CCA Today: How a Certified Crop Adviser approaches nitrogen management plans

By Eryn Wingate

Growers throughout California are improving fertilizer use efficiency in response to heightened regulatory pressure and rising production costs. The California State Water Resources Control Board requires growers throughout the state to complete Irrigation and Nitrogen Management Plans, or INMPs, to protect surface and groundwater resources from nitrogen runoff and leaching. While specific INMP requirements vary between regions, most growers must report planned and applied nitrogen fertilizer use, irrigation and harvest quantity. Mandated reporting, along with high fertilizer and water prices, motivates growers to manage nitrogen as efficiently as possible. 

Certified Crop Advisers with Nitrogen Management Specialty training can write and certify INMPs to help growers meet regulatory requirements, while sustaining or improving crop production and ROI. University of California researchers have established nitrogen uptake requirements for most crops, providing a baseline for nitrogen budgeting. CCAs tailor INMPs to each crop’s nitrogen requirements and adjust fertilizer application recommendations according to unique field conditions.

Before writing the INMP, CCAs take soil and water samples to measure available nitrogen levels before planting. CCAs then calculate the amount of nitrogen fertilizer required by subtracting the quantity of nitrogen already available in the soil and irrigation water from the crop’s total nitrogen uptake requirement. 

Some irrigation sources contain high nitrate levels, significantly contributing to the nitrogen budget. CCAs quantify pounds of nitrogen applied per acre-foot of water and reduce fertilizer application rates accordingly. Residual soil nitrogen similarly contributes to the nitrogen budget, but availability is more difficult to predict.

Nitrogen sources in the soil include nitrate and ammonium, as well as organic nitrogen locked in organic matter, previous crop residue and amendments like compost. Soil microbial activity transforms organic nitrogen into plant available forms at predictable rates that vary according to the type of organic matter and environmental factors like soil temperature and moisture. CCAs estimate the quantity of organic nitrogen that will likely become available over the course of the season and account for it in the fertilizer budget. 

State mandated INMPs require growers to report the total amount of nitrogen planned and applied throughout the season, but many CCAs will provide additional guidance on split application rates and timing, as well as nitrogen type and placement in the bed. Fertilization should match the crop’s growth and nitrogen uptake pattern, so that we apply the right amount at the right time. Most crops require very little nitrogen during establishment but absorb it at increasing rates during vegetative growth until a peak is reached prior to flowering and fruiting or harvest. Growers can further optimize nitrogen-use efficiency by adjusting fertilizer placement and selecting the types of nitrogen best suited to the crop, growth stage and soil type. 

Always remember, when it comes to nutrient management, it is important to apply the right rate, at the right time, at the right place using the right type of fertilizer.

Contact your Certified Crop Adviser for more information on INMPs and proper nitrogen management. 

Visit www.wrcca.org. Access California Fertilization Guidelines at www.cdfa.ca.gov/is/ffldrs/frep/FertilizationGuidelines/. 

Eryn Wingate is an executive board member of the Western Region Certified Crop Advisers and Lead Agronomist for Tri-Tech Ag Products Inc. She may be reached at info@wrcca.org.