P. A. Ferreira

Nutrient supply by mass flow and diffusion to maize plants in response to soil aggregate size and water potential

O transporte de nutrientes ate as raizes e essencialmente efetuado por fluxo de massa e difusao. O objetivo deste trabalho foi quantificar a contribuicao desses dois mecanismos na aquisicao de macronutrientes (N, P, K, Ca, Mg e S) e de micronutrientes cationicos (Fe, Mn, Zn e Cu) por plantas de milho, e o volume e a composicao do exsudato xilematico em resposta ao tamanho dos agregados e a disponibilidade de agua. O experimento foi conduzido em casa de vegetacao com amostras de um Latossolo Vermelho, retiradas sob dois sistemas de manejo: cerradao sem manejo (CER) e cultivo continuo com milho em manejo convencional por mais de 30 anos (CCM). Os tratamentos corresponderam ao arranjo fatorial [2 x (1 + 2) x 2], sendo dois sistemas de manejo (CER e CCM), (1 + 2) solo passado em peneira de 4 mm e duas classes de agregados (< 0,5 mm e entre 0,5 e 4,0 mm), e dois potenciais de agua do solo (-40 e -10 kPa). Eles foram dispostos em delineamento em blocos casualizados, com quatro repeticoes. Aos 70 dias apos a semeadura, finalizou-se o ensaio. A influencia do tamanho do agregado e do potencial de agua do solo nos mecanismos de transporte de nutrientes e maior nas amostras de solo com maiores concentracoes de nutrientes em solucao, sistema CER, tendo a difusao crescido em importância na condicao de maior disponibilidade de agua e nos agregados < 0,5 mm. O volume de exsudato xilematico colhido de plantas de milho aumenta com a diminuicao do tamanho do agregado e com o aumento da disponibilidade de agua do solo, no sistema CER. As maiores concentracoes de Ca e Mg no exsudato xilematico das plantas cultivadas em amostras retiradas do sistema CER, dependeram das altas concentracoes desses nutrientes na solucao do solo neste sistema de manejo.

Determinação de regiões homogêneas quanto à distribuição de freqüência de chuvas no leste do Estado de Minas Gerais

Hydroclimatically homogeneous areas in relation to the frequency distribution of daily rainfalls were characterized in the hydrographic area of the Atlântico eastern part, in the State of Minas Gerais, Brazil. The hydroclimatically homogeneous areas were delimited through the methodologies of multivariate statistical analyses (rotated principal components analyses and clustering analysis). The method of clustering analysis proposed by Ward was used, because it provided the best space distribution of the groups. The results indicated five and three groups for, respectively, the meso and macro scale hydro climatic classification criteria, in the studied area.

Sistemas de drenagem agrícola. Parte I: desenvolvimento do modelo e análise de sensibilidade

Este trabalho contempla o desenvolvimento de um modelo computacional, visando suprir as principais lacunas em relacao aos modelos existentes, e realizar analise de sensibilidade, objetivando verificar o efeito dos parâmetros de entrada sobre os resultados obtidos pela aplicacao do modelo. O modelo contabiliza diariamente os principais componentes do balanco hidrico em um volume de controle de base unitaria e altura igual a distância entre a superficie do solo e a camada impermeavel, situado a meia distância entre dois drenos paralelos, a mesma profundidade simulando, assim, a movimentacao do lencol freatico. O modelo utiliza funcoes de producao que consideram o estresse causado por excesso e por falta de agua na zona radicular, realiza analise economica para diversas configuracoes do sistema de drenagem determinando-se, entao, o espacamento economico entre drenos, alem de informar sobre a viabilidade economica do empreendimento. Com a analise de sensibilidade, verificou-se que os parâmetros profundidade media dos drenos, condutividade hidraulica horizontal do solo saturado, porosidade drenavel, parâmetros climaticos, coeficiente CN e custo de instalacao dos drenos subterrâneos, exercem maior influencia no calculo do espacamento economico entre drenos.

Transporte do amônio em colunas com agregados de um latossolo vermelho distrófico

To describe the transport of the ammonium ion in different classes of aggregates of a typic Haplortox, a laboratory experiment was carried out. The treatments corresponded to a 3 x 5 factorial, being three sources of NH 4 + [(NH 4 ) 2 SO 4 , NH 4 Cl, and NH 4 NO 3 ] and five aggregate classes (2.0-1.0, 1.0-0.5, 0.5-0.25, 0.25-0.105, and <0.105 mm). The experimental unit was a glass column saturated, under vacuum to which was applied a CaCl 2 0.005 mole L -1 solution. After saturation, the same solution was applied until constant percolation, followed by a seven pore volume pulse of solution of respective source - 0.01 mole L -1 NH 4 + (C o ). Fractions of the effluent, corresponding to 0.3 pore volume (p), were collected, and the NH 4 + concentrations were determined (C). C/C o relationships were calculated for every p fraction, and the experimental elution curves were traced. The highest retardation factors were calculated for the smallest aggregates, indicating a larger retention of ammonium, and the almost superimposed theoretical curves showed the predominance of the dispersive transport for ammonium. The NH 4 + percolation was not affected by the studied anions in the different aggregates classes.To describe the transport of the ammonium ion in different classes of aggregates of a typic Haplortox, a laboratory experiment was carried out. The treatments corresponded to a 3 x 5 factorial, being three sources of NH4 + [(NH4)2SO4, NH4Cl, and NH4NO3] and five aggregate classes (2.0-1.0, 1.0-0.5, 0.5-0.25, 0.25-0.105, and <0.105 mm). The experimental unit was a glass column saturated, under vacuum to which was applied a CaCl2 0.005 mole L -1 solution. After saturation, the same solution was applied until constant percolation, followed by a seven pore volume pulse of solution of respective source 0.01 mole L-1 NH4 + (Co). Fractions of the effluent, corresponding to 0.3 pore volume (p), were collected, and the NH4 + concentrations were determined (C). C/Co relationships were calculated for every p fraction, and the experimental elution curves were traced. The highest retardation factors were calculated for the smallest aggregates, indicating a larger retention of ammonium, and the almost superimposed theoretical curves showed the predominance of the dispersive transport for ammonium. The NH4 + percolation was not affected by the studied anions in the different aggregates classes.

Transporte de fósforo e de potássio em colunas com agregados de um latossolo vermelho distrófico

The objective of this work was to compare the diffusive-dispersive coefficients of phosphorus and potassium as well as to describe nutrient transport in different aggregate classes of a typic Haplortox, cultivated with maize over several years, by applying two theoretical models. The experiment was carried out using percolation columns and five classes of aggregate sizes (2.0-1.0, 1.0-0.5, 0.5-0.25, 0.25-0.105 and < 0,105 mm). The elution column consisted of a glass column with 2 cm internal diameter and 30 cm length, filled up with aggregates until 10 cm from the upper boundary. All columns were saturated with a 0.005 mol L-1 CaCl2 solution, under vacuum. The velocity of the effluent was controlled and kept near that obtained for the smallest aggregate class. The saturation solution was applied until reaching a steady flow. Then a slug of a 0.05 mol L-1 KH2PO4 (Co) solution was applied. In the collected effluent, concentration of phosphorus and potassium (C) was determined, which permitted to obtain the C/Co ratio as a function of the pore-volume number of the percolated solution. This allowed to obtain the experimental curve for these elements, which was compared with the theoretical breakthrough curves estimated by the two models; one of them considers only the dispersive transport while the other one considers the diffusive-dispersive transport. The diffusive-dispersive coefficient was higher for potassium than for phosphorus in those classes with greater-diameter aggregates. The opposite occurred in the smallest classes, which indicates that phosphorus moved faster than potassium in those aggregate columns, under the studied conditions. The model accounting only for the dispersive flow presented a better prediction for phosphorus and potassium transportation in all aggregate classes. The theoretical curves showed a better description for potassium than for phosphorus transport.

Ammonium transport in columns with aggregates of a typic of a haplortox

To describe the transport of the ammonium ion in different classes of aggregates of a typic Haplortox, a laboratory experiment was carried out. The treatments corresponded to a 3 x 5 factorial, being three sources of NH 4 + [(NH 4 ) 2 SO 4 , NH 4 Cl, and NH 4 NO 3 ] and five aggregate classes (2.0-1.0, 1.0-0.5, 0.5-0.25, 0.25-0.105, and <0.105 mm). The experimental unit was a glass column saturated, under vacuum to which was applied a CaCl 2 0.005 mole L -1 solution. After saturation, the same solution was applied until constant percolation, followed by a seven pore volume pulse of solution of respective source - 0.01 mole L -1 NH 4 + (C o ). Fractions of the effluent, corresponding to 0.3 pore volume (p), were collected, and the NH 4 + concentrations were determined (C). C/C o relationships were calculated for every p fraction, and the experimental elution curves were traced. The highest retardation factors were calculated for the smallest aggregates, indicating a larger retention of ammonium, and the almost superimposed theoretical curves showed the predominance of the dispersive transport for ammonium. The NH 4 + percolation was not affected by the studied anions in the different aggregates classes.To describe the transport of the ammonium ion in different classes of aggregates of a typic Haplortox, a laboratory experiment was carried out. The treatments corresponded to a 3 x 5 factorial, being three sources of NH4 + [(NH4)2SO4, NH4Cl, and NH4NO3] and five aggregate classes (2.0-1.0, 1.0-0.5, 0.5-0.25, 0.25-0.105, and <0.105 mm). The experimental unit was a glass column saturated, under vacuum to which was applied a CaCl2 0.005 mole L -1 solution. After saturation, the same solution was applied until constant percolation, followed by a seven pore volume pulse of solution of respective source 0.01 mole L-1 NH4 + (Co). Fractions of the effluent, corresponding to 0.3 pore volume (p), were collected, and the NH4 + concentrations were determined (C). C/Co relationships were calculated for every p fraction, and the experimental elution curves were traced. The highest retardation factors were calculated for the smallest aggregates, indicating a larger retention of ammonium, and the almost superimposed theoretical curves showed the predominance of the dispersive transport for ammonium. The NH4 + percolation was not affected by the studied anions in the different aggregates classes.

Ammonium transport in columns with aggregates of a dystrophic red latosol.

To describe the transport of the ammonium ion in different classes of aggregates of a typic Haplortox, a laboratory experiment was carried out. The treatments corresponded to a 3 x 5 factorial, being three sources of NH 4 + [(NH 4 ) 2 SO 4 , NH 4 Cl, and NH 4 NO 3 ] and five aggregate classes (2.0-1.0, 1.0-0.5, 0.5-0.25, 0.25-0.105, and <0.105 mm). The experimental unit was a glass column saturated, under vacuum to which was applied a CaCl 2 0.005 mole L -1 solution. After saturation, the same solution was applied until constant percolation, followed by a seven pore volume pulse of solution of respective source - 0.01 mole L -1 NH 4 + (C o ). Fractions of the effluent, corresponding to 0.3 pore volume (p), were collected, and the NH 4 + concentrations were determined (C). C/C o relationships were calculated for every p fraction, and the experimental elution curves were traced. The highest retardation factors were calculated for the smallest aggregates, indicating a larger retention of ammonium, and the almost superimposed theoretical curves showed the predominance of the dispersive transport for ammonium. The NH 4 + percolation was not affected by the studied anions in the different aggregates classes.To describe the transport of the ammonium ion in different classes of aggregates of a typic Haplortox, a laboratory experiment was carried out. The treatments corresponded to a 3 x 5 factorial, being three sources of NH4 + [(NH4)2SO4, NH4Cl, and NH4NO3] and five aggregate classes (2.0-1.0, 1.0-0.5, 0.5-0.25, 0.25-0.105, and <0.105 mm). The experimental unit was a glass column saturated, under vacuum to which was applied a CaCl2 0.005 mole L -1 solution. After saturation, the same solution was applied until constant percolation, followed by a seven pore volume pulse of solution of respective source 0.01 mole L-1 NH4 + (Co). Fractions of the effluent, corresponding to 0.3 pore volume (p), were collected, and the NH4 + concentrations were determined (C). C/Co relationships were calculated for every p fraction, and the experimental elution curves were traced. The highest retardation factors were calculated for the smallest aggregates, indicating a larger retention of ammonium, and the almost superimposed theoretical curves showed the predominance of the dispersive transport for ammonium. The NH4 + percolation was not affected by the studied anions in the different aggregates classes.