Effects of urban sewage sludge additive on growth and nutrient accumulation in Salix americana and Populus × euramericana cv. ‘74/76’ softwood cuttings

  Objective  In order to clarify the application effect of urban sewage sludge as an organic soil amendment on cuttings during the nursery culture, growth and nutrient accumulation in Salix americana and Populus × euramericana cv. ‘74/76’ softwood cuttings were studied at different sludge application rates.

  Method  In the nursery with sand land of plain area, the same aged semi-lignified branches of Salix americana and Populus × euramericana cv. ‘74/76’ were used as materials in a completely random block design at application doses of 3 kg/m² (T1), 6 kg/m² (T2) and 9 kg/m² (T3), and an untreated control (CK). Soil properties including soil bulk density and porosity were measured in advance. Survival rate in every treatment was counted at 35 days after cutting. The new shoot length and diameter of each treatment were measured at 35, 50, 65 and 80 days after cutting. Samples were sampled at the end to determine parameters in biomass, root morphology, and nutrient content.

  Result  Sludge application reduced soil bulk density and increased soil porosity. For Salix americana, with the increase of sludge application, the new shoot length showed an increasing trend at the start, followed by decreasing, and then increased again. The T1 treatment promoted the growth of Salix americana cuttings’ new shoots that had the most obvious promotion effect, which was significantly higher than the control. The biomass parameters, root morphological parameters, leaf carbon (C) content and carbon to nitrogen ratio (C/N) of Salix americana cuttings in the T1 treatment were also significantly higher than those in the control. Different treatments had no significant effect on the survival rate of Salix americana cuttings. For Populus × euramericana cv. ‘74/76’, the T3 treatment could significantly increase the survival rate and root biomass parameters of cuttings. With the increase of sludge application, the new shoot length, root surface area, root volume, and average root diameter of Populus × euramericana cv. ‘74/76’ cuttings first increased and then decreased, and both reached the maximum in the T2 treatment. C, nitrogen (N) contents and C/N in leaves of Populus × euramericana cv. ‘74/76’ cuttings all increased after applied sludge, and the best treatment effect was T3. There was a positive relationship between the biomass parameters and root morphology parameters, the total biomass was positively correlated with the aboveground and root biomass, which were also positively correlated with the total root length, root surface area, root volume and average root diameter.

  Conclusion  The proper application of urban sewage sludge is conducive to the growth of softwood cuttings of two tree species , and also to the absorption of some nutrients by their leaves. The sludge application amount of 3 kg/m² has the best promotion effect on Salix americana cuttings. The cuttings of Populus × euramericana cv. ‘74/76’ can adapt to the soil environment with a high amount of sludge, and the effect is better when the application amount is between 6 and 9 kg/m².