Good Management Practices for Fertilizer Use

Good Management Practices for Nitrogen Fertilization

Crop producers use a wide range of practices to supply nitrogen to their crops. The timing, rate and method of application, as well as the source of nitrogen and the use of additives, vary widely across the state and often between neighbors. Under certain weather conditions, nitrogen can be lost from the soil between application and crop uptake. This publication is intended to describe crop production practices that have the greatest potential for success in dealing with the complexities of managing nitrogen fertilizer.
Successful nitrogen management delivers enough nitrogen to the crop to optimize yield and profitability while minimizing losses to water and air. With nitrogen, economic success and environmental success overlap almost completely. Everyone wants the nitrogen to end up in the crop.

Guidance Principle:Manage nitrogen applications to maximize crop growth and economic return while protecting water quality. To select the nitrogen GMPs that achieve water quality goals for your operation, consider: Potential leaching hazard of the application site, overall costs and benefits, short-term and long-term effects on water quality most suitable practices to your site and your farm management plan.

General GMPs

Nitrogen application to growing crops (side dressing or topdressing)

• Establish realistic crop yield expectations for each crop and field based upon soil properties, available moisture, yield history, and management level. Yield expectations should be based upon established crop yields for each field, plus a reasonable increase (5% suggested) for good management and growing conditions.
• Manage irrigation water to maximize efficiency and minimize leaching by meeting the Irrigation BMPs or the SCS-approved Irrigation Water Management practice standard and specification.
• Identify fields with severe leaching potential or severe surface loss potential. Employ all appropriate BMPs on these fields to reduce nutrient movement to water.

Develop a yearly N management plan for each field and crop.

Nitrogen Application GMPs

Apply N fertilizers where they can be most efficiently taken up by the crop.

Climate change and global warming continue to be topics of considerable scientific debate and public concern. Increasingly, agriculture is viewed as a large contributor to GHG emissions which drive Global Warming Potential, and fertilizer N use has been identified as a major factor. This paper presents a review of the scientific literature on the impacts of fertilizer use and management on GHG emissions, and represents a brief overview of the current science.
Agriculture plays a substantial role in the balance of the three most significant GHGs whose   missions are influenced by humankind. The three gases are – CO2, N2O, and CH4. The GWP of each of these gases can be expressed in CO2 equivalents. The GWPs of N2O and of CH4 are 96 and 23 times greater, respectively, than a unit of CO2. Among the three gases, N2O may be the most important to fertilizer use because of its large CO2 equivalent influence on GWP.

Global Warming Potential of Intensive Cropping Systems

Although often considered a GHG source, in some conditions agriculture can also be a net sink for CO2 and actually cause a net reduction in global warming potential (GWP). Adequate fertilization can contribute to the increase of SOM or slow its decline. Inadequate fertilization limits crop biomass production, and can result in less C returned to the soil, lower SOM, and potentially impaired long-term soil productivity. 
Optimum N inputs are essential for supporting primary plant productivity and stabilization of SOM, upon which SOC storage depends. Combinations of fertilizer source, rate, timing and placement that optimize crop yields minimize the GWP of emissions per unit of production and reduce the need for conversion of natural lands to agriculture. Intensive crop management   practices to enhance nutrient uptake while achieving high yields can be a principal way to achieve reductions in GHG emissions from crop production. High-yielding crops can increase soil C storage.

The following crop, soil, and fertilizer management factors help minimize net global warming potential

Fertilizer Management Actions

1) Appropriate fertilizer N use helps increase biomass production necessary to help restore and maintain SOC levels 
2) BMPs for fertilizer N play a large role in minimizing residual soil NO3, which helps lower the risk of increased N2O emissions
3) Tillage practices that maintain crop residue on the soil surface can increase SOC levels, but usually only if crop productivity is maintained or increased;
4) Differences among fertilizer N sources in N2O emissions depend on site- and weather-specific conditions  
5) Intensive crop management systems do not necessarily increase GHG emissions per unit of crop or food production; they can help spare natural areas from conversion to cropland and allow conversion of selected lands to forests for GHG mitigation, while supplying the world’s need for food, fiber, and bio-fuel.

Short-term, a greater emphasis is needed in educating agricultural practitioners about

1) The basic principles of productive, sustainable cropping system management; 
2) Pathways of nutrient loss to air and water resources
3) Opportunities to mitigate GHG emissions through existing and promising fertilizer BMPs which address loss pathways 
4) Greater dialogue between agronomic scientists and environmental scientists, which encourages mutual understanding and collaboration, to avoid polarization and adversarial relationships on GHG emissions and other environmental issues. The GHG emissions issue increases the need for a high level of management applied to the use of fertilizers in cropping systems. As with all fertilizer BMPs, those selected need to be evaluated in the context of mitigation of all GHG emissions from the full cropping system.

Good Management Practices for Phosphorous Fertilization

Timing and placement of fertilizer applications can influence fertilizer use efficiency and ultimately crop production. An important objective underlying any fertilizer application is to ensure that nutrients are used efficiently by the target crop in order to achieve optimum yield and avoid detrimental effects to the environment. Appropriate crop nutrition management decisions include avoiding over-fertilization to target fields and/or misapplication of fertilizer sources to non-target areas. With respect to phosphorus (P) fertilizers, over-fertilization and/or misapplication can negatively impact the P concentration of water drained from agricultural fields.

Controlled P Fertilizer Placement

Fertilizer placement refers to the practice of positioning fertilizer in a specific area within the field (any number of banding strategies), generally near the plant roots, in contrast to broadcast strategies which apply fertilizer more or less evenly across the entire field surface. Fertilizer application strategies can greatly influence the efficiency of crop recovery of P, which in turn influences the potential for P transport loss via erosion and runoff events. The rate and method of P fertilizer application have direct effects on the quantity of P that can potentially be transported off of the farm. Goodmanagement practices and improved recognition of plant-available residual P levels in soils have decreased the overall use of P fertilizer. Consequently, the quantity of P leaving EAA agricultural lands in drainage water is very small relative to the quantity of P applied to the crop as fertilizer. The benefits of banding P fertilizers for various crops are well documented.

Reasons supporting the banding of P fertilizers includes:

• Banding P fertilizer has shown a marked positive effect on crop yield response depending on soil test levels. In soils with low levels of available P, placement of fertilizer P close to the root system results in greater P plant uptake and use efficiency by the crop.
• At low fertilization rates, the efficiency of P uptake by the crop is greater for banding than broadcast application, especially for P applications on soils with high P-fixation capacity, such as the organic soils.

Band application of P fertilizer increases P use efficiency by the crop.

• Band application of P fertilizer reduces the soil-fertilizer surface contact area, resulting in slowed P fixation (i.e., P that is chemically transformed and rendered unavailable to plants) rates by the organic soils of the EAA, resulting in increased quantities of P that is available for crop uptake. Banding of P fertilizer often decreases soil pH within the narrow application zone which encourages improved P availability over a longer period of crop growth. This phenomenon is particularly important for soils with naturally high P fixation capacities.
• Banding greatly reduces the likelihood of overlapping fertilizer applications, since fertilizer  placement is readily visible to the fertilizer rig operator.
• The most important advantage of banding is the significant reduction of the overall amount of P applied to a particular crop. Banding can reduce the amount of P fertilizer applied to lettuce by 66% compared to broadcast application. Banding is also a viable strategy to reduce the amount of P used in sweet corn production on organic soils, since it provides a method to achieve profitable sweet corn production while minimizing environmental risks.

Prevention of P Fertilizer Misapplication

Soils with high P fertility levels or soils that have annually received P fertilization rates that exceed those of crop removal, often exhibit high soil-test P levels. Application of P fertilizers to fields with soil test values well above levels identified as high or optimum is considered unnecessary and increases the possibility of P losses to surface waters. Preventing over-fertilization and misapplication of P fertilizers to non-target areas will aid in reducing farm drainage P loads.

Some practical recommendations to keep in mind to reduce the chances that P fertilizers are applied to non-target areas or over-applied to target areas: