Repeated Biomass Removal Affects Soybean Resource Utilization and Yield

to yield reductions (Higley, 1992; Hunt et al., 1994; Haile et al., 1998). Hunt et al. (1994) concluded that removal Soybean [Glycine max (L.) Merr.] producers in many regions of of leaf area delayed the time to achieve a critical leaf the USA are confronted with significant yield losses because of crop damage from white-tailed deer (Odocoileus virginianus). Our objecarea index (LAI) of 3.5, limiting light interception and tives were to quantify soybean resource utilization and yield responses dry matter accumulation. Haile et al. (1998) imposed to variety, row spacing, and simulated repeated biomass removal. defoliation treatments at R2 and concluded that yields Field research was conducted in 2000 and 2001 on a Quakertown silt were directly related to the light interception capacity loam soil (fine-loamy, mixed, mesic Typic Hapludult) near Pittstown, of soybean canopies after defoliation. Klubertanz et al. NJ. Biomass removal during early vegetative and vegetative/reproduc(1996) reported that soybean subjected to simulated tive growth extended the soil wetness duration index on average by 1.5 insect defoliation at R2 increased soil water content in and 2.9 d compared with the control from the 0to 30and 30to both years of their 2-yr study and delayed senescence 60-cm soil depths in 2000 and by 5.1 and 2.1 d in 2001. Biomass of lower leaves. Hintz et al. (1991) evaluated soybean removal during early vegetative growth delayed pod maturity up to 7 d response to stem cutoff and defoliation during vegetacompared with the control, but biomass removal during reproductive growth hastened pod maturity by as much as 3 d. Averaged across tive development and reported that averaged across row spacing and biomass removal, variety ‘APK394NRR’ yielded 12 stage of development when treatments were imposed, and 24% lower than ‘93B53’ in 2000 and 2001. In 2000, averaged the delay in maturity was greatest for plants injured by across variety and biomass removal, the 20and 41-cm row widths cutoff treatments and was least for defoliation treatyielded 19 and 16% less than the 76-cm row width. Averaged across ments in the absence of stem cutoff. variety and row spacing, all biomass removal treatments lowered yield Most of the published defoliation studies have focused compared with the control except the midvegetative/early reproducon insect defoliation using either single-day or sequential tive treatment in 2001 (661 vs. 663 g m!2). The greatest yield reductions defoliation approaches or simulated hail damage using occurred (up to 89%) when biomass was removed repeatedly during different defoliation or stem removal techniques. Morevegetative and reproductive growth. Management implications for over, most defoliation/biomass removal studies have evalsoybean producers include variety selection and row spacing to diminish the effects of deer damage. uated soybean response to defoliation in row spacings greater than 68 cm and do not simulate severe biomass removal. Our simulation technique was designed to mimic white-tailed deer damage. Ultimately, techniques T iming, intensity, and frequency of biomass resimilar to those presented by Singer et al. (2004) will moval affects soybean yield. Yield reduction is less be used to simplify the process of quantifying soybean sensitive to biomass removal during vegetative growth yield loss from deer depredation. In the short-term, data because soybean can develop new leaf area that can comare still required to determine biomass removal by manpensate for temporarily reduced assimilatory capacity. agement interactions on soybean responses. The objecSinger (2001) reported that yield reductions in indetertives of our study were to quantify soybean resource minate soybean from removing the top third of the plant utilization and yield responses to variety, row spacing, at V5 (Fehr and Caviness, 1977) were less than biomass and repeated biomass removal during vegetative and removed at R4. Francoeur (1995) evaluated severe simreproductive growth. ulated deer damage in 1-m rows during vegetative and reproductive growth and concluded that damage imposed at V10 lowered yield in 1 of 2 yr but damage at MATERIALS AND METHODS R4 decreased yield in both years. Fehr et al. (1977) A 2-yr study evaluating biomass removal in no-tillage soybean reported that yield of determinate cultivars was affected was conducted in 2000 and 2001 on a Quakertown silt loam more than indeterminate cultivars from 100% defoliasoil (fine-loamy, mixed, mesic Typic Hapludult) at the Rutgers tion when defoliation occurred from R2 through R6. University Snyder Research and Extension Farm near Pittstown, Average yield loss from half-plant cutoff was similar for NJ (40"30# N, 75"00# W, elev. 170 m a.s.l.). A three factor treatment structure in a split-split-plot randomized complete block determinate (33%) and indeterminate (34%) cultivars, design with four replications was established. The main factor but there was a significant interaction with growth stage was indeterminate soybean variety, either Pioneer Brand ‘93B53’ (Fehr et al., 1977). maturity group (MG) 3.5 or Agway ‘APK394NRR’ MG 3.9, Previous research has identified that reductions in the first split was three row spacings, 20-, 41-, and 76 cm, and light interception of defoliated treatments was related the second split was biomass removal at V1 $ V3 $ V6 (early vegetative), V6 $ R1 (midvegetative/early reproductive), R1 $ R4 $ R6 (reproductive), and (V1 $ V3 $ V6) $ (R1 $ R4 $ J.W. Singer and D.W. Meek, USDA-ARS, National Soil Tilth LaboraR6) (vegetative and reproductive) and a control. Main plot tory, 2150 Pammel Drive, Ames, IA 50011. Received 10 Feb. 2004. area was 64.7 m2, subplot area was 18.5 m2 for the 20and *Corresponding author ([email protected]). Published in Agron. J. 96:1382–1389 (2004).  American Society of Agronomy Abbreviations: DAP, days after planting; LAI, leaf area index; MG, maturity group; PAR, photosynthetically active radiation. 677 S. Segoe Rd., Madison, WI 53711 USA