Biomass production and nutrient dynamics of Acacia lenticularis (L.) Willd-Curcuma domestica Valeton agroforestry systems in north-west alluvial plain of Bihar

Abstract

The study was carried out in 15-year-old lower density (625 trees ha^-1) and higher density (1000 trees ha^-1) plantations of Acacia lenticularis (L.) Willd. The plantations were intercropped with turmeric (Curcuma domestica Valeton) local cv. ‘Rajendra Sonia’. The standing biomass of 15-year-old trees in high density plantation was higher (61.2 Mg ha^-1) than that of lower density (44.5 Mg ha^-1) plantation. Total vegetation biomass including turmeric was also higher in high density plantation (74.4 Mg ha^-1) than that of low density plantation (58.9 Mg ha^-1). Irrespective of the density of the plantation, the biomass of different components was in the order: stem > roots > branches > leaf. Relative contribution to total nutrient content in the different tree components was in the order: stem > branch > root > leaf. The amount of nutrients that returned through litterfall to the soil was distinctly greater in the high density plantation. Of the total annual nutrient uptake, 67% N, 48% P and 51% K returned to the ground through the leaves, branches, roots and crop residues by the high density agroforestry system, whereas, 55% N, 41% P and 39% K returned to the ground by the low density agroforestry system. Total nutrients released through litter and roots were 64% N, 46% P and 50% K of the total uptake by the high density agroforestry system, while 53% N, 39% P and 38% K of the total uptake by the low density agroforestry system. About 32-42% N, 47-55% P and 49-61% K of the total nutrient uptake were lost from the system in the harvest of turmeric. This study showed that the nutrient return through litterfall and roots under both the low and high density plantations almost balanced the removal of nutrients in turmeric harvest. Hence, the A. lenticularis agri-silvicultural systems are sustainable in terms of maintenance of nutrient status in soil.