The 4 Rs of nutrient management

By Makena Savidge and Daniel Geisseler*

The following was summarized from the publication "4R plant nutrition manual: a manual for improving the management of plant nutrition" by the International Plant Nutrition Institute (IPNI, 2012). Efficient nutrient management is essential in order to achieve environmental, economic, and social sustainability.

The efficiency of your nutrient management can be maximized by considering the four rights, or the 4 Rs, of nutrient management: right source, right rate, right place, and right time. Best management practices are constantly evolving as new research trials improve our understanding and nutrient management practices need to be tailored to suit each individual climate, crop, and available management options. The 4 Rs describe basic principles that help find the best nutrient management practices for a specific situation.

The right source

Though selecting the right nutrient source seems simple, it can actually become quite complex when considering all that must be "right" about it. Considerations include plant nutrition requirements, soil conditions, fertilizer delivery issues, environmental risks, product price, economic constraints, and how accessible the fertilizer and application tools are. Some of these may be easier to address than others, but it is important to try not to guess when it comes to the nutrient requirements of your crop. Simple diagnostic tests can be done to determine plant specific nutrient requirements for optimal growth, which can then accurately inform which fertilizer type and nutrient source to use. For example, fluid and suspension fertilizers are great choices if you are looking to incorporate more micronutrients, while compound fertilizers and bulk blends are great if you are looking for a specific nutrient ratio. The specific source of nitrogen fertilizer you choose can have differing rates of loss and impacts on air and water quality. Creating a nutrient management plan that minimizes losses begins with the source, but is highly dependent on the rate, place, and time of application.

The right rate

Determining the right rate of nutrient application is site specific, as it depends on yield potential, soil type, climate, economics, labor supply, and logistics. As all of these factors are different for each site, crop, and grower, selecting the right fertilizer rate requires consideration of the crop's nutrient demand at different stages of crop development and nutrient supply from soil and other non-fertilizer sources. Ultimately, you want to match the crop's nutrient needs with the nutrients supplied in order to maintain an adequate supply all season long. It is important to remember that a deficiency in one nutrient cannot be overcome by overapplying another. It is best to do soil and tissue testing to help determine a crop's nutrient needs and a field's ability to deliver them to determine the right nutrient rate. Soil and tissue testing also allow the nutrient plan to be adjusted during the growing season if needed.

TOP OF PAGE

The right place

It is also essential to target nutrient application to the right place, or more specifically, to the zone in the soil that is most accessible to the plant. This takes a careful consideration of nutrient source properties, crop needs and development, as well as field management to create the ideal fertilized soil volume in one targeted location. Highly concentrated zones of nutrients near a crop's root system will supply nutrients more quickly and for a longer period of time. Banding or increasing fertilizer in the root zone are great ways to create a more precise nutrient placement that will enhance plant nutrient uptake while minimizing losses. Certain management practices like tilling and row spacing may affect nutrient placement in the field by dispersing fertilizer in deeper soil profiles or affecting root volumes. Considering the crop type, its development and growth patterns, as well as accompanying management practices will help inform better nutrient placement and enhance nutrient concentrations where they will be more accessible to the plant. However, there is a limit to a root's ability to absorb nutrients quickly and over fertilizing will not result in faster or greater nutrient uptake. This limit varies by crop type, crop growth rate, and crop age. Thus reminding us to consider another nutrient right - timing.

The right time

Careful planning of the right time for nutrient application will help to optimize nutrient uptake and minimize nutrient losses. To do so, you must consider the properties of the nutrient source used, the crop type & its needs, soil structure & its ability to retain nutrients, and any climatic impacts that could accelerate losses. Some nutrient sources are inherently more susceptible to loss than others and the rate of loss may be accelerated by environmental conditions. Though this can be addressed by selecting delayed or controlled release fertilizers, careful timing of application throughout the season is an effective way to minimize losses of nutrients. A crop's nutrient needs are dependent on its stage of growth. It is best to apply fertilizer when the crop's needs are the highest. It is also important to consider a soil's supply capacity (i.e. its ability to retain and supply nutrients) to determine how frequently fertilizer needs to be applied to meet and maintain a crop's needs.

TOP OF PAGE

---

* Makena Savidge is a Junior Specialist in the Department of Land, Air and Water Resources at the University of California, Davis. Daniel Geisseler is a Cooperative Extension Specialist in the Department of Land, Air and Water Resources at the University of California, Davis.