Gilber Argenta

Clorofila na folha como indicador do nível de nitrogênio em cereais

The development of a portable chlorophyll meter, which allows instantaneous measurement without leaf destruction, has been used as a new tool to assess plant N status. The reading in the equipment indicates a relationship with leaf chlorophyll and they are calculated based on the emission of light quantity through of the leaf in two wavelengths with different chlorophyll absorbance. Some researchers have established association between SPAD reading and chlorophyll content and between chlorophyll content and plant N content. In rice, wheat, oat and maize there were determined good associations between SPAD reading and grain yield. The critical level of a portable chlorophyll meter, correspondent with adequated N level, determined in rice (panicle differentiation), wheat (leaf flag) and maize (silking) are of, respectively, 40-42, 41-42 and 58-62. However, since it is a new tool, this equipment presents some limitations such as: little variation between readings, the readings are influenced by other factors besides N and, especifically for maize, to present low correlation with grain yield in the initial stages of plant development. These limitations were be to solve or minimize through the utilization of correction factores such as the use of strip reference, specific leaf weight, leaf area and plant dry matter. Despite of the limitations presented, the use of the leaf chlorophyll content shows high potential as an indicator for nitrogen fertilization recommendation in cereals, especially if associate as soil indicators.

Resposta de híbridos simples de milho à redução do espaçamento entre linhas

The objective of this work was to determine the effects of using narrow row spacing on grain yield, grain components and on other agronomic traits of maize single-cross hybrids. Two experiments were conducted in the state of Rio Grande do Sul, Brazil. In the 1997/98 growing season, treatments were composed by two singlecross hybrids (Cargill901 and BraskalbXL212) and four row spacings (40, 60, 80 and 100 cm). In the 1998/99growing season, two single-cross hybrids were tested at two plant densities (50,000 and 65,000pl./ha) and four row spacings (40, 60, 80 and 100 cm). Maize grain yield was influenced by hybrid and plant density. The reduction in row spacing promoted a high grain yield specially for hybrids with a low plant height sown at the density of 50,000pl./ha.

Bases morfofisiológicas para maior tolerância dos híbridos modernos de milho a altas densidades de plantas

O lancamento de hibridos de milho tolerantes ao aumento da densidade de plantas contribuiu para o incremento do potencial produtivo da cultura na segunda metade do seculo XX. Objetiva-se com esta revisao de literatura discutir caracteristicas morfologicas, fisiologicas, fenologicas e alometricas que contribuiram para maior adaptacao do milho a elevadas densidades de plantas. Os processos de selecao utilizados pelos melhoristas minimizaram a natureza protândrica da planta, reduzindo o tamanho do pendao. Isso propiciou desenvolvimento alometrico mais equilibrado entre as inflorescencias masculina e feminina, limitou a esterilidade feminina e favoreceu a sincronia entre antese e espigamento. O ideotipo de planta compacto dos hibridos modernos, caracterizado pela presenca de plantas baixas, com menor numero de folhas e folhas eretas, melhorou a qualidade da luz no interior do dossel, contribuindo para reduzir a dominância apical do pendao sobre as espigas. A menor producao de fitomassa reduziu a competicao intra-especifica e aumentou a eficiencia de uso dos fatores ambientais, disponibilizando mais carboidratos para atender as diferentes demandas da planta na fase reprodutiva. O maior equilibrio nas relacoes entre fonte e dreno contribuiu para retardar a senescencia foliar, resultando em maior absorcao de nutrientes e maior eficiencia de uso do nitrogenio. O desenvolvimento de hibridos com menor estatura e espigas mais proximas do solo reduziu a quantidade de plantas acamadas e quebradas. A compreensao das bases morfofisiologicas responsaveis pela maior tolerância do milho a competicao intra-especifica auxiliara melhoristas e fisiologistas a maximizar a eficiencia do arranjo de plantas para alcancar altos rendimentos. Palavras-chave: Zea mays, estresse, populacao, rendimento de graos.

Resposta de híbridos de milho irrigado à densidade de plantas em três épocas de semeadura

A determinacao da densidade otima de semeadura do milho, alem de ser influenciada pelas caracteristicas dos hibridos, pelo nivel de fertilidade do solo e pela disponibilidade hidrica, pode tambem variar de acordo com a epoca da semeadura, uma vez que ela afeta o crescimento e desenvolvimento da planta. Com o objetivo de determinar a densidade otima de planta em hibridos de milho com elevado potencial de rendimento de graos, em tres epocas de semeadura, com relacao a rendimento de graos, componentes do rendimento e outras caracteristicas agronomicas, foram feitos quatro experimentos na regiao fisiografica da Depressao Central do Rio Grande do Sul, municipio de Eldorado do Sul, com suplementacao hidrica por aspersao. Os tratamentos constaram de quatro hibridos (Pioneer 3063, Pioneer 3207, XL 212 e Cargill 901), quatro densidades de plantas (50, 70, 90 e 110.000 pl/ha) e de tres epocas de semeadura (agosto, outubro e dezembro). Nao ha resposta a densidade de plantas dos hibridos de milho testados nas epocas de semeadura de agosto e dezembro. O aumento na densidade de plantas somente foi vantajosa na semeadura de outubro, quando se obtiveram maiores rendimentos de graos na densidade de 70.000 pl/ha, independentemente do hibrido avaliado, nas duas estacoes de crescimento.

Níveis de manejo na cultura do milho em dois ambientes contrastantes: análise técnico-econômica

The cropping strategies used on different maize production systems aim to maximize technically and economically the growers profit at each environmental condition. However, they do not allow a comparative analysis among different management strategies at an specific place neither provide the evaluation of their efficiency at different environments. This work was carried out to assess the technical and economical return of five maize management strategies at two contrasting environments. Two experiments were conducted in Southern Brazil during the growing season of 2000/2001: one in Eldorado do Sul, Rio Grande do Sul, and the other in Lages, Santa Catarina. Five production systems, corresponding to different management levels and grain yield expectations, were tested at each experimental site. S1, S2 and S3 represented management levels to obtain low (< 3 ton ha-1), medium (from 3 to 6 ton ha-1) and high grain yield, respectively. S4 and S5 were designed to optimize grain yield. The grain yield and gross income per hectare increased with the improvement in management strategies at both study sites. In Eldorado do Sul, it ranged from 3.0 to 15.0 t ha-1 and R

Efeitos do manejo mecânico e químico da aveia-preta no milho em sucessão e no controle do capim-papuã

104.86 to R

Sistemas consorciados de aveia preta e ervilhaca comum como cobertura de solo e seus efeitos na cultura do milho em sucessão

724.77. In Lages, it varied from 3.2 a 15.9 t ha-1 and 131.27 to 1,093.25. Maize presented higher economical return in Lages than in Eldorado do Sul, specially in the cropping systems proposed to optimize grain yield.

Manejo do nitrogênio no milho em semeadura direta em sucessão a espécies de cobertura de solo no inverno e em dois locais: II - efeito sobre o rendimento de grãos

n†The objective of this experiment was to evaluate the effects of mechanical and chemical management of oat straw and of sowing dates of maize after oat desiccation on maize grain yield and on alexandergrass (Brachiaria plantaginea Link) infestation. In 1997/98, treatments were composed by two mechanical management systems of oat (rolled or not) and bare area as the control, by two herbicides (glyphosate and paraquat) applied to desiccate oat straw and by two maize sowing dates after desiccation (one and 15 days). In the 1998/99†growing season, five management systems of oat straw (rolled, cleared and desiccated with glyphosate, glufosinate and paraquat) and a bare area used as check were tested. Delay of maize sowing date in 15 days after oat straw desiccation increased N accumulation, dry matter production per plant and grain yield of maize. Maize grain yield in succession to oat was not influenced by management system of oat straw. Rolling oat straw provided the best control of alexandergrass infestation.

Adubação nitrogenada em milho implantado em semeadura direta após aveia preta

With the increase of corn cultivation under the no-tillage system, various cover crop species have been evaluated to obtain a soil cover that benefits corn under succession and no-tillage. The objective of this work was to evaluate the effect of three sowing densities of black oat (Avena strigosa Scheig) and common vetch (Vicia sativa) in associated crops and as isolated crops and three levels of nitrogen fertilization (N), applied on corn (0, 60 and 160 kg ha-1 of N). Dry matter yield of the cover crop species was similar in associated systems and as isolated crops. The increase in the amount of N applied and the increase in the proportion of common vetch seeds in the associated systems increased the amount of N accumulated by corn plants. There was no interaction between the amount of N applied and the soil cover systems for corn grain yield. Without N fertilization, corn grain yield increased 321 kg ha-1 for each 10% of substitution of oat for common vetch in the associated systems. With 60 kg ha-1 of N, the response was quadratic. With the 160 kg ha-1 of N, there was no effect of soil cover on corn grain yield. Grain yield of corn cultivated after oat as isolated crop or associated with common vetch increased linearly with the increase of the amount of N fertilizer applied in corn. Under succession, using common vetch as an isolated crop, there was no response of corn grain yield to N fertilization.

Nitrogen management in maize in no-till system in succession to winter cover crops at two locations: II - effect on grain yield

The permanence of cultural residues on soil surface modifies the processes of immobilization and mineralization, reducing N availability to maize, especially in succession to grasses. The objective this study was to evaluate, in two locations, the effects of rate and timimg of N application in maize (0-0; 0-160; 30-130 and 60-100kg/ha, respectively, at sowing and sidedressed), in no-till system, established in two sowing dates after desiccation (1 and 20 days) of two winter cover crops (black oat and common vetch) and bare area without weeds, on N uptake. The research was conducted at two locations of the state of Rio Grande do Sul, Brazil, in the 1996/97 growing season. In Eldorado do Sul, N application at sowing was beneficial because it increased N uptake in relation to the treatment with total N sidedressed, regradless of the species of winter crop tested. At Passo Fundo, only in the stage of 3-4 leaves there was advantage of N application at sowing in relation to total sidedressed application. In the stages of 6-7 leaves, 10-11 leaves and of tasseling there were no differences among the treatments with N application. The delay of maize sowing date after desiccation in 20 days is a management practice that could be used, specially when maize follows black oat, since it increased, at the average at the N management systems, 54 e 75% N uptake, respectively in Eldorado do Sul and in Passo Fundo. N uptake by maize in succession to black oat was lower at Eldorado do Sul that in Passo Fundo, in all stages of development tested. The increment of N rate from 30 to 60 kg/ha did not increase N uptake by maize plants, regardless of cover crop in the winter.