NUTRITIONAL-REQUIREMENTS OF CLEMATIS-VITALBA L (OLD MANS BEARD)

The nutritional requirements of the naturalised vine, Clematis vitalba , were investigated in order to determine soil factors which might res trict its growth. Topsoil samples (0-10 cm), collected from 19 sites w here C. vitalba has naturally established in New Zealand, had moderate ly acid to near neutral pH values, high to very high percentage base s aturation, and medium to very high concentrations of the exchangeable cations Ca, Mg, and K, but tended to have low plant-available P and ph osphate-extractable sulphate concentrations. Extractable-Al concentrat ions were very low. Profile descriptions at these sites showed that al most all soils were being or had been rejuvenated by alluvium, colluvi um, or tephra. The soils had few physical impediments to root growth, so plants were readily able to exploit the soils and their nutrients. In a glasshouse experiment, growth of C. vitalba increased with increa sing rate of lime (CaCO3) and with increasing rate of applied P. Great est growth in these conditions was associated with: pH = 4.7; exchange able Al = 4.6 me./100 g; 0.02M CaCl(2)extractable Al = 3.5 mg/g; and O lsen P = 56 mg/g. Death of plants was associated with: pH = 3.7; excha ngeable Al = 12.6 me./100 g; 0.02M CaCl2-extractable Al = 107 mg/g; an d Olsen P = 5.0 mg/g. The response to lime was to high pH and/or low A l concentrations rather than to high concentrations of Ca, indicating that C vitalba is not a calcicole. Plant growth was found to be more c losely correlated with CaCl2-extractable Al concentrations than to pH or exchangeable Al concentrations. In a second (subtractive nutrient) experiment, growth of C. vitalba was reduced by low concentrations of soil N, P, Ca, S, and micronutrients. The depression in growth in the minus micronutrient treatment appeared to be caused by low plant Mn co ncentrations, or possibly by high Fe concentrations as a result of the lower Mn concentrations. Despite very low concentrations of K and Mg in the soil, significant growth responses to the addition of these ele ments were not obtained. The addition of Fe was found to depress root growth. The growth and spread of C. vitalba may be restricted by extre mely acid soil conditions and by very low concentrations of N, P, Ca, S, and possibly Mn in the soil. However, it does not appear to be unus ually sensitive to soil acidity or nutrient deficiencies.