Fertilizer Management for Grapevines
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.
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.
Sodium nitrate is mined from naturally occurring deposits in Chile and Peru, the location of the driest desert on earth where nitrate salts accumulate over time. Sodium nitrate is generally granulated and readily soluble when added to soil.
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. Neither total nor available phosphate analyses give a particularly accurate picture of how different phosphate materials will perform in natural systems, hence the importance of developing good powers of observation through on-vineyard experimentation.
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.
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.
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