The Vegetative Response of 'Concord' Grapevines to Soil pH © 2001

Terence R. Bates, Richard M. Dunst, Theodore Taft, and Michael Vercant
Department of Horticultural Sciences, Cornell University Vineyard Laboratory, Fredonia, N.Y. 14063

Abstract. One- and two-year-old 'Concord' (Vitis labrusca L.) grapevines were used to study the effect of soil pH on vegetative growth and nutrition. Ninety-eight, own rooted, 'Concord' nursery grapevines were planted in 94.6 L (25 gal) pots containing vineyard soil adjusted to a soil pH range of 3.5-7.5. After the first growing season, 49 of the vines were destructively harvested and measured for root and shoot growth. The remaining 49 vines over-wintered in the pots, were defruited in year two, and were destructively harvested at the end of the second growing season. Below 4.5 soil pH, there was a reduction in root biomass and a greater reduction in shoot biomass leading to a higher root to shoot ratio. Higher aluminum availability at low soil pH lead to lower total cation and phosphorus uptake. There were no significant differences in vegetative growth of young 'Concord' vines from a soil pH of 5.0-7.5. However, there was a trend toward lower shoot biomass and higher root to shoot ratio at the highest soil pH level. Phylloxera nodosities were present in equal densities on all roots of the soil pH study; however, the negative impact of phylloxera on vine dry mass was only significant on vines already under nutrient stress at the highest and lowest pH treatments.

Soils of the Lake Erie Regional Grape Belt can vary in texture, organic matter, pH, aeration, and moisture holding capacity . Low soil pH, which is characteristic of Lake Erie regional soils, affects nutrient availability and root growth . A 1934 study of Chautauqua county 'Concord' vineyards indicated a soil pH average of 5.4 and a yield average of 3.8 t·h-1 (1.7 tons·acre-1) . A 1997 soil sample survey from the Lake Erie Regional Grape program indicated a soil pH average of 4.5 (Fig. 1) and a yield average of 11.3 t·h-1 (5.0 tons·acre-1). While the 'Concord' grape industry has increased yield through a variety of viticulture practices, the average soil pH has decreased, presumably from the repeated yearly application of acidifying ammonium nitrate or urea fertilizers . One-year-old 'Concord' cuttings did not show a growth difference when grown in pot culture at soil pH 6.7 or 4.8, indicating the potential acid tolerance of Vitis labrusca . From 1958 to 1968, a 'Concord' study in Erie County, Pennsylvania did not show an effect of calcitic or dolomitic limestone on vine growth or yield (surface application rates of 6.8-18.0 t·h-1 [3.0-8.0 tons·acre-1] over a three-year period) . However, in that study, the limestone treatments only changed the soil pH in the upper 7.6 cm (3 inches) of soil where the limestone was incorporated and very little soil pH change was recorded below the 15.2 cm (6 inch) soil depth. Although the soil pH change was restricted to the to the top 7.6 cm, calcitic limestone increased soil calcium to a 15.2 cm depth and dolomitic limestone increased soil magnesium to a 30.5 cm (12 inch) depth, the deepest measurement taken. The increase in calcium and especially magnesium decreased the concentration of petiole potassium to the point of visual potassium deficiency and vine size reduction in some years. Potassium deficiency through calcium and magnesium competition as a result of dolomitic limestone application can be a problem in New York 'Concord' production. Often, this problem is exaggerated by dry soil conditions, which limits potassium availability in unirrigated vineyards, or high crop level, which increases vine potassium demand . Together, these studies on the response of 'Concord' to soil pH, limestone, and potassium have led to the argument against the addition of limestone to 'Concord' vineyards in Western, New York despite soil pH values below 5.0 in a majority of vineyards.

Although excessive hydrogen ions in the soil solution can have an effect on root cell membrane potential, low pH itself does not inhibit root growth. As the soil pH decreases from 5 to 3.5, aluminum solubility increases and it is the free and exchangeable aluminum ions that affect nutrient availability and root growth. High free aluminum and iron precipitates phosphorus, making it unavailable to the plant, and exchangeable aluminum displaces calcium and magnesium, decreasing their availability. In most plant systems, aluminum toxicity has a direct effect on root growth by inhibiting cell division in the root apical meristem. In spite of this, some species have developed strategies to avoid soil chemical stress and increase nutrient acquisition efficiency. In response to poor nutrient availability, roots generally have been shown to change growth patterns, to stimulate ion uptake and transport, to modify the rhizosphere chemistry, and to form associations with beneficial microorganisms in order to increase nutrient acquisition efficiency. The rhizosphere refers to the root-soil interface and it can differ substantially from the bulk soil in ion concentration, pH, redox potential, root exudates, organic carbon, and microbial activity. Nutrient availability in the bulk soil is a function of the soil chemical characteristics, a passive characteristic. Nutrient availability in the rhizosphere is a function of root physiology and biochemistry, an active process. Differential anion-cation uptake, proton pumping, chelating and reducing compound secretion, and beneficial microbial association are all physiological processes roots use to make the rhizosphere a more benign environment for root growth and ion uptake.

Mycorrhizas are the beneficial association between plant roots and mycorrhizal soil fungi. Several studies on Vitis vinifera roots document the beneficial association of vesicular-arbuscular mycorrhizae (VAM) in acquiring immobile soil nutrients such as phosphorus. VAM infection or its benefit to 'Concord' roots has not been documented; however, VAM has been shown to play an important role in other acid tolerant species. Phylloxera, a root pest, is common in New York vineyards where it attacks and galls the fine feeder roots of 'Concord'. Although the galling decreases the fine root surface area of the root system, it is generally accepted that phylloxera is not a major constraint to 'Concord' production.

This study investigates the response of 'Concord' grapevines to soil pH and mild nutrient stress. Attention is given to root growth, rhizosphere pH, nutrient absorption, phylloxera nodosities and mycorrhizae.

Materials and Methods

Ninety-eight 94.6 L (25 gal) plastic pots were filled with vineyard soil and pH adjusted with dolomitic limestone or ground sulfur. The native vineyard soil pH was measured with water at 5.2. Ground sulfur was used to create three soil pH treatments more acidic than 5.2 and dolomitic limestone was used to create three soil pH treatments more alkaline than 5.2 (Table 1). The experiment consisted of seven soil pH treatments x seven replicate pots x 2 growing years = 98 pots total.

Soil from a vacant plot at the Cornell Vineyard Laboratory in Fredonia, N.Y. was mixed with individual pot soil amendments in a cement mixer. After incorporation of the sulfur or lime, the amended soil was dumped into a 94.6 L (25 gal) plastic pot (MacKenzie Nursery Supply, Inc. Perry, Ohio). The pot was placed in a 61.0 cm (2 foot) deep trench and an own rooted 'Concord' nursery vine (Double A Vineyards, Fredonia, N. Y.) was planted in the pot. Drip irrigation was installed on the 98 pots and the vines were kept well watered for the life of the experiment.

In year one, all vines were pruned back to two shoots after the last threat of spring frost. Soil pH and leaf area development was monitored during the first growing season. On 10/6/98, 49 of the pots were destructively harvested. Root fresh mass, shoot fresh mass, bulk soil pH, and rhizosphere pH were measured at harvest. Soil pH was measured with a pH meter in a 50:50 mixture of soil and water by volume. Bulk soil pH was determined from soil collected from an area in the pot without grape roots and rhizosphere pH was determined from soil shaken from the grape roots. After harvest, vine tissues were dried at 60oC and dry mass was measured. For nutrient analysis, ground leaf and petiole samples were sent to The Pennsylvania State University Agricultural Analytical Services Laboratory (University Park, Pa.). Total nitrogen concentration of each sample was determined by combustion and other nutrient concentrations were determined through dry ash analysis.

In year two, the remaining vines were pruned to four shoots after the last threat of spring frost and the vines were defruited 30 days after bloom. On 10/13/99, the second year vines were destructively harvested and measured the same as year-one vines. Additional information was collected on phylloxera and mycorrhizal infection in 1999. Random fresh root sub-samples were collected and phylloxera nodosities were counted on the sub-samples. The sub-samples and main root systems were then dried at 60oC and weighed and phylloxera nodosities per root system were calculated on a dry mass basis. A second fresh root sub-sample was stained for VAM. For VAM staining, fresh roots were cleared in a solution of 5% potassium hydroxide heated to 80oC for 2 h; acidified in 1% hydrochloric acid for 12 h; stained in a solution of 500 ml glycerol, 450 ml water and 50 ml 1% hydrochloric acid and 0.25 g Typan Blue for 12 h; and destained for 24 h (destain = staining solution without Typan Blue) (All chemicals, Sigma). Roots were observed under a dissecting microscope for mycorrhizal infection.

Results and Discussion

Soil pH affected total vine biomass and vine root to shoot ratio in both 1998 and 1999 (Fig. 2 A and B).

Soil pH < 4.5. Below a soil pH of 4.5, total vine dry mass decreased and the root to shoot ratio increased. Tissue nutrient analysis shows the effect of aluminum toxicity on young 'Concord' vine nutrition (Fig. 3 A and B). Low soil pH (< 4.5) decreased the concentration of total cations in 'Concord' grapevine tissue. This was primarily a result of lower potassium and calcium concentrations. In addition, there was an increase in tissue aluminum and iron and a decrease in tissue phosphorus. Aluminum toxicity, whether a direct effect on root growth or an indirect effect on nutrient availability and uptake, decreased 'Concord' vine biomass and tissue nutrient concentration.

By comparing the bulk soil pH and the rhizosphere soil pH, vines growing in a bulk soil pH of 4.0 raised the rhizosphere pH over 0.5 pH units (Fig. 4). In well-aerated soils, rhizosphere pH modification is most often attributed to the amount of H+ and HCO3- secreted by the roots as a result of differential cation-anion uptake . Acid tolerant species have been shown to increase rhizosphere pH under acidic and high aluminum soil conditions better than non-acid tolerant species . Minor increases in rhizosphere pH above 4.0 can greatly reduce the amount and detrimental effects of soluble aluminum . However, the importance of rhizosphere pH in aluminum resistance over other mechanisims such as organic acid release from the roots is still in question (Kochian, 1995).

Observations of phylloxera infection in 1998 prompted the measurement of phylloxera nodosities on excavated roots in 1999. Phylloxera nodosities were present on all roots of the soil pH study and there was no effect of soil pH on the density of phylloxera nodosities (average of 37 nodosities·g root dry mass-1). However, nodosity counts were also variable (from 3 to 120 nodosities·g root dry mass-1). Therefore, vines were sorted according to soil pH and high nodosity density (> 37 nodosities·g root dry mass-1) or low nodosity density(<37 nodosities·g root dry mass-1). There was an interaction of soil pH and phylloxera infection on shoot dry mass at the low soil pH treatments (Fig. 5). Therefore, the combination of aluminum toxicity and phylloxera infection had a greater negative effect on vine growth than either individual factor.

Soil pH 5.0-7.0. From a soil pH of 5.0 to 7.0, there were no significant differences in vine, shoot, or root biomass. As the soil pH increased from 5.0 to 7.0 with dolomitic limestone, total tissue cations remained the same; however, there was an increase in tissue magnesium and a decrease in tissue potassium. There was also a decrease in tissue aluminum and iron and an increase in tissue phosphorus as the soil pH increased.

Although there were no differences in vine size or root to shoot ratio from a soil pH of 5.0 to 7.0 in the pot study, there were some differences in rhizosphere pH (Fig. 4). Vines in a bulk soil pH of 7.0 decreased the rhizosphere pH by 0.5 pH units. On the other hand, there was little difference between bulk soil pH and rhizosphere pH in plants growing in a bulk soil pH of 5.5.

Soil pH > 7.0. There appeared to be a trend toward decreased shoot growth with an increased root to shoot ratio above a soil pH of 7.0 in 1999. There are several possible explanations. It is possible that the addition of excessive rates of dolomitic lime induced potassium deficiency in those plants, which decreased shoot growth. Although tissue potassium concentration was lower in the lime treatments, there were no leaf symptoms of potassium deficiency and plant potassium demand should have been lowered with the crop removal. A second possibility may be the occurrence of iron, zinc, or manganese deficiency at the high lime treatment. Similar to the low soil pHtreatment (<4.5), the high pH treatment(>7.0) had an interaction with phylloxera infection (Fig 5). The possible combination of poor potassium nutrition at high soil pH and heavy phylloxera infection had a greater negative impact on shoot growth than each individual factor.

It is interesting to note that VAM were abundant in the sub-samples of all the roots and at all soil pH levels. Presumably, all of the vines had mycorrhizae in the nursery and entered the trial with innoculum. Soil pH did not appear to have an effect on infection rate; however, we did not attempt to measure the effect of soil pH on other aspects of VAM activity such as hyphae growth.

Combining the measurements of vine biomass, tissue nutrient concentrations, rhizosphere pH, and root health, the optimum soil pH for young non-bearing 'Concord' vines appears to be between 5.0 and 6.0. In this soil pH range, the roots are not subject to poor soil chemical conditions such as aluminum toxicity or phosphorus deficiency. In the acidic soils of the Lake Erie Grape Region, excessive limestone applications to adjust soil pH above 6.0 creates potential problems of calcium, magnesium, and potassium imbalances. 'Concord' grapevine roots show characteristics of acid tolerance through rhizosphere modification and VAM infection. Furthermore, adequate root growth and activity combined with balanced nutrient availability at 5.0-6.0 soil pH allows 'Concord' to overcome the negative effects of high phylloxera infection.

This study did not investigate the effect of soil pH and soil pH adjustment in a mature bearing 'Concord' vineyard. Deep incorporation of soil amendments is difficult in established vineyards, which has complicated the interpretation of similar experiments. In addition, potassium demand in 'Concord' fruit is relatively high and increases with increasing crop level. This may exaggerate magnesium and potassium imbalances in limed 'Concord' vineyards.

Literature Cited

	Fig. 1. 1997 vineyard distribution according to soil pH in the Lake Erie Regional Grape Belt. (n = 300 vineyards)

	Fig. 2 A and B. The effect of soil pH on the vine dry mass (A) and root to shoot ratio (B) of young, pot-grown, 'Concord' grapevines. (n = 6, bars = ± SE)

	Fig. 3 A and B. The effect of soil pH on potassium, calcium, and magnesium (A) or aluminum, iron, and phosphorus (B) 'Concord' leaf/petiole tissue concentrations taken in the fall (n = 6, bars = ± SE)

	Fig. 4. The change in rhizosphere pH from bulk soil pH in 'Concord' roots grown at different soil pH levels. Positive values represent and increase in rhizosphere pH and negative values represent a decrease rhizosphere pH relative to the bulk soil pH.

	Fig. 5. The interaction of soil pH and relative phylloxera infection on two-year-old 'Concord' shoot dry mass. (n = 3, bars = ± SE)

We thank Christine Cummings, Eileen Eacker, and Paula Joy for their viticulture assistance and Phil Throop for the vineyard survey information. This research was supported by the New York Wine and Grape Foundation and the Eastern Viticulture Consortium.

Click here for the 1999 report on the potted soil pH study.