Soil pH and calcium levels are determining factors in the success or failure of managing clubroot during the cultivation of Brassica spp. The aim of the present study was to evaluate the influence of soil attributes in tropical regions on the development of roots and clubroot and the accumulation of biomass and nutrients in cauliflower. One hundred and fifty-one samples of soil and plants were collected from 16 family farms that have a history of more than 50 years of regular cauliflower cultivation in Nova Friburgo, Rio de Janeiro, Brazil. Chemical and physical analyses were performed on the soil samples, and the severity of clubroot and the accumulation of biomass and macronutrients in individual plants and plant tissues. Clustering and main principal component analyses were performed on the data. The disease occurred on all farms, but with different intensities. A direct relationship was observed for the soil attributes (acidity and exchangeable aluminum content in particular) with the percentage of roots with clubroot and with the accumulation of biomass and macronutrients in the different plant organs. To reduce losses from clubroot in weathered soils, practices should aim to reduce the pathogen’s inoculum potential and improve the physical and chemical conditions of the soil, which would favor root development of the plants.

A first large-scale systematic survey of natural radioactivity contents of soils of the state of Rio de Janeiro is presented, focused on the establishment of Quality Reference Values (QRVs). Undisturbed soil samples were collected from 243 areas and analyzed by gamma spectrometry. The activity contents varied largely, ranging from 12.2 to 1,029 Bq kg⁻¹ for ⁴⁰K (geometric mean of 111.1 Bq kg⁻¹), from 3.5 to 99.8 Bq kg⁻¹ for ²²⁶Ra (geometric mean of 29.7 Bq kg⁻¹), and from 5.4 to 314.5 Bq kg⁻¹ for ²²⁸Ra (geometric mean of 67.1 Bq kg⁻¹). The highest contents of radium isotopes were found in soils developed on igneous rocks (Leptosol), and the lowest in a soil of sedimentary origin (Podzol). Among the different soil types, the radioisotope contents differed substantially. Separate QRVs were calculated for each radionuclide by the 75^th and 90^th percentile approach, and the QRVs were estimated for each soil type. The results emphasized the restrictiveness of QRVs based on the 75^th percentile or of a single overall QRV for all soils. Therefore, rather than estimating a separate QRV for each radionuclide for the State, we suggest the use of an upper threshold value, defined as the 90^th percentile, and a specific QRV for each soil type area.

Two greenhouse experiments were carried out to evaluate the phytoremediation potential, physiological responses and zinc (Zn) uptake kinetics of water lettuce (Pistia stratiotes L.). The phytoextraction experiment evaluated four doses of Zn (0.7 mg L⁻¹ – represented the Zn in the nutrient solution, 1.8, 18 and 180 mg L⁻¹ – corresponded to ten, hundred and a thousand times, respectively, the maximum permitted content for fresh water) at four different culture times (24, 48, 72 and 168 h). The Zn uptake kinetics of water lettuce were evaluated at two concentrations of Zn (1.8 and 18 mg L⁻¹). The water lettuce attained the highest percentage removal at the lowest evaluated doses (0.7 and 1.8 mg L⁻¹), reaching a maximum value of approximately 72% removal (when cultivated in 1.8 mg L⁻¹ of Zn after 168 h of culture). The Zn uptake increased with culture time, increasing the synthesis of carotenoids at all doses evaluated. The highest doses of Zn resulted in a reduction in photosynthetic efficiency. The results showed a high potential of water lettuce to absorb and tolerate Zn, accumulating preferably in the roots, demonstrating that these plants are able to absorb large quantities of Zn in contaminated solution.