ABSTRACT: No-tillage (NT) has been one of the main advances related to soil management in Brazilian agriculture in the last 30 years. However, its full adoption in lowland areas that are traditionally cultivated with flooded rice is still incipient (<5 %). The main reasons are associated with the soil hydromorphic condition and the management of highly recalcitrant residual crop biomass, demanding soil disturbance even occasionally. This review presents a historical survey about the soil management systems utilized in lowland areas in southern Brazil, emphasizing the experiences of NT adoption in areas with flooded rice. Results from studies focused on the main changes in chemical, physical, and microbiological soil properties due to NT adoption were addressed, as well as the NT effects on greenhouse gas emissions and crop yields. Finally, the main challenges and prospects for NT were discussed considering new emerging scenarios for flooded rice production in lowlands, especially soybean rotation and integrated agricultural production systems. No-tillage can increase the soil organic carbon, the cation exchangeable capacity and tends to promote the accumulation of nutrients as nitrogen in surface layers. Improvements in soil aggregation, porosity and water availability are usually observed in NT, but only if medium or long-term trials are considered. NT favors microbial activity in the shallower soil layer by promoting microbial biomass carbon (+45 %), microbial biomass nitrogen (+54 %) and basal respiration (+54 %) compared to conventional tillage (CT), while the activity of extracellular enzymes also may be stimulated. Crop yield tends to be similar among the soil managements systems over time. Seasonal CH4 emissions might be reduced by 21 % with NT adoption without increasing N2O. Plant breeding and geotechnology advances associated with soybean market valuation intensified the introduction of this crop in paddy fields. The main challenge for the full adoption of NT is the need for soil tillage after rice harvesting to correct soil surface irregularities or manage rice straw. In the future, advances in plant breeding and drainage techniques probably will favor the expansion of NT in southern Brazil lowlands. The traditional system of flooded rice cultivation, based on CT and monoculture associated with beef cattle under extensive grazing, is no longer viable and will not be further established.

ABSTRACT: The southern Brazilian lowlands have been historically used for flooded rice cultivation. Over time, heavy machinery and intensive tillage practices have resulted in soil structure disruption, soil compaction, higher production costs and lower agricultural profitability. This study aimed to evaluate the effect of different deployment times of no-tillage (NT). Soil properties including bulk density (BD), compression index (CI), preconsolidation pressure (σp), bulk density at preconsolidation pressure (BDσp), degree of compactness (DC), soil water retention curve (SWRC), plant available water (PAW) and total organic carbon (TOC) content were evaluated using a 30-yr non-cultivated field (NC), adjacent to the experimental plots as a control. The BD, σp, BDσp and DC decreased in response to NT adoption time while the soil water holding capacity increased, allowing for higher PAW. Results from this study demonstrated the positive effects of NT on the overall quality of soils.

Resumo O objetivo deste trabalho foi avaliar os efeitos do sistema plantio direto (PD) e do manejo com preparo convencional (PC) sobre atributos físicos e hídricos de um Planossolo Háplico cultivado com soja, em terras baixas do Sul do Brasil. Amostras indeformadas de solo foram coletadas às camadas de 0,00-0,10, 0,10-0,20 e 0,20-0,40 m, para a determinação dos atributos físico-hídricos, tendo-se monitorado o potencial mátrico do solo com sensores, ao longo de um ciclo de produção da soja. Os valores de macroporosidade foram menores do que 0,10 m3 m-3, independentemente do sistema de manejo do solo, o que restringe a possibilidade de cultivo da soja em sequeiro, pelo comprometimento da difusão de gases. Comparado ao PC, o PD promove a microporosidade na camada de 0,00-0,10 m, o que aumenta o conteúdo de água armazenada no solo e a disponibilidade hídrica para a cultura da soja, com reflexos positivos sobre a produtividade da cultura.

Abstract The objective of this work was to evaluate the effects of no-tillage (NT) and conventional tillage (CT) on the physical and hydric properties of an Albaqualf soil cultivated with soybean, in the lowlands of Southern Brazil. Undisturbed soil samples were collected at the 0.00-0.10, 0.10-0.20, and 0.20-0.40-m soil layers, in order to determine soil physicohydric properties, by monitoring the soil matric potential with sensors, over a cycle of soybean production. Macroporosity values were lower than 0.10 m3 m-3, irrespectively of the soil management system, which restricts the possibility of rainfed soybean cultivation because it affects gas diffusion. In comparison to CT, NT increases microporosity at the 0.00-0.10-m soil layer, which increases soil water content and soil water availability for soybean crop, with positive effects on crop yield.