Jorge de Castro Kiehl

Calagem em sistema de semeadura direta e efeitos sobre a acidez do solo, disponibilidade de nutrientes e produtividade de milho e soja

A field experiment was conducted in the state of Parana, Brazil, to evaluate the effect of liming on soil acidity, soil nutrient availability and yields of maize and soybeans on a Red Latosol (Oxysol), which had been cultivated for three, six and nine years under no-tillage (NT). Lime was broadcasted to the soil surface in four rates- 0, 33.3, 66.7 and 100% of the amount calculated to increase the soil base saturation (V%) to 70%; an additional treatment consisted of broadcasting the highest rate of lime and mixing it to the 0-20xa0cm layer of the soil. Calcium, magnesium and V% showed the most uniform distribution in the profile when the soil was cultivated under NT for nine years; in addition, exchangeable Al was low and pH was constant in all the studied soil layers. In the soil cultivated for three years, the highest figures for Ca and Mg in the 0-5xa0cm layer were observed when lime was broadcasted on soil surface at full rate, while pH and V% did not change with liming. The highest rate of lime mixed in the soil increased pH and Ca content of the 10-20xa0cm layer, as well as the Mg and V% of both layers of 10-20 and 20-30xa0cm. This treatment also reduced the Al content of the 20-30xa0cm layer. In the soil with six-year cultivation period pH, Ca and Mg of the upper layer generally increased with the highest rates of lime broadcasted to the soil surface. When mixed to the soil, lime reduced the exchangeable Al and increased the V% and the content of Ca and Mg of the deepest soil layers. In the soil cultivated for nine years, lime influenced only the surface layer; when applied on the surface, the increase in pH, V%, Ca and Mg by lime was generally higher than when mixed to the soil. Liming did not influence the contents of N, P, K and S in the soybean leaves. Maize and soybean grain yields were not influenced by liming, but the soil with six years of cultivation under NT produced the highest soybean yield.

Doses de nitrogênio e potássio no crescimento do trigo

The supply of potassium to plants stimulates the efficient use of nitrogen through plant uptake and assimilation, consequently increasing crop yield. The aim was to evaluate the effect of combined rates of nitrogen and potassium on growth and assimilation of nitrogen in wheat plants. The experiment was performed in a greenhouse, Piracicaba, SP Brazil. Three-liter pots were filled with 0-0.2 m depth samples of Arenic Hapludult. A fractionated 52 factorial was used, with combinations of five nitrogen rates (0; 70; 140; 210 and 280 mg dm-3) and five potassium rates (0; 50; 100; 150 and 200 mg dm-3), which were set in a randomized block design, with four replications. The combination of the highest nitrogen and potassium rates increased shoot growth and the chlorophyll content in leaves. The accumulation of nitrogen and potassium in leaves was increased only by rates of these nutrients separately. The potassium did not influence the nitrate reductase activity and the accumulation of nitrogen in plant tissue.

Enzymatic antioxidant responses to biostimulants in maize and soybean subjected to drought

Water stress is one of the most important environmental factors inducing physiological changes in plants, such as decrease in the water potential of the cells, the stomatal closure; and the development of oxidative processes mediated by reactive oxygen species (ROS). Antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) are efficient scavengers of ROS. The aim of this research was to examine how the application of biostimulant based on humic substances and aminoacids may affect activity levels of SOD, CAT, and APX of maize and soybean plants under well-watered or drought stress conditions. Pots (4.5 L) were filled with a Typic Hapludult soil where the biostimulants doses were applied. It was taken leaf samples in order to analyze SOD, CAT, and APX activities in plants. SOD and APX activity levels were increased by application of biostimulant 1 in maize subjected to stress. Catalase activity was not enhanced in plants by using the biostimulants. The composition of the biostimulants was not able to enhance stress tolerance in maize and soybean plants subjected to water stress.

Controlling ammonia losses during manure composting with the addition of phosphogypsum and simple superphosphate

Com o proposito de avaliar a eficiencia do gesso agricola e do superfosfato simples em controlar as perdas de amonia por volatilizacao durante o processo de compostagem de estereos, foi conduzido um experimento em frascos de vidro fechados de 1,6 litro de capacidade, nos quais diferentes quantidades (50, 100, 150 e 200 kg.t-1) daqueles materiais foram misturadas com um substrato composto de uma mistura de partes iguais (em massa) de estereos frescos de galinha e de bovino. A amonia perdida por volatilizacao foi determinada apos 7, 14, 21, 28 e 35 dias, coletando-se o gas em solucao de acido sulfurico encerrada em pequeno recipiente o qual era, por sua vez, colocado no interior do frasco. O acido remanescente apos o periodo de exposicao a amonia era determinado por titulacao com solucao de NaOH 0,025N. A quantidade de amonia perdida do estereo por volatilizacao diminuiu com a adicao de ambos os materiais estudados, mas para todas as doses aplicadas o gesso agricola foi mais eficiente do que o superfosfato simples. Os decrescimos da volatilizacao foram tanto maiores quanto mais elevadas eram as doses de ambos os aditivos. Houve evidencias de que a reducao das perdas de amonia deveu-se a presenca do gesso nos materiais estudados.

Formas químicas, disponibilidade de manganês e produtividade de soja em solos sob semeadura direta

This field study had the following objectives: to determine the most appropriate micronutrient extractor to evaluate manganese bioavailability in soils under no-tillage; to evaluate the interaction of soil manganese with humic acids in soils under no-tillage with and without manganese deficiency through electronic paramagnetic resonance (EPR); and to evaluate manganese fractions (exchangeable, organic, oxides and residual) after manganese addition in soils under no-tillage with and without previous manganese deficiency for soybean. Four sites (I to IV) were selected to study the response curve to manganese (0 to 48 kg ha-1) fertilization in soybean. Sites I to III were located in Tibagi, state of Parana (PR), Brazil and site IV was in Castro (PR). Manganese rates affected the manganese concentrations in the soil, but not the manganese concentrations in leaves and the amount of manganese taken up by plants. Exchangeable, organic and oxide forms of manganese increased with the increasing rates applied at site I, with the largest increase being observed for the organic fraction (changed from 5.4 mg kg-1 manganese in the control to 35.1 mg kg-1 of manganese in the highest manganese dose). Manganese was not detected by EPR in the solid samples of humic acid - pH 3.0. Manganese quantification in the same samples after nitric-perchloric digestion, along clear signals of manganese detected by EPR in samples of humic acid - pH 2.4, indicated that manganese in the samples was strongly linked to the functional (probably carboxylic) groups of humic acid. The fact that there was no effect of manganese on soybean yield might be due to the complexation of the nutrient by soil organic matter. In general, DTPA-TEA was the most reliable manganese extractor to evaluate manganese availability to soybean under no-tillage.

Extração e fitodisponibilidade de metais em resposta à adição de lodo de esgoto no solo

Diante dos riscos ambientais relacionados ao uso agricola de lodo de esgoto contendo metais foi realizado um experimento, com o objetivo de avaliar o efeito do lodo, combinado ou nao com P, K e PK, sobre o acumulo de metais na parte aerea das plantas e comparar a eficiencia de extratores na fitodisponibilidade de metais. Amostras da camada de 0-20 cm de um Argissolo Vermelho Amarelo eutrofico foram transferidas para vasos e tratadas com doses equivalentes a 0, 10, 20, 30, 40 e 50 Mg ha-1 de lodo (base seca). Apos 30 dias de incubacao, determinou-se os teores de Fe, Mn, Cu, Zn, Cd, Ni, Cr e Pb (extraidos por HCl 0,1 mol L-1, Mehlich-3 e DTPA pH 7,3), procedeu-se aplicacao de duas doses de P (0 e 100 mg kg-1) e duas dose de K (0 e 100 mg kg-1). Cultivaram-se plantas de milho (Zea mays L.) durante 50 dias, coletando-se a parte aerea para determinacao de metais. A aplicacao de lodo aumentou o teor de Fe, Mn, Zn e Cu no solo e o acumulo pelas plantas, enquanto a complementacao do residuo com potassio aumentou a producao de materia seca e diminuiu o acumulo de Zn. A reducao do pH e o Mn nativo do solo influenciaram no aumento da disponibilidade Mn. Todos os extratores foram eficientes para predicao da fitodisponibilidade de Zn e Cu. Para o Mn e Fe, os mais eficientes foram: HCl e Mehlich-3, HCl e DTPA, respectivamente. Para os demais metais, os extratores se mostraram pouco eficientes.

Influência do alumínio de um Podzólico Vermelho-Amarelo do Acre sobre o crescimento das plantas

The present study was carried out in 1995 to investigate why plants cultivated in a Red-Yellow Podzolic in the State of Acre, in the Brazilian Amazon, presenting high amounts of exchangeable aluminum, have not shown symptoms of toxicity to this element or yield reduction. The exchangeable Al3+ in the B horizon is higher than 14 cmolc dm-3. Samples of the A and B horizons were incubated with increasing rates of lime and subjected to determination of pH in H2O, pH in 0.01 mol L-1 CaCl2 and of the content of exchangeable Al extracted with 1 mol L-1 KCl, determined either by titration with 0.02 mol L-1 NaOH or by atomic absorption spectrophotometry. In a second experiment, two cultivars of rice plus common beans and corn were planted in pots containing samples of the A and B horizons of the soil; in 50% of the pots the samples were previously limed in order to increase the base saturation to 80%. After 60 days, plant roots and tops were removed, dried, weighed and subjected to determination of Al. In a third study, aluminum concentration in the soil solution was determined utilizing extracts collected from saturated samples previously incubated with increasing rates of lime. The concentrations of exchangeable Al determined by titration with 0.02 mol L-1 NaOH were similar to those obtained by atomic absorption spectrophotometry. The influence of liming on dry matter yield and the absorption of Al by the plants was small and no clear relation was found between plant development or toxicity symptoms and exchangeable Al in the soil. The non-limed soil showed high concentrations of Al in the solution; however, toxicity symptoms were not found in the plants. For the Red-Yellow Podzolic, the exchangeable Al and the concentration of Al in solution were not reliable indexes for estimating the toxicity of this element to plants.

Alteração de propriedades físicas e atividade microbiana de um latossolo amarelo álico após o cultivo com fruteiras perenes e mandioca

This study aimed at evaluating changes in the physical properties of an alic sandy-clay loam Yellow Latosol (Haplortox), located at Cruz das Almas, Bahia, Brazil, cropped for 15 years with banana, 38 years with citrus, 15 years with mango, and 14 years with cassava, compared with soil covered by native forest. In 1991, soil samples were collected for the A, AB, Bw1 and Bw2 horizons and soil bulk density, soil density, macroporosity, microporosity were determined, as well as the distribution of aggregates by size and microbiological activity. Soil bulk density increased and macroporosity decreased in mango and citrus areas, mainly in the upper horizon. Microporosity was lower for the soil under mango, in the upper horizon. The percentage of stable aggregates in water larger than 0.50 mm decreased in the soils under banana and mango. The soil microbiological activity was higher in the area covered by native forest.

CONTROLE DA VOLATILIZAÇÃO DE AMÔNIA EM COMPOSTAGEM, MEDIANTE ADIÇÃO DE GESSO AGRÍCOLA E SUPERFOSFATOS COM DIFERENTES NÍVEIS DE ACIDEZ RESIDUAL

Tem sido recomendada a adicao de superfosfato simples ou gesso agricola nas pilhas de estercos e de outros residuos orgânicos, com a finalidade de reduzir as perdas de amonia por volatilizacao durante a compostagem. Experimentos, contudo, tem mostrado resultados divergentes, quando avaliam a eficiencia desses produtos e as doses em que devem ser aplicados. E provavel que variacoes na acidez residual do gesso e do superfosfato simples possam explicar essas divergencias. Para verificar essa hipotese, realizou-se um experimento, utilizando, como aditivos, o gesso agricola, o superfosfato simples e o superfosfato triplo, cada um com dois valores de acidez residual (respectivamente, 0,13 e 0,20%; 7,02 e 2,36%; 2,38 e 1,86%). Em frascos de vidro de 1,6xa0litro de capacidade, foram colocados 10 g de substrato orgânico obtido por mistura de quantidades iguais, em massa, de estercos secos e frescos de galinha e de gado. Os aditivos foram misturados ao substrato em doses equivalentes a 0, 50, 100, 150 e 200xa0kgxa0t-1. A quantidade de amonia perdida por volatilizacao foi determinada aos 7, 14, 21, 28, 35 e 42xa0dias, coletando-se o gas em solucao de acido sulfurico encerrada em pequeno recipiente colocado no interior do frasco e titulando-se o acido remanescente apos o periodo de exposicao a amonia, com solucao de NaOH 0,01xa0molxa0L-1. As amostras de gesso agricola estudadas nao se mostraram eficientes em reduzir a volatilizacao de amonia da mistura de estercos. O superfosfato simples diminuiu a volatilizacao de NH3 em ate 4,8xa0vezes, tendo sido a amostra com maior acidez residual a mais eficiente. O superfosfato triplo foi o aditivo mais eficiente no controle da volatilizacao de NH3, quando aplicado em doses baixas, igualando-se ao superfosfato simples na maior dose. Aparentemente, a acao dos aditivos deveu-se a formacao de compostos amoniacais mais estaveis por meio de reacoes do gas NH3 com acidos e, ou, fosfato monocalcico presentes naqueles produtos.

Effect of water and citrate solubility on agronomic effectiveness of acidulated phosphates in three consecutive corn crops

No processo de acidulacao de fosfato de rocha, varios compostos classificados como impuros podem ser obtidos paralelamente aos fosfatos de calcio e de amonio. Tais compostos normalmente reduzem o teor de P soluvel em agua e a eficiencia agronomica dos fertilizantes. Com o objetivo de estudar este problema, desenvolveu-se um experimento em casa de vegetacao; tres cultivos sucessivos de milho foram feitos em amostras de um Latossolo Vermelho-Amarelo em esquema fatorial completo (6 x 2 x 2), com quatro repeticoes. Seis fertilizantes fosfatados acidulados comerciais foram adicionados a 2 kg de solo na dose de 70 mg kg-1 de P, a qual foi determinada de acordo com o teor de P soluvel em citrato neutro de amonio + agua (CNA + H2O) dos fertilizantes. Os fertilizantes foram aplicados na forma original ou lavados para remover a fracao de fosforo soluvel em agua e incorporados em volume total de terra ou com 1 % do volume. As plantas de milho foram colhidas apos 40 dias da emergencia e a materia seca e P acumulado foram determinados. No primeiro cultivo, e aplicacao localizada, a eliminacao do P soluvel em agua dos fertilizantes originais resultou em menor quantidade de P biodisponivel as plantas. Nos demais cultivos, os efeitos de fonte de fosforo, lavagem e metodo de aplicacao nao foram tao evidentes como no primeiro cultivo, sugerindo que as fontes de P testadas podem ter eficiencia semelhante quando se consideram varios cultivos. Concluiu-se que a fracao insoluvel em agua, porem soluvel em CNA, dos fertilizantes testados nao deve ser vista como totalmente inerte, uma vez que pode disponibilizar fosforo a longo prazo.