Laws of annual nutrient uptake in a Paulownia plantation

Characteristics of annual nutrient uptake of a 8-yr.-old Paulownia(Paulownia tomenlosa Steed×Paulownia fortunei Hemsl) plantation (spacing 6m×10m) at Fengqiu Paulownia Experimental Station in the Yellow River, Huaihe River and Haihe River plains were studied within 2 years.Annual total uptakes of 5 macronutrients (N,P,K,Ca and Mg)in 1989 and 1990 were 287.3238 and 242.4234 kg/(hm2.a),respectively. The study came to the following laws:(1)the nutrient uptakes of the Paulownia organs followed the order:leaves>branches>flowers>stems> roots;(2) the uptakes for different nutrient elements followed the sequence: N>Ca>K>P>Mg;(3)different organs of the Paulownia showed selective uptake and retention for the essential nutrients;(4) Paulownia's uptake of nutrient elements was mainly conducted during the period between the beginning of growth and the end of July.