Submitted to: Agroforestry Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/14/2012
Publication Date: 7/25/2012
Citation: Zaia, F.C., Gama-Rodrigues, A.C., Gama-Rodrigues, E.F., Fontes, A.G., Machado, R.C., Baligar, V.C. 2012. Carbon, nitrogen, organic phosphorus, microbial biomass and N mineralization in soils under cacao agroforestry systems in Bahia, Brazil. Agroforestry Systems. 86:197-212. Interpretive Summary: Phosphorus (P) is a major essential nutrient limiting crop production in the highly weathered tropical soils. A large portion of P in tropical soils is present in organic forms and its transformation to inorganic plant available forms is essential to improve soil fertility. Field experiments were undertaken in Bahia Brazil with different field conditions where: 30 and 70 years old cacao were grown under natural forest (cacao cabruca) and under the shade of Erythrina glauca trees, and an adjacent natural forest was used as a control. Soil samples were collected at different depths to evaluate organic P content. Organic P was positively correlated with available P, but was negatively related to organic matter. These cacao agroforestry systems showed that P dynamics in soil was not closely associated with organic matter. These results demonstrate that agroforestry systems adapted for cacao planting play an important role in nutrient cycling and could improve cacao growth and production. Findings of this research are helpful in development of long term effective fertilization programs for perennial crops such as cacao and will be used by farmers, extension workers and researchers.
Technical Abstract: Understanding the soil organic P cycle is important to improve the P fertilization management in low-input tropical agricultural systems. The aim of this study was to evaluate organic P (Po) content by Bowman extraction method and labile P fractions by NaHCO3 extraction in soil profiles under cacao agroforestry systems. Mean total Po was 193 mg kg-1, 155 mg kg-1, 122 mg kg-1 and 87 mg kg-1, respectively, in the depth 0 – 5 cm, 5 – 15 cm, 15 – 30 cm and 30 – 50 cm. Total Po accounted for 7.8 to 36.3% of the total P extracted for all the depth. Mean labile Po was 15.2 mg kg-1, 12.2 mg kg-1, 9.6 mg kg-1 and 6.6 mg kg-1 in the depth 0 – 5 cm, 5 – 15 cm, 15 – 30 cm and 30 – 50 cm, respectively. Labile Po accounted for 33.2 to 81.7% of the total labile P extracted for all the depth. In cacao agroforest, the total Po and labile Po contents were lower in the Latosol than in Cambisol group. Organic P (total and labile) was positively correlated with available P, but it was negatively related to organic C. Thus, organic P dynamics is not closely associated to organic C dynamics in soils under cacao agroforest. The organic P stock in the depth 0 – 50 cm was 790 kg ha-1 (total Po) and 55.5 kg ha-1 (labile Po), and the amounts of this P fraction suggest that it could be relevant for cacao nutrition considering the low amount of P exported through cacao seed harvest.