Management Zones For Variable Rate Application

Precision Farming Targets Nutrient Efficiency

The land that produces the world’s food, fiber and energy is incredibly diverse, matching a wide range of crops to compatible soil, climatic and topographical conditions. Even within a single farm field, however, a wide diversity in soil types and other properties can exist. Traditional field-wide soil test recommendations essentially average out those properties to determine a generalized fertilizer rate that can leave some areas within the field under-fertilized while some may be over-fertilized. The result, of course, is unrealized production potential on some acres and less-than-efficient nutrient use on others.

Nutrient management zones seek to locate similarities and differences within a crop field so those unique “zones” can receive nutrient rates based on their specific conditions. Before solutions can be designed to meet that challenge, however, a variety of spatial data must be gathered to identify the problems. The sources of this information are varied but are keyed to geographic information systems (GIS) and global positioning systems (GPS) to physically identify the location of sub-field areas with similar properties — and, therefore, similar yield potential and nutrient needs.

Information Key to Efficient Nutrient Utilization

Soil surveys, electrical conductivity, yield, elevation and remote-sensed imagery maps often form the basis of the analysis, enabling the establishment of management zone boundaries. If, for example, an upland portion of a field has less topsoil, the location of that relatively homogenous area would be identified and nutrient rates would be adjusted accordingly. Yield maps, generated from GPS data gathered at harvest, do not measure soil properties but are indicative of the productivity of a specific area and can contribute to the identification of management zones. Topographical information is considered because soil test nitrogen values can be correlated with landform and drainage. Additionally, prior use and management of a given field may be considered since past practices can impact the spatial variation of nutrients — an area where livestock were fed or hay was stacked, for example, would likely have very different soil test values than those of other areas.

Combining data layers from these sources and analyzing them statistically presents a road map to more efficient fertilizer use as well as protection of natural resources. Just how precise the boundaries of management zones are is dependent on farm goals, needs and equipment.

Utilizing data provided by nutrient management zone boundaries requires GPS-driven variable rate nutrient application equipment to respond to intra-field variations in soil and land properties. Data describing the geographic location of sub-field areas identified as being homogenous determines the optimum fertilizer rate applied to those areas. Data describing the geographic location of sub-field areas identified as being homogenous helps determines the optimum fertilizer rate applied to those areas. Matching farming practices such as fertilizer application more closely to crop needs reduces agriculture’s environmental footprint, improves decision-making and enhances the quality of farm products.

Applying Specific Information to Specific Locales

For South Dakota State University Soil Scientist Dr. David Clay, nutrient management zones and variable rate application address both agricultural productivity and environmental quality.

“By matching the fertilizer recommendation to the location, off-site transport of nutrients should be reduced,” he explains. “In many situations, the total amount of nutrients applied to a field is not reduced but we move materials that may have been applied to higher environmental risk areas — where a plant’s response to additional fertilizer may be minimal — to low environmental risk areas where responses are much higher.”

In South Dakota, Clay and other scientists team up with farmers, crop consultants, extension specialists and industry persons to broaden their perspective on precision farming issues and to arrive at locally adaptive recommendations. By integrating information from numerous sources within a given locale, the team can better define local problems and desired outcomes. In the case of nutrient management zones, helping farmers identify the most effective and efficient ways to address nutrient needs is a big step toward increasing overall agricultural efficiency.

“Precision farming is the tool for integrating the information age into agriculture and mathematics is the language of the information age,” Clay says. “Our hope is that in five years, local learning groups across the U.S. will routinely meet and discuss management techniques that reduce agricultural impact on the environment and improve efficiency.”

Increasing Nutrient Management Accuracy

With the information provided by nutrient management zones, precision agriculture techniques can deliver site-specific fertilizer rates. When the rate of application more accurately reflects the crop production needs within a field, the nutrients farmers rely on can be more effectively targeted toward producing food, fiber and energy.