Cook and his co-workers collected petioles from leaves opposite clusters during bloom. They found phosphorus concentrations between 0.04% and 0.07% (400 to 700 ppm).⁶ In California, phosphorus concentrations in petioles during bloom normally range from 0.3% to 0.6%,⁶ and petiole phosphorus concentrations lower than 0.10% (100 ppm) have been considered deficient.⁴ However, recent research indicates that the leaf tissue phosphorus concentration associated with deficiency may vary with scion and rootstock variety.

Ungrafted vines have been shown to generally differ in petiole phosphorus concentrations,^2,5 and the varieties Chardonnay and Chenin Blanc to differ in the leaf blade phosphorus concentration associated with maximum yield (Fig. 1).¹⁵ Scion and rootstock influence the extent that vine growth and leaf area are inhibited by phosphorus deficiency.⁷

In addition, rootstocks differ in their ability to take up phosphorus from the soil, to translocate phosphorus to the scion, and in their influence on phosphorus use efficiency by the scion.⁸ These observations suggest that a single leaf tissue phosphorus concentration may not accurately diagnose phosphorus deficiency in all scion-rootstock combinations. Until further research involving several scions, rootstocks, and soil phosphorus levels is conducted, the 0.10% criteria should be used loosely.

Plant nutrients required in large quantities, such as phosphorus, are called macronutrients. Macronutrient deficiencies are usually corrected by applications of fertilizers to the soil. In field trials, applications of phosphorus fertilizer to soils have successfully corrected phosphorus deficiencies.^6,15 Fertilizer was placed on the soil under the drip emitters by hand. Maximum fruit yields were achieved at 0.3 to 0.4-lb phosphorus per vine for vineyards with conventional vine densities.¹⁵ The beneficial effects of the fertilizer declines with time and reapplication becomes necessary after two or three years.

Triple superphosphate and monoammonium phosphate, two commonly used phosphorus fertilizers, were used in the trials.¹⁵ There was evidence in this and other studies that the nitrogen present in the monoammonium phosphate fertilizer enhanced phosphorus uptake and utilization by P-deficient plants.¹⁹

The application rates for phosphorus fertilizers are relatively high compared to those used for other macronutrients such as nitrogen. Such high rates are necessary because low pH, P-deficient soils adsorb or fix large quantities of phosphorus. This makes it necessary to apply P-fertilizer in a concentrated band or spot in order to overwhelm the soil’s adsorption capacity leaving some phosphorus available to the vines. With lower rates or broadcast applications, most of the applied phosphorus is adsorbed by the soils and not enough is left for the vines.

Lower application rates are required when correcting P deficiency with soluble phosphorus fertilizer applied through a drip system.^12,13 Savings will be realized both in the quantity of phosphorus fertilizer applied and the labor required for application.

Fertilizer may be applied through a drip system at any time during the season until leaf fall, but is probably most effectively applied during the spring and autumn while roots are rapidly growing.

It is essential that only soluble phosphorus fertilizers be applied and that only very low concentrations of calcium and magnesium be present in the water flowing through a drip system while phosphorus is being injected to avoid emitter clogging. When their concentrations are sufficiently high, calcium and magnesium combine with phosphorus to form the solid compounds calcium phosphate and magnesium phosphate. Precipitation of these compounds can be avoided by acidifying the irrigation water, which is accomplished through injection of acidic fertilizer or simultaneous injection of acid and fertilizer.

Many growers inject sufficient acid to lower the irrigation water pH between 5.5 to 6.0. Fertilizer is normally applied during the middle of an irrigation set to allow prewetting of the soil prior to the application and flushing of the drip system following the application.

Rock phosphate, the raw material from which commercial phosphorus fertilizers are made, is commonly used by organic growers to correct phosphorus deficiencies because other fertilizers accepted by organic certifying organizations contain much less phosphorus. (Examples of other phosphorus-containing fertilizers accepted by organic-certifying organizations include compost, bone meal, and kelp-based fertilizers.)

Rock phosphate will not be effective in correcting phosphorus deficiencies if it dissolves too slowly, allowing much of the phosphorus to be adsorbed by the soil and leaving little phosphorus for the vines.

Maximum effectiveness with rock phosphate occurs when it is derived from apatitic phosphate rocks containing a high percentage phosphorus (see Table I), finely ground, and applied at very high rates (two to three times higher phosphorus rates than conventional phosphorus fertilizer) in a concentrated band or spot.¹⁹ Rock phosphate has the disadvantages of uncertain effective phosphorus concentration and rate of release, and the inconvenience of greater bulk and dust compared with conventional phosphorus fertilizers.

Regardless of the type of phosphorus fertilizer, it is beneficial to apply it to low-P soils in advance of planting a new vineyard to allow it time to saturate the soil’s P-adsorption capacity and become available for vine uptake. This is most easily accomplished by shanking dry fertilizer adjacent to the vine row or injecting liquid fertilizer through the drip system. Hand application in the planting hole is more costly and may result in young, tender vine tissues coming into direct contact with concentrated fertilizer.

References

1. Bache, B.W. "Aluminum and iron phosphate studies relating to soils, II. Reactions between phosphate and hydrous oxides." J. Soil Sci. 15: 110-116 (1964).
2. Brunstetter, B.C., A.T. Myers, I.W. Dix, and C.A. Magoon. "A quantitative survey of eight mineral elements by a spectrographic method and of total nitrogen in young leaves of 25 varieties of American grapes." Proc. Am. Soc. Hort. Sci. 37: 635-638 (1939).
3. Burt, C., K. O’Connor, and T. Ruehr. Fertigation. Calif. Polytechnical State University, San Luis Obispo (1995).
4. Christensen, P., A.N. Kasimatis, and F.L. Jensen. Grapevine Nutrition and Fertilization in the San Joaquin Valley. Univ. Calif., Berkeley (1978).
5. Christensen, P. "Nutrient level comparisons of leaf petioles and blades in 26 grape cultivars over three years (1979 through 1981)." Am. J. Enol. Vitic. 35: 124-133 (1984).
6. Cook, J.A., W.R. Ward, and A.S. Wicks. "Phosphorus deficiency in California vineyards." Calif. Agric. 37: 16-18 (1983).
7. Grant, R.S. and M.A. Matthews. "The Influence of Phosphorus Availability, Scion, and Rootstock on Grapevine Shoot Growth, Leaf Area, and Petiole Phosphorus Concentration." Am. J. Enol. Vitic. 47: 217-224 (1996).
8. Grant, R.S. and M.A. Matthews. "The influence of phosphorus availability and rootstock on root system characteristics, phosphorus uptake, phosphorus partitioning, and growth efficiency." Am. J. Enol. Vitic. 47: 403-409 (1996).
9. Hsu, P.H., and D.A. Reenie. "Reactions of phosphate in aluminum systems, I: Adsorption of phosphate by X-ray amorphous aluminum hydroxide." Can. J. Soil Sci. 42: 197-209 (1962).

10. Marschner, H. Mineral nutrition of higher plants. Academic Press, London (1986).
11. Menge, J.A., D.E. Munnecke, E.L.V. Johnson, and D.W. Carnes. "Dosages responses of the vesicular-arbuscular mycorrhzal fungi Glomus fasciculatis and G. constrictus to methyl bromide." Phytopathol. 68: 1368-1372 (1978).
12. O’Neill, M.K., B.R. Gardner, and R.L. Roth. "Orthophosphoric Acid as a Phosphorus Fertilizer in Trickle Irrigation." Soil Sci. Soc. Am. J. 43: 283-286 (1979).
13. Rauschkolb, R.S., D.E. Rolston, R.J. Miller, A.B. Carlton, and R.G. Burau. "Phosphorus fertilizer with drip irrigation." Soil Sci. Soc. Am. J. 40: 68-72 (1976).
14. Sample, E.C., R.J. Soper, and G.J. Racz. "Reactions of phosphate fertilizers in soils." In: The role of phosphorus in agriculture. F.W. Khasawneh (Ed.). pp. 263-310. American Society of Agronomy, Madison (1980).
15. Skinner, P.W., J.A. Cook, and M.A. Matthews. "Responses of grapevine cvs. Chenin Blanc and Chardonnay to phosphorus fertilizer applications under phosphorus-limited conditions." Vitis. 27: 95-109 (1988).
16. Skinner, P.W., R.S. Grant, and M.A. Matthews. "Interaction of rootstock and mycorrhizae on dry matter distribution and nutrient levels of Cabernet Sauvignon (Vitis vinifera L.) Lamina." In: Proceedings of Second International Cool Climate Viticulture and Oenology Symposium. R. Smart, R. Thornton, S. Rodriguez, and J. Young (Ed.). (1988).
17. Skinner, P.W., and M.A. Matthews. "Reproductive development in grape (Vitis vinifera L.) under phosphorus limited conditions." Sci. Hortic. 38: 49-60 (1989).
18. Tinker, P.B. "Effects of vescular-arbuscular mycorrhizas on plant nutrition and plant growth." Physiol. Veg. 16: 743-51 (1978).
19. Tisdale, S.L., W.L. Nelson, and J.D. Beaton. Soil Fertility and Fertilizers. Macmillian, New York (1985).