Chapter 17

Fertilizer Management for Grapevines

Organic Fertilizers

Organic nutrient sources are highly heterogeneous and vary in quality and quantity. Organic fertilizers generally come from plants, animals, or minerals. Soil organisms break down the material into nutrients that vines can use. Some organic fertilizers contain significant amounts of only one of the major nutrients, such as phosphorus in bone meal, but they often have trace amounts of many other beneficial nutrients. Most organic fertilizers have low total nutrient content and release their nutrients slowly. To compensate for the low nutrient content and slow nutrient release, higher rates of organic fertilizers (compared to synthetic fertilizers) are needed to meet a crop’s nutrient needs. However, applying organic fertilizers year after year will build up a pool of nutrients in the soil such that, over time, the annual rate of application may decrease. Listed below are the advantages and disadvantages of organic fertilizers.

U.S. Department of Agriculture’s National Organic Program Rule

Most synthetic fertilizers are prohibited by the U.S. Department of Agriculture’s National Organic Program (NOP) rule [7 CFR 205.105(a)], with a few specific exceptions found on the National List [7 CFR 205.601(j)]. Note that the NOP forbids the use of human sewage sludge (biosolids) from a municipal wastewater treatment facility on an organic operation (§ 205.105 (g)).

Fertilizers Labeled as “Organic”

Fertilizer labeling laws are enacted state-by-state in the United States. The regulators of fertilizer labeling laws are organized through the Association of American Plant Food Control Officials (AAPFCO). Most states follow the AAPFCO model bill, which defines “organic fertilizer” as “[a] material containing carbon and one or more elements other than hydrogen and oxygen essential for plant growth” (AAPFCO, 2008).

Manure and Compost Amendments

While composts and manures are frequently considered to be mainstays of fertility management programs in organic systems, these amendments often vary widely in nutritive value and thus are increasingly being applied as a basic carbon source to enhance overall and long-term soil health. The carbon content of these materials is also quite variable, though it generally ranges from 20 to 40 percent on a dry-weight basis.


The use of livestock manure to build up soil health, specifically soil organic matter, is a practice that has been embraced by organic farmers. Increasing soil organic matter improves soil structure or tilth, increases the waterholding capacity of coarse-textured sandy soils, improves drainage in fine-textured clay soils, provides a source of slow release nutrients, reduces wind and water erosion, and promotes growth of earthworms and other beneficial soil organisms.


The most important benefit of using compost is the increase in soil organic matter in addition to adding nutrients to the soil. Generally, compost contains relatively low concentrations of nitrogen, phosphorus, and potassium compared to manure. Just like manure, the nitrogen content of compost will vary according to the source material and how it is composted. In general, nitrogen in the form of ammonium (NH4?) or nitrate (NO3¯) is low in compost compared to manure.

Application of Manure and Compost

Uniform surface application over the entire vineyard floor can be accomplished with a broadcast manure spreader prior to planting a vineyard, or in an existing vineyard, provided the equipment can fit into the vine rows (See Figure 17.2)

Mineral-based Fertilizers

Naturally occurring mineral-based fertilizers are considered organic only in the sense that they are not extensively processed. Mineral-based fertilizers such as gypsum, greensand, and hard-rock phosphate decompose slowly into soil, releasing minerals gradually over a period of years.

Nitrogen Sources

Sodium nitrate (NaNO3, 16% N) is mined from naturally occurring deposits in Chile and Peru, the location of the driest desert on earth where nitrate (NO3¯) salts accumulate over time.

Phosphate Sources

There are a number of alternative phosphate sources on the market, but it can be difficult for growers to determine which is the most appropriate for their vineyard. Much of the difficulty stems from confusion about the difference between total and available phosphate. Chemical phosphate fertilizer is sold on the basis of available phosphate expressed as P2O5 or known as diphosphorous pentoxide.

Potassium Sources

Alternative potassium sources are similar to alternative phosphates in that there are a variety of sources, with differing availability and fertility value. As with phosphate, there is a difference between available potassium and total potassium.

Calcium Sources

Gypsum and limestone are applied for their calcium content, and to help balance the pH of soil. In many alkaline or sodic soils, application of mined gypsum is a common practice to displace sodium from the soil. The sodium must be leached, usually by irrigation sufficient to wash the salts into the drainage system.


Organic farming focuses on the macronutrients of nitrogen, phosphorus, potassium, sulfur, calcium, and magnesium. However, the crops cannot reach full potential without the major micronutrients, which are boron, chloride, copper, iron, manganese, molybdenum, nickel, and zinc.


Cobalt, copper, iron, manganese, molybdenum, selenium, and zinc—can be applied to correct a deficiency provided that they are from sulfate, carbonate, oxide, or silicate sources.

Basalt Dust

Basalt dust, if available at a reasonable cost, can provide a wide range of trace minerals to agricultural systems over a period of several years; as with most rock powders, transportation costs are a major factor in determining cost-effectiveness.

Chelating Agents

Chelating agents are compounds to which an element in its ionic form can be attached. Micronutrients can be made more available to plants by chelation with various compounds.

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