Sugarcane root system: Variation over three cycles under different soil tillage systems and cover crops

Machinery traffic combined with soil management processes in the establishment of sugarcane areas degrades the soil structure, limiting root development and yield of the crop. The use of conservation tillage systems and cover crops can reduce such effects and improve its soil physical quality. Therefore, a field study was conducted over three agricultural years to assess the development of the sugarcane root system planted under different soil tillage systems and cover crops during three crop cycles. The study was carried out in 2014 in Ibitinga (Sao Paulo, Brazil) in an experimental design in split-plot scheme, with three repetitions and three soil tillage systems (no tillage, minimum tillage and minimum tillage with deep subsoiling) combined with four cover crops (sorghum, millet, peanut and sunn hemp), plus one control treatment consisting of conventional tillage and no cover crop use. The root system attributes (dry biomass, density, volume, length, and surface area) were evaluated every three months during the 2015/2016, 2016/2017, 2017/2018 crop years, in the 0.0-0.2 m, 0.2-0.4 m and 0.4-0.6 m layers. Although few significant differences were obtained in the root system of the sugarcane between the different soil tillage systems and use of cover plants, the accumulation of roots was evidenced during the second cycle of the crop, mainly due to the contribution of new roots, arising from the ratoons of the plants. Differences in the dry biomass of the roots were obtained in the minimum and minimum tillage with deep subsoiling, only at the time of harvesting the first crop cycle (cane plant, 395 days after planting) and in the second cycle, 665 days after planting. The highest concentration of root dry biomass was obtained in the 0.0-0.2 m surface layer, containing between 36 % and 62 % of roots. However, the significant differences of root dry biomass between the soil tillage and cover crops occur in the clayey layer at 0.30-0.6 m, where the management effects affected the root system. During the first three sugarcane cycles, the 0.0-0.2 m surface layer concentrated the highest amount of dry biomass of the roots, representing between 36 % and 62 % of the roots present in the first 0.6 m deep.