Crop rotation and the maintenance of plant residues over the soil can increase soil water storage capacity. Root access to water and nutrients depends on soil physical characteristics that may be expressed in the Least Limiting Water Range (LLWR) concept. In this work, the effects of crop rotation and chiselling on the soil LLWR to a depth of 0.1 m and crop yields under no‐till were studied on a tropical Alfisol in São Paulo state, Brazil, for 3 yr. Soybean and corn were grown in the summer in rotation with pearl millet (Pennisetum glaucum, Linneu, cv. ADR 300), grain sorghum (Sorghum bicolor, L., Moench), congo grass (Brachiaria ruziziensis, Germain et Evrard) and castor bean (Ricinus comunis, Linneu) during fall/winter and spring, under no‐till or chiselling. The LLWR was determined right after the desiccation of the cover crops and before soybean planting. Soil physico‐hydraulic conditions were improved in the uppermost soil layers by crop rotations under zero tillage, without initial chiselling, from the second year and on, resulting in soil quality similar to that obtained with chiselling. In seasons without severe water shortage, crop yields were not limited by soil compaction, however, in a drier season, the rotation with congo grass alone or intercropped with castor resulted in the greatest cover crop dry matter yield. Soybean yields did not respond to modifications in the LLWR.

RESUMOAs técnicas de estudo radicular são trabalhosas e, dentre os métodos mais utilizados no Brasil, destacam-se a trincheira ou parede do perfil, blocos ou monólito, placa com pregos e trado. Essas técnicas utilizam amostragem destrutiva e direta das raízes. SUMMARY: SOYBEAN ROOT ACTIVITY: METHODOLOGY DEFINITIONRoot study techniques are labor intensive. Among the most frequently used methods are the trench or profile wall, block or monolith, needle board and hand auger. These techniques use destructive and direct root sampling. With the objective of adapting an evaluation methodology of soybean root activity based on Rubidium Nitrate, an experiment was carried out in Botucatu, SP, Brazil, in two phases; one in the field and the other in a