A new approach to agricultural production and marketing, identity preserved products, is gaining in importance. This is made possible through new technologies and markets demanding products designed specifically for their needs. Examples of investment in identity preserved products include Pioneer Hi-Bred's new research facility for grain quality (Johnson 1995), DuPont's current emphasis on value-added maize (Freiberg 1994), and Iowa State University's value-added grain marketing program (Wrage 1995). However, marketing strategies for such new grain products must be outside the current norm of sale to a local elevator and resale of a bulk commodity to grain consumers.
Sorghum and maize grown for forage are already outside of the current marketing structure for grain crops. They are typically grown, stored, and fed on the same farm. Management decisions including choice of hybrids can be based on end use. As such, it could be argued that the current paradigm for production and utilization of forages in the United States, especially annual forages, is very favorable for the development and marketing of identity preserved hybrids and varieties designed for specific end users.
Quality of the non-grain components of the forage has been historically viewed as relatively poor. To date, breeding emphasis has been for high grain yields in both sorghum and maize. High grain content has been relied upon to provide high energy content in ensiled crops. For grazing and hay type forage sorghum, harvestable dry matter yield has been emphasized. However, if 50% or more of the dry matter of ensiled forages, and up to 100% of dry matter production of forage sorghum is non-grain, quality enhancement of the forage component should contribute significantly to improved animal performance.
Users of maize silage as a forage source have always been relatively quality conscious. Producers of sorghum for forage often utilize a very different decision tree. The decision to plant forage sorghum is often based on many factors which include government programs, anticipated rainfall, pasture conditions, availability of harvesting equipment, etc. However, the decision to select a particular hybrid or variety of forage sorghum is increasingly made on perceived quality. Often these perceptions are based on animal acceptance or palatability and can outweigh yield in the process of selecting a hybrid or variety.
Such increases in digestibility are associated with increased animal performance. Lusk et al. (1984) fed a brown midrib sorghum silage and a corn silage to dairy cows and showed milk and fat corrected milk production to be equal (normal sorghum is usually associated with lower animal performance). More recently in our lab, milk production from cows fed silage of a pre-commercial brown midrib sorghum, normal sorghum, maize, and alfalfa was measured (Grant et al. 1995). Milk production was similar for cows fed the brown midrib sorghum, alfalfa, and corn silage. Cows fed the normal sorghum silage produced approximately 23% less milk than those fed brown midrib silage (Table 1). Milk fat production was similar for cows fed the brown midrib sorghum, alfalfa, and corn silage. Cows fed the normal sorghum silage produced approximately 35% less milk fat than cows fed brown midrib sorghum, alfalfa, and corn silage. Incorporation of the brown midrib trait into sorghum clearly improves animal performance.
Although not widely documented in the literature, it is common knowledge among sorghum breeders that the brown midrib trait is also associated with decreased agronomic performance. This is being overcome with applied breeding effort. Although replicated comparisons were not made in our above study, the pre-commercial brown midrib sorghum hybrid and the normal sorghum hybrid both yielded nearly 9000 kg/ha dry matter with no apparent differences in lodging or disease noted at harvest. Regretfully, the fate of this brown midrib sorghum hybrid is currently unknown due to changes in ownership and management of the company that provided the hybrid. However, commercial availability of another brown midrib sorghum hybrid is anticipated for the crop year 1997 (Jerry O'Rear, Garrison & Townsend, Inc. pers. commun.). Considerable effort is currently being invested in development of brown midrib seed parent (female) inbred lines for use in hybrid production by this and other public sector research programs.
Another new approach to forage sorghum improvement involves the use of alternate sources of cytoplasmic male sterility. Stephens and Holland (1954) originally described a system, now known as the A1 system, for hybrid sorghum seed production based on the interaction of the nuclear and cytoplasmic genes of two races of sorghum, milo, and kafir. In this system, sorghum lines are classified based on their ability to restore fertility or maintain male sterility in A1 cytoplasm. This limits potential heterotic combinations, but because of A1 cytoplasm's stability and ease of use, it has been adopted as the commercial standard and is used for essentially all commercial hybrid sorghum seed production. Alternate sources of cytoplasmic sterility do, however, exist and offer unique opportunities (Schertz and Ritchey 1978).
As alluded above, many new heterotic combinations are possible using alternate sources of cytoplasmic male-sterility. One alternate male-sterile cytoplasm, A3, has very few known restorers of male fertility. This allows the production of male-sterile forage hybrids with a much reduced risk of volunteer outcrosses with weedy sorghums the subsequent year. Although male-sterile hybrids would obviously not be acceptable for grain production, such hybrids may offer improvements in quality for grazing applications by removing seed as a strong carbohydrate sink, and increasing the non-structural carbohydrates in the forage.
A common forage sorghum hybrid is A1 cytoplasmic male-sterile 'Redlan' (a grain sorghum seed parent line) pollinated with 'Greenleaf' sudangrass (Harvey 1977). We recently obtained A1 and A3 male sterile versions of 'Redlan' and three other seed parent lines, produced hybrid seed, and conducted an experiment to compare hybrid forages in these two cytoplasms. Preliminary results showed equivalent dry matter yields, days to 50% anthesis (a measure of maturity), and height between A1 and A3 versions of the same hybrids (Table 2).
Brown mid-rib mutants have been known in maize since at least 1926 (Eyster). However, widespread use of these mutants in commercial hybrids has not occurred because they are also associated with poor grain and stover yield, and susceptibility to lodging (Miller et al. 1983; Lee and Brewbaker 1984).
Several recent studies have investigated the relationships among various forage quality traits in maize (Allen et al. 1991; Wolf et al. 1993). Jung and Buxton (1994) utilized a multiple regression approach to identify the principle components of maize polysaccharide degradability (quality), and concluded that because of the complex interactions in cell-wall organization, no single cell-wall component, or simple combination, can accurately predict degradability of maize cell walls. Significant genetic variation for maize stover digestibility has been shown by several researchers (Hunt et al. 1992; Lundvall et al. 1994) (Table 4). Although as pointed out by Deinum and Bakker (1981), "breeding for stover quality will not be simple as a good correlation between stover quality and stover morphology has not yet been found," it appears that as concluded by Wolf et al. (1993) "future efforts to improve whole-plant digestibility should concentrate on stover digestibility."
Other potential new markets for sorghum and maize forages includes uses in the paper and construction industries. Sorghum stalk residue following grain harvest have been combined with high strength adhesives to produce a product very similar to wafer board (Barbara Kliment, Nebraska Sorghum, Board pers. commun.). This product demonstrates a viable alternate use of sorghum or maize stalks. However, it has not reached the commercial marketplace.
Another promising alternate use of sorghum stalk residues, the production of paper products, is receiving current market interest due to high pulp and paper prices (Tim Lust, National Sorghum Board, pers. commun.). The short cellulose fibers of sorghum stalks are similar to hardwood fibers. Production options include fine white paper, magazine print, copy paper, newsprint, and heavy unbleached paper for use in corrugated boxes.
We have also investigated the potential of using forage sorghum for remediation of chemically (N) contaminated soils, as well as genetic variation for this character (Pedersen et al. 1995). In general, sorghum has a very high N-uptake potential and an extensive root system which is very effective in scavenging N from the soil. Three hybrids each of six types of sorghum (tropical, forage, sudangrass, sorghum x sudangrass, grain, and sweet) were evaluated for N accumulation on a municipal biosolids disposal site. Tropical sorghum and sorghum x sudangrass had the highest dry matter production and accumulated the most nitrogen. Biomass produced was adequate for beef maintenance diets, and may be a useful biomass source for ethanol production from cellulose (Table 5).
|Normal sorghum||20 bz||0.7 b|
|bmr sorghum||26 a||1.1 a|
|Alfalfa||30 a||1.1 a|
|Maize||26 a||1.1 a|
|Seed parent||Dry matter yield (kg/ha)||Days to anthesis (days)||Height (cm)|
|Maize grain yield correlation (r)|
|Variable||Testcross A||Testcross B|
|Dry matter yield|
|Whole plant digestibility||-0.03||-0.02|
|In vitro dry matter digestibility (g/kg)|
|Inbred||Early-harvest stems||Leaves||Late-harvest stems|
|Type||Dry matter yield (Mg/ha)||Nitrogen accumulated (kg/ha)||IVDMD (%)|
|Sorghum x sudangrass||19.5||251||52|