Valterley Soares Rocha

Doses e formas de aplicação de nitrogênio no desenvolvimento e produção da cultura do trigo

Objetivou-se avaliar o efeito de doses e formas de aplicacao de nitrogenio sobre o desempenho e producao de duas cultivares de trigo. O experimento, conduzido em Vicosa-MG, de maio a setembro de 2005, foi instalado segundo um esquema fatorial 2x2x5 no delineamento de blocos casualizados, com quatro repeticoes. Os tratamentos avaliados consistiram da combinacao das cultivares de trigo, BRS 210 e Pioneiro, duas formas de aplicacao de adubo nitrogenado (dose total aplicada por ocasiao da semeadura ou 20 kg ha-1 na semeadura e o restante em cobertura no inicio da fase de perfilhamento) e cinco doses de nitrogenio (40, 60, 80, 100 e 120 kg ha-1) tendo como fonte o sulfato de amonio. A cultivar Pioneiro apresentou maior potencial produtivo que a cultivar BRS 210, mas foi menos resistente ao acamamento. O parcelamento da adubacao nitrogenada proporcionou maior acamamento e nao trouxe beneficios a produtividade dos graos. As doses de N promoveram resposta quadratica da produtividade dos graos, com ponto de maxima estimado na dose de 96,8 kg ha-1 e, aumento linear do acamamento de plantas da cultivar Pioneiro.

Effect of Nitrogen and Trinexapac-Ethyl Rates on the SPAD Index of Wheat Leaves

ABSTRACT The objective of this study was to evaluate the effect of nitrogen (N) and trinexapac-ethyl (TE) rates on the SPAD index in wheat flag leaf. The treatments were five N rates (30, 60, 90, 120, 150 kg ha−1) combined with four TE rates (0, 63, 125, 188 g ha−1). The experiment was carried out in a randomized block design with four repetitions. SPAD index, leaf N content and grain yield showed quadratic response to the increase in N rates, whereas area, wet and dry weight of flag leaf presented linear increase. TE caused linear increase in SPAD index, linear decrease in leaf area, reduction in grain yield with smaller N rates and increase with larger N rates. The N content, and the wet and dry weight of flag leaf were not affected by TE. SPAD calibration to estimate N status in wheat should be specific for each TE rate.

Análise de trilha para componentes do rendimento e caracteres agronômicos de trigo sob desfolha

The objective of this work was to evaluate the influence of yield components and plant characters in grain production, in wheat under defoliation, through correlations decomposition using path analysis. The experiment was accomplished in Vicosa, MG, Brazil, in 2004. The treatments consisted of three levels of defoliation and a control, with three wheat varieties - Anahuac, BRS 207 and BR 24 -, with four replicates. Defoliation was carried out by removing the blade of flag leaves from the second and third top leaves. The following parameters were evaluated: grain yield, hectolitric weight, one thousand-grain weight, number of spikes per plot, number of grain per spike, culm dry biomass, spike-straw dry biomass, total dry biomass, grain yield per spike, total dry biomass of individual culm, straw dry biomass of individual spike and total dry biomass per individual plant. The reduction in culm dry biomass led to lower losses of grain yield because of the higher remobilization of photoassimilates with defoliation. Thousand-grain weight and number of grain per spike were the main yield components. The direct selection for these characters is an efficient strategy to increase grain yield in wheat under defoliation.

Desempenho de genitores e populações segregantes de trigo sob estresse de calor

A expansao da triticultura para areas com temperaturas mais elevadas, como o Brasil-Central, constitui-se uma das principais medidas para diminuir a importacao de trigo. Assim, genotipos tolerantes ao calor serao de extrema importância para elevar a produtividade desta cultura. Objetivou-se com este trabalho detectar variabilidade genetica para tolerância ao calor, identificar populacoes e genitores mais tolerantes e quantificar o efeito de altas temperaturas sobre estes genotipos de trigo. Foram realizados dois experimentos em Vicosa (MG), utilizando-se o delineamento latice quadrado 16x16 com duas repeticoes, composto por 240 familias oriundas de oito populacoes segregantes mais 16 genitores. No primeiro experimento, semeado em fevereiro de 2007 (verao), foram avaliadas familias F2:4 e no segundo, em junho de 2007 (inverno), familias F2:5. Avaliaram-se os caracteres floracao, altura de planta, producao de graos e massa de mil graos. Diferencas de temperatura da emergencia ao florescimento foram determinantes na resposta dos genotipos entre os ambientes. Detectou-se variabilidade genetica para tolerância ao calor entre genitores e populacoes segregantes de trigo. Todos os caracteres avaliados tiveram reducao sob altas temperaturas, sendo a producao de graos o carater mais afetado, seguido da altura, floracao e massa de mil graos. Os genotipos mais tolerantes ao calor foram os genitores BR 24, Alianca e EP 93541 e as populacoes segregantes BH1146/BR24// Alianca/EP93541, BR24/Alianca//EP93541/CPAC9662 e Alianca/EP93541// CPAC9662/Pioneiro.

Rates of urea with or without urease inhibitor for topdressing wheat

The urease inhibitor NBPT(N-(n-butyl) thiophosphoric triamide) is a management alternative to increase urea efficiency in topdressing because it reduces NH3 volatilization. The objective of this study was to evaluate N recovery and yield performance of wheat ( Triticum aestivum L.) ‘BRS 254’ fertilized with different urea or urea + NBPT rates in topdressing. The experiment was conducted from May to September 2007 in Vicosa, Minas Gerais, Brazil. Treatments followed a 5 × 2 + 1 factorial design consisting of five N fertilizer rates (30, 60, 90, 120, and 150 kg ha-1) as urea or urea + NBPT (Agrotain® ) applied as topdressing and a control without N. The experiment was a randomized complete block design with four replicates. Adding NBPT to urea resulted in better N utilization by wheat plants. The 100 kg N ha-1 topdressing rate provided the best apparent N recovery by wheat plants, whereas 90 kg ha-1 provided the best N use efficiency.

Rates of nitrogen and growth retardant trinexapac-ethyl on wheat

The objective in this study was to evaluate the effects of nitrogen rates in association with rates of the growth retardant trinexapac-ethyl on wheat. The experiment was conducted in Vicosa, MG and arranged in a 5×4 factorial, randomized block design, with four repetitions. A combination of five nitrogen rates (30, 60, 90, 120 and 150kg ha-1) with four rates of trinexapac-ethyl (0, 62.5, 125 and 187.5g ha-1) were tested. Trinexapac-ethyl promotes reduction of soot dry mass and grain yield at the lowest N rates, but at the highest N rates there is increase in these characteristics. The combination between N and trinexapac-ethyl rates that promotes higher shoot dry mass is 150kg ha-1 and 187g ha-1 but that promotes higher grain yield is 100kg ha-1 and 120g ha-1, respectively.

Urease inhibitor (NBPT) and efficiency of single or split application of urea in wheat crop

O NBPT (N-(n-butil) tiofosforico triamida) e uma substância inibidora da urease, que se vem apresentando como das mais promissoras para a maximizacao do uso do nitrogenio da ureia em sistemas agricolas. O objetivo deste estudo foi avaliar o desempenho produtivo do trigo irrigado, submetido a fertilizacao com ureia ou ureia+NBPT aplicadas em dose unica ou parcelada. O experimento foi conduzido, de junho a outubro de 2006, em Vicosa-MG, Brasil. Seguiu-se o esquema fatorial 2×2, em que a ureia ou ureia+NBPT foram combinadas com duas formas de aplicacao: dose total na semeadura (60kg ha-1) ou parcelada (20kg ha-1 na semeadura + 40kg ha-1, em cobertura, no perfilhamento). O delineamento experimental foi o de blocos ao acaso com dez repeticoes. Conclui-se que o parcelamento da fertilizacao nitrogenada nao promove incremento de produtividade do trigo, sob as condicoes de cultivo empregadas; o uso de inibidor de urease aumenta a produtividade da cultura do trigo, quando a ureia e aplicada, em cobertura, durante o perfilhamento, mas, seu uso nao promove aumento da produtividade quando a ureia e aplicada no sulco, durante a semeadura.

Tolerância ao estresse térmico em genótipos de trigo

The objective of this work was to verify the effect of thermic stress conditions on the wheat culture, to evaluate the tolerance level of parents and segregant populations to these conditions, as well as to identify promising populations in order to obtain lines adapted to the Brazilian Central region. A circulant dialel was used among eight parents, comprising the cultivars Alianca, Anahuac, BH 1146, BR 24, BRS 207 and Pioneiro; and the lines CPAC 9662 and EP 93541. Thirty F2:4 families descending from the eight segregant populations and the eight genitors were evaluated. Experiments were carried out in the field and the sowings were performed in the summer (heat stress condition) and winter (favorable condition) of 2004. The lattice design with two replicates was used. Days to heading, plant height, average grain weight, and grain yield were evaluated. In the summer, high temperature reduced all characters evaluated, and thermic stress effects were determined by that reduction percent in comparison to winter cropping values. Differences among genotypes in both sowing dates were also observed. The most heat-tolerant materials were the parents Anahuac, BH 1146, BR 24 and EP 93541, and the segregant populations Alianca/EP 93541, EP 93541/CPAC 9662, and BH 1146/BR 24.

Growth retardants in wheat and its effect in physiological quality of seeds

Plant lodging in wheat has been controlled through growth retardants. However, there is lack of information on the effect of these products on the physiological quality of seeds. The objective of this study was to evaluate the physiological quality of wheat seeds obtained under different rates and application times of three growth retardants. The trial was carried out in Vicosa-MG, from May to September 2005, in a factorial and hierarchical scheme, in randomized block design with four replications and a control treatment. The treatments consisted of 500, 1000 and 1500g ha-1 of chlormequat; 40, 80 and 120g ha-1 of paclobutrazol and 62.5, 125 and 187.5g ha-1 of trinexapac-ethyl applied at the 6 or 8 growth stage based on the scale of Feeks and Large, and a control treatment without growth retardant application. Leaf application of growth retardants as chlormequat, paclobutrazol and trinexapac-ethyl did not affect the germination and vigor of wheat seeds.