1. 1Dept. of Entomology and Plant Pathology, Auburn University, AL
Production Practices Impact Yield Parameters and Disease Severity on Sweet and Forage Sorghum grown as Biomass Feedstock
A.K. Hagan1 and S. Scott2
1Dept. of Entomology and Plant Pathology, Auburn University, AL
2 E. V. Smith Research Center, Milstead, AL
INTRODUCTION
Sweet and forage sorghum (Sorghum bicolor L.) are being developed as a bioenergy and bioindustrial feedstock (1,3). The impact of production practices on the disease severity in forage and sweet sorghum grown as a bioenergy feedstock is largely unexplored. In Alabama, anthracnose caused by Colletotrichum sublineolum has often been the primary disease in forage than sweet sorghum (2). Previously, nitrogen (N) application rates of 22, 44, 88, and 132 kg ha-1 did not impact above ground dry matter (ADM) yield, total fermentable sugar concentration (°Bx), and total fermentable sugar yield (TFSY) as well as anthracnose severity at a dryland southwest Alabama site (2). In 2011, and 2012, the impact of planting date (PD), N rate, and sorghum type was assessed on ADM yield, °Bx, and anthracnose severity at a Central Alabama site.
Anthracnose severity on M81-E sweet sorghum receiving A) 22, B) 44, and C) 88 kg ha-1 N vs SS405 forage sorghum receiving D) 22, E) 44, and F) 88 kg ha-1. in 2012.
METHODS
A factorial with year, PD (April 11, May 12, and June 17, 2011; April 10, May 29, and July 2, 2012) as the whole plot, sorghum type (M81-E sweet sorghum in 2011 and 2012, 1990 and SS405 forage sorghum in 2011 and 2012, respectively) as the split-plot, and 22, 44, and 88 kg ha-1 N rate as the split split-plot was used. The study site was irrigated as needed. Final anthracnose severity was recorded on a 1 to 9 scale, where 1 = no disease and 9 = 76 to 100% of leaf canopy blighted, at the soft dough growth stage. Stalks were then cut 5 cm above the soil surface in 1.5 m of row, weighted to determine aboveground fresh weight and milled after deheading to collect juice to determine °Bx. Stalk samples were weighted, dried for 48 hr at 80°C, weighed to calculate ADM yield. Statistical analyses were conducted for non-normal anthracnose severity ratings on rank transformations of data, which were back transformed for presentation. Significance of treatment effects was tested by analysis of variance and Fisher’s protected least significant difference (LSD) test (P<0.05).
Figure 1. ADM yield as influenced by A) year, planting date, and sorghum type and B) planting date and N rate.
Figure 2. °Bx as impacted by A) year and planting date, B) N rate, and C) year and sorghum type.
Figure 3. Anthracnose severity as influenced by A) year, planting date, and sorghum type and B) N rate
RESULTS
A significant year × PD × sorghum type and PD × N rate interactions were noted for ADM yield. While, ADM yield for the forage sorghum at each PD was greater in 2011 than 2012, similar high and low yields were noted at the early and late PD, respectively, in both years for sweet sorghum (Fig. 1A). The sweet sorghum produced greater ADM yields than the forage sorghum in April and May, 2011 as well as April and July 2012, while similar yields for the two sorghum types recorded at the remaining PD. Greatest yield for sweet sorghum and forage sorghum were reported for May 2011 and April 2011, respectively with the lowest yields often recorded at the late planting date in both years. At all N rates, ADM yields were similarly high at the April and May PD compared with later PD (Fig. 1B). At the late PD, higher ADM yields were noted at the 88 than 22 kg ha-1 N rate, while intermediate ADM yields were reported for the 44 kg ha-1 N rate.
Significant interactions for year × PD and year × sorghum type were recorded for °Bx values, which were also impacted by N rate. Similarly greater °Bx values were reported at the April and May, 2011 and April 2012 PD, while similarly low °Bx values were found in 2012 at the May and July PD (Fig. 2A). °Bx values were equally greater at the 44 and 88 than 22 kg ha-1 N rates (Fig. 2B). While similarly greater °Bx values were obtained in both study years for the sweet sorghum M81-E, the forage sorghum had lower °Bx values in 2012 than 2011 (Fig. 2C).
A significant year × PD × sorghum type showed that anthracnose severity varied by each of these variables. Anthracnose severity also was impacted by N rate. At each PD, anthracnose severity was higher on both the forage and sweet sorghum in 2012 compared with 2011 (Fig. 3A). Regardless of the PD, less anthracnose-incited leaf blighting was suffered by the sweet than forage sorghum. On the sweet sorghum, anthracnose severity was greater as planting advanced from the initial to final PD in 2012 but not in 2011 when greater disease ratings were recorded for the May than April planting. On the forage sorghum, anthracnose severity was not impacted in either study year by PD. Mean anthracnose severity across both sorghum types was greater at the 88 compared with 22 kg ha-1 N rates, while intermediate disease ratings were recorded for the 44 kg ha-1 N rate (Fig. 3B).
SUMMARY
Here, as was noted in a concurrent study Alabama study (2), anthracnose is the primary disease in both forage and sweet sorghum with greater leaf blighting in the former than latter sorghum type. The interaction of PD, N rate, and/or sorghum type on anthracnose severity along with ADM yield, and °Bx had not previously been assessed. Here, the sweet sorghum M81-E had similar to superior ADM yield, along with higher °Bx (fermentable sugar concentration), and less anthracnose damage than the forage sorghum varieties 1990 (2011) and SS405 (2012). Previously, greater ADM yields and Bx along with less anthracnose were also noted for M81-E sweet sorghum than SS405 forage sorghum (2). Also, ADM yield, °Bx, and anthracnose severity in forage and sweet sorghum varieties established were not impacted by N rates ranging from 22 to 132 kg ha-1 actual N (2). Here, ADM, greater yields were noted as N rate increased from 22 to 88 kg ha-1 at the late but not two earlier PD. Also, greater °Bx and anthracnose severity were noted here at the highest than lowest N rate. ADM yield and °Bx were greater and anthracnose severity lower at the earlier than PD. Overall, M81-E sweet sorghum is more suited than a forage sorghum as a bioenergy feedstock due to its generally higher ADM yield and °Bx as well as reduced anthracnose susceptibility. An April or May planting date reduced anthracnose severity as well as increased ADM yields and fermentable sugar content, particularly for M81-E sweet sorghum. Overall, , planting M81-E sweet sorghum early at moderate N rates minimized the risk of anthracnose.
Literature Cited
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