Development of an allometric equation to estimate carbon in coffee (Coffea arabica L.) of medium height in the Municipality of Comasagua, Cordillera del Bálsamo, El Salvador

Abstract

The research was conducted during August 2018 to February 2020 in four farms in the municipality of Comasagua, department of La Libertad, El Salvador, located between 800 to 1,200 meters above sea level. The main objective was to develop an allometric equation to estimate the biomass and carbon content of coffee plants. A destructive method was used to collect the field information. It consisted of sectioning each of 72 coffee shrubs into their main parts: root, stump, sprouts, branches, leaves, flowers and fruits, according to their phenology. Analyzes of partial moisture and specific density of wood were carried out in the Agricultural Chemistry Laboratory and the Soil Laboratory of the Faculty of Agronomic Sciences of the University of El Salvador. Registration and management of dasometric and laboratory data were carried out using an Open Data Kit® (ODK®) application. A form was designed to record: v total height of the plant, height of sprouts, stump height, diameter at 15 centimeters from the stump, diameter at the base of the shoots, wet weight and dry weight of the sections. The laboratory analysis involved taking a subsample from each section to determine partial moisture and specific wood density in stumps and sprouts. The statistical analysis was carried out using the IBM SPSS® Statistics 23 and Excel® software, with the statistical complement XLSTAT® 2019. Different tests were conducted in order to check the normality of the variables. Through regression analysis, different models were developed combining the dependent and independent variable, until achieving an appropriate regression equation related to the phenomenon being studied. The above-ground dry biomass was composed of the stump plus sprouts, branches, leaves, flowers and fruits. The dependent variable in the model for stump was the dry biomass in kilograms and the independent variables included the diameter at 15 centimeters from the base and the height in meters. For the regrowth model, the variables were related to the dry biomass of regrowths plus branches, leaves in kilograms and the diameter of the base in centimeters. After validation of the regressions in the graph and considering the best fit of the curves, two power regression models were obtained: the stump with an R2 = 0.692 (p<0.01) and the regrowth with an R2 = 0.914 (p<0.01).