A fertilização nitrogenada de florestas com biosólidos constitui um meio de aceleração do crescimento das plantas potencialmente não impactante ao meio. Os efeitos de fertilização de nitrogênio atmosférico na relação simbiôntica e de fixação de nitrogênio Alnus rubra Bong. (amieiro vermelho) e Frankia foram avaliados em um estudo de campo. Biosólidos classe B digeridos anaerobicamente e uréia sintética (46% N) foram aplicados a taxas de 140, 280 e 560 kg ha-1 de N disponível em um solo tipo Areia Quartzosa. Ao contrário das plantas do grupo controle (17 µmol C2H4 g-1 hr-1) ou fertilizadas com biosólidos (26-45 µmol C2H4 g-1 hr-1), plantas fertilizadas com uréia não apresentavam fixação de nitrogênio após um ano de cultivo. Ao final do segundo ano, todas as árvores em todos os tratamentos fixavam N (7 µmol C2H4 g-1 hr-1; 4-16 µmol C2H4 g-1 hr-1; e 20-29 µmol C2H4 g-1 hr-1 para controle, uréia e biosólidos, respectivamente). Plantas cultivadas sob remediação com biosólidos apresentaram maior biomassa na parte aérea ao final do ano 2 (50 g; 51 g; e 190 g para controle, uréia, e biosólidos, respectivamente), e também maiores concentrações de nitrogênio foliar em ambos os períodos analisados (N foliar no ano 1 26 g kg-1, 27 g kg-1, e 40 g kg-1; N foliar no ano 2 17 g kg-1, 19 g kg-1, and 23 g kg-1, respectivamente para controle, uréia e biosólidos). A maior taxa de crescimento de A. rubra pode ter resultado em maior exigência em N e os biosólidos supriram quantidades adicionais de nutrientes capazes de sustentar o crescimento acelerado.

Nitrogen fertilization of forests using biosolids offers a potentially environmentally friendly means to accelerate tree growth. This field study was designed to analyze the effects of nitrogen fertilization on the symbiotic, nitrogen (N)-fixing relationship between Alnus rubra Bong. (red alder) and Frankia. Anaerobically digested, class B biosolids and synthetic urea (46% N) were applied at rates of 140, 280 and 560 kg ha-1 available N to a well-drained, sandy, glacial outwash soil in the Indianola series (mixed, mesic Dystric Xeropsamments). Plots were planted with A. rubra seedlings. At the end of each of two growing seasons trees were harvested and analyzed for the rate of N fixation (as acetylene reduction activity), biomass and foliar N. At year 1, there was no N fixation for trees grown with urea amendments, but control (17 µmol C2H4 g-1 hr-1) and biosolids (26-45 µmol C2H4 g-1 hr-1) trees were fixing N. At the end of year 2, all trees in all treatments were fixing N (7 µmol C2H4 g-1 hr-1, 4-16 µmol C2H4 g-1 hr-1, and 20-29 µmol C2H4 g-1 hr-1 for control, urea and biosolids respectively). Trees grown with biosolids amendments were larger overall (year 1 shoot biomass 10 g, 5 g, and 23 g for control, urea, and biosolids respectively, year 2 shoot biomass 50 g, 51 g, and 190 g for control, urea, and biosolids respectively) with higher concentrations of foliar N for both years of the study (year 1 foliar N 26 g kg-1, 27 g kg-1, and 40 g kg-1 for control, urea, and biosolids respectively, year 2 foliar N 17 g kg-1, 19 g kg-1, and 23 g kg-1 for control, urea, and biosolids respectively). Trees grown with urea amendments appeared to use the urea N over Frankia supplied N, whereas the biosolids trees appeared to be able to use both N in biosolids and N from Frankia. The results from this study indicated that the greater growth of A. rubra may have been responsible for the observed higher N demand. Biosolids may have supplied other nutrients to the trees to support this accelerated growth.

A aplicação de biosólidos em florestas representa uma potencial alternativa ambientalmente correta para aterros sanitários. Os efeitos de fertilização de nitrogênio na relação simbiôntica e de fixação de nitrogênio Alnus rubra Bong. (amieiro vermelho) e Frankia foram avaliados em um estudo de campo conduzido por dois anos. Um biosólido com concentração de metais muito acima dos marcos regulatórios (45 mg kg-1 Cd; 958 mg kg-1 Pb; 2623 mg kg-1 Zn) produzido há mais de 25 anos e um biosólido composto recente foram aplicados nas doses de 250, 500 e 1000 Mg ha-1, representando um cenário pior possível de concentração de metais. Ao final do segundo ano, a biomassa da parte aérea das plantas cultivadas sob ambos os compostos era maior que a das plantas controle, mas não foi observada inter-relação entre a concentração de metais no solo e a biomassa das plantas. As concentrações de Cd e Pb foliares permaneceram abaixo do nível de detecção em todas as plantas, mas a concentração de Zn foliar aumentou proporcionalmente ao aumento da adição do bioremediador, atingindo concentrações de 249 mg kg-1 e 279 mg kg-1 para os tratamentos alto metal e composto, respectivamente. Embora não tenham sido registrados efeitos negativos do biosólido com altos teores de metais, outras rotas de exposição podem levar a possíveis impactos ecológicos.

Forest application of biosolids offers a potential environmentally friendly alternative to landfilling. This two-year investigation was designed to analyze the effects of elevated soil metal concentration resulting from the land application of biosolids on the symbiotic, nitrogen (N) fixing relationship between Alnus rubra Bong. (red alder) and Frankia. High metal biosolids and a modern-day composted biosolid applied at high loading rates of 250, 500, and 1000 Mg ha-1, were used to represent a worst-case scenario for metal contamination. The high metal biosolids were obtained before the current regulations were formulated and had been lagooned prior to use in this study. Total cadmium (Cd), lead (Pb) and zinc (Zn) in the high metal biosolids were 45, 958, and 2623 mg kg-1 respectively. These metal concentrations are above current regulatory limits in the US. The compost was made using biosolids that are currently produced and had Cd, Pb and Zn of 0.8, 20 and 160 mg kg-1 respectively. Trees were harvested and analyzed for rate of N fixation (as measured by acetylene reduction activity), biomass, and foliar metals. Soils were analyzed for available N, total carbon and N, pH and total Cd, Pb and Zn. Rates of N fixation were not affected by soil amendment. In year 2, shoot biomass of trees grown in both the compost and high metal amendments were higher than the control. Shoot biomass increased with increasing amount of compost amendments, but decreased with increasing amount of high metal amendments. There was no relationship between soil metal concentration and plant biomass. Foliar Cd and Pb were below detection for all trees and foliar Zn increased with increasing amount of both compost and high metal amendment, with concentrations of 249 mg kg-1 for trees grown in the compost amendment and 279 mg kg-1 for the high metal amendment. The results from this study indicate that the growth of A. rubra benefited from both types of biosolids used in the study and that the Alnus/Frankia relationship was not negatively impacted by metal concentrations resulting from the high metal biosolids amendments.