Humus composition of soils under forest, coffee and arable cultivation in hilly areas of south Sumatra, Indonesia

Abstract

Summary To understand the effect of land use changes on the composition of humus in tropical soils, samples from land under primary forest, secondary forest, coffee plantation, and arable crops were investigated at three sites in south Sumatra, Indonesia. Total carbon and total nitrogen contents were 1.7 to 4.3 times and 1.1 to 2.8 times greater in the topsoil under primary forest than under the other types of land use. Following change from primary forest to other uses, the proportion of humic acids in the organic matter of the topsoils decreased while that of the fulvic acid fraction increased. Within the range of land uses, differences in the yields of humic acids and fulvic acid fractions were, respectively, larger and smaller than those in total carbon content. The humic acids were classified into the low and middle classes in the degree of humification. Absorption due to the green fraction of humic acids, Pg, was detected in the UV‐visible spectra of almost all the humic acids. No relation was observed between the degree of humification of humic acids or the strength of Pg absorption in their spectra and land use change. The fulvic acid fractions were fractionated on insoluble polyvinylpyrrolidone (PVP) into the adsorbed fractions consisting of humic substances and the non‐adsorbed fractions consisting of non‐humic substances. A positive correlation between the amount of the fulvic acid fraction and the percentage of the PVP‐adsorbed fraction within it indicated that the variation in the amount of the fulvic acid fraction was attributable to acid‐soluble humic substances. The ionization difference spectra of solutions between pH 12 and pH 7 suggested that the chemical structures of the PVP‐adsorbed fulvic acids have been altered by land use change.

Characterization of organic matter fractions in the top layer of soils under different land uses in Central‐Eastern Europe

“…In our study, the HA/FA ratio varied from 0.32 to 3.90 and from 0.28 to 10.29 for grasslands and arable lands, respectively, indicating differences in the intensity of OC humification processes and mobility of C in the soils (Figure a,b). Our results correspond to studies Watanabe, Rumbanraja, Tsutsuki, and Kimura (), You et al. (), Shen et al.…”

“…The higher proportion of HA/FA for grassland soils indicated higher humification rates. Additionally, HI values >1 (for most of the soils) indicated that the HA fraction persisted longer in the soil (Moraes et al., ; Watanabe et al., ). A low DT can be related to a strong interaction between the SOM and the soil mineral phase, resulting in high SOM stability in the more recalcitrant humin fractions (Guimaraes et al., ).…”

Organic-Matter Pools of Soil under Pines and Annual Cultures

“…In PI, the soil showed a wider C/N ratio, followed by SW and finally the annual cropping. These results are in agreement with the available literature, in which the replacement of the native vegetation by annual croppings leads to this difference (Watanabe et al 2001;Leite et al 2003b). Also, utilization of N fertilization has contributed to this fact, since the N loss by leaching in clay soils is less; therefore, N remains in the system and leads to a closer C/N ratio.…”

“…The soil N TN contents were reduced, similar to C TOC , after the slash and burn of the savannah. Almost all studies carried out in savannahs have proven this result (Watanabe et al 2001;Freixo et al 2002;Leite et al 2003bLeite et al , 2003cWendling et al 2005).…”

Indicadores químicos de qualidade da matéria orgânica de solo da sub-bacia do Rio das Mortes sob manejos diferenciais de cafeeiro

“…24 O cultivo de cafeeiro em área originalmente sob floresta primária, recém-desmatada, acarretou uma diminuição dos teores de C-AH e aumento de C-AF na superfície, enquanto que, em subsuperfície, houve diminuição de ambas as frações. 25 Na sub-bacia do Rio das Mortes, há uma expressiva escassez de dados a respeito da influência dos diferentes manejos das culturas implantadas sobre as propriedades da matéria orgânica do solo. Assim, este trabalho teve como objetivo avaliar a qualidade química da matéria orgânica do solo mais expressivo geograficamente dessa sub-bacia, cultivado com cafeeiro, sob manejos convencional e orgâ-nico, por meio de indicadores com níveis variáveis de sensibilidade às operações de preparo e cultivo do solo, que exercem forte influência sobre a dinâmica da matéria orgânica e de seus compartimentos (C orgânico total, C da fração leve e C nas frações ácidos húmico e fúlvico), tendo como referência solo sob mata nativa.…”