Vineyard weed management practices influence nitrate leaching and nitrous oxide emissions

Successive years of multiple tillage passes have been linked to reductions in soil carbon (C) and shifts in soil physical properties, which are often linked to changes in soil nitrogen (N) retention. ‘Under the vine’ cultivation is becoming a more common practice in vineyards as growers seek alternative means of weed control. Therefore, we (1) investigated the effects of cultivation or herbicide on soil N leaching during a 1 year cycle of vineyard management and (2) determined differences in short-term nitrous oxide (N2O) emissions and N transformations between ‘under the vine’ treatments during summer fertigation, a period in which we hypothesized that high N2O emission rates would occur under warm, moist soil conditions. Few differences were found in the chemical and physical characteristics of soil profiles in cultivated and herbicide treatments. In the surface depths, total C and microbial biomass (i.e., total phospholipid fatty acids) were greater in the tilled than herbicide soils. This contrasts with other findings, but suggests that the greater weed biomass in the tilled treatment contributed labile C to soil C pools. Greater soil nitrate was found at depth (1.2 m) in the herbicide than cultivated treatment. Also, the cultivated soil had nearly 50% less nitrous oxide emissions during fertigation than the herbicide soil. We suggest that greater weed presence, soil C and microbial biomass in the tilled treatment contributed to the greater N retention.