Nutritional status of apple orchards in the Åland Islands

Editors : Ramdane Dris, Raina Niskanen and Irma Voipio

Summary

Soil, leaf and fruit samples were collected in nine commercial apple orchards in the Åland Islands. The early cultivars (Maikki, Transparente Blanche, Samo, Melba, Red Melba), intermediate cultivars (Jaspi, Ranger, Raike, Red, Atlas) and late cultivars (Åkerö, Aroma, Lobo) were included in this study. Apple leaves were sampled three times during the fruit development. Soil characteristics and nutrients (N, P, K, Ca, Mg, B) in leaves and fruits were determined.

In the experimental orchards, soils were mainly coarse textured with pH range 6.2-7.8. At 0-50 cm depth, the mean concentrations of extractable nutrients (mg/l soil) were: N 7; P 30; K 216; ca 6000; Mg 180. The soil fertility classes for pH and Ca were high or very high, for other macronutrients satisfactory or good, and in the case of phosphorus high only.

The mean values of leaf macronutrients (g/kg dry matter) were: N 22.1; P 2.2; K 17.4; Ca 17.4; Mg 2.2. For boron, the mean concentration was 26 mg/kg dry matter. The concentrations of macronutrients were satisfactory but boron concentration was low. During the sampling period (July 22 - August 26), the N, P and K levels decreased, and that of Ca increased. The mean values for ratios of nutrient concentrations followed the tentative values (N/P 10; N/K 1.3-1.5; N/Ca 1.0-1.5; N/Mg 6-10; K/P 6.7-7.5; K/Ca 0.75-2.0; Ca/P 3.3-10.0; Ca/Mg 2-10) calculated on the bases of nutrient recommendations.

The mean nutrient concentrations in apple fruits (mg/kg fresh weight) were: N 470; P 100; K 1250; Ca 50; Mg 50; B 2. Nitrogen, phosphorus and potassium contents were rather low in apple fruits, but concentrations of magnesium and calcium were adequate. In most cases, the mean ratios of fruit nutrients followed the tentative values (N/P 4.6-6.4; N/K 0.39-0.44; N/Ca 10-14, N/Mg 10-14; K/P 11.8-15.5; K/Ca 26-32; Ca/P 0.46, Ca/Mg 1.0).

There were significant correlations between corresponding fruit and leaf macronutrients (g/kg dry matter), positive for nitrogen, phosphorus, potassium and magnesium and negative for calcium. Phosphorus and calcium levels in leaves and fruits correlated with soil pH more closely than with corresponding soil nutrients. Soil pH correlated significantly also with leaf potassium. In addition, leaf magnesium and fruit potassium correlated significantly with corresponding soil nutrients.

Contents

• Introduction
• Soil characteristics
• Nutrient concentrations in leaves
• Ratios of nutrient concentrations in leaves
• Nutrient concentrations in apple fruit flesh
• Ratios of nutrient concentrations in apple flesh
• Conclusions