Nutrient Management Research Database

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 (1.2m) 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.

This study took place in a vineyard planted with Chardonnay (Teleki 5C rootstock) in 1997 at a 1.8 x 2.4m spacing.

• 2 weed control treatments were started in 2001.  In one treatment,  weeds were managed with mechanical cultivation under the vine four to six times per year.  In the second treatment, weeds were managed by applying pre/post-emergent herbicide in winter, and a glyphosate/oxyflourfen application in summer as needed.
• Drip emitters were set up on one side of each of 4 adjacent vines per treatment, resulting in 4 combinations of irrigation/weed management treatments.
• Leaching of soil inorganic N was assessed at 1.25m depth using ion exchange resin bags.
• Soil was collected at 0-15, 15-30, 30-55, and 80-105cm above the resin bags and measured for gravimetric water content NO₃^--N, and NH₄^--N.  Soil bulk density, potential net N mineralization, dissolved organic C, potential soil respiration, texture, cation exchange capacity, pH, percent total N and C, Olsen P and exchangeable potassium, sodium, calcium and magnesium were measured as well.
• N dynamics were measured following fertigation and irrigation events, including N20 gas samples collected using the static chamber method.

• 50 h after fertigation, the 'Herbicide-drip' treatment decreased by 60% from its initial concentration, while the same decrease did not occur in the 'Cultivation-drip' treatment.
• Total N20-N emissions during the first fertigation cycle were 50% greater in the 'Herbicide-drip' treatment combination when compared to the 'Cultivation-drip.'
• Total C and microbial biomass were greater in cultivated treatments when compared to treatments that employed herbicide for weed control.