The dynamics of soil aggregation, including aggregate formation by biogenic and physicogenic processes, is affected by the soil management system. The present study aimed to divide soil aggregates into biogenic and physicogenic, and to characterise the aggregates in terms of soil exchange complex, distribution of total organic carbon (TOC), nitrogen (N) levels, and natural 13C and 15N abundance, and determine C levels in the soil organic matter (SOM) fractions of the aggregates. The areas studied were under a no-till system (NTS) established 15 years before, conventional tillage system (CTS) managed with ploughing and harrowing for 56 years, and a secondary forest (Forest) and pasture grass (Axonopus compressus) (Pasture) (both ≥30 years old). Undisturbed soil samples were collected at 0–5 and 5–10 cm. CTS was unsuitable for biogenic aggregate formation, and NTS and Forest areas showed similar biogenic and physicogenic aggregate content. The Pasture area promoted the formation of biogenic aggregates. In contrast to CTS, NTS increased TOC, calcium, magnesium, nitrogen and phosphorus levels. Considering the parameters evaluated, the Forest area showed the most variation (differences) between biogenic and physicogenic aggregates. Biogenic aggregates exhibited higher TOC and nutrient levels than their physicogenic counterparts. In the CTS area, the absence of legumes and the long-term and constant use of N-fertilisers resulted in 15N soil enrichment (at 0–5 cm). In the Pasture area, the absence of legumes and the constant deposition of cattle manure also increased 15N content relative to NTS and Forest areas. The Forest area had the lowest 15N values in the two layers and aggregate types studied. The levels of 13C reflect the type of material incorporated in the soil (mostly C3 plants in Forest and NTS areas and C4 plants in Pasture and CTS areas). The Pasture area favoured the formation of stable SOM, with higher levels of C content in humin fraction (C-HUM) and mineral-associated OC (MOC). CTS compromised SOM stabilisation, producing lower levels of C-HUM, MOC, and moderately oxidisable and resistant fractions. The biogenic aggregates enhanced soil fertility and contained higher C content in SOM fractions than the physicogenic aggregates. We conclude that biogenic rather than physicogenic aggregates can be considered reliable indicators of soil quality.

Resumo -O objetivo deste trabalho foi avaliar os teores de carbono orgânico total (COT), matéria orgânica leve (MOL) e fósforo remanescente (Prem), em áreas de cerrado sob sistema de plantio direto com diferentes cultivos de coberturas do solo, e compará-los aos de áreas sob preparo convencional e pousio. O experimento foi conduzido em campo, em um Latossolo Vermelho, de agosto de 2000 a março de 2007. O delineamento utilizado foi o de blocos ao acaso com parcelas subdivididas, sendo as parcelas constituídas pelos cinco sistemas de manejo do solo avaliados -pousio, preparo convencional e plantio direto com uso dos cultivos de cobertura crotalária (Crotalaria juncea), milheto (Pennisetum americanum) e braquiária (Urochloa brizantha) -, e as subparcelas pelos cultivos de soja e milho. Em março de 2007, coletaram-se amostras de solo das profundidades 0,0-0,025, 0,025-0,05, 0,05-0,10 e 0,10-0,20 m, das quais foram quantificados COT, MOL, estoques de COT e Prem. Em áreas sob plantio direto, o aumento nos teores de MOL pode reduzir a adsorção de fósforo ao solo. Sistemas de manejo que não envolvem revolvimento do solo favorecem o aumento do estoque de carbono orgânico nas camadas superficiais, enquanto o preparo convencional e o plantio direto com uso do milheto como planta de cobertura propiciam a incorporação mais profunda do carbono.Termos para indexação: Cerrado, estoque de carbono, plantas de cobertura, plantio direto, pousio, preparo convencional. Carbon, light organic matter and remaining phosphorus in different soil management systemsAbstract -The objective of this study was to evaluate the contents of total organic carbon (COT), light organic matter (MOL) and remaining phosphorus (Prem) on savanna areas under no tillage system using cover crops and to compare them to the ones observed under fallow and conventional tillage. The experiment was carried out in field conditions, in a Latossolo Vermelho (Rhodic Haplustox) from August 2000 to March 2007. A randomized complete block design was used, in a split-plot arrangement, with plots consisting of the five soil management systems evaluated -fallow, conventional tillage, and no tillage using sunn hemp (Crotalaria juncea), pearl millet (Pennisetum americanum), and palisade grass (Urochloa brizantha) as cover crops -, and sub-plots consisting of maize and soybean crops. In March 2007, the 0.0-0.025, 0.025-0.05, 0.05-0.10 e 0.10-0.20 m soil layers were sampled and assessed for COT, MOL, COT stocks and Prem. In the no tillage areas, increases in MOL content can reduce phosphorus adsorption in soil. Management systems without soil disturbance increases COT stocks in the superficial layers while conventional tillage and no tillage using pearl millet as cover crops provide a deeper incorporation of carbon in the soil.

RESUMOOs objetivos deste estudo foram avaliar a deposição de serapilheira ao longo de dois anos e a qualidade nutricional da serapilheira, em função do espaçamento de plantio visando à restauração florestal. Os espaçamentos de plantio 1 × 1; 1,5 × 1,5; 2 × 2 e 3 × 2 m, constituem as unidades amostrais dos tratamentos. No espaçamento 1 × 1 m foi observada a maior deposição de serapilheira, não havendo diferenças entre as unidades dos demais espaçamentos. A fração folha mostrou, em todos os espaçamentos, maior aporte de serapilheira (77%). O maior conteúdo de nutrientes foi observado no espaçamento 1 × 1 m. Em geral, constatou-se a seguinte ordem quanto o conteúdo de nutrientes da serapilheira N > Ca > K > Mg > P.Palavras-chave: nutrição florestal, ciclagem de nutrientes, material decíduo. Litter Production and Forest Nutrients in Forest Restoration Area with Different Planting Spacing ABSTRACTThe objectives of this study were to evaluate the deposition of litter over two years and the nutritional quality of the litter, depending on the planting space aimed at forest restoration. The planting space 1 × 1, 1.5 × 1.5, 2 × 2 and 3 × 2 m, are the sampling units of the treatments. In 1 × 1 m spacing greater deposition of litter, with no differences between the units other spacings was observed. Leaf fraction showed, in all spacings, greater intake of litter (77%). The higher nutrient content was observed in the 1 × 1 m spacing. In general, was observed the following order as the nutrient content of litter N> Ca> K> Mg> P.

The crop-livestock integration system significantly increases the carbon content in chemical fractions of soil organic matter (SOM). This study aimed to evaluate chemical indicators of SOM attributes for sites under brachiaria/livestock and pearl millet/no livestock in Goias, Brazil. A third area covered with natural Cerrado vegetation (Cerradão) served as reference. Soil was randomly sampled at 0-5, 5-10, 10-20 and 20-40 cm. Total organic carbon stocks (TOC), oxidizable carbon fractions (OCF) (F1>F2>F3>F4), carbon content in the humin (C-HUM), humic acid (C-HAF) and fulvic acid (C-FAF) fractions were evaluated. F1/F4, F1+F2/F3+F4, C-HAF/C-FAF and (C-HAF+C-FAF)/C-HUM indices were calculated, as well as stocks chemical SOM fractions. Brachiaria/livestock produced greater TOC stocks than pearl millet/no livestock (0-5, 5-10 and 10-20 cm). In terms of OCF, brachiaria/livestock generally exhibited higher levels in F1, F2, F4 and F1/F4 than pearl millet/no livestock. C-HUM (0-10 cm) and C-HAF (0-20 cm) stocks were larger in brachiaria/livestock than pearl millet/no livestock. Compared to the Cerradão, brachiaria/livestock locations displayed higher values for TOC (5-10 and 10-20 cm), C-HAF and C-HAF/C-FAF (5-10 cm) stocks. TOC, C-HAF stock and OCF show that land management with brachiaria/livestock was more efficient in increasing SOM than pearl millet/no livestock. Moreover, when compared with pearl millet/no livestock, brachiaria/livestock provided a more balanced distribution of very labile (F1) and recalcitrant (F4) carbon throughout soil layers, greater SOM humification. Brachiaria/livestock leads to higher values of F1 and F4 in depth when compared to pearl millet/livestock and provides a more homogeneous distribution of C-FAF and C-HAF in depth compared to Cerradão.