Jairo André Schlindwein

Métodos de extração de fósforo e potássio no solo sob sistema plantio direto

The current soil test method used to evaluate soil phosphorus and potassium available to the plants in soils from Rio Grande do Sul e Santa Catarina state is the Mehlich-1 solution. The soil test methods studies for these nutrients were conducted based on the conventional soil tillage. The aim of this work was to compare the soil phosphorus and potassium amounts extracted by the Mehlich-1 solution and the nutrients amounts extracted by the Mehlich-3 solution, and resin membrane in soils from the Rio Grande do Sul state, under no tillage soil system and nutrients crop response. The phosphorus amounts extracted by the resin method and by the Mehlich-3 solution were higher than that those extracted by the Mehlich-1 solution in both of them sampling depth. The correlation coefficients among the phosphorus amounts extracted by the methods were high association degree. The potassium amounts extracted by the methods were similar, and the correlation coefficients among the potassium amounts extracted by the methods were high association degree in all soil sampling depth. The soil testing methods that have studied in this work are efficient for soil phosphorus and potassium extraction in soils under no tillage; however, the lowest soil phosphorus amounts extracted by the Mehlich-1 solution, increase the laboratory errors.

Calibração de métodos de extração de potássio em solos cultivados sob sistema plantio direto

Fertilizer recommendations in Rio Grande do Sul and Santa Catarina (RS and SC) states are based on studies of crops grown under conventional tillage and knowledge accumulated over the years. In this period, the crop system and soil sampling depth were altered and crop yields increased; this can affect the critical values of K, the fertility status and fertilizer quantity required by crops. This study aimed to determine the levels of available K extracted by Mehlich-1, Mehlich-3 and ion-exchange resin from no tillage soils under soybean, wheat and corn. For this purpose, the K levels of soil samples from 17 experiments were used as well as grain yield data of soybean, wheat and corn grown under no-tillage in 48 studies carried out in RS. Based on the production functions the calibration curve and fertility status were determined. Results indicated that the plant response to K fertilization followed the order: corn> wheat > soybean. The critical K values extracted with Mehlich-1, Mehlich-3 and resin were 89.5, 91; 6 and 83.8 mg kg-1 K in the 0-20 cm layer and 117.2; 116.1 and 102.5 mg kg-1 K in the 0-10 cm layer, respectively, and exceeded those recommended by CFSRS / SC (2004) for soybean, wheat and corn grown under no-tillage.

Disponibilidade de potássio para as plantas em solos do sul do Brasil estimada por métodos multielementares

A avaliacao da disponibilidade de K para as plantas e feita pela estimativa de seus teores na forma trocavel. Metodos multielementares aumentam a eficiencia nos laboratorios de analises de solo, porem a capacidade de troca de cations (CTC) do solo pode alterar a predicao do K disponivel. O objetivo deste trabalho foi estimar o K disponivel para o milho e para a soja em solos representativos do Estado do RS, pelos metodos Mehlich-1 (M1), Mehlich-3 (M3), resina de troca ionica (resina) e Acetato de Amonio pHxa07,0 (AcNH4), bem como verificar se a CTC influencia a estimativa da disponibilidade de K no solo para as plantas. O experimento foi conduzido em microparcelas a ceu aberto e, apos 45xa0dias de cultivo, quantificou-se a materia seca da parte aerea das plantas e determinou-se o o teor de K no tecido. Foram feitas as correlacoes entre os teores de K extraidos pelos metodos e a relacao com a absorcao de K pelas plantas em todos os solos e separando os solos em classes de CTC. As quantidades de K extraidas pela resina foram aproximadamente 50xa0% menores que as das solucoes de M1, M3 e AcNH4. Os coeficientes de correlacao entre os teores de K extraido pelos metodos tiveram alto grau de associacao. A relacao entre os teores de K acumuladas pelas culturas e os teores extraidos pelos metodos nao diferiram, independentemente da separacao por classes de CTC. A disponibilidade de K para as plantas em solos do RS pode ser feita pelos metodos testados no presente trabalho. Nao houve diferenca entre os metodos na avaliacao da disponibilidade de K nas classes de CTC. O metodo da resina, embora nao diferindo dos demais na predicao do teor de K disponivel, apresenta desvantagem em relacao aos demais pela menor capacidade extrativa, o que resulta em classes de disponibilidade menores e propicia o erro analitico.

Fósforo disponível determinado por lâmina de resina enterrada

The in situ ion exchange resin membrane allows a partial simulation of the behavior of plant roots regarding phosphorus absorption from soil solution. Soil sampling is rendered unnecessary since the technique is used directly in the soil where the plants are grown and may be a promising methodology in the determination of phosphorus availability for crops. To evaluate the technique, a greenhouse experiment was carried out with resin membranes buried in the soil when plants were sown (day zero) and removed after 2, 5, 10, 20 and 40 days, to evaluate the amount of phosphorus extracted in different soils maintained at a moisture content near the water-holding capacity, under corn (method resin-cc) and water-saturated, without cultivation and under rice (method resin-sat). Soil samples were collected to determine available P by the methods resin membrane (standard), Mehlich-1 and Mehlich-3 and the extracted amount was correlated with P absorbed by crops. On average, Mehlich-1 extracted 1.3 and 1.9 times less phosphorus than the resin standard and Mehlich-3 methods, respectively; resin-cc method extracted, on average, 2.2 times less phosphorus than the resin-sat. The correlation coefficients among phosphorus extracted by the different methods and phosphorus absorbed by corn and rice increased in the sequence resin-cc < resin standard < Mehlich-1 < Mehlich-3 < resin-sat. The correlation coefficient between phosphorus extracted with buried resin and phosphorus absorbed by corn and rice plants was highest after a period of 10 days. Results indicate that the resin-sat method is suitable to determine soil phosphorus availability to plants.

Adjustment of the expedite method for clay content determination in Rondônia soils

Soil clay content is an important soil attribute and has been used to classification of phosphorus status in the soil in order to determinate the needing of phosphorus amounts to be applied to crops production. The aim of this research was to adjust the method for soil clay content determination, adopted by the laboratories of Southern Brazil (ROLAS-RS/SC), for soil clay content evaluation in Rondonia soils. The study was conducted using 50 soil samples from Rondonia State with wide range clay content. It was tested shaking periods (1.5, 2.0 and 2.5h) associated with periods for soil particles decantation (1.5 and 2.0h) to correlate with the standard method for soil texture testing, known as the pipette method. Clay content determined through this method was significantly correlated with pipette method. The better treatment was the combination of 2.0h of shaking and 1.5h of decantation, resulted in total period of 3.5h, which reduced the period to determine the soil clay content without loss of accuracy.