Sorghum Biomass Cropping Systems

Grant # 07S-02
Principal Investigator: Kenneth Moore
Student: Ben Goff
Organization: Iowa State University
Technical Area: Renewable Energy

Introduction
The advent of biorefineries capable of processing lignocellulosic biomass to produce sugars and their derivatives will create an opportunity to diversify Iowa cropping systems. Instead of focusing on grain production alone, farmers will be able to introduce biomass crops into their rotation with the goal of maximizing potentially convertible substrate yields. Since crops grown for biomass do not necessarily need to produce seed, there will be options to grow alternative crops that remain vegetative under Iowa growing conditions and to produce more than one crop in a growing season.

Sorghum [Sorghum bicolor (L.) Moench] is a diverse species with several well characterized genotypes that have excellent potential for biomass production. Among these are sweet sorghum, forage sorghum, tropical sorghum, and sorghum x sudangrass hybrids. Yields of each of these sorghum types can be quite high, but vary among hybrids within each type. Biomass yield of sweet sorghum grown in 2006 at the Iowa State University Sorenson Farm was 15 dry tons per acre.

Because sorghum harvested for biomass can be harvested before maturity, it is possible to grow it in a double-crop sequence with a winter annual. Winter annuals are planted in the fall, grow rapidly in the spring, and can be harvested anytime from late spring to early summer. Sorghum, which is well adapted to germination under limited moisture, could then be planted into the stubble of the winter annual crop. The primary advantages of a double-crop sequence are that it maximizes use of solar radiation for a longer period, and provides winter cover against wind and water erosion. Because sorghum and winter annuals have differing cardinal temperatures for growth, the double-crop sequence can take advantage of a longer growing season than either crop alone.

Two winter annuals that have high potential for biomass production are forage triticale [×Triticosecale rimpaui Wittm.] and Tifton burclover [Medicago rigidula (L.) All.]. Triticale biomass yields as great as 4 dry tons per acre have been reported for central Iowa. Burclover has not been evaluated in Iowa, but reportedly has produced similar yields in Wyoming. Using the legume burclover in a double-crop sequence with sorghum would have the additional benefit of providing nitrogen to the cropping system through nitrogen fixation.

The proposed study will provide fundamental data on the potential of various sorghum genotypes in single and double-crop sequences to maximize yield of potentially convertible substrate. Three genotypes of each of four classes of sorghum (sweet, forage, tropical, sorghum x sudan) will be evaluated in season long and double-crop sequences with winter triticale, burclover, and a mixture of the two.

Objectives

1. Determine biomass yield and composition of various sorghum genotypes grown as a seasonlong crop.
2. Determine biomass yield and composition of various sorghum genotypes grown in a doublecrop sequence with winter triticale, triticale with hairy vetch, or triticale with winter pea.
3. Determine the biomass yield and composition of triticale and legume mixtures grown in a double-crop or full-season system.
4. Evaluate and compare the production costs of each of the cropping systems.