Research paperBiomass and nitrogen content of fifteen annual warm-season legumes grown in a semi-arid environment

- Kauffman or Tropic Sunn crotalarias produce consistently high biomass in environments with 324 to 723 mm growing season rainfall or irrigation.
- Iron & Clay and Red Ripper cowpeas, Rio Verde and Tecomate lablab, or pigeonpea are suitable options for similar environments.
- Repeated harvest decreased biomass of crotalaria cultivars by 54 %, so end of season harvest is recommended for mechanical harvest.

Warm-season legumes can provide a low-input feedstock for biofuel, but research comparing the biomass and N content is lacking. The objective of this experiment was to evaluate and compare 15 annual, warm-season legumes in semi-arid climates as biomass feedstocks. A factorial randomized complete block design field experiment with four replications was conducted at sites near Beeville and Stephenville, TX, during the 2010 and 2011 growing seasons with an average 450 mm total rainfall and irrigation. Whole plot (1.5 m × 6 m; 25 cm row spacing) was legume species and subplot (1.5 m × 3 m) treatments included harvest every 30 d (initiated at first flower or canopy closure, whichever occurred first) or harvest once at the end of the season or plant death, whichever occurred first. 'Kauffman' and 'Tropic Sunn' (Crotalaria juncea L.) produced an average 8650 kg ha−1 and was the most consistent across environments. 'Iron & Clay' and 'Red Ripper' cowpeas (Vigna unguiculata (L.) Walp.; 4700 kg ha−1), and 'Rio Verde' and 'Tecomate' lablab (Lablab purpureus (L.) Sweet; 4000 kg ha−1), generally yielded less biomass than crotalaria. Because of their consistent biomass yields Iron & Clay cowpea, Red Ripper cowpea cut repeatedly through the growing season as well as Rio Verde and Tecomate lablab, or pigeonpea cut at the end of season are suitable biomass options for these and similar environments. Further experiments are needed to determine the potential role of these legumes as crop rotation, cover crop, or integrated livestock-bioenergy uses for biomass production.