1Department of Soil Science & Agricultural Chemistry
2Department of Agronomy 
Indira Gandhi Krishi Vishwavidyalaya, Raipur, Chhattisgarh 492001

The GreenSeeker is a tool that provides useful data to determine Normalized Difference Vegetative Index ( NDVI ) and Red to Near Infrared Ratios. There are many combinations of infrared imagery. Vegetative Index is often used to look at whole areas to measure overall health as time progresses.
    Nitrogen (N) is an essential plant nutrient and, next to water, is the most yield limiting factor.
    Initial sensors developed in 1989 focused on detecting and spraying weeds. In 1990, the first order bindweed detector/ sprayer were evaluated. By 1992, the first discussion between BAE and PSS researchers at OSU, Team-VRT (variable rate technology) took place concerning the possibility of sensing biomass. Through previous research, it was known that the biomass of winter wheat could be used as an indicator for N need.
    During 1993 and 1994, the first sensor readings were taken from ongoing N rate experiments in Bermuda grass conducted at Oklahoma State University, Stillwater, OK, and the Noble Foundation, Ardmore, OK.(D. Brian Arnall,1996)

Figure 1. Hand held Greenseeker

In March 1996, the very first variable rate N applicator was demonstrated to the public at a public field day in Hennessey, OK, where more than 100 people attended.

Figure 2. The first demonstration of sensor- based variable N application, Hennessey, OK.,1996 (Source: D. Brian Arnall,1996)

Main Characteristics
  • Green seeker can be hand held.
  • It is an active system;
  • It is an online system that can also be used offline;
  • Measures in the range of red light and near infrared light; each sensor measures 100 times per second;
  • Zoning maps may be recorded by soil types; can be used independently because it can communicate with almost all fertilizers with the ISOBUS command;
  • Calculates the Normalized Difference Vegetation Index (NDVI); the fertilizer standard (solid, liquid) is applied in relation to the measured values of the NDVI;
  • The Greenseeker software takes over the calculation of the application quantities and orders the granulated fertilizer spreader or the sprayer.

“Normalized Difference Vegetation Index” and it is the “sensor” value displayed on the optical sensor. NDVI is computed by the following formula:
 NDVI = (NIRref - Redref) / (NIRref + Redref)
 Where, NIRref or Redref represent reflectance in the near infrared and red bands. Many researchers have shown that NDVI is an excellent measure of total biomass.

The nitrogen sensor uses sunlight as a source of passive light. It calculates the spectral reflection of the culture by detecting the incident light of the sun and the light reflected by the culture.
    Then, to calculate the N supply, the sensor uses the transfer function between the spectral reflection parameters and the N quantity of the culture. (Jun Ni Q.J., 2015)

Downward sensor - Receives the light reflected by the crop, consisting of a mirror window, a strip filter, lenses, and a photocell. When the solar light with a certain flow density ω is reflected by the culture, it generates in the photocell an ISCD current according to the relation (D. PATRANABI 2003):
ISCD = S '× H
downward = S' × β '× N × Ψ S '= the responsiveness of the photocell
H downward = the light received by the photocell β '= the diminishing value of the photocell
N = culture reflection
Ψ = sensing angle of the sensor