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Harvesting

Yield Mapping

What is it?

Yield mapping produces a contoured field map showing high and low
yielding areas of the field. The development of satellite based in-field location systems such as Global Positioning Systems (GPS) has provided a stimulus for the development of yield mapping systems. The use of a GPS together with a grain flow sensor on the main elevator into the grain tank of a combine harvester and a computer-based recording system forms the basis of a yield mapping system. Recorded data is fed into an analysis program for smoothing/interpolation and plotting as a contour map of crop yield. Yield maps can improve the management of differing field areas and help optimise the use of inputs. Increased fertiliser costs have led to increased returns from adoption of this technology by farmers.

How can it help you?

The analysis of a sequence of yield maps can provide information that will help to:

• Define different areas of a field that could be managed in different ways so as to optimise the use of inputs and reduce costs
• Identify compacted areas, low yield potential or soil drainage problems
• Identify areas that could be taken out of primary production for inclusion into environmental schemes to improve profitability
• Provide improved management records costs have led to increased returns from adoption of this technology by farmers.

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How can it help the environment?

• Improved targeting of inputs
• Reduced amount of pesticides in the environment
• Reduced water and atmospheric pollution by avoiding excess application of fertilisers
• Aids the identification of areas of lower productivity that can be used to deliver environmental benefits, e.g. as set-aside or created habitats
  

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Availability and Use

Most manufacturers of combine harvesters now offer yield mapping as an optional facility and it is becoming a standard feature on larger machines. Systems can also be retro-fitted to existing
harvesters.

Yield maps from a single season can provide valuable data relating to crop performance in that season; however, more information can be obtained by analysing a sequence of yield maps collected over a number of cropping seasons. A detailed field assessment of the areas identified from a sequence of yield maps will be necessary to determine appropriate management strategies. The ability to handle large amounts of data within a computer system is important if the best possible information is to be
obtained from yield maps. Software are available commercially that will aid the interpolation of a sequence of yield maps; such approaches are being developed with increasing sophistication.

One of the major factors leading to variations in yield is soil conditions. Methods for mapping variability in soils directly using electro-magnetic induction (EMI) have been developed and good correlation has been demonstrated between field areas defined from yield maps and from EMI. The use of soil maps in conjunction with yield maps can increase the value of both maps and allow improved interpretation.

Crop responses to different soil conditions in different parts of a field will depend on the weather and seasonal effects as well as the underlying soil variability. Because of this, the interpretation of yield maps should use data collected over a number of seasons. For example, in a dry season, cereal
crops on the heavier parts of a field will tend to yield higher than on the lighter areas whereas the reverse may be true in a wet season eg 2008.

Note: The use of infra-red photography from either satellite or aeroplane and chlorophyll N sensor maps from tractor-mounted sensors e.g. Crop Circle can also aid interpretation of yield maps.

How much will it cost you?
Capital cost	In-field location equipment (e.g. GPS), and grain flow sensor together with recording system
	Some investment in computer systems in the farm office will be needed if it does not already exist
Operating cost	A small increase in operating costs because of data handling during harvesting, subsequent processing and interpretation
Cost benefits	High initial capital cost, but once established the system should give useful information at a low cost

Note:  Costs are reducing significantly as technology becomes standardised and use of computerised systems becomes more common
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