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Title: NITROGEN FERTILIZER USE EFFICIENCY BY FURROW IRRIGATED ONION AND CORN

Author
item HALVORSON, ARDELL
item FOLLETT, RONALD
item BARTOLO, M - CSU, AVRC, ROCKY FORD, CO
item SCHWEISSING, F - CSU, AVRC, ROCKY FORD, CO

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2002
Publication Date: 6/26/2002
Citation: Halvorson, A.D., Follett, R.F., Bartolo, M.E., Schweissing, F.C. 2002. Nitrogen fertilizer use efficiency by furrow irrigated onion and corn. Agronomy Journal. 94:442-449.

Interpretive Summary: Application of N fertilizer to irrigated onions on soils with high levels of available soil N may be contributing nitrate-N (NO3-N) to groundwater in southeastern Colorado. We determined the growth and N uptake patterns of onion grown on a silty clay soil, N fertilizer use efficiency (NFUE) by onion, and recovery of residual fertilizer N by corn following onion in rotation. Onions were sampled bi-weekly from plots receiving 0 and 224 kg N/ha. Non-labeled N fertilizer and labeled 15N fertilizer were band applied at the edge of onion beds in split applications of 112 kg N/ha each on 18 May and 25 June. Onion dry matter accumulation was slow for the first 110 days, followed by a rapid increase in biomass production and N uptake. Initial soil NO3-N levels were high, however, N fertilization resulted in an increase in bulb yield. Greatest demand for N by onion occurred during bulb development. Fertilizer N recovery by onion was low, 11 and 19 % for May and June N applications (average 15%). Much of the fertilizer N at onion harvest was in upper 60 cm soil profile, near the center of onion bed, but some had been leached to 180 cm soil depth. In 1999 corn, with no additional N fertilization, recovered 24% of the fertilizer N applied to onions for a total fertilizer N uptake by two crops of 39%. Onion growers should consider reducing N rates when soil N is high at planting and delaying N application until bulbing begins to improve NFUE. Planting corn rows near the center of the previous onion bed may result in greater N fertilizer recovery by corn.

Technical Abstract: Irrigated onion (Allium cepa L.) production, with high rates of N fertilization, may be contributing nitrate-N (NO3-N) to groundwater in southeastern Colorado and western U.S. This study determined the growth and N uptake patterns of onion grown on a silty clay soil, N fertilizer use efficiency (NFUE) by onion, and recovery of residual N fertilizer by corn (Zea mays L.) following onion in rotation. Onions were sampled bi-weekly from 18 May to 15 September 1998 from plots receiving 0 and 224 kg N/ha. Non-labeled N fertilizer and labeled 15N fertilizer were band applied at the edge of onion beds in split applications of 112 kg N/ha each on 18 May and 25 June. Onion dry matter accumulation was slow from planting to about day 110, followed by a rapid increase in biomass production and N uptake. Because soil NO3-N was high at planting, N fertilization resulted in only a small increase in bulb yield. Greatest demand for N by onion occurred during bulb development. Fertilizer N recovery by onion was 11 and 19% for May and June N applications (average 15%). Much of the fertilizer N remained in the upper 60 cm soil profile and had moved to the center of the onion bed by harvest. Fertilizer N detected at 180 cm depth also indicated some deep leaching.