Mércio Luíz Strieder

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.

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.

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

The objective of this work was to evaluate agronomic and economic performance of maize in five management levels and three sowing times. The experiment was conducted in 2001/2002 and 2002/2003, in Eldorado do Sul, RS, Brazil. Treatments consisted of three sowing times (August, October and December) and five management levels (low, average, high, potential I and II) which varied in relation to the soil winter cover, cultivar, plant arrangement and the level of chemical fertilizer, water supply and weed, insect and disease control. A randomized block design was used with split-plots and four replications. Sowing times were located in the main plots and the management level in the split-plots. The increments in maize yield in response to investments in management and cultivar were higher in August and October, and resulted in higher economic return, mainly in October. In December sowing, there was no economic return for the highest investment in management level. In August and October, it was possible to associate maximal economic and technical efficiencies through the management level increase and the choice of the greater potential yield cultivar. Index terms: Zea mays, agronomic and economic efficiency, cultivars, water regime, grain yield, gross margin.

Estratégias de manejo de coberturas de solo no inverno para cultivo do milho em sucessão no sistema semeadura direta

The no-tillage system is adopted by most of the farmers in Rio Grande do Sul, Southern Brazil. No-till system requires no ploughing and only a narrow and superficial band or slot is opened in the soil to allow sowing. The sustainability of this system is dependent on a diversified system of crop rotation and succession able to leave on the soil an adequate amount of crop residues. In Rio Grande do Sul black oat (Avena strigosa L.) is the most cultivated cover crop, in spite of fact that different cover crops are available to precede the maize crop. Both maize and black oat belong to the Poaceae family and the continuous use of black oat may bring some losses to maize in succession. Therefore, other winter cover crop species, belonging to other taxonomic families, such legumes and crucifers, have been studied as alternatives to the no-till system which includes maize as a cash crop in the summer. The objectives of this review are: i) to describe the main advantages and limitations of winter cover crops, cultivated in pure stands or mixtures and ii) to discuss cover crops management strategies that most benefit the maize crop in succession.

Adubação nitrogenada em milho pelo monitoramento do nível de nitrogênio na planta por meio do clorofilômetro

The objective of monitoring the adequate nitrogen (N) content in maize is to determine when a nutrient application becomes necessary, since the use of high doses of this nutrient may contaminate superficial and underground waters with nitrate. This experiment was conducted to evaluate the chlorophyll content in leaves, measured by a chlorophyll meter, as an indicator of the N level in maize, at four growth stages, in the state of Rio Grande do Sul, Brazil, during the growing season 1999/2000. Treatments consisted of two maize hybrids (Pioneer 32R21 and Premium) and eight nitrogen management systems. The tested variables (grain yield, N level and accumulation in leaf and plant) in the systems monitored by the chlorophyll meter did not differ in relation to the standard systems, where N was applied regardless of the readings. Monitoring of the N content in the hybrid Pioneer 32R21, reduced N applications by 50, 100 and 150 kg ha-1, respectively, in the S3, S4, and S5 systems, and in the hybrid Premium by 150 kg ha-1 in the system S5, without affecting the maize grain yield. Therefore, monitoring the N level in maize by the corresponding chlorophyll leaf content with a portable chlorophyll meter proved to be an efficient method to separate plants with N deficiency from those with an adequate level of this nutrient.

Crop management systems and maize grain yield under narrow row spacing

Reduction in row spacing provides a more uniform distribution among plants that can increase grain yield. The benefits of narrow row spacing can depend on the plant architecture and on the kind of crop management system. The objective of this study was to assess the effects of narrow row spacing on the grain yield of maize hybrids growing under different management systems. Six experiments were carried out in Eldorado do Sul, State of Rio Grande do Sul, Brazil, during the 2003/04 and 2004/05 growing seasons. Each experiment corresponded to a crop management system. Treatments consisted of two row spacings (0.8 and 0.4 m), two hybrids (Penta and Flash) and two plant densities, which varied with the crop management system and growing season. Besides plant density, the crop management systems differed in the quantities of fertilizers applied at sowing, side-dress and use of irrigation. A complete randomized block design was used in each experiment, in a 2 × 2 × 2 treatment factorial scheme with four replications. The increases in grain yield with narrow row spacing were small, ranging from zero to 14%. They depended on the growing season and were manifested only with yields higher than 10 t ha -1 , regardless of the hybrid. The number of grains per area was the component that best explained the response of grain to narrow row spacing, regardless of plant density, hybrid and crop management system. Narrow row spacing is a worth management strategy to enhance maize grain yield when high input cropping systems are used.

Desenvolvimento fenológico e agrônomico de três híbridos de milho em três épocas de semeadura

Variations in environmental conditions determined by different sowing dates have a great influence on maize ontogeny. This experiment was carried out to evaluate the phenological development of three maize hybrids, at three sowing dates. The experiment was carried out at the Depressao Central region of the state of Rio Grande do Sul-Brazil during 2000/2001 grows season. The single-cross very early hybrid Pioneer 32R21, the single-cross early hybrid Dekalb 214, and the double-cross normal hybrid Agroceres 1051 were evaluated at 08/22/2000 (early), 10/31/2000 (intermediate) and at 01/25/2001 (delayed) sowing dates, with no supplemental irrigation. All hybrids presented shorter developmental subperiods when sowing was delayed. Tassel and ear differentiation occurred, respectively, in the stages of 6 to 7 and 10 to 11 completely expanded leaves, regardless of hybrid cycle and sowing date. The highest leaf emission rate occurred when very early hybrid was sown in October. Delaying sowing resulted in a reduction of leaf area per plant mainly in early hybrids. Number of spikelets per ear, grain yield and grain weight were generally higher in October than in the other two sowing dates.

A resposta do milho irrigado ao espaçamento entrelinhas depende do híbrido e da densidade de plantas

The amount of solar radiation intercepted by the canopy has influence on maize grain yield and it can be enhanced by reducing row spacing and/or increasing plant density. This research was carried out aiming to evaluate the response of four irrigated maize hybrids to variations in row spacing and plant density, under high management level. Two experiments were performed in Eldorado do Sul, RS, Brazil. In 2001/02, treatments had composed by two maize hybrids (Flash and Attack), four plant densities (5.0, 6.25, 7.5 and 8.75 plants m-2) and four row spacings (40, 60, 80 and 100cm). In 2002/03, treatments were set as two maize hybrids (Garra and Penta), four plant densities (4.5, 6.0, 7.5 and 9.0 plants m-2) and four row spacings (40, 60, 80 and 100cm). The reduction in row spacing from 100 to 40cm and the increase in plant population from 4.5-5.0 to 8.75-9.0 plants m-2 has more pronounced effects on grain yield for the erect leaf hybrids Flash and Garra. Conversely, grain yield of decumbent leaf hybrids Penta and Attack was not altered by variations in plant density and row spacing. The effects of narrow row spacing on the agronomic characteristics were lesser magnitude that the obtained ones with variations in plant density.

Monitoramento do nitrogênio na planta e no solo para predição da adubação nitrogenada em milho

The objective of this work was to compare the monitoring of corn plant nitrogen status using two indexes of leaf relative chlorophyll content (critical leaf relative chlorophyll content - CRCC and sufficiency index - SI) determinated by chlorophyll meter and to evaluate the integration between plant and soil characteristics for monitoring the N content of the soil-plant system in corn. Two field experiments were conducted in Eldorado do Sul, State of Rio Grande do Sul, Brazil. The treatments were different N management systems, with different N application times and N rates, carried out with or without monitoring. In the monitored systems, CRCC and SI were used to indicate when N side-dress should be performed and it was tested, using the CRCC and soil nitrate content, one integrated monitoring system. Grain yield and grain yield increase, gross profit increase and the technical, economic and N use efficiency were often higher in the monitored systems than in the systems without monitoring. The efficiency of the monitoring methods, using the CRCC and using the SI and integrating the CRCC and soil nitrate content, was similar. Monitoring corn N status integrating the CRCC and soil nitrate content did not improve nitrogen use efficiency in the tested environment.

Validação de escala de desenvolvimento para cultivares brasileiras de arroz irrigado

The number of days after emergency is commonly used to define the rice plant stage, despite the existence of a growth scale. The use of chronological time is not ideal, once it is dependent of the cultivar life cycle and environmental conditions, which are known to affect the plant development. The goal of this study was to validate a rice growth scale for three Brazilian flooded rice cultivars, with different life cycles and in three sowing dates. The experiment was conducted in tanks in Porto Alegre, RS, Brazil. The three sowing dates were October 14, November 13 and December 18, 2003, and the cultivars chosen were BR-IRGA 409, medium cycle, IRGA 417, early cycle, and IRGA 421, very early cycle. Each cultivar was sowed in three lines, spaced 0.15m from each other, to produce a population of 250 plants m-2. Ten plants composed each sample. The R1 stage (panicle differentiation) was reached when the plants had seven expanded leaves in all treatments, independently of the chronological plant age. A reduction in the number of expanded leaves at the R2 stage (flag leaf collar formation) was only observed for IRGA 421 in the last sowing date. However, the number of days required for each cultivar to reach R2 stage was different. As the sowing date was delayed, the chronological time between each growth stage was reduced. The rice growth scale was much more efficient than the chronological age to determine the plant stage. Therefore, using the rice growth scale is possible to interfere at the correct moment, allowing high yields and rational resource use.