27-08-2012, 11:14 AM
On-the-go soil sensors for precision agriculture
[attachment=32801]
Abstract
The basic objectives of site-specific management of agricultural inputs are to increase profitability
of crop production, improve product quality, and protect the environment. Information about the
variability of different soil attributes within a field is essential for the decision-making process. The
inability to obtain soil characteristics rapidly and inexpensively remains one of the biggest limitations
of precision agriculture. Numerous researchers and manufacturers have attempted to develop
on-the-go soil sensors to measure mechanical, physical and chemical soil properties. The sensors
have been based on electrical and electromagnetic, optical and radiometric, mechanical, acoustic,
pneumatic, and electrochemical measurement concepts. While only electric and electromagnetic sensors
are widely used at this time, other technologies presented in this review may also be suitable to
improve the quality of soil-related information in the near future.
Introduction
Soil testing results are important inputs to the profitable application of fertilizer, lime,
and other soil amendments. When soil test results are combined with information about the
nutrients that are available to the various crops, a reliable basis for planning the fertility program can be established (Hoeft et al., 1996). An appropriate test may be based on local
soil and crop conditions as well as personal preference. A standard test usually includes
determination of available phosphorus (P), exchangeable potassium (K), calcium (Ca), and
magnesium (Mg), their saturation percentages, the cation exchange capacity (CEC), pH,
and lime requirement. Some laboratories may also test for organic matter (OM) content,
salinity, nitrate, sulfate, certain micronutrients, and heavy metals (Foth and Ellis, 1988).
In addition, the crop growth environment is affected by soil texture (sand, silt and clay
content), level of soil compaction, moisture content, and other mechanical and physical soil
properties.
Instrumentation and methods
The global positioning system (GPS) receivers, used to locate and navigate agricultural
vehicles within a field, have become the most common sensor in precision agriculture. In
addition to having the capability to determine geographic coordinates (latitude and longitude),
high-accuracy GPS receivers allow measurement of altitude (elevation) and the data
can be used to calculate slope, aspect and other parameters relevant to the landscape.
When a GPS receiver and a data logger are used to record the position of each soil sample
or measurement, a map can be generated and processed along with other layers of spatially
variable information. This method is frequently called a “map-based” approach. On the
other hand, some soil sensors may be used to vary application rates in response to sensor
output in real time without a GPS receiver (Morgan and Ess, 1997). Therefore, on-the-go
soil sensors can be a part of either “map-based” or “real-time” systems.
Mechanical sensors
Electrical, electromagnetic, optical and radiometric soil sensors provide capability to
evaluate variability of soil physical composition while traveling across the field. However, a
mechanical characteristic of soil such as soil strength (usually assessed through measuring
mechanical resistance) may provide additional useful information about soil conditions
(e.g., compaction). Regions of high mechanical resistance in the soil may arise naturally,
be caused by compaction from heavy farm machinery, or by the formation of plow pans.
In each case, soil particles are positioned closer to each other, and the process is referred
to as compaction. Compacted soils reduce growth rates of crop roots and thus limit the
availability of water and nutrients to the plant (Upadhyaya et al., 1999).
A standard vertical cone penetrometer is frequently used to measure soil resistance to
penetration (ASAE, 2002), which is believed to be a representation of soil compaction.
Even when automated, cone penetrometer measurements are typically time consuming and
the results are highly variable. To overcome these problems, a number of prototype systems
have been developed for on-the-go sensing of soil mechanical resistance.
Strain gauges and load cells provide a very convenient way of measuring forces acting
on tillage tools. They are relatively inexpensive, very robust (i.e. can withstand harsh field
environments), and are easily interfaced to a data acquisition system, thus making them
ideal for real-time applications. Load cells are routinely used to measure draft, vertical
load, side force, and moments acting on tillage implements. For example, in a study conducted
by Glancey et al. (1996), a tillage implement was calibrated using a three-point hitch
dynamometer in different soil conditions and at different speeds.
[attachment=32801]
Abstract
The basic objectives of site-specific management of agricultural inputs are to increase profitability
of crop production, improve product quality, and protect the environment. Information about the
variability of different soil attributes within a field is essential for the decision-making process. The
inability to obtain soil characteristics rapidly and inexpensively remains one of the biggest limitations
of precision agriculture. Numerous researchers and manufacturers have attempted to develop
on-the-go soil sensors to measure mechanical, physical and chemical soil properties. The sensors
have been based on electrical and electromagnetic, optical and radiometric, mechanical, acoustic,
pneumatic, and electrochemical measurement concepts. While only electric and electromagnetic sensors
are widely used at this time, other technologies presented in this review may also be suitable to
improve the quality of soil-related information in the near future.
Introduction
Soil testing results are important inputs to the profitable application of fertilizer, lime,
and other soil amendments. When soil test results are combined with information about the
nutrients that are available to the various crops, a reliable basis for planning the fertility program can be established (Hoeft et al., 1996). An appropriate test may be based on local
soil and crop conditions as well as personal preference. A standard test usually includes
determination of available phosphorus (P), exchangeable potassium (K), calcium (Ca), and
magnesium (Mg), their saturation percentages, the cation exchange capacity (CEC), pH,
and lime requirement. Some laboratories may also test for organic matter (OM) content,
salinity, nitrate, sulfate, certain micronutrients, and heavy metals (Foth and Ellis, 1988).
In addition, the crop growth environment is affected by soil texture (sand, silt and clay
content), level of soil compaction, moisture content, and other mechanical and physical soil
properties.
Instrumentation and methods
The global positioning system (GPS) receivers, used to locate and navigate agricultural
vehicles within a field, have become the most common sensor in precision agriculture. In
addition to having the capability to determine geographic coordinates (latitude and longitude),
high-accuracy GPS receivers allow measurement of altitude (elevation) and the data
can be used to calculate slope, aspect and other parameters relevant to the landscape.
When a GPS receiver and a data logger are used to record the position of each soil sample
or measurement, a map can be generated and processed along with other layers of spatially
variable information. This method is frequently called a “map-based” approach. On the
other hand, some soil sensors may be used to vary application rates in response to sensor
output in real time without a GPS receiver (Morgan and Ess, 1997). Therefore, on-the-go
soil sensors can be a part of either “map-based” or “real-time” systems.
Mechanical sensors
Electrical, electromagnetic, optical and radiometric soil sensors provide capability to
evaluate variability of soil physical composition while traveling across the field. However, a
mechanical characteristic of soil such as soil strength (usually assessed through measuring
mechanical resistance) may provide additional useful information about soil conditions
(e.g., compaction). Regions of high mechanical resistance in the soil may arise naturally,
be caused by compaction from heavy farm machinery, or by the formation of plow pans.
In each case, soil particles are positioned closer to each other, and the process is referred
to as compaction. Compacted soils reduce growth rates of crop roots and thus limit the
availability of water and nutrients to the plant (Upadhyaya et al., 1999).
A standard vertical cone penetrometer is frequently used to measure soil resistance to
penetration (ASAE, 2002), which is believed to be a representation of soil compaction.
Even when automated, cone penetrometer measurements are typically time consuming and
the results are highly variable. To overcome these problems, a number of prototype systems
have been developed for on-the-go sensing of soil mechanical resistance.
Strain gauges and load cells provide a very convenient way of measuring forces acting
on tillage tools. They are relatively inexpensive, very robust (i.e. can withstand harsh field
environments), and are easily interfaced to a data acquisition system, thus making them
ideal for real-time applications. Load cells are routinely used to measure draft, vertical
load, side force, and moments acting on tillage implements. For example, in a study conducted
by Glancey et al. (1996), a tillage implement was calibrated using a three-point hitch
dynamometer in different soil conditions and at different speeds.