[Nutrient accumulation and cycling in pure and mixed plantations of Azadirachta indica and Acacia auriculiformis in a dry-hot valley, Yunnan Province, southwest China].

To ease the implementation of effective nutrient management for plantations with different vegetation restoration patterns and to assist in the selection of appropriate species and forestation patterns, nutrient (N, P, K, Ca and Mg) accumulation and cycling were investigated and compared in three plantations (10-year-old Azadirachta indica, Acacia auriculiformis and mixed A. indica--A. auriculiformis plantations) in Yuanmou Valley, a dry-hot valley of Yunnan Province, Southwestern China. The result showed that total nutrient accumulations were 333.05, 725.61 and 533.85 kg x hm(-2) in pure plantations of A. indica and A. auriculiformis, and in A. indica--A. auriculiformis mixed plantation, respectively. The nutrient accumulation of various organs was ranked as branches > stems > roots > leaves > bark in the A. indica plantation and branches > stems > leaves > roots > bark both in the A. auriculiformis plantation and in the mixed plantation. Changes in accumulation of various nutrients in the mixed plantation were similar to that in the A. auriculiformis plantation (Ca > N > K > Mg > P), which were different from the A. indica plantation (Ca > K > N > Mg > P). Annual net nutrient accumulation, return and absorption in these plantations ranged from 62.72 to 162.19 kg x hm(-2) x a(-1), 48.82 to 88.86 kg x hm-2 a-1 and 111.54 to 251.05 kg x hm(-2) x a(-1), respectively, which were all the highest in the A. auriculiformis planta- tion, followed by the mixed plantation, and were the lowest in the A. indica plantation. The nutrient utilization coefficient, the cycling coefficient and the recycling period were estimated to be from 0.34 to 0.39, 0.35 to 0.44, and 6.54 to 8.17 a, respectively. The lower nutrient return and circulation rate of N or P in the A. indica plantation showed that this plantation had a poor ability to maintain soil fertility, while the highest nutrient circulation rate of N or P was observed in the A. auriculiformis plantation that displayed the advantage in maintaining soil nutrients and stand productivity. The nutrient return and nutrient absorption in the mixed plantation were 167.2% and 186.2%, of those in the A. indica plantation, and the circulation rate of N, P and K were higher than those in the A. indica plantation, while the recycling period of Ca in mixed plantation was 50% shorter than that in A. auriculiformis plantation. Soil fertility and nutrient supply were improved in the A. indica and A. auriculiformis mixed plantation.