Soil nutrient dynamics, harvest residue management and soil organic matter conservation for the sustainability of black wattle production systems in subtropical soils: a review

Abstract

Black wattle is a tree native to Australia and commercially planted in South Africa and Brazil. Replacement of exported nutrients by wood and bark harvesting, associated with the maintenance of harvest residues, increases productivity, thus maintaining production sustainability. Here, we review recent advances in soil nutrient dynamics, harvest residue management (HRM), and soil organic matter in black wattle plantations. Over the 7–11-year cycle of black wattle, N is the most exported macronutrient (458–1509 kg ha^− 1), followed by K (200–766 kg ha^− 1), Ca (270–717 kg ha^− 1), Mg (62–128 kg ha^− 1), S (29–57 kg ha^− 1) and P (16–40 kg ha^− 1). The average increase in bark yield to 20 kg P ha^− 1 applications on sandy soils was 2.7–2.9 t ha^− 1 and on clay soils from 2.8 to 8.7 t ha^− 1. Sandy soils with low K are more responsive to fertilizer, and rates must consider the K content and cation exchange capacity. Ca and Mg addition responses are more likely when in the topsoil they are in low concentrations (< 0.75 and 0.41 cmolc dm^− 3, respectively). Micronutrient fertilization reduces the occurrence of gummosis caused by Phytophthora spp, and B deficiency is the most common and can be supplied by fertilization or foliar application (1 g B L^− 1). Few studies have evaluated the impact of black wattle HRM on soil organic matter (SOM) and its effects on production. However, conserving SOM should be considered an essential practice for the sustainability of black wattle production.