Harvest Methods for Estimated Ethanol Yields from Relative Fermentable Carbohydrate Accumulation in Maize Hybrids

Recurring energy shortages suggest the need for evaluation of alternate fuel energy sources. Conversion of plant carbohydrate to ethanol, as a fuel source, is considered a viable option with efficient energy-producing crops such as maize, Zea mays L. Three maize hybrids ('Coker 77" 'Pioneer 3369A" and 'Sokota Sugar Chop') were grown in a Norfolk loamy sand (fine-loamy. silicious Typic Paleudult) from 1981 to 1983 to evaluate four procedures for harvesting. The objective was to identify procedure(s) that maximize carbohydrate production potential. measured as estimated fermentable carbohydrate converted to ethanol. Ethanol yield estimates. calculated from grain or stalk sugars. or both. to make possible direct comparisons of harvest treatments. were analyzed as a split-plot design with 10 replicates. Whole plots were hybrids. and subplots were harvest treatments. The treatments consisted of (i) covered ear shoots (EC): (ii) removed ear shoots (ER): (iii) grain and stalks harvested simultaneously (P-SimH): and (iv) stalks harvested separately. 1 to 2 weeks after grain harvest (PSepH). Coker 77 produced the least grain but significantly greater estimated ethanol yields than did the other hybrids in 2 of 3 yr because of greater stalk sugar yields. The P-SepH and P-SimH treatments of this hybrid produced less than twice as much estimated ethanol per plant. and other hybrids produced about three times as much as the EC and ER treatments of Coker 77. Differences between the P-SimH and P-SepH treatments were nonsignificant. and simultaneous harvest of grain and stalk sugar at physiological maturity proved an efficient procedure to produce high estimated ethanol yields. Additio1UJl index l«Jrds: Zea mays L.. Corn stalk sugars. Energy crops. Ethanol production, Carbohydrate conversion. I NCREASES in petroleum prices and continuing feed grain surpluses in the United States have encouraged consideration of the maize, Zea ivfays L., plant carbohydrates as a renewable energy source. Interest in maize stalk sugars was also stimulated when Illinois researchers reported a positive relationship between stalk sugar concentration and resistance to disease and cold injury (4). Sayre et al. (6) reported that high concentrations ofsugars accumulated in the stalks of maize plants that were not permitted to produce grain. 758 Hume and Campbell (5) demonstrated that soluble solid concentrations in stalks increased until the end ofthe growing season when pollination was prevented, but that stalk soluble solids declined during grain-fill because of rapid translocation to the grain. Rapid techniques for measuring soluble solids in stalk juices were used by Campbell and Hume (2). Cunningham et al. (3) reported that hybrids developed for high stalk sugars in Spain (I) had sugar contents of 2.0 to 3.5 times those of a Corn Belt hvbrid developed for grain production. The objective of this study was to e.valuate several harvesting procedures for maximizing potential fermentable carbohydrate production Of maize by comparing estimated relative ethanol yields. Materials and Methods Three hybrids were chosen for this study: 'Coker 77', a full-season hybrid with Slay-green qualities; and 'Pioneer Brand 3369A' and 'Sokota Sugar Chop'. which mature 5 to 7 days and 7 to 9 days earlier than Coker 77, respectively. The hybrids were planted in a Norfolk loamy sand (fineloamy, silicious Typic Paleudult) at Tifton, GA, as a randomized complete block experiment on 22 April, 6 May, and 2 ~ay, i~ 1981, 1982, and 1983, respectively. A splitplot deSIgn with ten replicates was used in which hvbrids were whole plots and four harvesting treatments were subplots. Subplots were single rows, 6.1 m long, with 0.76 m between rows and an average plant spacing of 0.20 m in the row (about 64 000 plants ha . '). Harvest treatments were (i) covered ear shoots (EC) to prevent pollination; (ii) ears removed (ER) during silking to prevent grain formation; (iii) ears and stalks harvested at 6 to 7 weeks after anthesis (grain at 300g kg I moisture) (P-SimH); and (iv) ears and stalks harvested separately at 6 to 7 weeks and 8 weeks after anthesis (P-SepH), respectivelv. Both EC and ER were harvested 6 weeks after anthesis: Wet weights were recorded for 10 plants per plot and for three typical stalks that were I Contribution of the Insect Biology and Population Management Res. Lab.. USDA-ARS, in cooperation with the Univ. of Georgia Coll. of Agric. Exp. Stns., Coastal Plain Stn.. Tifton. GA. Received 16 June 1986. C Research geneticist. USDA-ARS-IBPMRL. P.O. Box 748. Tifton. GA 31793; research chemists. Northern Agric. Energy Ctr.. USDA·ARS. Peoria. IL; and deceased. Published in Agron. J. 79:758-760 (1987).