Anderson Clayton Rhoden

Mineralização anaeróbia do nitrogênio em solos de várzea do Rio Grande do Sul

The soil nitrogen mineralization potential (N0) and mineralization rate (k) are indexes that can be used to predict N availability in a period of time, which associated with soil attributes, can explain N absorption in flooded rice plants. The objective of this study was to evaluate the N mineralization in 15 flooded soils of Rio Grande do Sul (RS) state and its relationship with N absorption by flooded rice plants. Samples collected from 0-0.2m layer of 15 soils from rice paddy fields in the RS state were used for the mineralization experiment. Flooded rice plants were grown for 60 days in pots containing four kg of each soil. The N mineralization was evaluated in a laboratory experiment, in anaerobic conditions for 24 weeks. The content of soil organic C was highly associated to the N absorbed by the plants (r=0.90; P<0.01), as well as to the mineralized N (r=0.91; P<0.01) and to the content of N absorbed by the plants (r=0.92; P<0.01). The N0 values for the fifteen soils varied from 107.70 to 207.64mg kg-1 and they were higher for observed mineralized N (98.3 to 191.3mg kg-1 of soil). The mineralization rate constant varied from 0.1492 to 0.2438 week-1, and the mineralization speed was higher at initial period, until the fourth week of incubation. It was verified a close relationship between the N absorbed by rice plants and the nitrogen mineralization potential and with the content of soil organic C. The mineralization rate was significantly related to the clay content of the soil (r=0.77; P<0.01). The potential of N mineralization can be used as an index of N availability to rice flooded plants.

Concentração de nutrientes na solução do solo, sob diferentes manejos do arroz irrigado

Looking for crop alternatives management for irrigated rice possible, different systems of ryegrass straw management and aplication of fertilizers were evaluated, in relation to nutrient concentration in the solution were at there places. The experiment was conducted at the Federal University of Santa Maria, located in Central Depression Region of Rio Grande do Sul State, Brazil in the agricultural year of 2000/01. The experiment was in a randomized block with four replications, in split-split-plots design with three factors: ryegrass straw in three levels (i) no-tillage with ryegrass whole plant, (ii) ryegrass plant incorporated in soil and (iii) without ryegrass plant; time of fertilizers nitrogen and phosphorus application for rice (i) without fertilizer, (ii) fertilizer applied at the ryegrass sowing time and (iii) fertilizer applied at rice planting; and three places of sampling (i) surface water (ii) 3 cm depth and (iii) 30 cm depth in mini lysimeters. The results showed that ryegrass straw incorporation increases the potassium concentration in the water over the soil surface and contributes to percolation of calcium, magnesium, sodium, manganese and zinc in the soil profile. The concentration of there ions and potassium in the stagnant rice water remained below the established critical limits of environmental contamination stated by low.

Manejo da palha de azevém, da adubação de base e da água de drenagem na produção de arroz irrigado

Cultivation systems with minimum tillage are used to minimize red rice incidence, improving crop yield and the agricultural exploration of lowland soils. However, some limitations are present such as toxic substances due to anaerobic straw decomposition (prejudicial to rice plant establishment), as well as alterations on some available nutrients under flooded soil water conditions. The objective of this work was to compare different drainage systems; ryegrass straw management and time of fertilizer application on yield and yield components of rice plants. The experiment was conducted at the Federal University of Santa Maria, Rio Grande do Sul State-Brazil. Three ryegrass straw levels (no-tillage with ryegrass were evaluated, ryegrass plant incorporated with rotary tilling and without ryegrass plant), three fertilization conditions (without fertilizer; fertilizer applied at the ryegrass sowing time and fertilizer applied at rice sowing time) and two drainage management (conventional flooded and flooded without drainage). Results demonstrated that yield and yield components of rice production was not affected by fertilizer application at ryegrass sowing or at rice sowing. Meanwhile, deep-water drainage suppression reduces the grain yield and yield components.