Effect of compaction on microbial activity and carbon and nitrogen transformations in two oxisols with different mineralogy

Abstract

SUMMARYThe use of machinery in agricultural and forest management activities frequently increases soil compaction, resulting in greater soil density and microporosity, which in turn reduces hydraulic conductivity and O 2 and CO 2 diffusion rates, among other negative effects. Thus, soil compaction has the potential to affect soil microbial activity and the processes involved in organic matter decomposition and nutrient cycling. This study was carried out under controlled conditions to evaluate the effect of soil compaction on microbial activity and carbon (C) and nitrogen (N) mineralization. Two Oxisols with different mineralogy were utilized: a clayey oxidic-gibbsitic Typic Acrustox and a clayey kaolinitic Xantic Haplustox (Latossolo Vermelho-Amarelo ácrico -LVA, and Latossolo Amarelo distrófico -LA, respectively, in the Brazil Soil Classification System). Eight treatments (compaction levels) were assessed for each soil type in a complete block design, with six repetitions. The experimental unit consisted of PVC rings (height 6 cm, internal diameter 4.55 cm, volume 97.6 cm 3 ). The PVC rings were filled with enough soil mass to reach a final density of 1.05 and 1.10 kg dm -3 , respectively, in the LVA and LA. Then the soil samples were wetted (0.20 kg kg -1 = 80 % of field capacity) and compacted by a hydraulic press at pressures of 0, 60, 120, 240, 360, 540, 720 and 900 kPa. After soil compression the new bulk density was calculated according to the new volume occupied by the soil. Subsequently each PVC ring was placed within a 1 L plastic pot which was then tightly closed. The soils were incubated under aerobic conditions for 35 days and the basal respiration rate (CO 2 -C production) was estimated in the last two weeks. After the incubation period, the following soil chemical and microbiological properties were --N in the LA and CO 2 -C in the LVA. It also decreased the C MIC at higher compaction levels in the LA. Thus, soil compaction decreases the TOC turnover probably due to increased physical protection of soil organic matter and lower aerobic microbial activity. Therefore, it is possible to conclude that under controlled conditions, the oxidic-gibbsitic Oxisol (LVA) was more susceptible to the effects of high compaction than the kaolinitic (LA) as far as organic matter cycling is concerned; and compaction pressures above 540 kPa reduced the total and organic nitrogen in the kaolinitic soil (LA), which was attributed to gaseous N losses.Index terms: soil bulk density, carbon mineralization, net N mineralization, microbial biomass carbon. de 0, 60, 120, 240, 360, 540, 720 (COT), RESUMO: EFEITO DA COMPACTAÇÃO SOBRE A ATIVIDADE MICROBIANA E TRANSFORMAÇÕES DO CARBONO E NITROGÊNIO EM DOIS LATOSSOLOS COM DISTINTAS MINERALOGIAS A mecanização em atividades agrícolas e florestais tem incrementado a compactação do solo, o que resulta no aumento da densidade e microporosidade, bem como na redução da condutividade hidráulica e das taxas de difusão de O 2 e CO 2 , entre outros efeitos negativos. Assim, a compac...

Produtividade Do Eucalipto, Atributos Físicos Do Solo E Frações Da Matéria Orgânica Influenciadas Pela Intensidade De Tráfego E Resíduos De Colheita

“…Em especial, redução na difusão de O 2 é esperada. Esse ambiente menos oxidativo no solo causado pela compactação reduz a atividade microbiana (Silva et al, 2011), o que pode ter contribuído para a menor taxa de decomposição da serapilheira depositada no solo do tratamento SR neste estudo. Adicionalmente, tal padrão de resposta pode também explicar os maiores teores de COT observados nos solos onde recebeu maior número de passadas.…”

Applicability of soil column incubation experiments to measure CO2 efflux

“…Therefore, during the incubation period, soil aeration resulting from the air-filled porosity would be higher under the T treatment than that under the NT treatment. High aeration because of tillage increased the O 2 level in the soil, which accelerated microbial respiration (Gomez and Garland, 2012;Silva et al, 2011), and thus might contribute to the higher cumulative CO 2 efflux from the tilled soil. Gas diffusion is the main mechanism of gas transport within and between soils and the atmosphere, and hence the gradient method based on Fick law (Eq.…”

Modeling rhizosphere carbon and nitrogen cycling in Eucalyptus plantation soil

“…Substrate availability for these processes is modulated by soil protection that 25 in turn depends mainly on the amount of clay, mineralogy and of soil carbon content (degree of saturation of clays by organic carbon). If the soil has higher protection capacity, the microbiota is more likely to not have its nutritional demand satisfied and therefore be limited in biomass growth (Silva et al, 2011). On the other hand, if soil has minimal C and N protection, these resources are more likely to be affected by microbial attack (Silva et al, 2011).…”

“…If the soil has higher protection capacity, the microbiota is more likely to not have its nutritional demand satisfied and therefore be limited in biomass growth (Silva et al, 2011). On the other hand, if soil has minimal C and N protection, these resources are more likely to be affected by microbial attack (Silva et al, 2011).…”

“…Extremes of porosity reduce microbial biomass and, consequently the C and N mineralization (Silva et al, 2011). This change occurs because soil porosity affects the concentration and transport of O2 (Torbert and Wood, 1992), as well as the liquid and solute movement and C and N protection by the soil matrix (Silva et al, 2011).…”