Wheat is the major small grain crop produced in the U.S., but several other small grain crops such as barley, oat, rye, and rice are also produced. The straw (stems and leaves) of these crops could be used for bioenergy and bioproducts. Additionally, the residue from grain sorghum could be collected and used for biobased products.
Barley is produced in 22 states, primarily in the Northern Plains, Pacific States, Lake States, and Mid-Atlantic states, and is used primarily for livestock feed and for use in the brewery industry. Barley production has been steadily declining in recent years. In 2000, about 5.2 million acres were harvested, but only 2.95 million acres were harvested in 2006. The national average yield for 2000-2006 is 61 bushels/ac and has ranged between 55 bu/ac and 69.6 bu/ac (USDA-NASS). Yield variability on a local level is substantially higher. Barley is often grown in rotation with row crops such as corn and soybean and with wheat. Nearly 68% of barley acres are produced using conventional tillage methods, with 25% of the acres using reduced till methods, and 7% using no-till operations (CTIC, 2000). The USDA projects average national barley grain yields of 70.2 bu/ac and 3.0 million harvested acres by 2016 (USDA OCE, 2007). The Food and Agricultural Policy Research Institute projects average national barley grain yields of 69.8 bu/ac and 2.45 million harvested acres by 2016 (FAPRI, 2007). A workshop of crop and livestock experts (RCA III Symposium, 1997) projected that under the mostly likely scenario, average national barley grain yields of 85 bu/ac and 110 bu/ac could be achieved by 2030 and 2050 respectively (compared to the 1990-1992 yields of 58 bu/ac). This projected yield increase is attributed to a combination of genetic, management, and equipment improvements.
Oat grain production is limited and geographically dispersed, occuring in 25 states distributed throughout the U.S. Oats are produced for human consumption and for animal feed (mainly horses). A little over 4 million acres are planted each year, but harvested acres have declined from 2.33 million in 2000 to 1.58 million acres in 2006. National average yields (from 2000 to 2006) have ranged between 56.4 bu/ac and 64.7 bu/ac (USDA-NASS). Barley is often grown in rotation with corn, soybean, or wheat. Nearly 74% of oat acres are produced using conventional tillage methods, with 19% of the acres using reduced till methods, and 7% using no-till operations (CTIC, 2000). The USDA projects average national oat grain yields of 66.5 bu/ac, and 1.9 million harvested acres by 2016 (USDA-OCE, 2007). The Food and Agricultural Policy Research Institute projects average national oat grain yields of 65.8 bu/ac and 1.49 million harvested acres by 2016 (FAPRI, 2007). The RCA III Symposium (1997) projected that under the mostly likely scenario, average national oat grain yields of 90 bu/ac and 120 bu/ac could be achieved by 2030 and 2050 respectively (compared to the 1990-1992 yields of 59 bu/ac). This projected yield increase is attributed to a combination of genetic, management and equipment improvements.
Rye is produced in limited quantities in the U.S. Over the past seven years, an average of 283,000 acres have been harvested annually (range of 263,000 to 319,000), with national average yields ranging from 24.7 bu/ac to 28.3 bu/ac (USDA-NASS). Production occurs principally in Georgia and Oklahoma, and occasionally in North and South Dakota. Data regarding rotational and tillage practices and projected future harvested acres and grain yields are unavailable.
Rice production is limited, but highly concentrated. About 3.2 million acres of rice (range of 2.82 to 3.36 million between years 2000-2006) are harvested annually in just six states (Arkansas, California, Louisiana, Mississippi, Missouri, and Texas). Within these states, production is often concentrated in a few counties. Thus, while rice straw is a limited resource for the U.S. as a whole, in the areas where production occurs, it could be an important biomass resource. Nearly 88% of rice acres are produced using conventional tillage methods, with 3% of the acres using reduced till methods, and 9% using no-till operations (CTIC, 2000). Prior to planting rice, the previous year’s residue must be reduced. This is accomplished by the use of intensive tillage operations or by in-field burning. Air pollution controls in some states are eliminating burning; alternative means are being sought for disposing of the large quantities of residue produced.
Average national rice grain yields have ranged from 6,281 to 6,988 lbs/ac between years 2000-2006. The USDA projects average national yields of 7,496 lbs/ac, with 3.07 million harvested acres by 2016 (USDA-OCE, 2007). The Food and Agricultural Policy Research Institute projects average national rice grain yields of 7,555 lbs/ac, with 3.01 million harvested acres by 2016 (FAPRI,2007). The RCA III Symposium (1997) projected that under the mostly likely scenario, average national rice grain yields of 13,000 lb/ac and 13,500 lb/ac could be achieved by 2030 and 2050, respectively (compared to 1990-1992 yields of 5,637 lb/ac). This projected yield increase is attributed to a combination of combined genetic, management and equipment improvements.
Sorghum production is concentrated in the Plains States. It is produced in the U.S. for both silage and for grain. When produced for silage, the entire plant is harvested and fed to livestock, and thus is unavailable for bioenergy. Grain sorghum, however, harvests the seed; therefore, the remaining stalks and leaves could be available for bioenergy and bioproducts. Between 2000 and 2006, an average 6.97 million acres were harvested annually, with national average yields ranging between 50.6 and 69.6 bu/ac (USDA-NASS). Sorghum is often produced in rotation with soybeans in the southern U.S. (USDA-ERS, 2006). About 14% of sorghum acres are planted with no-till methods, 18% with reduced till methods, and 68% rely on conventional till practices (CTIC, 2000). The USDA projects average national sorghum grain yields of 68.4 bu/ac, and 4.7 million harvested acres by 2016 (USDA-OCE, 2007). The Food and Agricultural Policy Research Institute projects average national sorghum grain yields of 65.9 bu/ac, and 5.25 million harvested acres by 2016 (FAPRI,2007). The RCA III Symposium (1997) projected that under the mostly likely scenario, average national sorghum grain yields of 89 bu/ac and 102 bu/ac could be achieved by 2030 and 2050 respectively (compared to the 1990-1992 yields of 65 bu/ac). This projected yield increase is attributed to a combination of combined genetic, management and equipment improvements.
The quantities of straw available depend on the quantities produced, minus the quantities that must remain on the field. Crop residues play a vital role in maintaining soil characteristics (e.g., soil organic matter and soil moisture), controlling erosion and chemical runoff, and ensuring the long-term productivity of the soil. Sufficient residue quantities must be left to maintain these functions.
In the absence of data on residue yields, the quantities of grain straw produced per acre are estimated by multiplying the grain yield by a residue-to-grain ratio (i.e., harvest index). Most studies assume a residue-to-grain ratio of 1.5:1 for barley; 1.4:1 for oat; 1.5:1 for rye; 1.5:1 for rice; and 1:1 for sorghum (Brown, 2003; Heid, 1984; Larson, 1997a, 1997b). Additionally most, but not all, studies assume a grain weight of 48 lbs/bu for barley; 32 lbs/bu for oat; 56 lbs/bu for rye; and 55 lbs/bu for sorghum. Using these assumptions, and the 2005 harvested acres and grain yields, an estimated 37 million dry tons of straw were produced by these five crops (table 1). Figures 1 through 5 show the geographic distribution of barley, oat, rye, rice, and sorghum straw production.
Not all of the straw produced can be removed. Crop residues play a vital role in maintaining soil characteristics (e.g., soil organic matter and soil moisture), controlling erosion and chemical runoff, and ensuring the long-term productivity of the soil. Sufficient quantities of straw must be left on the field to maintain these functions. The quantities that must remain depend on a number of factors including which crop is produced, whether the crop is produced in a continuous cropping system or in rotation with other crops, the timing and type of management practices used to produce the crops (particularly tillage operations), the physical characteristics of the soil (e.g. soil type and erodibility), field characteristics (e.g. slope), and climate. At present, for these crops, there are few analyses that rigorously examine the quantities of residues that must remain on the field to maintain soil quality.
Few studies have evaluated the potential quantity and costs of collecting barley, oat, rye, rice, and sorghum straw. Perlack et al. (2005) estimated that 0.1, 0.7, 5.7, and 0.0 million dry tons of oat, barley, rice, and sorghum residue are currently available for bioenergy or bioproduct uses (based on assumed acreage of 1.9, 4.3, 3.3, and 8.6 million acres of production, respectively and residue production of 1.7, 1.8, 2.9, and 1.4 dry tons/ac, respectively). Perlack et al. estimated, that these quantities could increase to 15.1 million dry tons (0.7, 2.8, 10.3, and 1.3 million dry tons of oat, barley, rice, and sorghum residue, respectively) by mid-century assuming modest increases in grain yields. Using a high grain yield increase assumption, Perlack et al. estimated an increase to 24.6 million dry tons (1.2, 4.7, 14.7, 4.0 million dry tons of oat, barley, rice, and sorghum residue, respectively) by mid-century. No economic analysis was conducted.
Rooney (1998) estimated that no barley, oat, or sorghum straw could be available for bioenergy and bioproducts, based on 1996 acres and yields. The analysis assumed that 65% of the straw generated needed to remain on the field and eliminated quantities for areas where, after leaving 65% of the straw, the quantities available for collection were less than 1 dt/ac. Using the same assumptions, he estimated that 2.67 million dry tons of rice straw could be available at an average cost of $43.06/dt (range of $22.84 to $70.67, depending on location). The price is based on the cost of collecting the straw and includes a $3.36/dt straw fertilizer replacement cost.
Gallagher (2003a; 2003b), using 1997 harvested acres, grain yields, and input costs, estimated that 4.6 million dry tons of barley straw, 0.63 million dry tons of oat straw, and 1.01 million dry tons of sorghum straw (almost all in Kansas) could be available for bioenergy uses at prices between $14/dt and $42/dt, depending on crop and region. He estimated that 4.62 million dry tons of rice straw could be available at prices of $20 to $25/dt. The analysis assumed that sufficient straw quantities were left to provide 30% coverage of the field surface (715 lbs/ac). Gallagher included acres for which the erosion level was below the tolerance level when 715 lbs/ac of residues were left. The analysis was based on representative soil types by major crop production region. Price estimates included the cost of chopping and baling the straw, on-farm hauling of bales, and fertilizer replacement costs of $7.49/dt, $7.86/dt, $5.42, and $5.92/dt for barley, oat, rice, and sorghum straw removed, respectively.
Fife (1999) estimated that 108,000 to 132,000 dry tons of rice straw could be removed annually in Colusa County, CA at a cost ranging from $17 to $27/ton ($1999; moisture content not specified). Costs include baling and moving the bales to the edge of the field.