Abstract

The negative effects of tilled fallow on soil quality may be reduced by utilizing legume green manure crops. A study was conducted to determine the suitability of biennial sweetclover [Melilotus officinalis (L.) Lam.] as a partial fallow replacement on the northern Great Plains. Sweetclover undersown in field pea (Pisum sativum L.), flax (Linum usitatissimum L.), or oriental mustard [Brassica juncea (L.) Coss.] and killed in June of the subsequent fallow year attained shoot biomass yields of 3110 to 5370 kg ha⁻¹, depending on the year and companion crop with which it was grown. Living sweetclover plus its residues after being killed provided excellent ground cover to reduce the risk of erosion throughout the 20-mo fallow period. Sweetclover compared to tilled fallow reduced soil water content at the time of seeding spring wheat (Triticum aestivum L.) in 2 of 3 yr. Available soil N in April before seeding spring wheat was 16 to 56 kg ha⁻¹ greater in sweetclover green manure than in fallow treatments. Wheat yields were 47 to 75% greater in the sweetclover than in the fallow treatments. However, the many positive attributes of sweetclover green manure must be weighed against potential reductions in companion crop yield. Undersown sweetclover reduced flax yield in 1 of 3 yr and mustard and field pea yield in 2 of 3 yr, with yield losses ranging from 10 to 55%. Additional research is needed to determine agronomic practices that would reduce competitive interactions between sweetclover and its companion crop.

Copyright © 2001. American Society of Agronomy. Published in Agron. J.93:863–868.