Production & Economic Benefits of Variable Rate Applications in Cropping Systems

Precision agriculture is a farming management concept based on observing, measuring and responding to inter- and intra-field variability in crops. In other words, it is an approach to managing soils and crops to reduce decision uncertainty through better understanding and management of spatial and temporal variability. It involves a range of management practices that attempt to utilize site-specific information at the field level, such as soil characteristics and weather conditions, in order to adjust the inputs used and ultimately achieve optimal output.

Precision agriculture is also known under many different terms including precision farming, information-intensive agriculture, prescription farming, target farming, site specific crop management, variable rate management, variable rate technology and Global Positioning Systems (GPS) agriculture, among other terms.

This article will focus on the production and economic benefit of variable rate technology. The main goal of variable rates is to vary input (seed, fertilizer, water, pesticide) amounts to match the spatial yield potential of a particular site and therefore minimize input costs while maximizing the economic return to the producer.

There are two basic methods for implementing variable rates: map and sensor based. Map-based variable rate systems adjust the input application rate based on information contained within an electronic map of field’s properties. This system is capable of determine the machine’s position within the field and relates that position to desire application rate through reading the map.

Sensor-based variable rate systems do not use application rate/prescription maps. They use data from real-time sensors to electronically control site-specific field operations. Sensors located on the applicator measure soil properties and crop characteristics ‘on the-go’. The continuous information stream enters a control system, which calculates soil or plant input requirements. This information is transferred to a controller, enabling delivery of the input to the specific location which was measured by the sensor. Both systems have advantages and disadvantages, and a combination of these systems in variable rate applications will most likely produce the best economic or environmental benefits.

Another important piece of information is to identify management zones. These zones illustrate a field’s natural variability and are used for writing prescription maps and identifying if a variable rate application of a giving input is beneficial. The management zones are generated from yield maps, soil testing (electrical conductivity and electromagnetic properties) and elevations.

Variable rate applications increase producer’s economic returns through strategically optimizing input amounts placed in each zone. The applications allow producers to focus inputs on zones that yield the highest return, while reducing inputs in zones of lower productivity.

The potential benefits of variable rate applications can be reduced by a number of factors that are beyond the control of the producers. Weather, in particular precipitation, temperature and timing of these events, in relation to crop development stages, can diminish crop growth factors and/or all other inputs.

The large variability in soil type across some fields can lead to inaccurate nutrient recommendations for particular management zones unless highly extensive soil sampling occurs. The costs of detailed soil sampling and analyzing is preventing dense grid soil sampling.

If the use of variable rate applications adds time to planting, spraying or harvest operations, the cost of downtime must be taken into account by the farmer. Also, variable rate application machines tend to be more complicated and thus farmers must take into account how reliable the extra components and systems are and the extra costs and difficulties associated with repairing them in contrast to simpler machines.

Investment appraisal and partial budgeting analysis to determine applicable conditions for farmers must be included to determine the potential economic benefits of variable rate applications, For example, in a wheat production study, applying nitrogen fertilizer by considering soil nutrient variation was economically justified with a minimum 1% yield increases and 4% savings in fertilizer. The key factor for adoption of variable rate applications is the degree of variability within a field. Higher variability leads to easier implementation of variable rate technology.

In a series of studies to determine the economics of nitrogen (N) managing strategies in continuous corn in Colorado, it was found that less N fertilizer (up to 46%) was used under variable N rates in comparison to uniform N management. Net returns were up to $12.00 per acre higher when using N management strategies compared to uniform N management. Several studies have shown variable rate application in combination with management zones can potentially improve farm profitability, but stressed that the economic return depends on farm soil and resource attributes, inherent variability in production for these resources and previous management decisions.

For more information on Variable Rates, please contact your local Colorado State University Extension offices or visit us at: http://www.ext.colostate.edu/.

Article by Wilma Trujillo