Soil mineral nitrogen availability predicted by herbage yield and disease resistance in red clover (Trifolium pratense) cropping

Nitrogen (N) is the most limiting nutrient in crop production. Legumes such as red clover can provide N through biofixation, but securing nitrogen in soil for subsequent crop production must also be considered. Variety selection and management in red clover cropping can influence soil mineral nitrogen (SMN) availability. A field trial to investigate this was conducted with six varieties, under one and two cut management, over 2years. Dry matter (DM) and N yield, Sclerotinia resistance and SMN availability were assessed. Low DM and N yields (1.6-2.4tDMha(-1) and 54-83kgNha(-1)) in the first year of cultivation allowed similar to 40kgNha(-1) to become available, but high DM and N yields (10.2-14.6tDMha(-1) and 405-544kgNha(-1)) allowed similar to 20kgNha(-1) to become available. Wetter weather in 2015 caused significantly more SMN losses than 2016 (20kgNha(-1) in 2015 and 5kgNha(-1) in 2016). The varieties Amos, Maro and Milvus lost significantly more SMN in the winter period, which may have been caused by more severe infection of Sclerotinia (these varieties were 50-80% more severely infected other varieties). Varietal effect was non-significant for winter losses in 2016, where no significantvarietal differences in Sclerotinia infection were observed. 1 cut made similar to 41kgNha(-1) available in the growing season of 2015, whilst 2 cut made significantly less (37kgNha(-1)). Cutting was non-significant in 2016 but 1 cut was less susceptible to losses in the winter period. Cutting in 2015 did not significantly affect herbage DM and N yields in the first or second cut of 2016.