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60 p r a c t i c a l w i n e r y & v i n e ya r d M a r c H 2 0 1 4 g r a p e g r o w i n g Management implications of soil water deficits in vineyards The model developed for diffusion of K in soil predicts that soil moisture deficit will slow the diffusion of K in soils with high or low soil K content. In essence, soil moisture deficit should lead to reduced uptake on both low- and high-K soils. It also predicts that availability of K will be reduced under soil water deficit or increased by irrigation, regardless of K levels in the soil (Table V). This diffusion model was tested for North Coast vineyards in a Pinot Noir vineyard in Carneros, Calif. 7,8 The vines were either fertilized at a rate of 8 pounds of K 2 SO 4 per vine in spring 1988 or not fertilized. In 1989, both the K-fertilized and unfertilized plots were either irri- gated using the grower 's standard prac- tice of applying 10 gallons per vine per week, or at a rate four times grower prac- tice beginning two weeks after bloom in order to maintain soil moisture content near field capacity. The midday leaf water potentials of grapevines irrigated according to the grower's normal practices (10 gallons per week) declined to -1.4 MPa shortly after véraison, while the midday leaf water potential was maintained at -1.0 MPa or lower with supplemental irrigation. 8 Petiole analysis at bloom in 1989 indi- cated no effects of K-fertilization or irri- gation (Figure 1). At véraison, however, the petiole K levels in K-fertilized plots were as high as bloom-time levels, while the K status of unfertilized vines had declined. Moreover, supplemental irriga- tion increased the availability and uptake of K after véraison for both K-fertilized and unfertilized plots. Fe Zn Mn Cu B 27 28 28 14 ... 28 29 26 13 ... ns ns ns ns ... 32 29 250 6 ... 33 27 238 7 ... ns * ns ns ... 32 26 275 7 ... 33 27 242 7 ... ns Ns ns ns ... 151 32 139 10 ... 144 30 117 10 ... ns Ns ns ns ... ppm Dry Weight Bloom pe oles Irrigated Non-irrigated Significance* Véraison pe oles Irrigated Non-irrigated Significance* Harvest pe oles Irrigated Non-irrigated Significance* Véraison leaf laminae Irrigated Non-irrigated Significance* Ns, * Non-significant and significant at P < 0.05 level N P K Mg Ca 1.24 0.59 1.11 0.32 1.73 1.14 0.54 0.93 0.32 1.71 * * ns ns ns 0.49 0.21 1.20 0.85 3.85 0.43 0.14 0.71 0.91 3.56 ns * * ns * 0.42 0.12 0.70 1.00 4.51 0.45 0.11 0.22 1.08 4.33 ns ns ** ns ns 1.82 0.18 0.70 0.60 3.30 1.81 0.13 0.52 0.58 3.09 ns * * ns * Percent Dry Weight Bloom pe oles Irrigated Non-irrigated Significance* Véraison pe oles Irrigated Non-irrigated Significance* Harvest pe oles Irrigated Non-irrigated Significance* Véraison leaf laminae Irrigated Non-irrigated Significance* Ns, * Non-significant and significant at P < 0.05 level Table 1. Irrigation effects on macro-nutrient status of Cabernet Sauvignon on calcareous soils. 6 Table II. Irrigation effects on micro-nutrient status of Cabernet Sauvignon on calcareous soils. 6 Table III. Influence of volumetric water content of the soil on the K concentration of the soil solution, the concentration of K in a given volume of soil, soil buffer power and effective diffusion coefficient of K. 2 Volumetric K concentra on Concentra on of K Soil buffer Diffusion water content of soil solu on in given soil volume power Coefficient (cm 3 / cm 3 ) ( mol/cm 3 ) ( mol/cm 3 ) (cm 3 /sec) 0.19 1.36 0.26 2.68 2.55 x 10 -7 0.26 1.18 0.31 3.09 4.91 x 10 -7 0.34 1.06 0.36 4.42 6.40 x 10 -7 Get the Digital Editions free! Send your email address to subs@winesandvines.com.