Harvest has begun, and we can see that light at the end of the tunnel signaling the end of another grape-growing season. However, it is easy to forget about the more critical phenological changes a grape vine makes in its growth cycle – pre-dormancy root development and nutrient storage. This is the time when the vines fatten up before hibernation. They draw nutrients away from the leaves, expand roots to capture more nutrients, and store those nutrients in woody tissue so they can supply the energy necessary for bud-break and early shoot/root expansion next year. We recommend you reserve a liquid fertilizer application, post-harvest, to address this opportunity and provide a solid foundation, nutrient-wise, for next season. Key components in this fertilizer application can include nitrogen (N), potassium (K), calcium (Ca) and zinc (Zn), depending on soil/tissue availability and harvest removal numbers.
It is very important to understand that we are mining nutrients from the soil when we pull fruit off the vine and haul it off. For every ton of grapes harvested, we remove approximately 8 pounds of N, 3 pounds of phosphorus, and 13 pounds of K. The plant needs to replace those nutrients, either through mining the soil with its roots or supplemental fertilization. The Best Management Practice (BMP) nutrient budget Helena recommends takes all inputs into consideration (soil, water, organic matter and fertilizer). Note that credits are given for soil nitrogen, water nitrogen and organic matter. The resulting deficit needs to be made up through fertilization. A vine has two peak N uptake windows. The first is from bud-break through bloom, and the second is post-harvest, prior to dormancy. You should apply 80 percent of the vines N requirements in that first window and the remaining 20 percent post-harvest.
The other key component in post-harvest fertility is K, which is readily available in most soils. However, vines usually can’t uptake enough K to satisfy crop requirements during peak demand. This spike in demand starts just before fruit set and continues through sizing, then peaks again prior to dormancy. K moves into the roots through diffusion (very short distances in the soil) so drought, deficit irrigation, high salinity, sandy soils and high soil levels of calcium and magnesium can all adversely affect K uptake. The key concept in potassium fertility is getting readily-available K into the vine early and often so the plant has time to metabolize it and actively translocate carbohydrates to the fruit as well as internal storage structures. A major challenge for conventional potassium fertilizers is increasing the mobility of K in the soil. In Helena’s soil-applied portion of the program, Nucleus® 0-0-21 or Nucleus 0-0-15 is recommended. These Nucleus products utilize Konduit™ Formulation Technology to increase the solubility and mobility of K in the soil. This package overcomes fertilizer inefficiencies and K fixation by soil colloids. Another benefit is unsurpassed compatibility with other liquid fertilizers, making it an ideal blending partner.
One of Helena’s recommended post-harvest blends is a 12-0-8 with 3 percent Ca, 2 percent Zn, and 10 percent humic acid. It utilizes Nucleus 0-0-21, Axilo® Ca, Axilo Zn, Hydra-Hume® and Standout® for immediate nutrient availability, rapid uptake and root stimulation.
With a Grape Wise plan tailored to your vineyard, Helena consultants will provide agronomic information and expert recommendations throughout the growing season. Ensure your vines are well fed for maximum quality and yields. Contact your local Helena representative to develop your Grape Wise plan today.
— Paul W. Crout, CCA, PCA, Senior Product Manager/Agronomist