Fertilizer Management for Grapevines
Methods of Fertilizer Application
Fertilizer placement is an integral part of efficient vineyard management. Correct placement often improves efficiency by which vines take up nutrients and consequently encourages acceptable yields and the production of marketable fruit. Many placement techniques are available for growers.
Broadcasting
Broadcasting spreads fertilizer across the soil surface (See Figure 17.3). Broadcast fertilizer can be left on the soil surface or incorporated by a tillage operation after application. With incorporation, these nutrients are mixed into the surface layer of the soil where root interception is more likely to occur. Broadcasting is generally the fastest and least costly fertilizer application method. Elemental sulfur is particularly suited to broadcast applications because the granules are left on the soil surface and exposed to weathering processes, which oxidizes the sulfur to plant available forms.
Ammonia Volatilization
Loss of nitrogen fertilizer through ammonia volatilization is a concern in vineyards because solid nitrogen sources applied to the soil surface are often not incorporated. Up to 50 percent of the nitrogen in solid urea or ammonium-containing fertilizer sources can volatilize to the atmosphere when applied to grapevines under two circumstances: (1) surface-applied ammonium fertilizer sources on calcareous or freshly-limed soils; and (2) surface-applied urea on acidic or alkaline soils.
Banding
Compared to broadcast and incorporated fertilizer, the banded application keeps contact between soil and fertilizer to a minimum (See Figure 17.4). This reduces fixation or “tie up” of phosphorus and potassium in the soil. Fixation of phosphorus varies with soil pH. In very acid soils (pH <5.0), the fixation occurs as insoluble iron and aluminum phosphates.
Fertigation
Fertigation refers to injecting fertilizer into an irrigation system. This is accomplished in drip (trickle) by using some type of injector to meter the concentrated fertilizer solution into the irrigation water (See Figure 17.6). In addition to greater flexibility in application timing and optimal placement, fertigation increases the rate of nutrient uptake and predictability of vine response to fertilization compared to broadcast and band applications.
Foliar Application
Traditional soil fertilization methods, while commonly used, often fall short in meeting the micronutrient needs of plants due to various soil-related factors, such as pH levels, organic matter content, and microbial interactions, which influence nutrient availability. To address these limitations, foliar application has emerged as a targeted and efficient approach for enriching vineyard crops with essential micronutrients. By enabling the direct absorption of nutrients through the leaves, foliar feeding offers a more immediate and effective means of correcting deficiencies, particularly under conditions that restrict soil nutrient availability. Foliar application is the practice of spraying nutrient solutions directly onto plant foliage and has gained considerable traction in vineyard management. This method enables rapid nutrient absorption through the stomata and epidermis of leaves, bypassing the complexities of soil dynamics that often restrict micronutrient availability.
Foliar Fertilizers
Foliar fertilizers play a crucial role in the precise management of micronutrient deficiencies in vineyard crops (Table 17.4). These fertilizers can be broadly categorized based on their solubility and chemical composition, which significantly affect their stability, bioavailability, and efficacy. Chelated micronutrients are predominantly favored in foliar applications due to their superior stability and enhanced bioavailability. Chelating agents such as EDTA and EDDHA are commonly employed to form stable complexes with micronutrients, thereby preventing precipitation and facilitating efficient uptake by foliage. These chelated forms ensure that micronutrients remain soluble under varying environmental conditions, enhancing their accessibility to plant tissues.
Use of Adjuvants
Incorporating surfactants or other adjuvants can enhance nutrient penetration and absorption, particularly in plants with waxy leaf surfaces. Adjuvants reduce surface tension, facilitating better nutrient distribution and uptake, ultimately improving the effectiveness of foliar applications
Timing and Frequency
The timing of foliar applications is critical for maximizing nutrient uptake. Foliar fertilizers are best applied in the early morning or late evening to avoid the sun and heat, when the air is cool and humidity is high. Applications are typically scheduled during periods of active growth, such as early vegetative development, pre-flowering, and fruit set, when nutrient demands are at their highest.
Factors Influencing Efficacy
Environmental conditions that cause stomata (leaf openings) to close reduce the efficiency of nutrient uptake. Temperature, humidity, and wind speed have a significant impact on the uptake of foliar nutrients. Optimal environmental conditions typically include moderate temperatures, high humidity, and low wind to enhance leaf wetness duration and nutrient uptake.
Water-stressed vines have reduced stomatal activity and slower fertilizer uptake. Dense canopies reduce inner leaf coverage. Foliar fertilizers are most effective when applied to younger leaves and fruits
Foliar nutrient sprays are most effective when deficiency is mild to moderate. The chemical form of micronutrients impacts their stability and bioavailability.
Application Techniques
Effective foliar application requires proper spraying techniques to ensure uniform coverage and optimal absorption. Common methods include:
Risk of Over-Application
One of the primary challenges with foliar fertilization is the risk of over-application, which can lead to nutrient toxicity and result in adverse physiological effects, such as leaf burn and tissue damage. Unlike soil applications, where excess nutrients may leach or become bound within the soil matrix, foliar-applied nutrients are readily available for immediate uptake, heightening the risk of phytotoxicity if applied in excess.
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