No abstract

* Os autores agradecem o apoio financeiro da FAPESP e aos revisores anônimos pelas suas sugestões para o enriquecimento do artigo científico.

Core Ideas A full set of N2–fixing nodules can supply soybean N demands.Seed inoculation increased nodulation and grain yield of field‐grown soybean.Additional spray inoculations (V1, V3, V6, R1, or R3) resulted in further increases.New nodules and grain yield increases can be achieved by additional inoculations. Highly productive soybean [Glycine max (L.) Merr.] genotypes require that large amounts of N be supplied throughout the growth cycle to attain high yields. The nutrient can be obtained through biological N2 fixation by elite bradyrhizobial strains if a set of fully functional nodules is available. This study was conducted during two crop seasons in the central‐west region of Brazil to investigate if additional inoculations via spray applications of bradyrhizobia at different stages of the growth cycle can result in increased nodulation and grain yield. Even though the soils had high populations of soybean bradyrhizobia, seed inoculation at sowing increased grain yield by 28 and 27% in the first and second seasons, respectively, compared to the non‐inoculated control. Additional inoculations performed until the R6 stage significantly increased soybean nodulation, which might indicate that plants were able to overcome the limitations of autoregulation of nodulation, allowing the development of new functional nodules to sustain the increased demand for N at latter stages of the growth cycle, especially during pod filling. In response to the increased nodulation, grain yield gains of 2 and 7% were obtained in the first and second experiments, respectively, relative to inoculation at sowing only. Our results indicate that soybean roots can form new nodules in response to additional inoculations, promoting increased N2 fixation and higher grain yield.

O objetivo da pesquisa foi verificar a melhor época de aplicação de dessecantes, a fim de permitir a colheita de sementes de soja com a máxima qualidade fisiológica e sanitária. Assim, foi semeada a cultivar IAC-15 na área experimental da FE/UNESP - Campus de Ilha Solteira, localizada no município de Selvíria, MS. O delineamento experimental utilizado foi o em blocos casualizados, estando os tratamentos dispostos em esquema fatorial 3 x 3 e 4 x 4 de produtos e épocas de aplicação, nos anos agrícolas de 1996/97 e 1997/98 respectivamente. Os dessecantes utilizados no ano agrícola de 1996/97 foram o paraquat, diquat e mistura paraquat + diquat nas doses de 400, 300 e 200+150 g ha-1 respectivamente. Em 1997/98, foram utilizados os mesmos dessecantes, nas mesmas doses, acrescentando-se, nesse caso, mais um tratamento, ou seja, o produto glufosinato de amônio, na dose de 400 g ha-1. Como épocas, foram realizadas três aplicações em 1997 e quatro em 1998, todas em intervalos de cinco dias a partir do estádio R6. Nas condições ambientais em que se realizou a pesquisa, a melhor época de dessecação foi quando as plantas estavam com 80% a 90% de vagens com coloração amarela e marrom e teores de água nas sementes entre 45% e 60%. Com relação aos dessecantes, não se obteve, com qualquer dos produtos testados, potencial fisiológico e sanitário suficientes para a comercialização das sementes.

Termos para indexação: colheita, dessecação, glifosato, paraquat. TIMING OF DESICCANT APPLICATION IN SOYBEANS: PHYSIOLOGICAL QUALITY OF SEEDSABSTRACT -The objective of this study was to evaluate the effect of different desiccants on the physiological quality of soybean seeds when applied to different reproductive stages. The experiment was conducted in the 2005/06 crop season using a randomized block design of four repetitions and two varieties. For the very early maturing MSOY 6101 variety, a factorial 3x3x5x2 design was used, with two desiccant treatments (glyphosate and paraquat) and a control (no desiccation), applied at three growth stages (R 6 , R 7 and R 8 ), with five sampling times (2; 4; 6; 8 and 10 days after application) and two evaluation positions on the plant (apex and base). The early maturing MG/BR 46 (Conquista) cultivar was evaluated in a 3x2x5x2 design with treatments applied at only two growth stages (R 7 and R 8 ). The results showed that glyphosate adversely affected physiological seed quality, mainly for root length, whereas paraquat caused no apparent effect. The seeds from desiccant applications in the R 6 stage showed a lower physiological quality compared to those obtained from applications in the R 7 and R 8 stages.