fertilizer types, the cyano-fertilizer resulted in a significantly higher fresh weight (kg/plant) than the fish emulsion; nonetheless, the 56 kg N/ha application rate yielded significantly lower than the 28 kg N/ha rate across fertilizer types.  There were no significant differences in leaf N concentration or in total N uptake.  However, fertigation significantly reduced both N₂O and NH₃ emissions of the fish emulsion and cyano-fertilizer as compared to the solid, pre-plant applied fertilizers (blood and feather meals), and residual inorganic N in the soil (0-60 cm) was significantly higher in the feather meal and fish emulsion treatments compared to the blood meal and cyano-fertilizer treatments at the 28 kg N/ha application rate.  Fertigation is an important tool for optimizing plant growth while minimizing N losses through volatilization and denitrification.