USE OF A PORTABLE CHLOROPHYLL METER TO DETECT DIFFERENT NUTRITIONAL STATUS IN Brachiaria decumbens

Abstract

Uniform fertilizer application as is used in conventional agrigulture is inefficient in the case of variable soil nutrition. Thus, the use of tools capable of identifying this variability may assist in site-specific application, allowing that each area receive the amount of fertilizer required. The objective of this work was to use a portable chlorophyll meter (SPAD 502) to detect different nutritional status resulting from different nitrogen fertilization rates in Brachiaria decumbens. This study was developed in a field already established with this forage, in the Forage Sector of the Department of Animal Science, Federal University of Viçosa, Brazil. Thirty plots measuring 3 x 3 m were defined that received the treatments of five different rates of nitrogen fertilizer (0, 50, 100, 150 and 200 kg ha-1) during the period of January to May of 2006. A completely random design with six replications was used. The nitrogen (N) leaf content analysis in the laboratory was used as a reference method. Regression analysis were performed, with lack-of-fit test between the studied variables (SPAD measurements, N leaf content and dry matter) and applied N. A correlation analysis was also performed between SPAD measurements and leaf N content. The results showed that with the exception of the first acquisition period, the SPAD was capable of detecting the effects of the differents N application doses. The correlation analyses also indicated that the chlorophyll meter can be considered an indicator of nutritional status of this forage.