Management of rice straw in rice-soybean succession in tropical lowland

This study aims to investigate alternative management practices for rice straw in tropical lowland rice-soybean systems. The goal is to twofold: first, to identify methods that maximize the yield of the subsequent soybean crop, and second, to quantify the effects of these practices on soil properties. "Ten treatments (below) consisting of a combination of rice straw management (burning, removal and incorporation with disc harrow, leveling disc harrow, and knife-roller) with soybean sowing (no-tillage and conventional) were evaluated in a completely randomized design, with six replications. The disc harrow operated at 0.20-0.25 m, the leveling disc harrow at 0.10 m, and the knife-roller at 0.13 m depth. The total plot area was 600 m2 (10 m wide and 60 m long). Tillage treatments were: Burning (M1) Straw removal (M2) Incorporation with one pass of a disc harrow (GA) and two (M3) or three (M4) passes of a leveling harrow (GN) Incorporation with one pass of a roller knife (RF) and no-till soybean planting (M5) Incorporation with one pass of RF and two (M6) or three (M7) passes of GN Incorporation with two passes of RF and no-till soybean planting (M8) Two (M9) or three (M10) passes of GN." "Grain yield was determined in an area of 2.55 m², corresponding to six 2.5 m rows spaced 0.17 m apart, which was expressed in kg ha-1, after moisture was adjusted to 13%. The yield components were determined: the number of panicles in one meter of the planting row; plant height, measured from the soil level to the tip of the panicle in five tillers. The HI was obtained by the ratio between grain yield and total dry matter in 1 m2. The number of grains and empty spikelets in ten panicles and the mass of 100 grains. The determination of the industrial quality of grains in 100 g samples of processed seeds. Rice and soybean grain yields were determined annually and the cumulative yields of these crops were calculated." The experimental design is completely randomized, with six replicates. "2015 and 2017: 0-10, 10-20cm 2023: 0-10, 10-20, 20-30, 30-40cm" "This study investigated the following chemical properties of the soil: pH, and the levels of calcium (Ca2+), magnesium (Mg2+), hydrogen (H+), aluminum (Al3+), phosphorus (P), potassium (K+), copper (Cu2+), zinc (Zn2+), iron (Fe3+), manganese (Mn2+), and organic matter. -Soil pH was measured in water. -Calcium and magnesium were extracted using a 1 molar potassium chloride (KCl) solution and then analyzed by atomic absorption spectroscopy. -Potential acidity (the combined amount of hydrogen and aluminum) was determined through titration with a 0.5 molar calcium acetate solution at a pH of 7. -Phosphorus, potassium, and micronutrients were extracted with Mehlich 1 solution (a mixture of 0.5 N hydrochloric acid (HCl) and 0.025 N sulfuric acid (H2SO4)) and analyzed by inductively coupled plasma atomic emission spectroscopy. -Soil organic matter (SOM) was estimated by multiplying the total organic carbon content of the soil by 1.724. This calculation was based on the chromic acid titration method. The specific methods used for these analyses were referenced from Teixeira et al. (2017) and Soltanpour et al. (1996)." "2015 and 2017: 0-10, 10-20cm 2023: 0-10, 10-20, 20-30, 30-40cm - In 2015 and 2017, soil organic carbon content was estimated indirectly by measuring soil organic matter (SOM) using the chromic acid titration method (Teixeira et al., 2017). The total soil organic carbon content was obtained by multiplying the SOM by a factor of 1.724. - In 2023, soil organic carbon content was measured directly using dry combustion with Total Organic Carbon (TOC) analysis. - Soil carbon stocks were calculated using soil bulk density. A volumetric ring was used to determine the bulk density at different depths (0-10 cm, 10-20 cm, 20-30 cm, and 30-40 cm). Since bulk density varied between treatments, estimates of soil organic carbon stocks (in Mg ha-1) were based on equivalent soil masses (Sisti et al., 2004)." The following soil physical properties were measured: bulk density, total porosity, microporosity, and macroporosity. Additionally, plant available water capacity was determined following the method of Teixeira et al. (2017). The S index, an indicator of soil physical quality, was calculated based on Dexter (2004). Finally, air capacity (AC) was assessed using the method outlined by Reynolds et al. (2002). Clay loam texture "-Sample collection: Soil samples for biological properties were collected at a depth of 0-10 cm. -Enzyme analysis: Betaglucosidase, aryl-sulfatase, and acid phosphatase activities were determined following the methods described by Tabatabai (1994) as modified by Lopes (2013). The analysis was performed using dried air-sampled soil."