Suchergebnisse

The changes in soil potassium pools under intense cropping and fertilized with potash fertilizer are still little known to the soils of Paraná State. The effects of potassium fertilization and successive cropping on changes in K pools in different soils of Paraná, Brazil, were investigated in this study. Twelve soil samples, collected from the upper layer 0–0.20 m, were fertilized or not with K and subjected to six successive cropping (i.e., soybean, pearl millet, wheat, common beans, soybean and maize). All the crops were grown for 45 days, and at the end of the second, fourth and sixth cropping, the soil from each pot was sampled to determination of the total K, non-exchangeable K, exchangeable K and solution K. The result showed that the soil potassium pools varied widely. Total K concentration ranged from 547 to 15,563 mg kg–1 (4,714 mg kg–1, on average). On the average, structural K, non-exchangeable K, exchangeable K and solution K of the soils constituted 84.0, 11.3, 4.6 and 0.1% of the total K, respectively. Soils differ in the ability to supply potassium to the plants in the short to medium term, due to the wide range of parent material and the degree of soil weathering. When the soils were not fertilized with K, the successive cropping of plants resulted in a continuous process of depletion of non-exchangeable K and exchangeable K pools; however, this depletion was less pronounced in soils with higher potential buffer capacity of K. The concentrations of K non-exchangeable and exchangeable K were increased with the addition of potassium fertilizers, indicating the occurrence of K fixation in soil. After the second cropping, the soil exchangeable K levels remained constant with values of 141 and 36 mg kg–1, respectively, with and without the addition of K fertilizer, reflecting in establishing of a new dynamic equilibrium of K in the soil.</p>

Beneficial effects of silicon (Si) in the plants growth under conditions of drought stress have been associated with to uptake and accumulation ability of element by different species. However, the effects of Si on soybean under water stress are still incipient and inconclusive. This study investigated the effect of Si application as a way to confer greater soybean tolerance to drought stress. The experiment was carried out in 20-L pots under greenhouse conditions. Treatments were arranged in a randomized block design in a 2 × 4 factorial: two water regimes (no stress or water stress) and four Si rates (0, 50, 100 and 200 mg kg–1). Soybean plants were grown until beginning flowering (R1) growth stage with soil moisture content near at the field capacity, and then it started the differentiation of treatments under drought by the suspension of water supply. Changes in relative water content (RWC) in leaf, electrolyte leakage from cells, peroxidase activity, plant nutrition and growth were measured after 7 days of drought stress and 3 days recovery. The RWC in soybean leaves decreased with Si rates in the soil. Silicon supply in soil with average content of this element, reduced dry matter production of soybean under well-irrigated conditions and caused no effect on dry matter under drought stress. The nitrogen uptake by soybean plants is reduced with the Si application under drought stress. The results indicated that the Si application stimulated the defense mechanisms of soybean plants, but was not sufficient to mitigate the negative effects of drought stress on the RWC and dry matter production.

Understanding the influence of row spacing and plant density on grain yield and yield components of crambe is critical in order to obtain higher grain yields. Therefore, the objective of this study was to evaluate the effects of row spacing and plant density on grain yield and its components in crambe in two distinct regions of Brazil (Marechal Candido Rondon-PR, MCR-PR, and Botucatu-SP, BTU-SP). Narrow and wide row spacing (0.20 and 0.40 m) combined with four plant densities (15, 25, 35, and 45 plants m-1) were evaluated in a randomized block layout with four replications in a 2 × 4 factorial design. The experiment at BTU-SP was run under rainfed conditions with supplementary irrigation, whereas the experiment at MCR-PR was run under rainfed conditions without supplementary irrigation. Both experiments were run in soils classified as Oxisols. There was no interaction between row spacing and plant density. Highest grain yield with supplementary irrigation was observed at 0.20 m row spacing. Without irrigation, row spacing did not affect grain yield owing to the plasticity of crop. The highest grain yield was observed with approximately 30 plants m-1 at both experimental locations. A strong negative correlation was observed between final plant population and number of grains per plant. There was high plant mortality, particularly at high plant densities cultivated under irrigation. Higher mortality occurred because of high intraspecific competition and a larger disease incidence due to the higher humidity in the irrigated experiment. A mechanism of self-adjustment by plant density was observed in crambe, with its intensity dependent on plant density and environmental conditions, such as water and nutrient availability and light incidence.