The purpose of this research was to identify the soil organic matter (SOM) fractions changes in a crop rotation system under no-till system (NTS). This research was carried out from October 2010 to February 2014 in a Rhodic Hapludox. The experiment was set up in completely randomized blocks in a factorial design with eight cover crops and three soil depths (0-5, 5-10 and 10-20 cm) with four repetitions. Cover crops: fall-winter corn, intercropping fall-winter corn with Brachiaria ruziziensis, intercropping fall-winter corn with B. brizantha cv. Marandu, intercropping fall-winter corn with Crotalaria spectabilis, B. ruziziensis, B. brizantha cv. Marandu, Pennisetum glaucum L. and set-aside area. The results of SOM granulometric fractionation showed that 6.5% of the total organic carbon (TOC) stocks were in the particulate organic carbon (POC) fraction. The low values of POC observed in this research are associated with the weather condition of experimental site, which shows high temperature and moisture. In relation to the labile carbon (LC), the highest LC stock was observed in 0-5 cm depth, which differed from the 10-20 cm depth. The POC, LC and labile nitrogen (LN) were the SOM fractions that showed to be more sensitive to detect the changes promoted by the cover crops and soil depths in NTS, as well as the carbon management index (CMI). The intercropping fall-winter corn with B. brizantha cv. Marandu and B. ruziziensis were efficient in increasing the CMI in deeper depth (10-20 cm).

ResumoA deposição de resíduos orgânicos através da colheita mecanizada da cana-de-açúcar é uma prática crescente no sistema de produção canavieiro. A manutenção desses resíduos na superfície do solo depende principalmente das condições ambientais. A adubação nitrogenada sobre os resíduos secos tendem a retardar a decomposição desses, proporcionando benefícios como o aumento da MOS. Diante disto, o objetivo da pesquisa foi avaliar o efeito da aplicação de diferentes doses de nitrogênio sobre os resíduos culturais de cana-de-açúcar, quanto a sua decomposição e contribuição para o sequestro de carbono no solo. O experimento foi realizado em Dourados-MS e consistiu de um delineamento experimental em blocos casualizados. Os resíduos secos foram colocados em litter bags e os tratamentos foram arranjados em parcelas subdivididas, sendo as quatro doses de nitrogênio (0,50, 100 e 150 kg ha -1 N) as parcelas, e as sete épocas de coleta (0, 30, 60, 90, 120, 150 e 180 dias) as subparcelas. Foram analisados a taxa de decomposição dos resíduos, carbono orgânico total e carbono lábil no solo. A aplicação de doses crescente de N proporcionou aumento nas suas taxas de decomposição. Apesar disso, destaca-se a aplicação de N-mineral como uma estratégia de manejo para obter maiores teores de carbono lábil no solo. Palavras-chave: Adubação nitrogenada, manutenção de palhada, carbono orgânico total, carbono lábil AbstractThe deposition of organic residues through mechanical harvesting of cane sugar is a growing practice in sugarcane production system. The maintenance of these residues on the soil surface depends mainly on environmental conditions. Nitrogen fertilization on dry residues tend to retard decomposition of these, providing benefits such as increased SOM. Thus, the object of this research was to evaluate the effect of different doses of nitrogen on sugar cane crop residues, as its decomposition and contribution to carbon sequestration in soil. The experiment was conducted in Dourados-MS and consisted of a randomized complete block design. Dried residues were placed in litter bags and the treatments were arranged in a split plot, being the four nitrogen rates (0, 50, 100 and 150 kg ha -1 N) the plots, and the seven sampling times (0, 30, 60, 90, 120, 150 and 180) the spit plots. Decomposition rates of residues, total organic carbon and labile carbon on soil were analysed. The application of increasing N doses resulted in an increase in their decomposition rates. Despite this, note also the mineral N application as a strategy to get higher levels of labile carbon in soil.

The purpose of this study was to assess the changes in soil chemical properties affected by the cover crops cultivated in crop rotation in short-term of no-till implementation under Rhodic Hapludox soil. This research was carried out from October 2010 to February 2014. The experiment was set up in completely randomized blocks in a factorial design with eight treatments (cover crops) and three soil depths (0-5, 5-10 and 10-20 cm) with four repetitions. The cover crops were: fall-winter maize (T 1), intercropping fall-winter maize with B. ruziziensis (T 2), intercropping fall-winter maize with B. brizantha cv. Marandu (T 3), intercropping fall-winter maize with Crotalaria spectabilis (T 4), B. ruziziensis (T 5), B. brizantha cv. Marandu (T 6), Pennisetum glaucum L. (T 7) and fallow (T 8). The T 6 and T 7 affected exchangeable Mg +2 , it was observed higher exchangeable Mg +2 in T 6 (2.39 cmol c dm-3) and T 7 (2.43 cmol c dm-3) in comparison to T 1. The phosphorus content showed interactive effect between cover crops and soil depth. In the comparison among the depths, the P contents were higher in 5-10 cm, which showed improvement of 24.6% and 25.2% in comparison to 0-5 and 10-20 cm layers, respectively. The cover crops evaluated in this research affected the exchangeable Mg +2 and K + , as well as Mg +2 and K + saturation. The P content changed in response of cover crops, which was important to observe that this nutrient may increase the content with adoption of cover crops in no-till system. The species used in this research might be recommended to integrate a crop rotation system with the possibility of increasing P availability in topsoil depth in no-till system.

This study aimed to evaluate total carbon and nitrogen and stocks of the humic fractions of soil organic matter under different cropping systems at the experimental farm at the Federal University at Grande Dourados -UFGD. Soil samples were collected from two layers (0-10 and 10-20 cm) from an oxisol with a clay texture. The systems studied were as follows: non-tillage (NTS), tillage (TS), eucalyptus and pasture. Natural vegetation from Dourados, Mato Grosso do Sul, Brazil was used for comparison. For statistical analysis of the C and N stocks, the model: Y = μ + Ai + rep (A) ik + Eijk was used. The replacement of TN one for CT decreased the total organic carbon and C in the stocks of humic substances (fulvic acid, humic acid and humin) in the soil just three years after adoption, especially in the 0-10 cm layer. However, soils under eucalyptus trees acquired increased carbon stock in the most active fractions, such as the fractions of fulvic and humic acids (0-20 cm layer). Regardless of the cropping system, the largest C and N stocks were measured for the humin fraction, followed by humic acid and fulvic acid. The total N and humic and fulvic acid levels under the conditions of maintenance of TN for 15 years increased when compared with CT, but not in soils under eucalyptus trees. Key words: Oxisol, non-tillage, humic acid, fulvic acid ResumoO objetivo deste trabalho foi determinar os estoques de C e N totais nas frações húmicas da matéria orgânica, em diferentes sistemas de manejo do solo na fazenda experimental da Universidade Federal da Grande Dourados -UFGD. Para isso, foram coletadas amostras (0-10 e 10-20 cm) em um Latossolo Vermelho distroférrico, textura argilosa, nos sistemas de plantio direto (SPD) e convencional (SPC), e os solos cultivados com pastagem e com eucalipto, como referência foi utilizado solo coletado em área de floresta nativa, em Dourados-MS. Para análise estatística dos estoques de C e N foi utilizado o modelo estatístico: Y = μ + Ai + rep(A)ik + Eijk. A substituição do sistema SPD pelo SPC resultou em perdas no COT e C das substancias húmicas (ácido fúlvico, húmico e humina) no solo em apenas três anos de adoção, principalmente na profundidade de 0-10 cm, todavia, quando substituído pelo eucalipto proporcionou aumento do estoque de C em frações mais ativas, como frações de ácido húmico e fúlvico (0-20 cm). Independente do sistema de manejo ou uso do solo, os maiores estoques de C e N foram para a fração humina, seguida do ácido húmico e ácido fúlvico. Para o N total e N-AH e N-AF a permanência do SPD por 15 anos, promoveu aumento em relação ao SPC, todavia não constatou-se essa diferença com eucalipto. Palavras-chave: Latossolo, plantio direto, ácidos humicos, ácidos fúlvicos