Michael da Silva Serpa

Densidade de plantas de milho híbrido em semeadura precoce no Rio Grande do Sul

A escolha da densidade de plantas e a sua adequacao a epoca de semeadura sao praticas de manejo importantes na determinacao do rendimento de graos de milho. Este trabalho foi realizado a fim de avaliar os efeitos da densidade de plantas sobre o rendimento de graos e seus componentes em dois hibridos cultivados em semeadura precoce (agosto) no Rio Grande do Sul. O experimento foi conduzido em Eldorado do Sul, em 2006/07. Os tratamentos consistiram de quatro densidades de plantas (5,5; 7,3; 9,1 e 11pl m-2) e dois hibridos, um de folhas decumbentes (Dow 2B587) e outro de folhas eretas (NB 4214). A semeadura foi realizada em 22 de agosto de 2006. O rendimento de graos do hibrido de folhas decumbentes aumentou linearmente com o incremento na densidade de 5,5 ate 11pl m-2, alcancando 16t ha-1. Ja no hibrido de folhas eretas, o rendimento aumentou de forma quadratica, sendo maximizado na densidade de 9,4pl m-2. O numero de espigas por metro quadrado foi o componente que melhor explicou o aumento da produtividade com o incremento na densidade de plantas. O uso de densidades superiores a 9pl m-2 e uma estrategia efetiva para aumentar o rendimento de graos sob alto nivel de manejo em semeadura precoce (agosto).

Estratégias de manejo da palha de azevém para cultivo do arroz irrigado em sucessão

The adoption of crop rotation and crop sequence systems is one of the fundamental prerequisites for the sustainability of agricultural production. Therefore, the objective of this study was to evaluate the effects of ryegrass desiccation time and nitrogen fertilizer applied at sowing of irrigated rice, in succession, as a management strategy in irrigated rice cultivation. The field experiment was carried out in two growing seasons (2008/09 and 2009/10), in Cachoeirinha, State of Rio Grande do Sul, Brazil, on a typical dystrophic Ta Haplic Gleysol. The design was a randomized complete block, with three replications. The treatments, laid out in split plots, consisted of four periods of ryegrass desiccation (90, 70, 50 and 30 days before sowing rice in the first year, and 49, 34, 19 and 6 in the second year of cultivation), and five nitrogen fertilization systems of rice, consisting of a combination of four N rates applied at sowing (0, 10, 20, and 40 kg ha-1) and four N rates as top dressing (150, 140, 130, and 110 kg ha-1), resulting in a total of 150 kg ha-1, plus a control without N application throughout the crop cycle. The initial establishment of rice plants grown in succession was not affected by the presence of upright-standing dry ryegrass plants. In both years, rice grain yield was not influenced by the desiccation time of ryegrass nor the N rate applied at sowing.

Densidade de plantas em híbridos de milho semeados no final do inverno em ambientes irrigados e de sequeiro

The objective of this work was to determine plant density of maize hybrids sowed early (August and September), at the end of winter in the South of Brazil, in irrigated and rainfed environments. Two experiments were set in 2008/2009 (one irrigated throughout the whole cycle and another only from V15 to R2) and three in 2009/2010 (in addition to the previous levels, an experiment under natural rainfall was included). In each experiment, four densities (5, 7, 9, and 11 plants per square meter), four hybrids in 2008/2009, and three hybrids in 2009/2010 were evaluated. In 2008/2009, there were periods of water deficit that added 84 mm in the stages V3, V11 to V15, and R4. In 2009/2010, water deficiency occurred only in the R5 stage. In both years, maximum grain yield exceeded 13 Mg ha‑1 and was obtained with densities higher than nine plants per square meter, regardless of water availability and hybrid. The use of high densities is an efficient strategy to optimize maize grain yield sowed during late winter in the warmer regions of the South of Brazil, as long as there is no water deficit between V15 and R2.