Vitor Paulo Vargas

Perfilhamento, área foliar e produtividade do milho sob diferentes arranjos espaciais

The objective of this work was to evaluate the effect of plant spatial arrangement on maize tillering, leaf area, and grain productivity. The experiments were carried out in the spring/summer of the 2007/2008 and 2008/2009 growing seasons. Treatments consisted of four plant densities (three, five, seven, and nine plants per square meter) and three row spacings (0.4, 0.7, and 1.0 m). The leaf area index (LAI) and grain yield of hybrid P30F53 were assessed, as well as the tiller contribution to these characters. In 2007/2008, there was no water deficit, LAI values were higher than 7, and tillers contributed with 65% of total LAI at the lowest plant density. In this year, grain yield average (13.7 Mg ha-1) was not affected by treatments, and tillers contributed with 44% of total yield at the density of three plants per square meter. In 2008/2009, there was water deficit before flowering and during grain filling, which decreased tillering and tiller contribution to LAI. Grain yield in this year increased from 9.7 to 11.7 Mg ha-1 with increasing plant densities, but tiller contribution to grain yield was lower. Tillering increases phenotypic stability of grain productivity to variations in plant spatial arrangement.

Disponibilidade de nitrogênio, sobrevivência e contribuição dos perfilhos ao rendimento de grãos do milho

Nitrogen influences the processes of morphogenesis and tillering in Poaceae. However, its effect on maize tillering is unknown. The purpose of this study was to assess whether N rates and application time affect tiller emission, survival and contribution to maize grain yield. The experiment was set up in Lages, Santa Catarina State, Brazil, in the growing seasons of 2006/07 and 2008/09. The experimental design was arranged in randomized blocks with split plots. In the first year, the main plots consisted of two maize hybrids (AS 1560 and P30F53), the split plots of three N rates (0, 100 and 200 kg ha-1 N), and the split-split plots of three rates of N sidedressing (V4, V4 + V8 and V8). In the second year, four N rates were evaluated in the main plots (0, 50, 100, and 200 kg ha-1 N) and the same sidedress rates in the split plots. The percentage of plants with tillers, number of tillers per plant, grain yield and yield components were assessed. The tillering capacity and grain yield of hybrid P30F53 were greater than of AS 1560. Nitrogen sidedressing reduced tiller mortality at harvest in the first year, and until flowering in the second season. Nitrogen sidedressing at V4 stimulated tiller emission and survival at harvest 2008/09. Nitrogen sidedressing increased grain yield in both study years, and enhanced the direct contribution of tillers to grain yield in 2006/07. The time of nitrogen sidedressing did not affect grain yield, regardless of the growing season. Maize tillering capacity differed among hybrids. In environments with adequate N availability, tillers contribute to increase maize grain yield.

Perfilhamento como característica mitigadora dos prejuízos ocasionados ao milho pela desfolha do colmo principal

O objetivo deste trabalho foi verificar se os perfilhos podem mitigar os prejuizos ocasionados pela desfolha do colmo principal em milho. Os experimentos foram implantados em Lages, SC, em 20/10/2006 e 31/10/2008. O delineamento experimental utilizado foi o de blocos ao acaso, com parcelas subdivididas. Na parcela principal, foram testados dois destinos dos perfilhos: manutencao ate a colheita e remocao quando o colmo principal apresentava nove folhas expandidas (V9). Nas subparcelas, avaliaram-se quatro epocas de desfolha do colmo principal: V9, V15 (quinze folhas expandidas), VT (pendoamento) e folhas preservadas ate a colheita. Avaliou-se o hibrido P30F53, a densidade de 55 mil plantas por hectare. Determinaram-se: a produtividade total, a do colmo principal e a dos perfilhos. As desfolhas realizadas em V15 e VT diminuiram a produtividade, em comparacao ao tratamento sem desfolha, independentemente do destino dos perfilhos. Quando o milho foi desfolhado em V15 e VT, a produtividade total das parcelas em que os perfilhos foram mantidos foi maior do que daquelas em que eles foram removidos. Isto indica que os perfilhos foram beneficos ao colmo principal do milho, quando houve restricoes a producao de carboidrato oriundas da perda de area foliar proximo do florescimento.

A remoção dos perfilhos não aumenta o rendimento de grãos do milho, independentemente da época de semeadura

Historically, tillers have been considered detrimental to maize because they do not produce ears and may act as sinks competing for carbohydrates with the main stem. This work was carried out aiming to evaluate the effect of tiller removal on maize grain yield at different sowing dates. The experiment was set during the 2006/07 and 2008/09 growing seasons. A randomized complete block design disposed in split-plots was used. Two sowing dates were tested in the main plots: second half of October (recommended) and second half of December (late). Four tillers fates were evaluated in the split-plots: tiller removal when the main stem had six expanded leaves (V6), nine expanded leaves (V9), fifteen expanded leaves (V15) and tiller maintenance until harvesting. Hybrid P30F53 was sowed at 55,000 plants ha-1, with a row spacing of 0.7m. The percentage of plants with tillers and the number of tillers per plant were higher when maize was sown in October than in December. There was no grain yield difference between treatments where tillers were preserved and those where they were removed at V6, V9 or V15, regardless of sowing date. Such behavior demonstrates that tillers are not sinks that compromise maize agronomic performance. Furthermore, tillers may contribute positively to grain yield when maize is sown in October.

Os atributos nas folhas são mais eficientes que o N mineral no solo para avaliar a disponibilidade desse nutriente para o milho

In Southern Brazil, N availability to maize is evaluated based on soil organic matter, without considering N content in the soil or in the leaves. This work aimed to evaluate the efficiency of soil (NO 3 - -N and NH 4 + -N levels) and plant (total N tissue, chlo- rophyll content and chlorophyll relative index) parameters as indicators of N availability during maize ontogeny. Maize was submitted to different nitrogen rates and side-dress application times. The study was carried out in Lages, Santa Catarina State, Brazil, during the 2008/2009 growing season. The experiment was set in a randomized block split plot design. In the main plot four N rates were evaluated: 0, 50, 100 and 200 kg ha -1 . Two timings of N side-dress application were assessed in the split plots: all N applied when maize had four or eight expanded leaves and half rate applied when maize had four and the other half when it presented eight expanded leaves. Evaluations were performed between the growth stages of six expanded leaves and silking. The soil N content did not correlate with grain yield or any other plant characteristics regardless of growth stage. Therefore, they were not adequate to predict N availability to maize. Grain yield was not related to the chlorophyll relative index or total N level in leaves during early stages of crop development, but it was correlated with them when the evaluations were made from the 9 th expanded leaf onwards. Plant characteristics were more suitable than soil parameters to predict N availability to maize and the crop grain yield.