Changes in soil physical and chemical properties in long term improved natural and traditional agroforestry management systems of cacao genotypes in Peruvian Amazon

Authors: AREVALO, ENRIQUE - Tropical Crop Institute (ICT); CANTO, MANUEL - La Molina National Agrarian University; ALEGRE, JULIO - La Molina National Agrarian University; LOLI, OSCAR - La Molina National Agrarian University; JULICA, ALBERTO - La Molina National Agrarian University; Baligar, Virupax

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2015
Publication Date: 7/16/2015
Publication URL: http://handle.nal.usda.gov/10113/63033
Citation: Arevalo, E., Canto, M., Alegre, J., Loli, O., Julica, A., Baligar, V.C. 2015. Changes in soil physical and chemical properties in long term improved natural and traditional agroforestry management systems of cacao genotypes in Peruvian Amazon. PLoS One. 10(7):1-29.

Interpretive Summary: Traditional slash and burn agriculture practiced in the Peruvian Amazon region is leading to soil degradation and deforestation of native forest flora. The only way to stop such destructive processes is through the adoptation of sustainable alternatives such as growing crops in agroforestry systems. Growing cacao in an agroforestry system generates an intensive productive use of the land, maintains and improves the physical, chemical and biological properties of tropical soils, and plays an important role in improving cocoa production and fertility of degraded tropical soils. The aim of these field study was to evaluate the impact of long term improved natural agroforestry systems (INAS) and an improved traditional agroforestry system (ITAS) of cacao management on soil physical and chemical properties in an area planted with 60 cacao types (59 domestic and international genotypes and one spontaneous hybrid). Our results indicate that management practices have tremendous impact on soil properties. Soil pH, cation exchange capacity, exchangeable magnesium and sum of the bases were higher in the INAS than the ITAS. In both systems, soil organic matter content, extractable phosphorous and potassium and exchangeable cations increased with years of cultivation. The levels of physical and chemical properties of soil under cocoa genotypes showed a marked difference in both systems. Therefore success of sustainable cacao production systems in the Peruvian Amazon areas is dependent on the proper management of the physical and chemical properties of these soils. Findings of this study will be useful to resource poor cacao farmers of the Amazon region to develop a cacao management system that improves soil physical and chemical properties thereby enhancing the fertility and productivity of soils. Knowledge of soil fertility status will assist in the development of highly productive sustainable and economically viable cacao production systems for the Peruvian Amazon region.

Technical Abstract: Traditional slash and burn agriculture practiced in the Peruvian Amazon region is leading to soil degradation and deforestation of native forest flora. The only way to stop such destructive processes is through the adoptation of sustainable alternatives such as growing crops in agroforestry systems. Growing cacao in an agroforestry system generates an intensive productive use of the land, maintains and improves the physical, chemical and biological properties of tropical soils, and plays an important role in improving cocoa production and fertility of degraded tropical soils. The aim of these field study were to evaluate the impact of long term improved natural agroforestry systems (INAS) and an improved traditional agroforestry system (ITAS) of cacao management on soil physical and chemical properties in area planted with 60 cacao accessions (59 domestic and international genotypes and one spontaneous hybrid). Both systems of cacao production were installed in an area with 30-years of secondary forest. For evaluation of changes of soil physical and chemical properties with time due to imposed cacao management systems, plots with 10 cacao genotypes ((ICS-95, UF-613, CCN-51, ICT-1112, ICT-1026, ICT-2162, ICT-2171, ICT-2142, H-35, U-30) and one plot with spontaneous hybrid were selected. Soil samples were taken at 0-20 cm, 20-40 cm and 40-60 cm depths in 2004 before the installation of the management systems, and then followed at two years intervals (2006, 2008 and 2010). Physical properties such as bulk density, porosity, and soil moisture content at field capacity and wilting point varied significantly during the years of assessment in the different soil depths and under the cocoa genotypes assessed. Soil pH, CEC, exchangeable Mg and sum of the bases were higher in the INAS than the ITAS. In both systems, SOM contents, extractable P and K and exchangeable K, Mg and Cu and Al saturation increased with years of cultivation, however the increase was greatest in the first 0 to 20 cm of soil depth. Overall improvement of SOM and soil nutrient status was much higher in the ITAS than INAS. The levels of physical and chemical properties of soil under cocoa genotypes showed a marked difference in both systems.