Chlorophyll Meter May Benefit Farmers and the Environment

AUBURN, Ala.—For most farmers, the rule of thumb for calculating the nitrogen needs of various row crops has been based more on educated guesswork than on specific measurements. But soon the mere press of a thumb may provide farmers a fast, precise way to appraise the need for this vital plant nutrient, resulting in financial and environmental benefits.

A research project being conducted through the Alabama Agricultural Experiment Station (AAES) at Auburn University, in cooperation with the USDA Agricultural Research Service (USDA-ARS), is exploring the possibility of using a hand-held chlorophyll meter to determine nitrogen requirements for cotton, corn, and wheat.

AAES researchers Wes Wood, Wayne Reeves, Paul Mask and Keith Edmisten began the study to see if the meter's chlorophyll measurements could be correlated with nitrogen application rates for these crops. Preliminary results show that a correlation does exist and the meter has potential as a management tool.

According to the four, who are all faculty members in Auburn's Department of Agronomy and Soils, refining nitrogen application offers several benefits. More precise rates would help farmers save money by helping them avoid over application of nitrogen. Since too much nitrogen can reduce yields and quality of cotton and wheat, precise application rates can help protect these crops from excessive nitrogen. And more accurate nitrogen application also would help ensure that excess fertilizer nitrogen is not introduced into the environment.

The researchers noted that nitrogen estimation for many crops is an inexact science. "We don't typically use tests to measure nitrogen for a crop the way we do for other nutrients," explained Mask, an associate professor in the Agronomy and Soils Department and also a grain crops specialist with the Alabama Cooperative Extension Service (ACES). He noted that most nitrogen application is based on past experiences with the crop, weather and climate.

One reason for the absence of testing is that most of the available tests are not reliable measures. "To date, soil testing has not been successful in determining nitrogen needs in the Southeast because of the climate in the area," said Wood, an assistant professor in the Department. He explained that the abundant rainfall in the region can leach nitrogen from the soil. Warm temperatures and high moisture characteristic of southeastern climates also promote microbial action that can affect the availability of nitrogen to the plants.

"Out west, under much drier conditions, they can use soil testing because they get an accumulation of nitrate in the soil profile. It is easy to run out and do a soil test and determine how much available nitrogen they will have when they are ready to plant," continued Wood.

Reeves, a USDA-ARS scientist with the National Soil Dynamics Laboratory located on the Auburn campus and an adjunct associate professor of Agronomy and Soils, added that colder winter temperatures experienced in the western United States help preserve nitrogen levels in the soil.

Edmisten, also an assistant professor of Agronomy and Soils and an ACES cotton specialist, noted that other types of tests, such as petiole analysis for cotton, can be used to determine nitrogen needs, but these require destruction of plant material to obtain samples, take several days to process, and are influenced by soil moisture. Recognizing the need for a faster, more accurate method of nitrogen evaluation, the four researchers saw potential in a Japanese-made chlorophyll meter. The meter, which reads the greenness of plants, has been used primarily for measuring chlorophyll in rice and provides instant information.

The Auburn researchers are among the first scientists in the nation to apply this meter to upland crops. "The Japanese did a little bit of work with corn using the meter and decided that corn had too high a content of nonchlorophyll nitrogen to make a correlation," said Wood.

The Auburn research team thought differently and began exploring the meter's use on corn, cotton, and wheat through tests conducted at the E.V. Smith Research Center in Shorter. Preliminary results suggest that there is a distinct correlation between nitrogen needs, yield and the meter's readings.

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Auburn, AL 36849
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Contact Jamie Creamer, 334-844-2783 or jcreamer@auburn.edu
Contact Katie Jackson, 334-844-5886 or smithcl@auburn.edu

02/10/92