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Reduce Nutrients in Surface and Ground Water

Reduce nutrients in surface and ground water. 
Focus Resource Concern for April 2012


PHOENIX, April. 3, 2012 Proper use of nutrients, organic or inorganic types, is a conservation priority in Arizona.  Managing nutrients properly involves applying them in the correct amount, from the proper source, with appropriate placement, and at the appropriate time.  This is basically the 4 R’s of nutrient management—right rate, right source, right place, and right Time.  Implementing the 4 R’s will help ensure fertilizer applications meet the crop yield objectives and minimize the potential for nutrients to degrade water supplies (surface and groundwater) and air quality.  To apply nutrients properly there a few things you need to know.

Know Your Crop Nutrient Requirements
First, you need to understand the nutritional needs of the crops being grown as well as their expected yields.  The nutritional requirements (amount of N-nitrogen, P-phosphorus, and K-potassium) vary by crops species, their stage of growth, crop variety -in some cases, expected yields, and your type of soils.  The University of Arizona has established nitrogen requirements crop type and yield for the majority of crops being grown in Arizona.

Know Your Soils
Second, it is important to know key characteristics of your soils and the roles they play in nutrient management.  Some of the more important soil characteristics include Cation Exchange Capacity (CEC) and pH.  Cation Exchange Capacity is an important measure of the soils fertility and potential productivity.  Typically, soils with higher silt and clay content have higher CEC values while soils with high sand content have low CEC values.  Soils with good CEC values (>10) have a greater ability to attract and hold positive charged particles (cations) which include most plant nutrients.  Soil reaction or pH is an important measure of nutrient availability, solubility of toxic elements, and microbial activity.  The pH range where nutrients are most available for plant growth is between 6.5 and 7.5. 

A soils test, conducted properly, will provide essential information regarding the amount of the primary plant nutrients already in the soil.  Thus, providing the information needed on how much additional fertilizer is needed to grow the crop.  Information to help reduce production costs while helping to protect Arizona’s water resources.

Know Your Water
Third, knowing the quality of your irrigation water will provide additional information on any additional, if any, nitrogen that is being applied to the crop.  Water tests most often report nitrogen content as Nitrate-Nitrogen (NO3-N) with the units as part per million (PPM) or milligrams per liter (mg/l).  To determine how much nitrogen is being applied multiply the test results by 0.23 and then by the number of acre inches of water applied.  Example, the water analysis shows 2 PPM NO3-N and you apply 36 inches of water to the crop.  Therefore, an additional 17 pounds of nitrogen is being applied to the crop (2 X 0.23 X 36). 

The NRCS does not make crop fertility recommendations.  It is the role of NRCS to assess, based on producer provided information and State information, if there is a potential risk to ground or surface waters from excessive applications of nutrients.  The Cropland Inventory Workbook is one method to document how a crop is grown and provide the information needed to conduct this assessment.

NRCS practices that help manage nutrients properly includes: Nutrient Management, Irrigation Land Leveling, Irrigation Systems (Sprinkler, Surface/Subsurface, & Micro-irrigation), Irrigation Water Management, and Residue Management (Seasonal, Strip/No-Till, Mulch Till, and Ridge Till).