Impact of Vineyard Floor Management Practices on Weed Communities and Soil Quality

Vineyards in the low rainfall areas of central California have vegetation in the row middles and no vegetation in a swath 0.46–0.61 m wide in the vine rows. The vine rows are kept free of vegetation by the use of pre- and/or post-emergent herbicides, mechanical cultivation, and hand hoeing. In a study conducted from 2001–05 we observed that the choice of weed control strategy resulted in distinct weed communities over time. In this same study, vine rows were kept weed free and row middles were cover cropped or kept bare; soil organic matter, microbial biomass and nutrient levels were evaluated in all treatments. The cover crops, cereal rye (Secale cereale L.) or triticale (X Triticosecale Wittm. Ex A. Camus.), were planted in strips 0.93 m wide. We observed significant increases in soil organic matter, microbial activity and some nutrients in the row middles that were cover cropped. However, no improvements in soil health parameters were observed in vegetation free vine rows adjacent to cover cropped row middles.  Given the benefits that cover crops provide to the soil system, we conducted a follow-up trial from 2006–09 to evaluate ways to include a barley (Hordeum vulgare L.) cover crop in the vine row. Treatments include killing the cover crop when it was 0, 15.2, 30.1, 45.7, and 61.0 cm tall to manage the competition of the cover crop on the vine growth and soil moisture used by the cover crop. In a low rainfall area, any water used by the cover crop would have to be replaced by irrigation, which would increase the cost of production.  We observed that killing the cover crop when they were 30.1 inches tall safeguarded the yield of the vines and increased the levels of soil organic matter by the third year of the trial. Cover crops grown in the vine row reduced nitrogen levels in the vines, indicating that care must be taken to offset this negative impact of this practice; however, vine row cover crops increased potassium and phosphorus levels in vines. Evidence indicated that vine row cover crops improved irrigation water infiltration from drip emitters because higher levels of soil moisture were observed in the vine row cover crop treatments vs. uncover cropped treatments during the summer irrigation season. This research indicated that vine row cover crops can be successfully managed to improve soil quality while not adversely affecting crop growth.