Crop producers go high-tech with GPS technology

Global Positioning Systems prepare a digital map for precise soil acidity identification

A study conducted by Iowa State University soil scientists suggests Global Positioning Systems (GPS) available to corn and soybean producers can markedly improve the management of soil acidity and lime application. The research is published in the January/February 2003 issue of Agronomy Journal.

Soil acidity can limit plant growth, and due to soil formation processes and management practices, there exists large pH variability within producers’ fields. Lime often needs to be applied to maintain profitable crop production; however, traditional methods make it impractical to change lime application rates over a field. Producers usually apply a uniform rate although they recognize only a small proportion of the field receives the optimum application.

New technologies can change these situations. Global positioning systems (GPS) and advances in computer software allow for precise identification of soil sample positions in the field and improved soil-test mapping. Variable rate technology (VRT), which combines GPS, computer-based controllers, and digital soil-test maps, provides a practical way for applying desired lime rates over a field.

The study was conducted by Dr. Antonio Mallarino and graduate research assistant Agustin Bianchini in central Iowa during two years in one field and three years in another field, and received support from the Iowa Soybean Association and a local producer. The two fields had very high pH variability.

The study suggests that while a new zone soil sampling approach based on various information layers may not provide better information than the denser grid sampling approach used by many producers, it is less costly and adapts well to different field and economic conditions. Zone sampling uses a variety of information layers (such as yield maps, aerial crop canopy images, digitized soil survey maps, and electrical conductivity maps among others) to define sampling areas within a field.

The lime application portion of the study showed the VRT method resulted in more efficient lime management, reducing the lime need to 60% compared with the traditional uniform-rate application method and reduced soil pH variability.

Although the results showed no cost-effective sampling approach will completely alleviate the limitation of current VRT equipment to manage the small-scale pH variability existing in many fields, a combination of GPS, zone soil sampling, and VRT provides a reasonable and efficient management of soil acidity and lime application.

Agronomy Journal, http://agron.scijournals.org is a peer-reviewed, international journal of agriculture and natural resource sciences published six times a year by the American Society of Agronomy (ASA). Agronomy Journal contains research papers on all aspects of crop and soil science including military land use and management, agroclimatology and agronomic modeling, environmental quality, international agronomy, agricultural research station management, and integrated agricultural systems.

The American Society of Agronomy (ASA), the Crop Science Society of America (CSSA), and the Soil Science Society of America (SSSA) are educational organizations helping their 10,000+ members advance the disciplines and practices of agronomy, crop and soil sciences by supporting professional growth and science policy initiatives, and by providing quality, research-based publications and a variety of member services.