Improving Onion Production While Reducing Nitrate Loading

Onion is an economically important crop in southeastern Oregon and southwestern Idaho.  Onion is grown in rotation with corn, wheat, sugar beet, potato, bean, and other crops. Traditionally, onion production was under furrow irrigation using heavy inputs of water and nitrogen (N) fertilizer. By 1987 the groundwater in Northeastern Malheur County, Oregon, had become contaminated with nitrate and residues of the herbicide DCPA. An official groundwater management area was established by the Oregon Department of Environmental Quality along with an action plan and well monitoring network. The action plan allowed for a trial period of years to see whether voluntary changes would improve contamination trends. Researchers, producers, and agencies cooperated to develop production options that had the possibility of being both environmentally protective and cost effective. Options to improve irrigation practices, increase N fertilizer use efficiency on several rotation crops, and find a cost effective replacement for DCPA were tested.  Irrigation research demonstrated the opportunity for increased onion productivity through both irrigation scheduling and adoption of drip irrigation. Fertilization research demonstrated that N applications were more efficient with different timings and in smaller increments.  Lower cost herbicides could replace DCPA. Research results were effectively delivered through many means and voluntarily adopted. Both groundwater nitrate and DCPA residues are declining. Onion productivity has increased.