Interactive Effects of Potassium and Calcium on K/Ca Ratio and Its Consequences on Apple Fruit Quality in Calcareous Soils of Iran#

Abstract

This research was carried out during the 2000–2001 growing season in a low-density orchard, on a calcareous soil (Fine loamy, mixed, mesic Typic Calcixerept) in northwest Iran, using 25-year old “Golden Delicious” (Malus domestica Borkh.) apple trees on M.9 rootstock. The interactive effects of potassium (K) and calcium (Ca) on K/Ca ratio and its consequences on apple fruit quality were studied. Treatments included: T 1 = control [nitrogen (N), phosphorus (P), and manure]; T 2 = T 1 + micronutrients (deep placement) based on soil test recommendations; T 3 = T 2 + (KCl)1 based on soil test recommendations; T 4 = T 3 + spray of CaCl2 at four times; T 5 = same as T 4 but sprayed at eight times; T 6 = T 2 + (KCl)2 (50% above soil test); T 7 = T 6 + spray of CaCl2 at four times; T 8 = same as T 7 but sprayed at eight times; T 9 = same as T 8 but with an equal amount of K from K2SO4 source. Leaf samples were collected in early July and fruit samples collected in early October and were analyzed for N, K, and Ca. Thirty fruit samples were randomly selected and stored at 1°C for 45 or 90 days prior to determination of their storage life. There was a range in K and Ca level in the leaves, although both K and Ca concentrations exceeded their critical threshold values. The concentration of K in the fruit was high, but Ca was low. There was a positive correlation between leaf K and fruit K and between fruit K and total soluble solids concentration (SSC); between fruit Ca and apple fruit firmness; but negative correlations existed between K/Ca ratio and apple fruit firmness at harvest. Apple fruit SSC was increased by K-fertilization and storage period. Fruit firmness in harvest samples was the highest in plots which had received Ca sprays. Apple firmness at harvest was generally low for all treatments and reduced by duration of storage and differences among treatments were not large after 90-day storage. Variation of K/Ca ratio in the apple leaves was slight (0.9–1.4), but a wide range was observed for fruit (19–46). The highest ratio (46) occurred for T 6 and the lowest ratio (19) for T 8 and T 9. An inverse relationship between K/Ca ratios and fruit firmness indicated that on calcareous soils, at least 8-foliar applications of CaCl2 solution were necessary for “Golden Delicious” apple. #Contribution no. 2191, PARC-Summerland.