Integrating forest residue and mineral fertilization: effects on nutrient acquisition, nutrient use efficiency and growth of eucalypt plants

Abstract

Tropical eucalypt plantations are important sources of forest products and services. In these systems, nutrient management is a key practice, and consistent efforts are necessary to optimize the use of nutrient sources and maintain the sustainability of the forests. In this work, we evaluated the effects of nutrient management practices (fertilization and forest harvest residue management (FHRM)) and their interactions on the growth (root and shoot growth), nutrient acquisition, partitioning of nutrients, and nutrient use efficiency of trees in tropical eucalypt plantations. The experiment was conducted for five years, under field conditions, in a representative area of eucalypt production in Três Lagoas, MS, Brazil. The treatments consisted of two FHRM systems (with or without forest residues on the forest floor) combined with three levels of fertilization (replacement, potential fertilization and control (without fertilization)) in a full factorial, in randomized blocks, with three replicates. The addition of forest harvest residue (FHR) increased the mass of fine roots by 41%. There was no effect of the treatments on the aboveground plant biomass or wood volume. In general, lower fertilization rates combined with FHR provided a similar acquisition of macro- and micronutrients by plants as the treatments with high fertilization. The acquisition of N and P by plants decreased in treatments with FHR. However, this effect was offset, at least in part, by a higher internal N and P use efficiency in plants. A similar pattern was observed for the other macro- and micronutrients (i.e., a lower nutrient uptake was compensated by a higher internal nutrient use efficiency in plants). Our findings add evidences that fertilization can be reduced in some tropical eucalypt plantations, although the responses of eucalypts to fertilization are generally significantly high in these regions, and the amount of fertilizer applied cannot be reduced deliberately. Our findings also indicate that combining FHR with fertilization is an important strategy to sustainably replace nutrients in these systems, even when nutrient-poor residues are used. The quantitative data we provide in this work may also help modelers to improve empirical and mechanistic models of nutrient dynamics in forest plantations.