Submitted to: Biology and Fertility of Soils
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2009
Publication Date: 5/1/2009
Citation: Sotomayor-Ramirez, D., Espinosa, Y., Acosta Martinez, V. 2009. Land use effects on microbial biomass C, ß-glucosidase and ß-glucosaminidase activities, and availability, storage, and age of organic C in soil. Biology and Fertility of Soils. 45(5):487-497. Interpretive Summary: Information is lacking about C and N turnover, distribution and storage capacity of Vertisols of the tropics as affected by land-use. These soils play a significant role in the amounts of carbon (C) sequestered from the atmosphere which can mitigate increased atmospheric CO2. Scientists from the University of Puerto Rico located in Mayaguez, PR, the Institution of National Investigation of Agriculture (Instituto Nacional de Investigaciones Agrícolas; INIA) in Maracay, Venezuela and the United States Department of Agriculture (USDA-ARS) of Lubbock, Texas studied a representative Vertisol soil in Puerto Rico after 25 years of conversion from sugarcane to other cultivation practices, forest and pasture. The research demonstrated higher C accumulation in the soil under forest than under pasture. Both systems showed higher C accumulation and mineralization, microbial biomass C and N and C cycling enzyme activities compared to the soil under agriculture. The results of this collaborative effort showed a significant reduction in nutrient cycling potential and organic matter turnover in soils under agriculture in comparison with undisturbed counterparts under forested N-fixing trees, non N-fixing trees, and Pasture. In addition, the study showed that proliferation of an N fixer like Leucaena as volunteer species is probably a better option for recuperating resting or abandoned cropland than a non N fixer like Eucalyptus.
Technical Abstract: There is scant information that describes the functioning of Vertisols in the tropics with regards to C and N storage capacity and turnover, distribution, and biological indicators of ecosystem health as affected by land-use. These soils play a significant role in the amounts of carbon (C) sequestered from the atmosphere which can mitigate increased atmospheric CO2. We studied a Vertisol (Fine, smectitic, isohyperthermic Typic Haplusterts) of Puerto Rico under cultivation, forest and pasture (for at least 25 years) at four depths: 0-15, 15-30, 30-60, and 60-100 cm. Two forests were studied (replicated plots) under pure stands of Eucaliptus robusta or Leucaena leucocephala. The pasture site had mixed species of Urochloa spp., Digitaria eriantha, Cynodon nlemfuensis and Pennisetum purpureum, which were cropped for haylage. Soil organic carbon (SOC) contents (0-100 cm) were similar for Leucaena (22.8), Eucalyptus (18.6), and Pasture (17.2 kg C/m2), which were higher than soils under Agriculture (13.0 kg C/m2). Soil organic nitrogen (SON) contents (0-100 cm) were not influenced by landuse with values ranging from 2.28 kg N/m2 for Leucaena forest to 1.70 kg N/m2 for Agriculture. The microbial biomass carbon (MBC) and nitrogen (MBN) showed this trend at 0-15 cm: Pasture > Leucaena = Eucalyptus forests > Agriculture. Land use effects on biological indicators were clearly observserd at 0-15 cm which were higher than at 15-30 cm (P<0.01). The proportions of MBC and MBN comprising SOC and SON were nearly 1.0% in Pasture and less than 0.50% in the Leucaena, Eucalyptus, and Agriculture. ß-glucosidase activity at 0-15 cm was in the order of: Leucaena = Eucalyptus > Pasture > Agriculture, while ß-glucosaminidase activity was in the order of: Eucalyptus > Leucaena = Pasture > Agriculture. The results demonstrate a significant reduction in nutrient cycling potential, and organic matter turnover in soils under agriculture in comparison with undisturbed counterparts under forested N-fixing trees, non N-fixing trees, and Pasture.