Plowing

ABSTRACT Physical fractions (free light fraction, intra-aggregate light fraction and heavy fraction) of soil organic matter (SOM) are good indicators of soil quality for sustainable land use. The objective of this study was to evaluate the effect of cover crops on total organic carbon (TOC) and physical fractions of soil organic matter in soil under a no-tillage system (NTS) and a conventional tillage system (CTS, one plowing and two disking). A three-year field experiment was carried out as a cover crop-rice (Oryza sativa)-cover crop-rice rotation. Treatments included cover crops (Panicum maximum, Brachiaria ruziziensis, Brachiaria brizantha, and pearl millet (Pennisetum glaucum), fallow, till or no till. The SOM was physically fractionated in free light fraction (FLF), intra-aggregates light fraction (IALF) and heavy fraction (HF). The levels of C in whole soil were also evaluated, as well as C in the light fractions (FLF + IALF) and in the HF. Results indicated that concentrations of C in the FLF and IALF in surface soils (0–0.05 m) were much higher (10.8 and 1.95 g kg−1, respectively) than that in the 0.05–0.1 m soil depth (7.68 and 1.54 g kg−1, respectively) and in the 0.1–0.2 m soil depth (4.98 and 1.24 g kg−1, respectively). The NTS resulted in higher levels of FLF (12.2 g kg−1) and IALF (2.19 g kg−1) than with CTS (1.37–7.30 g kg−1). Millet had the highest C (19.5 g kg−1) and N (1.1 g kg−1) concentrations in soil. There was an accumulation of TOC and total N in the surface soil with cover crops, and concentrations of TOC were higher in the HF (79.0%) than in the light fractions (21.0%). Although SOM changed little during the two years of this experiment, the various C fractions were significantly affected by the tillage treatments. We conclude that SOM physical fractionation allowed seeing significant differences caused by the soil management in the organic matter dynamics in a short period of time.

A densidade do solo é um parâmetro de fácil quantificação, relacionando-se com outras propriedades intrínsecas, tais como: textura e teor de matéria orgânica. A distribuição do tamanho de poros, a resistência do solo à penetração das raízes e a água disponível também estão relacionadas com a densidade do solo. Na comparação entre sistemas de preparo, a densidade do solo tem sido usada freqüentemente. No entanto, não tem sido levado em conta o fato de que os sistemas de manejo do solo e das culturas contribuem para a variabilidade espacial da densidade do solo. Os fatores que causam essa variação são o tráfego das máquinas nas operações de manejo, os processos de secamento e umedecimento do solo e o efeito do sistema radicular das plantas. O objetivo geral deste trabalho foi avaliar a distribuição da densidade do solo em dois sistemas de manejo em um solo cultivado com milho. Foi estudado um Latossolo Roxo sob semeadura direta e preparo convencional do solo, amostrado em transeções p...

L’etude proposee a pour objet l’amelioration de la production fourragere de pâturages naturels moyennement degrades, par l’ensemencement a l’aide d’une legumineuse locale (Alysicarpus ovalifolius (Schum. et Thonn.) Leonard) en milieu paysan. La methodologie utilisee a consiste a mettre en place un hectare protege et un hectare non protege et a y effectuer les traitements relatifs au labour du sol et a l’ensemencement avec A. ovalifolius. Les resultats de quatre annees de suivi montrent que la mise en defens associee au labour et aux semis a un effet positif sur la richesse floristique. Les graminees sont dominantes, mais on note une variation de la composition floristique interannuelle a leur detriment et au profit des legumineuses et de quelques autres especes. L’etablissement d’A. ovalifolius s’est assez bien effectue des la premiere annee (20 % de contribution specifique) dans la parcelle mise en defens, labouree et ensemencee, avant que l’espece n’amorce une colonisation des par...