Response of Indeterminate and Determinate Soybean Cultivars to Defoliation and Half‐plant Cut‐off¹

Abstract

The estimation of yield loss from defoliation and stem cut‐off is based on the assumptions that soybean (Glycine max (L.) Merr.) cultivars do not differ appreciably in their ability to recover from plant injury, recovery is similar across locations, and percentage yield loss at all reproductive stages can be approximated from research involving only three of the stages. The objective of our study was to test the validity of the assumptions by comparing the response of indeterminate and determinate soybean cultivars to 100% defoliation and 100% half‐plant cut‐off at six reproductive stages from R2 to R7. Two indeterminate cultivars, ‘Hark’ and ‘Beeson’, were studied at Ames, Iowa, and Lafayette, Ind., and two determinate cuitivars, ‘Hill’ and ‘Lee’ were evaluated at Stuttgart, Ark.The determinate cultivars had significantly greater yield reduction from 100% defoliation than did the indeterminate cultivars at all reproductive stages, except R7. Average yield reduction from defoliation for all stages was 59% for the determinate cultivars, compared with 39% for the indeterminate cultivars. Maximum yield loss from 100% defoliation occurred at R4 (86%) and R5 (88%) for determinate cultivars and at R5 (82%) for indeterminate cultivars. Average yield loss from half‐plant cut‐off was similar for indeterminate (34%) and determinate (33%) cultivars, but there was a significant interaction with stages. Yield loss for indeterminate cultivars increased from R2 to R5, then remained constant from R5 to R7. The yield loss from half‐plant cut‐off with determinate cultivars increased progressively rom R2 to R7. The determinateness of a cultivar should be considered when assessing yield reductidn from defoliation and half‐plant cut‐off during reproductive development. Damage from hail, insects, and other factors will be most accurately estimated by establishing separate loss values for indeterminate and determinate types.There was no significant difference between Iowa and Indiana in the percentage of yield loss from 100% defoliation. For the cultivars and locations studied, location effects were not important in the estimation of yield loss from plant injury.Yield loss from 100% defoliation at the six reproductive stages did not follow the relationship predicted from previous studies. Our data indicated that maximum loss for indeterminate cultivars occurred at R5, not R4 as has been assumed. Some yield loss occurred at R7 indicating that the description used to identify plants at physiological maturity was incorrect. A new description based on pod or seed maturation is needed to identify plants that have reached physiological maturity.

Nitrogen uptake, fixation and response to fertilizer N in soybeans: A review

“…Data set B was analyzed for grain yield response to N fertilization. Data from studies that used foliar N fertilization were analyzed separately from those with only soil-applied N. Each group was further sub-divided according to N application timing, i.e., either before or after the R3 stage (Fehr and Caviness, 1977), primarily because it is after R3 when soybean N demand reaches its seasonal peak (Hanway and Weber, 1971). Studies in which a significant yield response to applied N occurred (P < 0.05) were designated as "N-responsive", and the response was quantified in terms of absolute (ΔY) and relative (%) yield increase over a control without N addition.…”

Soybean yield and yield component distribution across the main axis in response to light enrichment and shading under different densities

“…Fences were installed at late vegetative or early flowering stage, which is the growth stage R1 (Fehr and Caviness 1977), and were left in place for the remainder of the growing season. Fences prevented encroachment of plants from neighboring rows into the growing space, and thus increased the radiation interception area of the sample row.…”

Épocas De aplicação de dessecantes na cultura da soja: qualidade fisiológica de sementes

“…A aplicação de dessecantes na cultura da soja é recomendada quando as plantas apresentam 80% de vagens amareladas e 20% de secas, com folhas amareladas (Bastidas et al, 1971), ou quando as vagens estão amarelando e 50% das folhas já estão amarelas (Fehr et al, 1977), ou ainda, quando os ramos e vagens estão marrons e as folhas caídas (Hammerton, 1972).…”