W. R. Cowley Texas A&M University Agricultural Research and Extension Center Weslaco, Texas and B. A. Smith USDA ~eslaco, Texas

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1 Fertilization, Soils and Cultural Practices SWEET SORGHUM AS A POTENTIAL SUGAR CROP IN SOUTH TEXAS W. R. Cowley Texas A&M University Agricultural Research and Extension Center Weslaco, Texas and B. A. Smith USDA ~eslaco, Texas ABSTRACT Investigations with sweet sorghum were begun by the Texas Agricultural Experiment Station at Weslaco, Texas, in 1961 as part of a 3-phase program with sugarcane and sugarbeets to determine their potentials as sugar source crops. Cultural practice research at Weslaco has included studies with dates of planting, plant populations, fertilizers and irrigation. Rio sweet sorghum may be planted from March until August, maturing in days to afford a possible harvest period from July until December. Yields are strongly influenced by daylength and solar radiation. Yield performance follows the pattern of longer days and maximum radiation to afford sugarlacre yields in the range of Ib. High plant populations are required for maximum yields. Plant spacings of 3 inches in 38-inch drills were found to be optimum. Sucrose and purity values were not found to be significantly correlated with spacing or yield. Results of irrigation research in 1967 indicated a total consumptive water use (irrigation plus rainfall) of acre incheslton of stalks produced. Moisture use data indicated peak demands for moisture at the boot and bloom stages of crop development. Moisture extraction patterns in a sandy loam soil indicated primary root activity in the top 3 ft of the profile but with significant root development to depths of 5 ft. Data in regard to fertilizer requirements of sweet sorghum produced on Lower Rio Grande Valley soils are not yet definitive in terms of yield and juice quality responses. Moderate levels of soil nitrogen are required for maximum yields. No correlation was found between nitrogen levels and juice qualities. Plant analyses from date of planting trials indicate absorption of iron and manganese from the soil in substantial amounts; plant zinc contents in midseason growths, however, were only slightly above deficiency levels. No consistent responses were obtained from soil applications of minor elements. Although research yet remains to be done to perfect systems for the production and processing of sweet sorghum, advancements in these technologies do indicate potentials of this sugar source crop as an enterprise in south Texas. INTRODUCTION The production of sugar producing plants and the recovery of sugar from them have challenged the ingenuity of man from the beginning of civilized

2 - -- W. R. COWLEY, B. A. SMITH 629 societies. Inextricably associated with the advancement in standards of living, sugar, as a high energy-yielding food product, has and will continue to be universal in usage and demand. Sugarcane and sugarbeets, long used as major sources of rkcoveradle sugar, have been subjected to intensive w~rld-wide research and improvement (2,5). Other crop plants, too, have been investigated with varying degrees of success. Sweet sorghum, sorghum bicolor (L) Moench, long used as a source of sirup, likewise has been the object of research relative to crop production and to the recovery of crystaline sugar (1,5). Sweet sorghum stocks were introduced into the US more than 100 years ago and were rather intensively studied during the late 1800's by Wiley, Neal and others (see ref. 1). The genetic stocks with high levels of sucrose and purity, early introduced from Africa, were highly susceptible to diseases; furthermore, the technologies of plant breeding were not at that time sufficiently advanced to cope with these limitations. Confronted also with deficiencies in processing technologies, major effort in this field of research was abandoned prior to As World War I1 caused disruption of world economy of sugar, there was renewed interest in the potentials of sweet sorghum. There were some pilot plant evaluations made under the stress of the war emergency and the associated limitation of off-shore supplies (2). Further introduction of sorghum stocks were made from Africa, India and other tropical countries. Importations were continued through post war years to assemble a large pool of genetic stocks, each of which had 1 or more desirable characters such as sucrose, purity, vigor, or disease resistance (3). With research centered at USDA stations at Meridian, Mississippi and Beltsville, Maryland, breeding programs have since been directed toward the development of commercial type varieties for forage, sirup, and high sucrose content (3). Production research with sweet sorghum was initiated by the Texas Agricultural Experiment Station at the Texas A&M University Agricultural Research and Extension Center, Weslaco, Texas, in 1961 as a part of a 3-phase program to evaluate sorghum, sugarcane and sugarbeets as sugar source crops (4). This research effort was largely motivated by the Cuban crisis and the resultant possibility of necessary revision in sources of national sugar supplies. The sweet sorghum stocks used in the Texas program had their origin from the USDA pool of genetic materials. d RESULTS AND DISCUSSION Variety Evaluation Studies, In cooperation with the USDA Crops Research Division, selected varieties and breeding lines were initially evaluated for production and juice quality potentials in the period A breeding line, designated as Mer 55-1, performed well during the period, with estimated sugar yields in the range from lb/acre when harvested at optimum maturity. Mer 55-1 was subsequently released jointly in 1965 by the USDA, the Texas Agricultural Experiment Station and the Mississippi Agricultural Experiment Station as the variety Rio (3). Rio is a selection from the progeny of a cross between the disease-suscep-

3 630 FERTILIZATION, ETC. tible variety Rex and the disease-resistant importation MN Rex is a high sucrose, early maturing type of unknown origin selected in Kansas about MN 1048 is a stock introduced from Africa in Rio was selected from a F, progeny at Meridian, Mississippi in Rio is resistant to rust, Puccinia purpurea, cke., to leaf anthracnose, Colletotrichum graminicolum (ces.), and moderately resistant to downy mildew, Sclerospora sorghi (Kulk). Grown in 3 trials at Weslaco, Texas during the initial period of testing, Rio produced average sugar yields of 212 lb/ ton of cane. In succeeding years, a cooperative screening program has included a large number of breeding lines and genetic stocks. Many lines of differing genetic combinations have exhibited yielcl potentials superior to that of Rio; few, however, have equaled Rio in levels of sucrose and purity. Two breeding lines, Mer 64-3 and Mer 65-2, developed in the cooperative program, are candidates for elevation to varietal status and release for commercial production. Mer has been proposed for release as the variety Roma. Roma, which. hacl its origin in the breeding program at Meridian, Mississippi, is a progeny of a cross between Mer and MN 1060 (7). Mer is a selection from a cross of Early Folger 9097 and Hodo. MN logo was imported from Africa in 1945 and is resistant to downy mildew. Roma is resistant to downy mildew, rust, leaf anthracnose and red rot. In 4 tests at Weslaco, Roma produced 142y0 of the stalk yield of Rio and 122y0 of the calculated yield of sugar. Roma is later in maturity than Rio by about 10 days. The coefficient of apparent purity of juice of Roma is slightly lower than that of, Rio; but it has the advantage of superior stalk yield. Motivated by the progress in the program, there was assignment at Weslaco of personnel from the USDA Southern Utilization Research and Development Division in Operating from the Food Crops Utilization Research Laboratory, research has since been in progress to characterize the chemical constituents of sweet sorghum juices and to develop processing techniques, for the manufacture of sugar. Analytical data from this program greatly expedited production evaluations of breeding lines and genetic stocks. The assignment of 2 patents (9,lO) attests to the success of the research in the development of processing technologies. With completion of construction of a pi101 plant facility, processing trials were conducted during an 8-week campaign in the summer season of Research on Cultural Practices Major production research has been conclucted with the variety Rio. Date of planting trials have shown that Rio may be planted in the Lower Rio Grande Valley of Texas from March until August, maturing in days to afford a possible harvest period from July until December. Averages of data recorded for the 5-year period are shown in Table I. These data, although variable with individual years, indicate that stalk yields of some 11 tons/ acre can be expected from March plantings; yields increase to tons from April plantings and peak at levels in-the 16- to 20-ton range from plantings made in May. Yields show some decline from plantings in the succeeding months of June and July. Yields are obviously affected by day length and solar radiation. Sucrose contents and purity levels have little relationship with yielcls; these values are generally in the range of 15% sucrose and 70y0 purity.

4 w. R. COWLEY, B. A. SMITH 631 Table 1. Mean yield and quality data of Rio sweet sorghum from monthly plantings at Weslaco, Texas, for the 5-year period tems - March April May June Julyz yield (tonslacre) sucrose (%) , 14.0 purity (%) Sugar (Ib/ ton) sugar (lblacre) Calculated recoveries (available 96' sugar table) 2 Four-year average; yields and juice quality of the July, 1967 planting were adversely affected by Hurricane Beulah in September and are not included. That yields of sweet sorghum are influenced by solar radiation has been shown by Hipp, Cowley, Gerard and Smith (8) from studies made with different planting dates during the 3-year period According to the data reported, about 75% of the differences in yields could be attributed to the variability in solar radiation received by the plants between boot stage and that of early seed set. Maximum solar radiation occurs in south Texas during June, July and August; maximum yields are correspondingly obtained in plantings made in April, May and June. The plant population levels required for maximum production were indicated by trials conducted by Cowley and Gerard (6). The data showed that a plant spacing of 3 inches (in 38-inch drills) was higher yielding than a 6- inch spacing or that of a 4-plant, hill drop arrangement. Sucrose and purity values, however, were not significantly affected by spacing. Irrigation requirements for maximum production of sweet sorghum will vary with date of planting and the seasonal evaporation losses. Research with April plantings in 1967 (6) indicated a total consumptive water use (rainfall plus irrigation) of acre incheslton of stalks. These moisture use data indicate peak demands at the boot and bloom stages of crop development. Moisture extraction patterns in a sandy loam soil indicate primary root activity in the top 3 ft of the profile, but with significant root development and moisture extraction from the 4th and 5th ft. The Rio variety characteristically produces a heavy seed head; late season irrigation may increase susceptibility to lodging under conclitions of high winds. Lodging with associated breakage of root systems has been observed to result in lower levels of sucrose add purity. The irrigation of alternate rows during a 3- to 5-day period at this stage of susceptibility to lodging was found to significantly alleviate this late season problem. 1) Fertilizer Studies Data in regard to fertilizer requirements of sweet sorghum produced on Lower Rio Grande Valley soils are not yet definitive in terms of yield responses and juice qualities. Other workers have reported detrimental effects upon cane quality with applications of excess nitrogen. Fertilizer trials conducted in 1966 (6), however, indicated no correlation of nitrogen levels with those of sucrose and purity. Phosphate levels in sorghum juices have been found by Smith (11)

5 632 FERTILIZATION, ETC. to affect clarification in processing procedures; these have not yet been related to soil P levels existing during the crop production season. Minor element experiments conducted in 1964 (6) revealed no consistent responses in terms of yield and juice qualities to varying levels of soil applications. Plant analyses hom date of planting trials in 1966 (6) indicated that sorghum plants absorbed soil manganese and iron at substantial levels; zinc levels found in mid-season growths were fairly low, indicating the possibility of deficiencies. The expanse of root systems could provide for absorption of adequate trace nutrient supplies from fairly low soil levels (6). Miscellaneous Studies The storage of harvested sweet sorghum prior to processing is an important factor in efficient mill operation. Limited storage trials (6) indicate rapid deterioration in quality under the conditions of high summer temperatures. It is indicated that in the absence of controlled storage environment, the cane must be milled in a 24- to 48-hr period after cutting. With decreasing labor supply, it is a foregone conclusion that mechanical means of harvesting will be required for a successful sweet sorghum enterprise. Mechanical harvesting machinery has not yet been adapted for such operations, which will also require removal of the leaves and seed heads. The use of herbicides in sweet sorghum production has not been comprehensively investigated. It has been postulated, however, that weed control chemicals used in grain sorghum may be similarly effective. The major insect pest of sweet sorghum in south Texas is the sugarcane borer, Diatraea saccharalis. Both chemical and cultural control practices will be required in a successful enterprise. Other insects which may damage sweet sorgllum are aphids, Rhofialosifihum maidis, and worms, Heliothis sp. Downy mildew, Sclerospora sorghi (Iculk.), is a disease of sweet sorghum which must be controlled through the development of resistant varieties. Rio and Roma exhibit moderate to high levels of resistance. Although much research yet remains to be done to perfect systems of production and processing of sweet sorghum, the recent advancements of these technologies do indicate potentials of this crop as an enterpiselin south Texas. REFERENCES 1. Brandes, E. W Progress with sugar sorgo. USDA. Yearbook of Agri., Brandes, E. W., and G. B. Sartoris Sugarcane: its origin and improvement. USDA Yearbook of Agri., : Coleman, 0. H., W. R. Cowley, D. M. Broadhead, IC. C. Freeman, and I. E. Stokes Rio, a new disease resistant variety of sweet sorghum for Southern United States, AR Cook, George H Resulis of field and laboratory experiments with sweet sorghums. New Jersey Agr. Exp. Sta. Bulletins 18, 24, 25, 30, Coons, G. H., F. V. Owen, and Dewey Stewart Improvement of the sugar beet in the United States. Advances in Agronomy 1955, 7: Cowley, W. R Sweet sorghum in south Texas: yield potentials and cultural practices. Jour. Rio Grande Hort. Soc., 23: Freeman, I<. C., W. R. Cowley, D. T. Rosenow, B. A. Smith, D. M. Broadhead, N. Zumo, and 0. H. Coleman Rotna: a new variety of sweet sorghum for potential sugar production in south Texas (Publication pending).

6 W. R. COWLEY, B. A. SMITH Hipp, R. W., W. R. Cowley, C. J. Gerard, and B. A. Smith Influence of solar radiation and date of planting on yield of sweet sorghum. Crop Sci., 10: Smith, B. A Process for removing starch from sorghum juices. U. S. Patent NO. 10. Smith, B. A Process for removing starch from sorghum juices. U. S. Pateht NO. 3,464, Smith, B. A., R. C. Smith, R. V. Roma, R. A. de la Cruz, and F. P. Griffiths Removal of starch from sweet sorghum juices. Sugar J., 32:25-30.