Paulo Regis Ferreira da Silva

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.

Leaf relative chlorophyll content as an indicator parameter to predict nitrogen fertilization in maize

The development of a portable chlorophyll meter (SPAD 502), that takes instantaneous measurements of greenness without leaf destruction, has emerged as a new tool to assess plant N status. This trial was carried out to determine the adequate SPAD readings to predict maize nitrogen needs in four growth stages. The experiment was conducted in the state of Rio Grande do Sul, southern Brazil, during the 1998/ 99 growing season. Treatments were two maize hybrids (Pioneer 32R21 and Cargill 901) and nine side-dressed nitrogen levels (0, 50, 100, 150, 200, 300, 400, 500 and 600kg ha -1 ). Nitrogen was side-dressed at the soil surface in four equal doses, according to the levels established on each treatment. The first, second, third and fourth applications were made in the stages of three to four, six to seven, 10 to 11 and 14 to 15 fully expanded leaves, respectively. Urea was used as the N source. Since there was no difference in the SPAD readings among maize hybrids, average values at each stage were used. Readings were carried out in the stages of three to four, six to seven, 10 to 11 fully expanded leaves and at silking. Chlorophyll evaluation samples were taken at twothirds of the distance from the leaf tip towards the stem. The two upper leaves were sampled on each growth stage before maize flowering. The index leaf (first leaf below the ear) was evaluated during silking. Chlorophyll meter readings above 45.4, 52.1, 55.3, and 58.0 represented the adequate values for the stages of three to four, six to seven, 10 to 11 expanded leaves and at silking, respectively, to achieve high grain yield. The variation in SPAD readings were highest in the early stages of plant growth.

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.

Grain yield and kernel crude protein content increases of maize hybrids with late nitrogen side-dressing

Physiological changes incorporated into current maize hybrids suggest the occurrence of modifications in the nitrogen uptake dynamics, improving plant ability to uptake N during grain filling. This may justify late N side-dressing whenever environmental constraints prevent adequate nitrogen supply during crops vegetative development. This study evaluates effects of nitrogen fertilization at booting and silking on grain yield and kernel crude protein contents of commercial maize hybrids. Two experiments were set up in Eldorado do Sul, RS, during the 2001/2002 and 2002/2003 growing seasons. In 2001/2002, treatments were composed of two hybrids (Agroceres 303 and Pioneer 32R21), three nitrogen rates applied during maize vegetative development (30, 80 and 130 kg ha -1 ) and three nitrogen rates applied at silking (0, 50 and 100 kg ha -1 ). In 2002/2003, four hybrids (Agroceres 303, Pioneer 32R21, Dekalb 215 and Syngenta Penta) and four nitrogen rates side-dressed at booting (0, 50, 100 and 150 kg.ha -1 ) were assessed. There were significant increments in grain yield and kernel crude protein content with nitrogen fertilization at booting and silking. Grain yield response to late N side-dressing differed among cultivars. The impact of nitrogen fertilization at silking was higher at the smallest rate of N during the plant vegetative development. Enhancements in grain yield with late N side-dressing resulted from increases in grain weight. Modern hybrids can uptake nitrogen during silking, contradicting the hypothesis that late N side-dressing is not efficient to improve maize grain yield.

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.

Maize response to nitrogen fertilization timing in two tillage systems in a soil with high organic matter content

No-tillage systems, associated to black oat as preceding cover crop, have been increasingly adopted. This has motivated anticipated maize nitrogen fertilization, transferring it from the side-dress system at the stage when plants have five to six expanded leaves to when the preceding cover crop is eliminated or to maize sowing. This study was conducted to evaluate the effects of soil tillage system and timing of N fertilization on maize grain yield and agronomic efficiency of N applied to a soil with high organic matter content. A three-year field experiment was conducted in Lages, state of Santa Catarina, from 1999 onwards. Treatments were set up in a split plot arrangement. Two soil tillage systems were tested in the main plots: conventional tillage (CT) and no-tillage (NT). Six N management systems were assessed in the split-plots: S1 - control, without N application; S2 - all N (100 kg ha-1) applied at oat desiccation; S3 - all N applied at maize sowing; S4 - all N side-dressed when maize had five expanded leaves (V5 growth stage); S5 - 1/3 of N rate applied at maize sowing and 2/3 at V5; S6 - 2/3 of nitrogen rate applied at maize sowing and 1/3 at V5. Maize response to the time and form of splitting N was not affected by the soil tillage system. Grain yield ranged from 6.0 to 11.8 t ha-1. The anticipation of N application (S2 and S3) decreased grain yield in two of three years. In the rainiest early spring season (2000/2001) of the experiment, S4 promoted an yield advantage of 2.2 t ha-1 over S2 and S3. Application of total N rate before or at sowing decreased the number of kernels produced per ear in 2000/2001 and 2001/2002 and the number of ears produced per area in 2001/2002, resulting in reduced grain yield. The agronomic efficiency of applied N (kg grain increase/kg of N applied) ranged from 13.9 to 38.8 and was always higher in the S4 than in the S2 and S3 N systems. Short-term N immobilization did not reduce grain yield when no N was applied before or at maize sowing in a soil with high organic matter content, regardless of the soil tillage system.

Sistemas de coberturas de solo no inverno e seus efeitos sobre o rendimento de grãos do milho em sucessão

The black oats use (Avena strigosa) as species of soil covering in the winter, cause immobilization of the nitrogen (N), that reduces the plant development and grain yield of maize cultivated in succession. Thus, the black oat intercropped systems with leguminous as common vetch (Vicia sativa) and brassicas as oilseed radish (Raphanus sativus) is aimed at increasing nitrogen (N) disponibility in the system and the permanence timing of its residues in the soil. Two experiments were carried out in the growth seasons of 2001/2002 and 2002/2003, in Rio Grande do Sul, Brazil. The first one was aimed at evaluating the effect of three winter species of soil covering, grown as a single culture and as intercropped crops on maize grain yield, with and without nitrogen side-dressed. The second one was aimed at determining the most adequate seed ratio of oilseed radish and black oat in intercropped systems, as soil covering crops in the winter preceding maize, under different nitrogen levels side-dressed. In Experiment I, treatments were composed by N application of 180kg ha-1, a control without N side-dressed and seven winter soil covering systems. In the Experiment II, treatments consisted of two levels of N side-dressing application in maize, a control without N side-dressed, and of three seed ratio of oilseed radish and black oat, as single and as intercropped crops and a control without crop in the winter. In all intercropped systems, independently of seed ratio used, the oilseed radish was mostly responsible for the yield of dry mass of the systems. The intercropped systems of common vetch or oilseed radish with black oat minimize the negative effect of oat on maize grain yield cultivated in succession in systems with low N availability and, even with high N supply, maize grain yield also increases when grown after common vetch.

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

Desempenho agronômico e econômico do milho em diferentes níveis de manejo e épocas de semeadura

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