Why is Root Biology So Important in the Vineyard?

In the late 1950’s, Dr. Nelson Shaulis planted a factorial experiment at the Cornell Vineyard Lab in Fredonia known as the "West Tier" experiment. Currently, the treatments in the trial include pruning severity, training, shoot positioning, floor management, nitrogen fertilization, and rootstocks -- 96 treatment combinations in all! On the subject of root biology, Shaulis’ West Tier teaches us one simple lesson: "Viticultural practices that stimulate root growth and activity increase vine size and productivity, while inhibiting root activity can be a management tool for controlling excessive vigor." Simple? Maybe not so simple when you consider that just about every vineyard management decision we make directly or indirectly impacts grape roots. Pre-plant decisions such as soil type, depth, and drainage establish rooting potential. Vineyard activities such as weed control, fertilization, and irrigation have direct effects on grapevine roots through water and nutrient availability. Furthermore, canopy and crop management has indirect impacts on root growth and function through carbohydrate assimilation and partitioning.

The goal of the Concord juice industry is to sustainably produce the largest crop of mature fruit. If we argue that there is a strong relationship between vine size and yield (and there is) and that root management is a tool for controlling vine size, then the attainment of this goal will depend largely on how we manage grapevine root systems. In the West Tier factorial, we measure a significant increase in vine size and a 3 to 4 ton/acre yield increase through simple weed control (light cultivation) and fertilization (50 pounds actual nitrogen per year). However, most commercial juice grape vineyards are under more restrictive or simply different soil conditions than the Vineyard Lab. Vine size (or root biology) limitations with respect to soil type, water holding capacity, soil pH, etc. on different sites may require different management than cultivation and nitrogen. To address this, current root management projects at the Vineyard lab investigate the response of Concord grapevines to nitrogen fertilization, irrigation and pruning, weed management, phylloxera and crop load, rootstocks and soil type, and soil pH.

Low soil pH (pH 5.0 or lower), that is characteristic of Lake Erie regional soils and some Finger Lake soils, affects nutrient availability and 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 precipitates phosphorus, making it unavailable to the plant, and exchangeable aluminum displaces calcium and magnesium, decreasing their availability. Aluminum toxicity can also affect root growth by inhibiting cell division in the root apical meristem.

High pH soils, either natural limestone based soils or soils amended through the application of lime, present a whole new set of nutritional circumstances for Concord roots. As the soil pH increases from 5 to 8, aluminum insolubility removes it from the playing field, which alleviates some of the phosphorus, calcium, and magnesium problems. However, iron also precipitates out of the soil solution limiting its availability.

Hydrogen (H), aluminum (Al), potassium (K), calcium (Ca), and magnesium (Mg) are similar in that they exist as positively charged ions (cations) in the soil solution and can compete with each other in the soil solution or in root uptake. We remove excessive H and Al as problems in acidic soils by spreading lime. However, dolomitic limestone adds Ca and Mg to the soil that can compete with K uptake. Concord fruit requires a lot of K so higher producing vineyards have a higher K requirement. To make matters worse, K availability is dependent on soil moisture. To avoid the ‘big crop - dry weather’ situation leading to potassium deficiency, some growers apply a maintenance dose of potash every year. Although this may push them to the edge of magnesium deficiency, it is a situation many growers are more comfortable living with. As you can see, the balance of K, Ca, and Mg in pH adjusted soils is a bit more tricky and it is the basis for the controversy surrounding lime based vs. potassium based nutrient recommendations.

One- and two-year-old Concord grapevines were used to study the effect of soil pH on vegetative growth and nutrition. Ninety-eight Concord nursery grapevines were planted in 25-gallon 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, both root and shoot growth (vine size) was decreased. Higher aluminum availability at low soil pH led 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 infections were present in equal densities on all roots of the soil pH study; however, the negative impact of phylloxera on vine biomass was only significant on vines already under nutrient stress at the highest and lowest pH treatments. In other words, overlaying nutrient stress (caused by soil pH) with pest stress (caused by phylloxera) gave the young vines a ‘double whammy.’

In the spring of 1999, a new experimental vineyard planting was established at the Vineyard lab to study the effects of soil pH on Concord grapevine growth and nutrition in a cropping situation. Vineyard blocks have been set up with soil pH of 4.5, 5.5, 6.5, and 7.5. We predict that the combination of mild nutrient stress (through soil pH) and crop stress (high crop nutrient demand) will indicate the optimum soil pH for Concord production. Since we used dolomitic limestone to adjust the soil pH and we intend on using high crop loads, specific attention will be given to the balance and management of cations (K, Ca, Mg, etc.) in the grapevines.