Soil management and diverse crop rotation can mitigate early-stage no-till compaction and improve least limiting water range in a Ferralsol

No-till management systems tend to cause soil compaction in the early years of their establishment. Soil compaction reduces crop production due to restrictions on root development. Management strategies combining crop rotation and soil conservation practices still need to be researched as potential strategies to mitigate no-till soil physical constraints in tropical regions with prolonged drought periods and still promote agricultural sustainability. The objective of this study was to determine if soil specific management could mitigate early-stage no-till compaction and improve least limiting water range in a Rhodic Ferralsol. We hypothesized that no-till cropping systems with concomitant conservation practices –soil fertilization, crop rotation, and intercropped brachiaria grass– would improve soil physical quality (SPQ) and still achieve high crop yields in a tropical region with dry winters and frequent dry spells during wet season. Six no-till cropping systems were tested: soybean monoculture (T1); corn monoculture (T2); corn and soybean rotation (T3); corn and soybean rotation with intercropped brachiaria (T4); and two more with increased fertilization: corn and soybean rotation with intercropped brachiaria (T5), and corn and soybean rotation (T6). Least limiting water range (LLWR) was used as an indicator of SPQ. LLWR is computed as a function of bulk density (Bd), and it is defined as the range of soil water content in which physical constraints to plant growth are at minimal. Its critical limits are water contents associated with field capacity and air-filled porosity (upper limits), along with wilting point and soil resistance (lower limits). For each Bd, there is a LLWR value: the span between the upper limit and the lower limit. An adaptation of LLWR, in which we substituted the wilting point by the critical water content (θ*), was also tested (LLWR*). Critical Bd (BdC) value was 1.30 Mg m⁻³ for LLWR and LLWR*. In monoculture treatments (T1 and T2) the maximum Bd values exceeded the BdC (LLWR = LLWR * = 0) and negatively correlated with crop yield. Alternatively, cropping systems with diverse crop rotation (corn/soybean/brachiaria) showed greater values of LLWR and LLWR* and less soil compaction than monoculture systems. Usage of LLWR* evinced water stress was the main limiting plant growth factor; viz. θ* was more limiting than mechanical resistance and deficient aeration. These results support the hypothesis that the use of soil conservation practices and crop rotation during initial years of no-till farming contributes favorably to SPQ without compromising crop production.