Integrated crop-livestock systems in lowlands with rice cultivation improve root environment and maintain soil structure and functioning

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.