Nutrient uptake, accumulation, and utilization efficiency comparisons in plantations containing different generations of Chinese fir

The differences in nutrient absorption, accumulation, and utilization efficiency were analyzed at the first and the second rotations in Chinese fir (Cunninghamia lanceolata) plantations using a 40 year database of biomass and nutrient levels from Huitong National Research Station of Chinese Fir Plantation Ecosystem in Hunan Province, Central South University of Forestry and Technology, China. The results showed that the N, P, K, Ca, and Mg concentrations in the second rotation were 2.85-3.48, 0.16-0.25, 1.86-2.72, 2.10-2.50, and 0.77-1.31 g/kg higher than in the first rotation respectively. The nutrient accumulation of the first generation was 9.14%, 2.01% and 0.22% higher than that of the second generation at 7, 20, and 25 years old, respectively, while that of was 6.72% and 3.44% lower than that of the second generation at 11 and16 years old, respectively. Chinese fir continuous planting does not necessarily lead to the second generation of forest tree layer nutrient accumulation decreased. Annual absorption of nutrients in the first rotations (1-7 years old) was 9.14% higher than the second rotations at the same age. However, at the ages of 8 to 11, 12 to 16, 17 to 18, and 21 to 25, they were 13.04%, 2.52%, 7.93%, and 14.58% less than the second rotations, respectively. In the same age classes, the second rotations required 1.28, 3.19, 4.28, 4.09, and 4.09 kg more nutrients for each year class, respectively, to produce 1 ton of dry matter compared to the first rotations. These results indicate that successive rotations bring about an increase in nutrient uptake, and a decrease in nutrient use efficiency in the second rotations across the central south subtropical regions.