Nutrient Management Research Database

Experiments were conducted at several sites to investigate different approaches to increasing the efficiency of potassium fertilizer use on clay soils, and to evaluate whether improved plant potassium status leads to improved efficiency of nitrogen fertilizer utilization. The problem of potassium deficiency on heavy soils creates a special need for efforts to improve efficiency because high rates of applications are required to obtain plant responses. Our objectves were to test the potential of altered fertilizer placement, altered irrigation regimes, supplemental gypsum applications, and selection of rootstocks in winegrapes for decreasing the need for high rates of fertilizer applications. High rates of potassium sulfate (8lbs or greater of potassium sulfate per vine) and supplemental irrigation (2 to 4 times the standard rate) to decrease potassium fixation and increase the availability of potassium for root uptake. This has successfully increased vine potassium status and maintained high potassium status beyond veraison. A slight increase in root growth in the upper 30cm of soil due to both potassium and water applications may have contributed to increased potassum uptake. Use of gypsum and potassium sulfated increased soluable potassium in the soil, vine potassium status, and yield above that of potash alone. The use of gypsum can be recommended when applying potassium on similar soils. At the Healdsburg Chardonnay site, treatments that combined nitrogen and potassium applications exhibited the greatest vine potassium status and yields.

• Experiments were conducted to investigate approaches to address potassium deficiencies in Pinot Noir and Chardonnay planted on heavy clay soils at three different vineyard sites in Carneros, Yountville, and Healdsburg.
• The Carneros site received various fertilizer and irrigation treatments.
• TheYountville site had four separate treatments with 8lbs of Potassium per vine with 6 different rootstocks:
  • potassium and drip added;
  • potassium no drip;
  • no potassium with drip added;
  • no potassium, no supplemental drip
• TheHealdsburg site received 5 treatments:
  • untreated control
  • potassium sulfate
  • potassium sulfate and gypsum at similar rates
  • potassium nitrate
  • calcium nitrate.

• In Carneros, yields increased with greater applications of potassium and irrigation water, the highest yields were found in vines that received 8lb potassium sulfate per vine and 2 to 4 times the standard rate of irrigation.
• At the Yountville site, yield increases were dependent on rootstock selection, as well as potassium and irrigation amounts.
• Yields varied from about 5 to almost 10 kg per vine, with 5C and 110R having high yields and St. George, lower yields.
• At the Healdsburg site, supplemental Gypsum increased yields over other treatments.
• Across the trials, yields increased due to more clusters per vine.
• Vine potassium status increased in the irrigated and fertilized treatments in Carneros.
• The Yountville site demonstrated that plant uptake of irrigation water and potassium is somewhat dependant on rootstock selection.
• In Healdsburg, the use of gypsum and potassium together increased yields and plant potassium status to a greater extent then just using potash alone.
• Potassium deficiency in heavy clay soils is a challenge.
• In these trials, both the supplemental irrigation and the addition of gypsum increased the availability of soluble potassium to the vines, when potassium fertilizers were applied to the heavy clay soils.
• Root maps also show greater root growth in soil areas where most of the potassium was available.
• The author believes that the enhanced root growth, due to more water and potassium, allowed for greater vine uptake of potassium.