Irrigation and nitrogen management effects on seed and transplant onions

The primary objective of this field experiment was to determine the yield response of seeded and transplanted onions to nitrogen fertilizer under drip irrigation.;Seed and transplant onions (Allium cepa L.) were grown in 18 lysimeters filled with a Kidman loam soil and eight lysimeters filled with a sandy loam soil. These onions were subjected to variable irrigation and nitrogen rate treatments. Both irrigation and nitrogen water were applied through a drip irrigation system. Nitrogen was applied in proportion to the estimated weekly onion water use. A control plot received no nitrogen. The growth and development of the onion was also monitored and plant water use characteristics were determined. Nitrogen water was collected and measured. However, due to lack of germination, the seeded onions were dropped from the study.;There was a significant increase in yield response between the control treatment and the other nitrogen treatments. There was no relative increase in yield response between the low and high nitrogen application treatments. For two irrigation application levels, calculated weekly and cumulative evapotranspiration from a soil water budget closely matched theoretical estimates. There was very little variation in the total soil water content within the onion root zone with time for all imposed irrigations. The potential for nitrate leaching also increased with increased nitrogen application. Finally, it was concluded that nitrogen application rates could further be reduced if direct application of nitrogen is carried out through drip irrigation systems.