(CEC) cation exchange capacity,

represents the total value of exchangeable hydrogen, calcium, magnesium, potassium, aluminum, and sodium cations in the soil. Cation exchange occurs on the surface of humus colloids and clay particles as well as on plant root surfaces.

center pivot irrigation,

refers to a sprinkler irrigation system that consists of a long pipe with multiple water outlets that is pivoted about a center point by the motion of rolling towers that elevate the pipe above the crop.

(CIMIS) California Irrigation Management Information System,

is a computerized crop weather information system available to the public and operated under the collaboration of the State Department of Water Resources, the University of California, local water districts, and various other agencies.

(CRADA) Cooperative Research and Development Agreement,

is a type of federal agreement authorized by the 1980 Stevenson-Wydler Technology Innovation Act and its 1986 amendment, the Federal Technology Transfer Act. CRADA permits federal laboratories to enter into agreements with universities, private companies, nonfederal government entities, and others to link laboratory's fundamental or pretechnology research capacity with commercial research and marketing expertise of the private sector. The acts establish funding guidelines and rules regarding ownership of the intellectual property developed under CRADAs.

crop model,

refers to a mathematical representation used to simulate crop growth.

(DGPS) differential global positioning system,

is a method to improve the position accuracy of GPS by using a second stationary GPS receiver positioned at a known location. The second receiver computes the error in the signal by comparing the true distance from the satellites to the GPS measured distance.

(DSS) decision support systems,

is an integrated system of expert knowledge, management models, and timely data to assist producers with daily operational and long-range strategic decisions.

drip irrigation,

is a form of microirrigation in which water usually is delivered to the soil near the plants through a network of tubing with closely spaced, low-flow rate emitters.

evapotranspiration,

refers to water loss from soil evaporation and crop transpiration. Evapotranspiration is typically monitored using networks of weather stations that cover large areas.

floater,

refers to high flotation vehicles typically used by custom chemical and fertilizer dealers for field applications.

georeferencing,

is the process of associating position information with data of any kind. Georeferencing is necessary to represent spatial relationships between data points.

(GIS) geographic information systems,

hardware, software, data, organizations, and institutional relations to automate, manage, analyze, and display georeferenced information of and about the earth.

(GLONASS) GLObal Navigation Satellite System,

is a space-based radionavigation system operated and managed by the military of the former Soviet Union.

(GPS) Global Positioning System,

is a space-based radionavigation system originally designed primarily to provide highly accurate radionavigation capability to U.S. military forces, while also providing an unencrypted signal of degraded accuracy to civilian users. Positioning is achieved through the use of simultaneously received satellite transmissions from four or more satellites above the horizon. The GPS receiver allows latitude, longitude, and altitude coordinate information to be associated with data obtained from a specific site on the field.

grid soil sampling,

refers to the method in which a field is divided into square sections (grids) of several acres or less. Samples may be collected from each section and analyzed for soil nutrients such as phosphorus and potassium.

ground-based sensors,

refer to devices mounted on machines that travel over the ground and that measure local soil or plant conditions.

(IPM) integrated pest management,

refers to pest management strategies based on judicious use of chemical pesticides with other management tactics such as cultivation methods, crop and varietal choice, attraction of natural enemies or other biological control methods, pheromone traps, and other ecologically-based measures.

kriging,

is a geostatistical technique used to fit a model to a semi-variogram (a depiction of the spatial correlation between multiple data pairs), and using this function to interpolate values at unknown points as a function of spatial correlation.

multispectral,

refers to an electromagnetic sensor that collects data in multiple spectral wave bands, typically visible and infrared, simultaneously.

(NDVI) normalized difference vegetation index,

is the ratio of the difference between the red and near-infrared bands divided by their sum used to identify and enhance the vegetation contribution in a digital remote sensing analysis.

panchromatic,

refers to an electromagnetic sensor that collects data in a single wave bands that span the colors of the visible spectrum.

post processing,

is the differential correction of GPS positions at some time after the data are recorded.

real-time,

describes sensing or control actions that occur instantaneously, or nearly instantaneously. An example of real-time sensing and control would be a device that optically recognizes a weed and immediately directs a spray onto that weed.

remote sensing,

is the acquisition of information by a recording device not in physical contact with an object being studied. Devices such as cameras, radar, lasers, or radio receivers can collect information from remote locations such as airplanes or satellites.

scouting,

as referred to in agriculture is a visual assessment of crop condition including growth stage/maturity, plant vigor, and presence of disease, weed, and insect pests.

(SA) selective availability,

is a purposeful degradation in GPS navigation and timing accuracy that is accomplished by intentionally varying the precise time of the clocks on board the satellites, which introduces errors into the GPS signal. With selective availability, the civilian signal is limited to an accuracy of 100 meters, 95 percent probability. Military receivers with the appropriate encryption keys can eliminate the effects of SA and obtain an accuracy of approximately 21 meters (95 percent) probability.

spatial variation,

refers to differences in field conditions, such as crop yield, from one location in a field to another.

temporal variation,

refers to differences in conditions, such as soil nitrogen, from one sampling period to another.

turnkey system,

refers to the integration of information technologies into a system that is ready to operate.

(VI) vegetation index,

is a ratio created by dividing the red by the near-infrared spectral bands used to identify and enhance the vegetation contribution in a digital remote sensing analysis.

(VRT) variable-rate technology,

refers to a system that varies the rate of agricultural inputs such as seed, fertilizer, and crop protection chemicals in response to changing local conditions.

yield mapping,

refers to the process of collecting georeferenced data on crop yield and characteristics, such as moisture content, while the crop is being harvested. A yield mapping system combines the output of a yield monitor with the position information provided by a DGPS receiver.

yield monitors,

are devices that estimate the yield per area by measuring the flow rate of the crop and the area covered by the harvester.