Effects of cultural practices on soil respiration in hazelnut orchards and a comparison with an adjacent natural oak forest

Soil respiration (R_S) is one of the largest terrestrial sources of CO₂ causing global warming and may vary according to land use and vegetation type. Türkiye is in the first place in the world in terms of area of hazelnut orchards that are generally converted from natural forests. The aim of this study was the comparison of the effects of cultural practices (pruning, fertilizing, and pruning+fertilizing) on R_S in hazelnut orchards and that of the adjacent natural oak forest. Every trial site had a statistically similar annual mean R_S, which ranged from 0.15 to 1.55 g C m^-2 day^-1. The R_S on the sites was different only in the spring season and was similar in the other seasons. The R_S of the pruned and fertilized hazelnut orchard (H_pf) in the spring was 58% greater than the unmaintained hazelnut orchard (H_c) and oak forest and 28% greater than the only fertilized hazelnut orchard (H_f). The R_S of H_pf was also greater than other sites in most monthly measurements. While the positive correlation between soil moisture and R_S was on an annual basis (r = 0.44), it was higher in summer (r = 0.61) and autumn (r = 0.55) seasons. The negative correlation between soil temperature and R_S in the summer and autumn seasons evolved positively in winter. The results of the study suggest that the maintenance practices applied in the hazelnut garden could increase R_S in the spring when soil moisture and temperature are optimal but have no effect in other seasons or on an annual basis.