Chapter 16

Vineyard Nutrient Management

Soil Analysis

Soil analysis can reveal what is potentially available to the vine, but does not give a good indication of soil/ vine interaction for established vineyards. Soil properties, varietal and rootstock differences, the diverse microclimates of vineyard sites along with various cultural and irrigation practices all impact how a vine absorbs nutrients from the soil. The value of soil analysis is mostly in the determination of problems related to certain chemical imbalances or excesses such as pH problems (alkalinity and acidity), salinity, cation imbalances, and excess boron, but beyond these factors, the chemical analysis of soils is of very little value. Soil tests rarely are representative of the entire rooting depth of grapevines.

Pre-Vine Soil Analysis of Vineyard Site

Soil nutrient analysis can be used in vineyard establishment to determine if there are extremes in mineral nutrient levels. This can serve as a forewarning of fertilizer requirements or the need for immediate treatment prior to or during vineyard establishment. In particular, soil analysis data can allow good decisions to be made on such things as soil amendments (e.g., lime, organic matter or gypsum) and point to the need for applications of other nutrients such as nitrogen, phosphorous, and potassium.

Sampling Soil from Established Vineyards

Soil analysis is a useful tool to provide basic information on the fertility of soil in established vineyards. The soil analysis reports can also help provide information on problems such as salinity, acidity, and sodicity as well as confidence that fertilizer has moved into the root zone as expected. Soil analyses, however, cannot be used as a sole predictor of fertilizer requirements in established vineyards because it is near impossible to calibrate the analyses properly to the nutritional needs of the vines. This is because is not easy to obtain representative samples since the roots of a grapevine grow at various depths in the soil that can vary greatly in chemical composition even over short distances.

Soil pH

Soil pH affects mineral solubility and thereby availability. Soil pH values between 6.0 and 7.0 provide the optimum availability of nutrients in vineyard soils (See Figure 16.1). At a low pH, beneficial elements such as molybdenum (Mo), phosphorus (P), magnesium (Mg) and calcium (Ca) become less available to vines. Other elements such as aluminum (Al), iron (Fe) and manganese (Mn) may become more available, and Al and Mn may reach levels that are toxic to vines.

Soil Texture Effects on Nutrient Availability

Sandy soils have many large pores making water movement and drainage more rapid. This often results in the leaching (i.e., loss) of mobile nutrients such as nitrate. Where sands are water-repellent, water movement is slow and nutrient availability at depth is usually poor. Generally, these soils have low levels of organic matter which gives them a low fertility status. Sandy soils retain a low amount of water for vine use which can make irrigation scheduling and nutrient application via fertigation difficult.

Nutrient Mobility in Soils

Nutrients differ in their mobility in the soil, which affects their ability to be lost through leaching. As a good general rule, ammonium (NH4?), potassium (K?), calcium (Ca2?), and magnesium (Mg2?) are more mobile than the micronutrients (Cu2?, Fe2?, Fe3?, Mn2+, and Zn2?).

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