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Integrated Crop Livestock Systems (ICLS) are important alternative for diversification and sustainable food production, while conserving soil. The effects on soil structure of adopting ICLS in lowlands are widely unknown. Our hypothesis was that the adoption of ICLS, in lowland production systems for flooded-irrigation rice cultivation, improves the structure and functionality of the porous soil system, mainly stimulated by the increased root growth from pastures. The objective was to investigate how different managements of integrated systems in lowlands influence the structure and quality of a Planosol in southern Brazil. The evaluation was carried out between the fifth and sixth year of an experiment consisting of four agricultural production systems, based on irrigated rice cultivation, in a randomized block design with three replications. The systems were RFR-ct: rice – fallow – rice, without animal grazing in winter and with soil disturbance (conventional tillage) in the spring; RGrR-nt: rice - grazed ryegrass - rice, with no till; RGrSGrR-nt: rice - grazed ryegrass - soy - grazed ryegrass - rice, with no till; e P4R-nt: pasture (ryegrass + white clover + birdsfoot trefoil) in winter, and succession field in the summer, being continuously grazed and cultivated with rice under no-tillage every four years. Samples with preserved structure were collected at three seasons: after the grazing cycle (spring 2018), after harvesting the summer crops (fall 2019), and after another grazing cycle (spring 2019). Soil bulk density, total porosity, macroporosity, microporosity, water retention curve, pore size distribution, porosity and organic material by computed tomography (CT), and root biomass were determined. The results indicated that the ICLS, even without tillage and with animal trampling, kept the same physical condition as tilled system, and the system with rice in succession to ryegrass increased available water. Thus, soil tillage as a strategy to improve its physical structure is unjustifiable. The CT revealed that periodic tillage forms spherical, poorly connected pores, while root growth in ICLS created a continuous, connected porosity. Therefore, similar physical properties do not correspond to equal soil structure and functionality. Presence of organic material in the soil, roots or crop residues are crucial to porosity maintenance in all systems. • Similar bulk soil properties may produce dissimilar soil functionality. • Animal trampling in ICLS in lowlands did not increase topsoil bulk density. • Cover in ICLS plays an important soil structure protective role in loamy soils. • Root growth of grasses in ICLS promotes a continuous, connected porosity. • Periodic tillage in lowlands forms spherical, poorly connected pores. [ABSTRACT FROM AUTHOR]

• Exchangeable K forms were not sensitive to detect different amounts of K added. • K addition greater than the export resulted in the fixation of K surplus by the soil. • Rotation of rainfed crops with paddy rice increased the fixation of K by the soil. • Non-exchangeable K was more useful to understanding the soil K dynamics. • K fertilization in 2:1 claymineral soils should focus on the reposition of exported K. Diversified farming systems is a challenge in lowland soils around the world. In Southern Brazil, integrated crop-livestock systems (ICLS) have been used for grain crops and livestock production under no-till. However, their impacts on soil K dynamics are still poorly explored. The aim of this study was to quantify the K forms in the soil and the K budget after 66 months of different flooded rice production systems under no-till ICLS in a subtropical paddy field. Four production systems were established in 2013: (i) flooded rice monocropping under conventional tillage (CT) and winter fallow (R-CT); (ii) no-tillage (NT) flooded rice monocropping with ryegrass pasture in winter (R-ICLS); (iii) NT flooded rice and soybean rotation in the summer and ryegrass pasture in winter (RS-ICLS), and (iv) NT flooded rice, soybean, maize and stapf grass rotation in the summer period and ryegrass and clover pasture in the winter (RSM-ICLS). In 2018, soil samples were taken at the 0–10, 10–20 and 20–30 cm soil layers. Exchangeable potassium (K), non-exchangeable K, structural K, and total K were evaluated. Exchangeable K was not affected by the treatments. The higher the difference between inputs and outputs of K in the systems evaluated, the higher was the content of structural and total K in the soil. However, the K budget in the system was not sufficient to fully explain the variation in the non-exchangeable K content in the soil. Comparing the systems with the same frequency of flooded rice cultivation, the difference between inputs and outputs of K was about 2.3 times higher in the R-ICLS system (830 kg ha−1 of K) compared to R-CT (366 kg ha−1), which increase in 70 % the concentration of non-exchangeable K in the 0–30 cm soil layer (622 and 361 mg kg−1 in the R-ICLS and R-CT, respectively). In the systems where flooded rice rotates with rainfed crops (RS-ICLS and RSM-ICLS), the drying cycles resulted in K fixation with higher energy, turning the surplus of K added via fertilization into structural forms. These results indicate that lowland soils cultivated with K fertilization rates greater than the export of K can result in a fixation of K, decreasing its availability in the short-medium term. Moreover, it strongly emphasizes that adequate K fertilization in lowland soils with 2:1 clayminerals should focus on the reposition of exported K in order to prevent temporary fixation of K by fixation on structural forms. [ABSTRACT FROM AUTHOR]