Nutrient Management Research Database

More fertilizer doesn’t always mean more profit. That’s one conclusion from a 10-year study conducted by Agricultural Research Service and Colorado State University (CSU) scientists. Soil scientist Ardell Halvorson, at the ARS Soil Plant Nutrient Research Unit, in Fort Collins, Colorado, led the investigation, which focused on nitrogen fertilizer management for various rotations of irrigated crops. The research examined cropping practices in the Arkansas River Valley, an agricultural region of Colorado where vegetables and melons are grown in rotation with wheat, corn, alfalfa, and soybeans. The area has high levels of nitrate-nitrogen in the fields and groundwater—due, in part, to heavy application of nitrogen fertilizer and prevalence of shallow-rooted crops such as onions. From 1998 to 2008, the Fort Collins researchers evaluated and compared potential management strategies for reducing nitrogen and nitrate-nitrogen levels in soil and, consequently, groundwater. Their research-based recommendations could have important economic and environmental benefits for the region.

• This article summarizes the findings of a 10-year study focusing on managing fertilizer nitrogen for onions, wheat, alfafa, corn, and watermelon.
• As in California, heavy use of nitrogen fertilizers has resulted in nitrate pollution of groundwater.
• In the area studied, melons are grown in a rotation including wheat, corn, alfalfa, and soybeans.

• Onions were found to take up only around 15% of N applied. Over several years the top 6 feet of soil had accumulated around 700 lbs of N per acre! A unfertilized corn crop was able to scavenge another 24% of the N applied.
• Growing alfalfa, a legume that introduces N to the soil, for 5 years consecutively allowed for the following corn crop to show similar yields whether or not it was fertilized.
• They found that onions grown under drip irrigation required less water than those furrow irrigated. Profits for both systems were maximized at the rate of 120 lbs N per acre.
• As fertilizer costs increase, efficiently managing nitrogen becomes a more important part of managing profitable operations.