Nitrogen Accumulation and Initial Growth Response in Lettuce Planted at Different Periods After Hairy Vetch Incorporation

One-month-old lettuce seedlings were planted in the field with and without prior hairy vetch (Vicia villosa L.) incorporation (HV and Fallow, respectively). The periods between hairy vetch incorporation and lettuce planting were 1 day, 8 days and 15 days. The inorganic nitrogen concentration in the soil was higher after hairy vetch incorporation, as well as the nitrogen concentration in the lettuce leaves from the HV plot compared to the Fallow plot, at any planting period. When lettuce seedlings were planted 8 days after hairy vetch incorporation, the leaf dry weight in the HV plots was 11% lower than that in the Fallow plots 4 days after planting; however, leaf growth recovered and the dry weight was 24% higher 12 days after planting, which could be due to enhanced leaf growth as the result of additional accumulated nitrogen provided by the hairy vetch. In the incubation experiment, it was suggested that the inhibitory effect of hairy vetch decomposition was not due to allelopathic substances. Therefore, in the hairy-vetch-incorporated field, growth suppression in the lettuce plants occurred early and continued for a short period after hairy vetch incorporation, but the damage due to the growth suppression effect was minor. More importantly, nitrogen supplied from the hairy vetch promoted lettuce growth after the inhibition period.