Soil compaction is one of the most relevant crop yield-limiting factors in no-till (NT) farming systems in southern Brazil. This study aimed to identify strategies to mitigate soil compaction and increase crop productivity at low, medium and high yield environments within a field. Treatments evaluated were: control (without intervention), PG (phosphogypsum), MC (mechanical chiselling), PCC (polyculture of cover crops), MC + PG, PCC + PG, MC + PCC and MC + PCC + PG. Soil physical and chemical attributes (soil macroporosity, bulk density, penetration resistance) and soybean yield (Glycine max L.) and black oat (Avena strigosa Schreb) biomass production were evaluated. In the low and medium yield environments, MC + PCC + PG promoted the highest soybean yields: 5,455 kg ha −1 and 5,534 kg ha −1 , respectively. In the high yield environment, PCC + PG promoted the highest soybean yield (5,579 kg ha −1), whereas MC decreased yields relative to the control. Black oat biomass production responded to the treatments similarly to soybean yields. Overall, integrating two or three decompaction strategies improved soil physical attributes in a greater proportion relative to single strategies and to the control, enhancing both soybean and black oat performances. Selection of the right decompaction strategies for each yield environment might help increase productivity under NT and optimize the use of time, labour, fuel and other resources. Highlights • Soil compaction limits crop yields under no-tillage farming in southern Brazil. • Low, medium and high yield environments were delineated with precision agriculture tools. • Single or integrated mechanical, chemical and biological soil decompaction strategies were tested. • Soil decompaction strategies to increase soybean yields are specific to yield environments.

The aim of this study was to investigate impacts of Amazon Forest (AF) fire and conversion to pasture on carbon accumulation in particle size fractions and organic matter (OM) composition of an Acrisol. Soil samples were collected (0.00-2.00 m depth) in three sites: native AF (NAF); AF under natural regeneration for two years after burning (BAF); 23-years old Brachiaria pasture after AF burning (BRA). Assuming NAF area as reference, BAF and BRA areas showed negative carbon balance when carbon emitted to the atmosphere at AF burning is taken into account. Soil OM aromaticity and hydrophobicity, assessed via 13 C nuclear magnetic resonance, in BRA and BAF were similar to that in NAF. Fire and post-fire land use altered the carbon distribution in sand, silt and clay along the soil profile and seem to have affected organo-mineral and OM self-assemblage interactions, since the relation between total soil carbon and carbon in clay was asymptotic in BAF and linear in NAF and BRA.

Cover crops (CC), particularly legumes, are key to promote soil carbon (C) sequestration in no-tillage. Nevertheless, the mechanisms regulating this process need further elucidation within a broad comprehensive framework. Therefore, we investigated effects of CC quality: black oat (Avena strigosa Schreb) (oat), common vetch (Vicia sativa L.) (vetch), and oat + vetch on carbon dioxide-C (CO2-C) emission (124 days) under conventional- (CT), minimum- (MT) and no-tillage (NT) plots from a long-term experiment in Southern Brazil. Half-life time (t1/2) of CC residues and the apparent C balance (ACB) were obtained for CT and NT. We linked our data to long-term (22 years) soil C and nitrogen (N) stocks and crop yield data of our experimental field. Compared to CT, NT increased t1/2 of oat, oat + vetch and vetch by 3.9-, 3.1- and 3-fold, respectively; reduced CO2-C emissions in oat, oat + vetch and vetch by 500, 600 and 642 kg ha−1, respectively; and increased the ACB (influx) in oat + vetch (195%) and vetch (207%). For vetch, CO2-C emission in MT was 77% greater than NT. Legume CC should be preferentially combined with NT to reduce CO2-C emissions and avoid a flush of N into the soil. The legume based-NT system showed the greatest soil C and N sequestration rates, which were significantly and positively related to soybean (Glycine max (L.) Merrill) and maize (Zea mays L.) yield. Soil C (0–90 cm depth) and N (0–100 cm depth) sequestration increments of 1 kg ha−1 corresponded to soybean yield increments of 1.2 and 7.4 kg ha−1, respectively.