We examined the influence of land use change, tillage system and soil texture on organic carbon (C) stocks and on organic matter composition of tropical and subtropical soils from Brazil at four long-term experiments (11-25 years) based on fine-and coarse-textured soils. Soil samples were collected from the 0-5, 5-10 and 10-20 cm layers of conventional tillage (CT) and no-till (NT) plots, and of the adjoining soil under native vegetation (NV) of Cerrado (tropical) or grassland (subtropical). Conversion of NV to CT resulted in losses of 7-29% of the original C stock of 0-20 cm; conversion to NT increased this C stock by 0-12% compared with CT. Organic matter composition of the 0-5 cm layer, assessed by solid state CPMAS-13 C-NMR, ESR and laser induced fluorescence spectroscopies, was affected by land use and tillage systems. Conversion of NV to CT decreased O-alkyl and increased aromatic, carbonyl, aromatic/O-alkyl ratio, free radicals concentration and fluorescence signal. The opposite trend was observed when NT replaced CT. The relative losses and gains of C and qualitative changes resulting from land use and tillage were less evident in fine-than in coarse-textured soils, suggesting a greater resistance and a smaller resilience of fine-compared with coarse-textured soils. The direct relation between increase in C stock and increase in potentially labile moieties (e.g. O-alkyl) and the decrease in more recalcitrant moieties (e.g. aromatics) in NT soils suggests that spatial inaccessibility by aggregates is playing a major role, compared with selective preservation, in promoting C accumulation in NT soils.

RESUMO(1) Recebido para publicação em junho de 1997 e aprovado em setembro de 1998.

Com o objetivo de estudar a influência da cultura de cobertura do solo antecessora sobre os componentes de produção da cultura do milho, desenvolveu-se um experimento em um Latossolo Vermelho distroférrico no Núcleo Experimental de Ciências Agrárias - NCA, da Universidade Federal do Mato Grosso do Sul - UFMS, Campus de Dourados - MS. O delineamento experimental foi em blocos casualizados, com os tratamentos arranjados em esquema de parcelas subdivididas, com quatro repetições. As parcelas experimentais foram constituídas pelas culturas antecessoras (ervilhaca peluda e nabo forrageiro) e as subparcelas foram representadas por cinco doses de nitrogênio em cobertura (0, 50, 100, 150 e 200 kg de N ha-1) na cultura do milho, divididas em duas aplicações, nos estádios de quatro e de oito folhas. As culturas antecessoras apresentam efeitos diferenciados sobre os componentes de produção do milho cultivado subseqüentemente. A ervilhaca peluda é mais efetiva do que o nabo forrageiro quanto às características de: matéria seca da parte aérea, diâmetro da espiga, peso de mil grãos e teor de nitrogênio nos grãos de milho. Independente da cultura antecessora, a adição de nitrogênio eleva a produtividade de grãos de milho.

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Land use and coverage surveys show that 30.5% of Brazil's territory was dedicated to the production of food, fibers, biofuels, and raw materials. This paper fills a gap and provides information to society and decision-makers about the effectiveness of the adoption of conservation agriculture (CA) principles with zero tillage (ZT/CA) and integrated crop-livestock-forest (iCLF-CA) systems as the central policies to mitigate soil erosion, the main agent of land degradation and productivity loss. The increase in CA area by 2030 was estimated using Holt's damped technique for ZT/CA and simple linear models for iCLF-CA. The annual potential for soil erosion with intensive conventional tillage and monocropping, considering land use and cover in 2017, is 3.0 billion tons. The economic impact, based only on replacement of nutrient losses, is estimated to be 15.7 billion US$ yr −1 . To control soil erosion by water, to intensify agricultural production, and mitigate the greenhouse gas emissions are the goals of the PRONASOLOS, a national program for detailed soil survey and interpretation.

RESUMO -Em Mato Grosso do Sul, existem jazidas de calcários provenientes de rocha sedimentar, aos quais são atribuídos empiricamente maior reatividade inicial em relação aos calcários de rocha metamórfica. Na Embrapa-Centro de Pesquisa Agropecuária do Oeste (CPAO), em Dourados, MS, avaliou-se, em casa de vegetação, a eficiência relativa de frações granulométricas de calcários, em Latossolo Vermelho-Escuro álico franco-areno-argiloso e Latossolo Roxo distrófico muito argiloso. Em cada solo, aplicou-se dose de calcário estimada para elevar o pH em CaCl 2 para 6,0. Os tratamentos, dispostos em delineamento inteiramente ao acaso, consistiram de: testemunha sem calcário e a aplicação de quatro frações granulométricas (malhas de 4,00 a 2,00; 2,00 a 0,84; 0,84 a 0,30 e 0,30 a 0,21mm) de três calcários: calcítico de origem sedimentar (CS) e calcítico (CM) e dolomítico (DM) de origem metamórfica. Não se verificaram diferenças na efetividade dos calcários calcítico e dolomítico, de mesma natureza geológica, em elevar o pH do solo. A eficiência relativa dos corretivos foi influenciada pela sua natureza geológica, granulometria, tipo de solo e tempo de incubação. A eficiência relativa inicial do CS foi superior às fontes metamórficas, e se manteve igual ou superior após três meses de incubação.Termos para indexação: reatividade, incubação, pH do solo, material de origem, sedimentar, metamórfica, tamanho de partícula. RELATIVE EFFICIENCY OF MATO GROSSO DO SUL LIMESTONES GRANULARITY FRACTIONSABSTRACT -In Mato Grosso do Sul, Brazil, there are limestone mines formed from sedimentary rocks, which have higher initial reactivity than that of metamorphic rock limestones. At Embrapa-Centro de Pesquisa Agropecuária do Oeste (CPAO), Dourados, Mato Grosso do Sul State, Brazil, the relative efficiency of limestone granularity fractions were evaluated under greenhouse conditions, using Dark-Red Latosol and Dusky-Red Latosol soils, both Oxisols. Each soil was amended with a dosage of lime high enough to elevate the pH (CaCl 2 ) to 6.0. The treatments, at a completely randomized experimental design, were a control (without lime) and four granularity fractions: 4.00 to 2.00 mm; 2.00 to 0.84 mm; 0.84 to 0.30 mm; and 0.30 to 0.21 mm. Three limes were tested: calcitic of sedimentary origin (CS) and calcitic (CM) and dolomitic (DM) of metamorphic origin. No differences were observed on the effectiveness of the limes of the same origin in increasing the soil pH level. The relative efficiency of the different limes was influenced by the geologic origin, the granularity, the soil type, and the incubation period. The initial CS relative efficiency was higher than the ones from metamorphic origin, and was higher or at least equal up to three months of incubation.

aBstractimproper land use has lead to deterioration and depletion of natural resources, as well as a significant decline in agricultural production, due to decreased soil quality. Removal of native vegetation to make way for agricultural crops, often managed inadequately, results in soil disruption, decreased nutrient availability, and decomposition of soil organic matter, making sustainable agricultural production unviable. Thus, the aim of the present study was to evaluate the impact of growing irrigated mango (over a 20 year period) on the organic carbon (Oc) stocks and on the fractions of soil organic matter (sOM) in relation to the native caatinga (xeric shrubland) vegetation in the lower são Francisco valley region, Brazil. The study was carried out on the Boa Esperança Farm located in Petrolina, Pernambuco, Brazil. In areas under irrigated mango and native caatinga, soil samples were collected at the 0-10 and 10-20 cm depths. After preparing the soil samples, we determined the Oc stocks, carbon of humic substances (fulvic acid fractions, humic acid fractions, and humin fractions), and the light and heavy SOM fractions. Growing irrigated mango resulted in higher Oc stocks; higher c stocks in the fulvic acid, humic acid, and humin fractions;