Seasonal Changes and Distribution of Nutritional Elements in Thompson Seedless Grapevines

¹ Farm Advisor, University of California Agricultural Extension Service, Fresno County, 1720 S. Maple, Fresno, California 93702.

A four-year study was conducted on seasonal changes and quantitative distribution of the important mineral nutrients in 'Thompson Seedless' petioles and shoot tips. Year-to-year variations in nitratenitrogen and potassium levels were great. The period bracketing bloom showed the most rapid change in nitrate-nitrogen, phosphorus, and potassium levels. The most stable period was 3 to 4 weeks after bloom. Of the nutrients studied, potassium showed the only distinct positive correlation with bloom.

The position on the shoot of the petiole sampled influenced the levels of potassium, calcium, and magnesium. However, nitrate-nitrogen, phosphorus, boron, zinc, iron, and manganese levels were not greatly affected by petiole position.

The possible influence of seasonal temperature differences on changes in nutrient levels in the Fresno area is discussed.