Long-term effects of recycled paper alkaline waste use on soil, litter, weeds, and development and nutrition of Pinus taeda L.

There is a lack of long-term information on the use of industry forest residues in Pinus taeda L plantations for purposes of enhancing sustainability. The study goal was to evaluate tree growth and nutrition, soil chemical properties, litter accumulation, and weed occurrence in a Pinus taeda L. system amended with alkaline residues from recycled paper. The residues were broadcasted at planting using different rates (0, 10, 20, 30, and 40 t ha⁻¹) on a sandy soil with low fertility. Tree diameter and height along with soil chemical properties were monitored for 15 years. At 15 years samples of litter, weeds, and soil were collected for evaluation. Over 15 years of monitoring, no changes in tree growth or final yield were observed despite increased Ca and reduced Mn foliar tissue concentrations. Low Mg concentration in needles combined with symptoms resembling Mg deficiency and a high increase in Ca levels, suggest that this nutrient could be a limiting factor in tree response. At the same time, a reduction in weed mass with residue application was verified. Residue amendment increased soil Ca and attenuated acidity down to 60 cm after 15 years with the maximum effect on soil properties at ~ 13 years. Litter decreased from 36.2 (control) to 26.9 Mg ha⁻¹ (highest rate) but increased Ca and diminished Al concentrations. The alkaline residue (rich in Ca) improved soil chemical properties at the surface and subsurface, decreased weed growth, increased Ca and reduced Mn in needles, but probably failed to increase tree yield due to an Mg deficiency.