Precision Agriculture And Global Positioning System

Introduction

Land that is used for agricultural purposes varies significantly both on a microscopic and macroscopic scale with respect to topography and climate. With this there may exist a range of soil types, properties and other naturally occurring, variable phenomena that contribute to an ecosystem that is considerably diverse across a particular landscape, irrespective of its spatial extent. Precision Agriculture is a farming management concept based around the use of information technology to respond to site specific crop and livestock variability. As a result of the existence of a variable landscape, productivity from a farming perspective will also fluctuate. This has been known since land was first cultivated, but little was able to be done to address such an issue until the relatively recent advent and development of what has become known as Precision Agriculture (PA). The primary goal of PA is to maximise productivity and output in the most efficient way possible. It represents a key component in the evolution of agricultural practices.

The core catalyst of the development of PA was the introduction of Global Navigation Satellite Systems (GNSS), primarily GPS (Global Positioning System). GNSS is a nonspecific term describing a constellation of satellites with the capability to provide positioning, navigation and timing services on a regional and/or global scale. Whilst GPS (a United States owned and managed satellite constellation) remains the most prevalent GNSS, other countries/continents have developed/are developing their own systems to provide additional, independent positioning, navigation and timing capabilities. These include GLONASS (Russia), Galileo (European Union) and BeiDou (China), with many more being developed. Modern agriculture has been revolutionised due to the positioning and navigational capabilities of GNSS. The ability to collect spatially referenced data has altered farm management, efficiency, productivity and profitability in a myriad of ways. In conjunction with the development of GNSS, technology has evolved enabling the considerable number of factors that impact the productivity of a property to be measured. Given this, various techniques have been established combining positioning data and the measurements of the aforementioned factors.

The degree of positioning and navigational accuracy required from GNSS in PA is heavily dependent on the site location and application. Within the last decade, there has been a considerable movement towards sub-decimetre accurate navigation systems primarily due to technology being more financially accessible, but also due to the development and improved availability of higher accuracy correctional services such as CORSnet-NSW-a NSW based continuously operating reference station network. A CORS can take the place of traditional base station used in differential GNSS positioning and typically give position at an accuracy of +/- 20mm at the receiver’s location. This result can only be achieved under specific conditions. That being that the receiver is within approximately 10-15km of the station or up to 70km if the receiver is suitably positioned geometrically within a network of reference stations. Essentially this is because the positional corrections broadcast by the reference station/s generally are not considered valid outside of these radii.

Precision Agriculture Technologies

The array of precision agriculture techniques are continuously expanding. The concept first emerged in North America late in the 20th century through an experiment analysing the effects of varied inputs of lime (to lower soil pH) across a number of cropping paddocks. The outcome of this experiment indirectly saw the production of the first input recommendation maps for fertilisers, herbicides and pesticides, a concept that is now used extensively throughout the world. Following this, accurately referenced spatial data was able to be used in conjunction with real time measurement techniques to develop precise management methods such as:

• machine guidance systems: machinery is operated/directed automatically using GNSS
• terrain mapping: topographic maps of paddocks can be produced using geographic information systems (GIS) and GNSS
• yield mapping and monitoring: mass flow sensors measuring specific characteristics of a harvested crop can be used in conjunction with GNSS to produce a map displaying spatially variable yield rates across a property
• variable rate application (VRA): quantity of seed/pesticide/herbicide etc. to be ‘applied’ can be varied dependent on spatially variable characteristics of soil/seed/chemical. etc.

The realm of precision agriculture extends far beyond the applications mentioned above. However, the scope of this paper will focus specifically on yield mapping and monitoring and variable rate application. Today, these two methods are used extensively by producers across the globe. The benefits of their use are evident in the considerable commercial development of such techniques.

Site-Specific Crop Management

Both yield mapping and monitoring and variable rate application are examples of site-specific crop management (SSCM). SSCM involves the amendment of resource application and agronomic practices to better complement soil and crop requirements as they vary spatially in the field. The five main components of SSCM are:

• spatial referencing: GNSS-the main technology behind SSCM
• crop, soil and environment monitoring: sensors and monitors used to measure crop, soil, landscape and environmental variables.

Technology continues to develop to better improve the range of cropping attributes that can be measured in real time at high spatial densities

• attribute mapping: filtering and display of observed data
• decision support systems: decision of whether or not unique treatment is warranted in areas of the property made on the basis of spatial variability
• differential action: requires information regarding by what magnitude an action should be varied with respect to its position.