25 Jun 2004
A violet laser diode and a miniature spectrometer are helping researchers in Ghana predict crop yields.
Laser-induced fluorescence from the chlorophyll in cowpea leaves can help predict the crop yield before harvest, according to researchers in the African country of Ghana. (Meas. Sci. Technol 15 1255)
The team believes that the laser-based technique compares well with conventional methods and could be an important screening technique for plant breeders.
The cowpea is one of the most important pulses produced in Ghana but often suffers from poor yields due to the country's arid environment. To overcome this, the Ghanaian government is developing new cowpea varieties that tolerate or resist the factors that contribute to low yields.
This is where Benjamin Anderson and his colleagues from Ghana's University of Cape Coast come in. The researchers have been studying the new varieties and predicting the potential crop yields using a technique known as laser-induced chlorophyll fluorescence (LICF).
The LICF system uses a battery-powered Nichia laser diode emitting up to 3 mW at 396 nm. Light from the laser is fired down a fiber and induces chlorophyll fluorescence at 683 nm and 731 nm in a cowpea leaf. These fluorescence peaks are recorded by a spectrometer and analysed to indicate the photosynthetic activity of the plant.
The study covered five varieties of cowpea and ten plants of each were grown. Fluorescence signals were recorded after the sixth, seventh and eighth week of growth.
Anderson and colleagues say that the peaks and areas under the spectral curves relate to the chlorophyll concentration. "This is an important indication to use to assess the photosynthetic activity of the plant at the early stages of growth," say the team. "These results suggest that chlorophyll fluorescence peak intensity and area ratio might be used to predict, before harvest time, the variety that can give higher performance values and a better yield."