Short term nitrogen availability following overwinter cereal/grass and legume cover crop monocultures and mixtures in South Coastal British Columbia

ABSTRACT:

This 1995 to 1996 study was conducted to determine the effects of cereal/grass and legume cover crop monocultures and mixtures on short term N availability. Cover crop treatments included winter wheat (Triticum aestivum L.), fall rye (Secale cereale L.), annual ryegrass (Lolium multiflorum L.) planted in monoculture and in mixtures with crimson clover (Trifolium incarnatum L.), crimson clover, winter wheat + hairy vetch (Vicia villosa) and bare control. Incubation studies using the cover crop residues were set up for a sixteen week incubation period under field conditions using the in situ resin core method. At the end of the incubation period, total net N release by winter wheat, fall rye, and annual ryegrass ranged from 48 to 80 kg N ha⁻¹ in 1995 and 41 to 92 kg N ha⁻¹ in 1996. Crimson clover mixtures with winter wheat, fall rye, or annual ryegrass had total net N released ranging between 42 to 106 kg N ha⁻¹ in 1995 and 83 to 104 kg N ha⁻¹ in 1996. In contrast, total net N released by winter wheat + hairy vetch was 160 kg N ha⁻¹ in 1995 and 170 kg N ha⁻¹ in 1996. Total net N released by crimson clover was 158 kg N ha⁻¹ in 1995 and 41 kg N ha⁻¹ in 1996. Critical N concentration above which N mineralization occurred was determined as 14.1 g kg⁻¹ and this corresponded to a critical C:N ratio of 31.7. Winter wheat + hairy vetch mixture seems to be more reliable than cereal/grass + crimson clover mixtures in terms of N contribution on decomposition, and legumes in mixtures may reduce the potential for short term N immobilization.