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Dr. Joan R. Davenport, soil scientist, WSU IAREC Prosser
One can see from looking across the gently rolling topography and large cropped fields in a southeastern Washington landscape that conditions influencing plant growth will vary. Technological advances in tools like the Global Positioning System (GPS), Geographic Information Systems (GIS), and Variable Rate Application Technology (VRT) offer opportunities to treat different areas in this type of landscape with different management approaches. Currently popular terms used to describe this approach are Precision Agriculture or Site Specific Crop Management (SSCM). An integral part of this approach is to variably manage a field for maximum economic crop yield and quality while attaining environmental benefits.
So, what is "precision agriculture" and how near is it to becoming a widely adopted farming practice?
Taken as a whole, the SSCM approach is to monitor fields and manage variability to provide a crop with the correct amount of a given input it requires when (temporally) and where (spatially) it is needed. Applying materials where they are most effective, reducing both under and over applications, brings economic and environmental benefits. Obviously, the larger a field, the harder this is to do. The home vegetable gardener may do this, but operating this way across a large field requires a lot of assistance. That is where the above list of tools comes in.
Access to the Global Positioning System (GPS) fueled the original concept of SSCM. GPS uses satellites to locate any geographic position according to latitude, longitude, and altitude. The technology is now so affordable that cars often come equipped with simple GPS systems. A key aspect of GPS is that the more accurately the user needs to locate a point, the more expensive the equipment is. Most systems for cars or for agricultural field equipment locate within a few meters or yards. For research, a special type of GPS (DGPS) fine tunes the readings to within 30 cm (1 foot) or less.
Prior to current SSCM approaches, software systems were developed for use in combination with a GPS unit and digitized (converted into computer format) soil surveys to spread fertilizer across a field by soil type. Early work exposed a number of problems with this approach. First, application was either on or off. Second, and more importantly, information in the soil survey was not designed for this use, and so the great differences expected from "farming by soil type" were not obtained. Also, most of the early attempts at using this approach occurred in the Midwest. Much of the ongoing research is still in areas where irrigation is supplemental to rainfall, which is an important issue in terms of the potential impact of SSCM.
Much has occurred to advance SSCM toward becoming a real option. The other two technologies mentioned earlier are key. Geographic Information Systems (GIS) are computer programs that store multiple measurements from a single location as "georeferenced" data (data that have a geographic location via latitude and longitude). These varying measurements can be compared to each other and to patterns across an area. This concept is generally referred to as data layering, where each measurement is considered a data layer. For example, multiple soil samples taken across a single field may be analyzed for a host of different properties. If the soil samples were taken in a georeferenced manner, then soil pH, soil texture, and soil nitrogen content could represent three different data layers. One can then look at a "picture" that graphically shows high and low areas of soil pH and soil nitrogen. Additional information like crop yield can be added. Building up data from year to year or within a season allows temporal patterns to also emerge. The GIS allow relatively easy handling of much more complex information than was previously available.
Variable Rate Application Technology (VRT) is a generic term for any agricultural application equipment that can apply different amounts of a material across a field based on information coding and georeferencing. Availability of VRT equipment is increasing rapidly. Currently, VRT fertilizer equipment is commercially available and in use by some commercial applicators. In fact, soon-to-be marketed VRT fertilizer spreaders for perennial crops (tree fruits, grapes) were developed in central Washington. Other VRT equipment either in development or at the prototype level includes irrigation equipment and applicators for crop protection chemicals (herbicides, fungicides, insecticides). Additionally, for annual crops, different types of variable rate planters and seeders are in various stages of development. And, for many crops, equipment for monitoring yields as the crop is harvested is anywhere from off the shelf (as with wheat) to in development (as with grapes).
However, precision agriculture is at a turning point. The technological advances to implement SSCM have outstripped the research needed to gain the economic and environmental benefits from using the technology. Although growers using the limited SSCM practices have seen improvements in yield and crop quality, to take these improvements to the level that this technology could provide requires additional work. For a whole host of crop management inputs, understanding and development of a few critical elements are missing.
Research is needed
To accurately and adequately apply materials to an area, certain monitoring is needed. For example, to determine how much and what levels of fertilizer are needed across the field, one would have to collect soil samples at a rate that would cost too much to analyze and remove too much soil. Research is needed to understand what type of sampling area is optimal to balance the economics of testing and the return from changing management. This involves thinking beyond the boundaries of the present approach that soil test values for a given element are the best and only measurement for determining how much of that nutrient to apply as fertilizer. To this end, research is being conducted to reevaluate and expand our understanding of crop response to include factors beyond a single soil test measurement. Factors varying little from year to year (e.g. soil texture) and some routine aspects of soil chemistry that impact an array of nutrients (e.g. soil pH) may provide alternatives.
As well as developing knowledge and understanding of scope and scale of testing, research is also being conducted to develop alternative methods of monitoring fields. The concept of remote sensing is something that is practiced to a limited extent in agriculture through techniques like aerial infrared photography. However, looking at alternative types of sensors may provide techniques to remotely monitor important factors in the field such as soil moisture (for crop water management) and certain climatological factors (e.g. leaf wetness, canopy temperature) that have implications in both water and disease management.
Where are we now?
Many tools to begin farming in a way that addresses field variability to improve both environmental and economic impacts are either in place or nearly so. By applying materials when, where, and at what rate they are required, economic gains occur from improvements in yield and quality plus any associated cost reduction. Environmental gains occur through reducing the potential of off-target application.
Some aspects of precision agriculture are ready for certain
crops. Yield monitoring and variable rate fertilizer applications
are providing benefits. This is more true in the irrigated agricultural
systems of the Pacific Northwest, where the ability to control
water application increases the effectiveness of SSCM. However,
to increase the gains that this technology has to offer, research
is needed to develop ways to apply the technology to the fields.
Research lags far behind application technologies, and needs to
be developed quickly.
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