Nutrient Management Research Database

Nitrogen fertilizer is an indispensable input to modern agriculture, but it also has been linked to environmental degradation and human health concerns. Recognition of these trade-offs has spurred debate over its use. However, data limitations and misinformation often constrain discussion, cooperative action and the development of solutions. To help inform the dialogue, we (1) evaluate existing data on nitrogen use, (2) estimate typical nitrogen fertilization rates for common crops, (3) analyze historical trends in nitrogen use, (4) compare typical nitrogen use to research-established guidelines and (5) identify cropping systems that have significant influence on the state's nitrogen cycle. We conclude that a comprehensive grower self-monitoring system for nitrogen applications is required to improve nitrogen-use information and to better support evidence-based decision making. The discussion here presents a primer on the debate over nitrogen fertilizer use in California agriculture.

This article discusses research from one part of the California Nitrogen Assessment, a comprehensive examination of existing nitrogen science, policy and practice in California.  The authors here present a summary and analysis of inorganic nitrogen fertilizer flows, management practices and related policy in California.  They also provide information on nitrogen application rate recommendations and assess them for adequacy given current cropping conditions.  

The objectives were to:

1. Identify data sources and limitations.
2. Establish average nitrogen application rates by crop.
3. Determine historical trends in nitrogen use.
4. Compare average nitrogen application rates with nitrogen rate guidelines.

This article discusses research from one part of the California Nitrogen Assessment, a comprehensive examination of existing nitrogen science, policy and practice in California. While it does not present new research, it does assess existing bodies of knowledge to make observations on the use of inorganic nitrogen for several cropping systems within California.  

Highlights of the analysis include:

• Experts believe growers apply more fertilizer nitrogen than the amount that growers report applying.
• Between 1973 and 2005, N use increased by 25% on average for the 33 crops investigated.
• For most crops, less N was applied per unit of product in 2005 than in 1973.
• A dataset of recent N guidelines compiled from UC ANR publications. 
• Cotton, almonds, rice, wheat, processing tomatoes, and lettuce received that largest portions of overall nitrogen fertilizer applied, accounting for 64% of total nitrogen use.