No-tillage for flooded rice in Brazilian subtropical paddy fields: history, challenges, advances and perspectives

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 CH 4 emissions might be reduced by 21 % with NT adoption without increasing N 2 O. 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.

Long-term cover crops in paddy field increase enzyme activity and carbon stock and enable the system fertilization

“…Organic compounds are often protected from the action of the enzymatic complex of microorganisms in these soil structures (Burns et al, 2013) by reducing carbon oxidation and increasing carbon and nitrogen contents in the soil. In this sense, the associated adoption of cover crops and no-tillage are fundamental practices for increasing soil microbiological activity and increasing C and N stocks (Sousa et al, 2021). Although little practiced in much of the area cultivated with rice in Brazil (< 5%) (Sousa et al, 2021) other recent works demonstrate that no-tillage in environments cultivated with rice can contribute to the increase of carbon stock, mainly in the topsoil (Denardin et al, 2019).…”

“…In this sense, the associated adoption of cover crops and no-tillage are fundamental practices for increasing soil microbiological activity and increasing C and N stocks (Sousa et al, 2021). Although little practiced in much of the area cultivated with rice in Brazil (< 5%) (Sousa et al, 2021) other recent works demonstrate that no-tillage in environments cultivated with rice can contribute to the increase of carbon stock, mainly in the topsoil (Denardin et al, 2019). In that same experimental station, in a 20-year experiment under NT, it was also verified that no-tillage was important for the increase of enzymes such as β-glucosidase and urease, being mainly attributed to the increase in labile carbon fractions (Carlos et al, 2021).…”

“…The increase in carbon contents is related to the physical, chemical and biological quality of the soil, as well as the mitigation of global warming. These happen through the sequestration of C-CO 2 from the atmosphere with the adoption of cover crops associated with no-tillage in many places in the world (Congreves et al, 2017;Dossou-Yovo et al, 2016;Sousa et al, 2021) and in sub-tropical conditions (Assmann et al, 2014;Bayer et al, 2002;Martins et al, 2017).…”