Submitted to: Agroforestry Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2002
Publication Date: 9/1/2003
Citation: MENDONCA, E.S., STOTT, D.E. CHARACTERISTICS AND DECOMPOSITION RATES OF PRUNING RESIDUES FROM A SHADED COFFEE SYSTEM IN SOUTHEASTERN BRAZIL. AGROFORESTRY SYSTEMS. 2003. 57:117-125. Interpretive Summary: Increased use of agroforestry systems is occurring in southeastern Brazil as a way to combat soil erosion as well as improve or maintain soil fertility. We harvested the prunings of several trees and bushes commonly found in these type of management systems in the eastern portion of the State of Minas Gerais. The cash crop in these systems is coffee beans. We wanted to know the pattern of decomposition associated with these prunings, link the decomposition pattern with the initial chemical composition of the prunings, and assess the effect of mixing the leaves of different tree species on the decomposition pattern. We also used the CENTURY model (obtained from W.J. Parton, USDA-ARS, Fort Collins, CO) to simulate the decomposition of the tree prunings and used the model to estimate their decomposition rate coefficients. The pruning residues were high in polyphenols and lignins with high carbon-to-nitrogen and carbon-to-phosphorus, and were low in calcium, magnesium and potassium. The decomposition rates of the prunings were relatively slow as compared to small grains or other grain crops. The low decomposition rates were related the ratio of lignin plus polyphenolic contents divided by the nitrogen content as well as the low calcium, magnesium and phosphorus contents. The size of the residue, as indicated by the projected surface area, also impacted the decomposition rates. The decomposition rates could be improved by mixing the leaves of different species. The rates of mineralization from most of the residue indicated that there is a potential to supply the needs of a crop of maize. However, residues of certain species, if decomposed alone, would not supply sufficient nutrients and need to be mixed with leaves of other species. This work impacts the subsistence farmers in the region, allowing them to more closely estimate the amount of nutrients available to crops, and to potentially grow another cash crop. For farmers operating beyond subsistence levels, it would allow reductions in nitrogen fertilization and reduce environmental problems associated with excess nitrogen.
Technical Abstract: In the Zona da Mata Mineira of Southeastern Brazil the development of sustainable land requires the integration of crops with trees. The objectives of this study then were to (i) characterize prunings from the main tree species in an agroforesty system; (ii) determine the effects of the physical and chemical characteristics of the prunings on their decomposition patterns in the laboratory; (iii) assess the effect of mixing leaves of different species on decomposition rates; and (iv) propose a decomposition index for the residues studied. The study was carried out with pruning residues from Cajanus cajan, Solanum variable, Cassia ferruginea, Piptadenia gonoacantha, Croton urucurana, and Melinis multiflora. The materials were characterized for total C, N, P, Ca, Mg and K contents; lignin, cellulose, hemicellulose and soluble polyphenols contents. The pruning residues had high polyphenols and lignin contents, high C:N and C:P ratios, and low contents of Ca, Mg and K. The low decomposition rates of the prunings were related to the P, K, hemicellulose and polyphenol contents. The rates of N mineralization from most of the residues indicate that there is a potential to supply the needs of a crop of maize. The residues of some species, if decomposed alone, would not supply sufficient nutrients, and need to be mixed with leaves of other species.