Humberto Bohnen

Eficiência de absorção, translocação e utilização de fósforo por variedades de trigo

Com vistas em obter variedades de trigo mais eficientes na absorcao e, ou, utilizacao de fosforo, e importante a investigacao das causas da maior eficiencia de certas variedades. Realizou-se um experimento em solucao nutritiva, com quatro concentracoes de fosforo (1,6; 4,8; 12,9 e 32,3 µmol L-1), comparando cultivares considerados eficientes (Toropi e IAC 5) e ineficientes (IAS 20 e CNT 8) quanto a absorcao de fosforo, translocacao e utilizacao do nutriente, materia seca produzida e morfologia das raizes (comprimento, raio medio e area superficial). O cultivo foi realizado em outubro e novembro de 1993, em casa de vegetacao da Faculdade de Agronomia da UFRGS (Porto Alegre-RS). As variedades nao se diferenciaram quanto ao conteudo de fosforo na planta. Nao houve relacao entre a absorcao de fosforo e a morfologia das raizes. Os cultivares Toropi e IAC 5 mostraram-se mais eficientes na utilizacao de fosforo, bem como na translocacao desse nutriente para a parte aerea.

Resposta do arroz irrigado ao suprimento de amônio e nitrato

In rice cultivated under flooded conditions, the anaerobic condition favors the formation of NH4+ in the soil, and is therefore considered the main available N source for this crop. However, the process of O2 transport through the aerenchyma and its release by roots, create a favorable environment for nitrification in the plant rizosphere. Nitrification intensity determines the proportions between available NH4+ and NO3- . In this case, it is believed that the presence of NO3- can favor rice growth and simultaneously avoid NH4+ toxicity. This experiment was carried out to evaluate the effect of different proportions between NH4+ and NO3- in nutrient solution on rice growth. The experiment was performed in a greenhouse, from September to November 2007, in a nutrient solution with the following NH4+ and NO3- proportions: 100:0, 75:25 and 25:75, in a 10.0 mmol L-1 N concentration. The plots were fulfilled with a inert substrate to create conditions to root growth. The genotypes IRGA 417 and Sasanishiki were compared and the biomass production, root length, root distribution and the N, Ca, Mg and K uptake were evaluated. The presence of NH4+ in the 100:0, 75:25 proportions resulted in plant toxicity, however, as the NO3- proportion increased, toxicity was reduced. The combined supply of NH4+ and NO3- increased biomass production compared to solely NH4+ supply. The rice root system of the two cultivars developed mainly in the 0-10 cm layer and the - greatest root length was observed in the treatment NH4+ 75:25 NO3- for IRGA 417. The presence of NH4+ in soil solution affected negatively calcium absorption, whereas no affect was observed on N, Mg or K absorption. The total absorbed N, K, and Ca indicated a higher absorption efficiency with the combined supply for IRGA 417, but for cultivar Sasanishiki no differences were verified. It was concluded that NH4+ is toxic to rice plants, and is not the main available source of nitrogen. Nitrate is indispensable to increase the N uptake, normal plant growth and total cation absorption.

TOLERÂNCIA AO ALUMÍNIO EM PLÂNTULAS DE MILHO

A selecao para tolerância ao aluminio e complicada pela desuniformidade natural dos solos e pela dificuldade de avaliar danos na raiz. Assim sendo, e importante desenvolver metodos eficientes de caracterizacao da tolerância ao aluminio em condicoes controladas de ambiente. O presente trabalho teve por objetivo adequar o metodo de solucao minima para a avaliacao da tolerância ao aluminio em genotipos de milho. O trabalho consistiu de dois experimentos. O primeiro foi feito para ajustar o metodo de avaliacao atraves do emprego de solucao minima, e o segundo, para avaliar um conjunto de 22 genotipos de milho fornecidos pela Empresa Agroeste Sementes Ltda. A avaliacao dos genotipos foi realizada com uma solucao que continha diferentes concentracoes de aluminio e calcio. As medias para todas as variaveis analisadas mostraram a diferenca entre os hibridos e entre as concentracoes de aluminio empregadas. As concentracoes de 6mg-1 de aluminio e 40mg-1 de calcio foram consideradas mais eficientes para a discriminacao da tolerância ao aluminio, sendo posteriormente empregadas para o trabalho com as linhagens. No segundo experimento, os resultados possibilitaram identificar linhagens com tolerância ao aluminio.

Alterações no teores de nutrientes em dois solos alagados, com e sem plantas de arroz

Flooding a soil and growing plant on it can change its biological and chemistry properties, in comparison with a non-flooded environment. An experiment was conducted in order to study the nutrients dynamics in the solution of two soils (Planossolo and Gleissolo) during the rice cycle. Rice plants were cultivated in 50L containers having devices to collect soil solution at several depths (2.5, 5.0, 7.5 and 31cm). In the soil solution, with and without plant, P, K, Ca, Mg, Fe and Mn, were measured at 10, 19, 44, 77, and 113 days after the flooding. Potassium was especially sensible to the rice plant and depth of sampling

Tolerância de genótipos de soja ao alumínio em solução

The knowledge of the soybean (Glycine max L.) genotypes reaction to aluminum (Al) present in acid soils is important for the development of efficient breeding programs. A series of ex- periments were carried out to determine the levels of Al and calcium (Ca) in low salt solutions and the most appropriate time for screening. The next experiments were conducted to rank Brazilian soybean cultivars and breeding lines according to their tolerance to Al with some American cultivars, consid- ered as standards. A solution with 0.2 mg L -1 of Al and 50 mg L -1 of Ca was used and the primary root length obtained in the ninth day was utilized to screen 148 soybean genotypes for Al tolerance. Among these genotypes, 21 were Al-tolerant : Biloxi, Bragg, BRAS85-1736, BRAS86-3672, BR-13 (Maravilha), BR-37, Cobb, EMGOPA-302, EMGOPA-304 (Campeira), FT-1, FT-5 (Formosa), FT-6 (Veneza), FT-Guaira, FT-Manaca, IAS 4, IPAGRO-21, Ivai, MSBR-17 (Sao Gabriel), OCEPAR-6, Planalto and Tiaraju. Seventy three genotypes had intermediate tolerance and 54 were non-tolerant to Al.

Rendimento e acúmulo de nutrientes pelo arroz em solução nutritiva com e sem a adição de silício

Silicon has been considered a beneficial element for plants that accumulate it, specially rice, thus it is quite common its addition to deficient soils. However, its effects seem to depend more on environmental and indirect factors related to soil and silicon sources characteristics. With the objective to study the effect of silicon as the single growth factor of rice (Oryza sativa cv. BR-IRGA 410), an experiment was carried out using nutrient solution under greenhouse conditions, with and without the addition of silicon as SiO2 (powder). Results did not show yield increase in dry matter of roots, stem + leaves and grain. Only husk yield increased with silicon addition. With silicon addition to the nutrient solution, all parts of the plant showed higher concentration of silicon but not the grains. Silicon addition significantly reduced boron and phosphorus concentrations in the roots and boron, calcium, iron and manganese concentrations in the husks. Silicon did not affect the concentration of all other nutrients in the stem + leaves and grain.

Componentes da parede celular e digestibilidade in vitro de palha de arroz (Oryza sativa) com diferentes teores de silício

Silicon (Si) is absorbed by plants and accumulated in shoot, what can affect nutritional quality of forages. The objective of this work was to evaluate the cell wall composition, estimated by FDA, FDN and lignin, and in vitro digestibility of rice shoots cultivated in nutritious solution with and without Si. There were differences in organic matter and ash contents, and there were no differences in total wall, cellulose and lignin. There were more minerals associated with cell wall of rice straw with Si, which presented less hemi-cellulose deposition in this material. Silicon did not affect in vitro digestibility of rice straw.

Composição da solução de um solo alagado conforme a profundidade e o tempo de alagamento, utilizando novo método de coleta

When collecting flooded soil solution, it is important to avoid molecular oxygen contact to prevent redox reactions that can modify its chemical composition. This work, carried out in a greenhouse, analyzed the redox status and chemical composition of an Albaqualf, in different depths and duration of flooding, aiming to propose a new methodology to collect flooded soil solution. The study was conducted using 7.0 kg plastic pots, filled with soil material from the surface layer (0-20 cm) in a completely randomized design, with three replications. The collecting device consisted of a spiral polyethylene tube (70 cm long and 0.6 cm internal diameter) with small holes (1 mm diameter), covered with a nylon filter (400 mesh) and located in soil depths at 2, 5 and 10 cm. A glass tube was connected to this device to collect the solutions. Soil was maintained flooded during 109 days and soil solution samples were collected every week. The soil solution was analyzed for Eh, pH, Mn, Fe, Ca, Mg and K. Results of the redox status and the cation values in the solution, at different times and depths, allowed to conclude that this method can be used to study the flooded soil environment although further studies are necessary.

Oxidação de ferro em raízes de dois cultivares de arroz em solução de solo inundado

Rice cropped under waterlogged conditions may present symptoms of nutritional disorders similar to those caused by iron (Fe) toxicity. The symptoms do not occur in the same intensity in all cultivars and are more frequent in modern cultivars. The aim of our study was to evaluate the plant capacity of oxidizing reduced iron (Fe2+)on the root surface in green house conditions, comparing two rice cultivars (BR IRGA 409 and EPAGRI 108) with different degrees of susceptibility to iron toxicity and two different concentrations of soluble iron. The completely randomized experimental design consisted in a factorial of 22 with an extra treatment in which the plants were maintained in nutritive solution only. In order to obtain solutions with different of Fe2+ concentrations, two kinds of soils (Gleissolo Lamico and Planossolo Hidromorfico) were used. The plants were initially cultivated in complete nutrient solution during 30 days and afterwards in solutions extracted from waterlogged soils during 24 hours. The plant oxidative capacity was estimated based on the amounts of Fe compounds on the root surface. BR IRGA 409 expressed the same oxidative capacity as the EPAGRI cultivar, therefore oxidation capacity was not the differenciating variable between the two cultivars in relation to high or low sensitivity to iron toxicity. The Planossolo solution, because of its higher Fe2+ concentration (280 mg L-1), allowed a higher accumulation of Fe oxides on roots than the less concentrated Gleyssolo solution(118 mg L-1). The oxide plaque on roots of the EPAGRI 108 cultivar, tolerant to iron toxicity, was less active in P adsorption than that of the BR IRGA 409 cultivar, considered sensitive.

ABSORÇÃO DE NUTRIENTES E CRESCIMENTO DO ARROZ COM SUPRIMENTO COMBINADO DE AMÔNIO E NITRATO

Rice is classified as an ammonium (NH4+)- tolerant plant due the predominance of this ion in flooded soils. However, in the oxygenated zones of flooded soil and in the rice rhizosphere, nitrate (NO3-) can be formed and become an important nitrogen (N) source for the crop. This experiment was carried out to evaluate the effect of different ammonium:nitrate proportions on rice development in nutrient solution. The experiment was carried out in a greenhouse, from January until February 2008 in a nutrient solution with the following NH4+: NO3- proportions: 100:0, 75:25; 50:50; 25:75 and 0:100, at 5.0 mmol L-1 N. The genotype IRGA 417 was used and the biomass production, the nitrogen, calcium, magnesium and potassium contents in tissue and xylem sap were evaluated. The presence of ammonium at the proportions 100:0 and 75:25 resulted in plant toxicity, as well as for nitrate at the proportions 25:75 and 0:100. The combined supply of ammonium and nitrate increased biomass production in relation to solely NH4+ or NO3- supply. Ammonium in solution affected negatively Ca and Mg, whereas no effect was observed on N or K tissue contents. However, in the xylem sap, both K, Ca and Mg contents were affected by ammonium. The higher total absorbed quantities of N, K, Ca, and Mg and better rice development indicated that the combined supply results in higher nutrient absorption efficiency than solely ammonium or nitrate supply.