Impact of Land Degradation on Soil Microbial Biomass and Activity in Northeast Brazil

Land degradation causes great changes in the soil biological properties.The process of degradation may decrease soil microbial biomass and consequently decrease soil microbial activity.The study was conducted out during 2009 and 2010 at the four sites of land under native vegetation(NV),moderately degraded land(LDL),highly degraded land(HDL) and land under restoration for four years(RL) to evaluate changes in soil microbial biomass and activity in lands with different degradation levels in comparison with both land under native vegetation and land under restoration in Northeast Brazil.Soil samples were collected at 0-10 cm depth.Soil organic carbon(SOC),soil microbial biomass C(MBC) and N(MBN),soil respiration(SR),and hydrolysis of fluorescein diacetate(FDA) and dehydrogenase(DHA) activities were analyzed.After two years of evaluation,soil MBC,MBN,FDA and DHA had higher values in the NV,followed by the RL.The decreases of soil microbial biomass and enzyme activities in the degraded lands were approximately 8-10 times as large as those found in the NV.However,after land restoration,the MBC and MBN increased approximately 5-fold and 2-fold,respectively,compared with the HDL.The results showed that land degradation produced a strong decrease in soil microbial biomass.However,land restoration may promote short-and long-term increases in soil microbial biomass.

Soil Microbial Biomass After Three-Year Consecutive Composted Tannery Sludge Amendment

Brazilian industry produces huge amounts of tannery sludge as residues,which is often disposed by landfilling or land application.However,consecutive amendment of such composted industrial wastes may cause shifts in soil microbial biomass(SMB) and enzyme activity.This study aimed to evaluate SMB and enzyme activity after 3-year consecutive composted tannery sludge(CTS) amendment in tropical sandy soils.Different amounts of CTS(0.0,2.5,5.0,10.0,and 20.0 t ha^(-1)) were applied to a sandy soil.The C and N contents of SMB,basal and substrate-induced respiration,respiratory quotient(qCO_2),and enzyme activities were determined in the soil samples collected after CTS amendment for 60 d at the third year.After 3 years,significant changes were found in soil microbial properties in response to different CTS amounts applied.The organic matter and Cr contents significantly increased with increasing CTS amounts.SMB and soil respiration peaked following amendment with 10.0 and 20.0 t ha-1 of CTS,respectively,while qCO_2was not significantly affected by CTS amendment.However,soil enzyme activity decreased significantly with increasing CTS amounts.Consecutive CTS amendment for 3 years showed inconsistent and contrasting effects on SMB and enzyme activities.The decrease in soil enzyme activities was proportional to a substantial increase in soil Cr concentration,with the latter exceeding the permitted concentrations by more than twofold.Thus,our results suggest that a maximum CTS quantity of 5.0 t ha^(-1) can be applied annually to tropical sandy soil,without causing potential risks to SMB and enzyme activity.

Microbial enzymatic stoichiometry and the acquisition of C, N,and P in soils under different land-use types in Braziliansemiarid

This study hypothesized that different land-use affect the microbial enzymatic stoichiometry and C-,N-,and P-acquisition in Brazilian semiarid soils.Thus,the enzymesβ-glucosidase(C-acquiring enzyme),urease(N-acquiring enzyme),and acid phosphatase(P-acquiring enzyme)were assessed in soil samples collected at 0−5 and 5−10 cm depth from a tropical dry forest,a protected area with Angico,a protected area with Ipê,scrub area,and an agricultural area with maize.The values of C-,N-,and P-acquiring enzymes were used to calculate the enzymatic C:N,C:P,and N:P ratios.The values of C:P and N:P ratios were higher at 0−5 cm depth,while no significant variation,between soil depth,was observed for C:N ratio.The values of C-and N-acquiring enzymes were higher at 0−5 cm in tropical dry forest areas and Angico forest,respectively.In all land use types,the values of vectors L and A were higher than 1°and 45°,respectively.This study showed that both land-use and soil depth influence the enzymatic stoichiometry,showing higher values of C-and N-acquiring enzymes in native and protected forests at soil surface.