Soil organic phosphorus (P) increases in mixed plantations of Acacia mangium and Eucalyptus urograndis in Planosol from Brazil

Key message Mixed plantations 50A:50E promotes an increase in the organic P compartment in the soil, especially in fractions of greater lability. Mixed plantations of Eucalyptus and nitrogen (N)-fixing tree legumes (NFT) benefit the cycling of nutrients in Eucalyptus stands due to the increased absorption of phosphorus (P) and greater input of organic matter. The objective was to quantify the different fractions of P in terms of lability and its correlation with the fractions of organic matter, to clarify the effect of mixed plantations on the modifications of different P and carbon (C) fractions in Planossolo Haplico (Planosol). Monospecific stands of Eucalyptus urograndis (0A:100E) and Acacia mangium (100A:0E) were established in addition to mixed plantations: one presenting 50% planting density of each species (50A:50E) and the other with double planting density (100A:100E). The soil samples were collected at depths of 0-5 cm and 5-10 cm and the total organic carbon, particle size fractions, labile carbon, total phosphorus, labile organic and inorganic phosphorus, moderately labile and moderately resistant and residual phosphorus were determined. It was observed in the mixed plantations 50A:50E, the highest values of total phosphorus and concentration of organic P (56.84%), highlighting the fractions of greater lability in addition to presenting a lower C:Po ratio (187.28) and higher labile carbon concentration at both depths. Mixed plantations 50A:50E promote an increase in the organic P compartment in the soil, mostly in fractions of greater lability. Monospecific stands of A. mangium and E. urograndis seem to have P cycling limited by the supply of P and N, respectively. Labile carbon, presents itself as an important indicator of soil quality.

Automated summary

Mixed plantations of Eucalyptus and nitrogen-fixing tree legumes promote an increase in the organic phosphorus compartment in the soil, particularly in more labile fractions. Monospecific stands of Acacia mangium and Eucalyptus urograndis seem to have limited phosphorus and nitrogen cycling, respectively. Labile carbon is an important indicator of soil quality.