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Title: IRRIGATED CORN RESPONSE TO NITROGEN FERTILIZATION IN THE COLORADO ARKANSAS VALLEY

Author
item Halvorson, Ardell
item SCHWESSING, FRANK - CSU, ROCKY FORD, CO
item BARTOLO, MICHAEL - CSU, ROCKY FORD, CO
item Reule, Curtis

Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 1/15/2004
Publication Date: 3/1/2004
Citation: Halvorson, A.D., Schwessing, F.C., Bartolo, M., Reule, C.A. 2004. Irrigated corn response to nitrogen fertilization in the colorado arkansas valley. Symposium Proceedings. 10: 157-163.

Interpretive Summary: High levels of residual nitrate-N (NO3-N) are present in the soil profile of fields cropped to vegetables, alfalfa, and grain crops in the Arkansas Valley of Colorado. The groundwater in this area also contains high levels of NO3-N. This study evaluated the effects of N fertilizer rate (six N rates) and N source (urea and Polyon®) on corn yields for 4 years following 5 years of alfalfa and one year of watermelon production. Corn grain yields were not increased by N fertilization in 2000, but were increased by increasing residual soil N levels in 2001, and by N fertilization in 2002 and 2003. Averaged over years, N source did not significantly affect corn yields. When averaged over 4 years, corn grain yields were near maximum with the application of 75 to 100 lb N/a per year. Silage yields increased with increasing N rate each of the years, except in 2001. Soil residual NO3-N levels increased with increasing N fertilizer rate. Residual soil NO3-N levels tended to decline with each additional corn crop. The 3 year (2000-2002) average N fertilizer use efficiency was 64% at the lowest fertilizer N rate and less than 40% at the higher N rates. Thus, N fertilizer application to corn in Arkansas River Valley produced in rotation with vegetable crops and alfalfa may need to be reduced to prevent NO3-N contamination of groundwater in this area. Based on this study, it appears that a minimal amount (75 to 100 lb N/a) of N fertilizer may be needed to maintain high grain and silage corn yields in the Valley in rotation with vegetable crops and alfalfa. Fertilizer N appears to be moving out of the root zone with downward movement of irrigation water.

Technical Abstract: High levels of residual NO3-N are present in the soils in the Arkansas River Valley where alfalfa, grains, and vegetable crops are produced. Nitrogen requirements to optimize yield potential of crops, such as corn, following vegetables needs to be evaluated to reduce NO3-N leaching potential in the Valley where high NO3-N levels have been reported in the ground water. The effects of N source (urea and Polyon®3) and fertilizer N rate on corn yields were evaluated for 4 years. Corn grain yields were not significantly increased by N fertilization the 1st year following watermelon, but increased with increasing residual soil NO3-N levels the 2nd year without additional N fertilization, and increased by N fertilization in the 3rd and 4th years. Averaged over years, N source did not significantly affect corn yields. Averaged over years, corn grain yields were near maximum with an average application of 75 to 100 lb N/a per year. Silage yields increased with increasing N rate each year, except for the 2nd yr. Soil residual NO3-N levels were increased with increasing N rate the 1st year. Residual soil NO3-N levels declined following the 2nd corn crop with no additional N fertilizer applied. Irrigation water was limited and became unavailable due to drought conditions the first week of August for the 3rd crop. Therefore, the 3rd corn crop suffered from severe drought stress and reduced yields. The 3-year average N fertilizer use efficiency was 64% at the lowest fertilizer N rate and less than 40% at the higher N rates. Residual soil NO3-N levels declined with each additional corn crop in the check (no N added) treatment. Nitrogen application to corn in Arkansas River Valley produced in rotation with vegetable crops and alfalfa may need to be reduced to prevent NO3-N contamination of groundwater in this area. Based on this study, it appears that a minimal amount (75 to 100 lb N/a) of N fertilizer may be needed to maintain high grain and silage corn yields in the Valley in rotation with vegetable crops and alfalfa. Fertilizer N appears to be moving out of the root zone with downward movement of irrigation water.