ABUNDÂNCIA NATURAL DE 15N E FORMAS DE NITROGÊNIO EM ARGISSOLO CULTIVADO COM EUCALIPTO E ACÁCIA

http://dx.doi.org/10.5902/1980509821121The nutrients nitrogen and one of the most demanded by plant species, and its presence in soil under organic or mineral forms available to plants is linked to quality and quatity of plant residues added to the soil. The study aimed to evaluate the influence of cultivation of eucalyptus and acacia in the composition of organic and inorganic N forms and the natural abundance of 15N in an Ultisol. For this, we collected soil and litter samples in continuous short-rotation eucalypt (Eucalyptus urophylla x Eucalyptus grandis hybrid) (seven years) compared to a rotation system including acacia (Acacia mangium Willd.) after short-rotation eucalypt; and long-rotation eucalypt (24 years). A native vegetation (Atlantic Forest) was used as a reference for the original site condition representative for the northern coast of  Espírito Santo state. To do so, we evaluated the content of total organic C, total N, N-NH4+, N-NO3-, C/N ratio, fractionation of organic N and 15N natural abundance in soil and litter. Among the forms of organic-N hydrolyzed, the N-amino was the fraction with the highest contribution of organic N (39%), followed by the fraction of N-unidentified (27%), the fraction of N-amide (18%) and N-hexosamine (15%). The acacia plantation presented smaller natural abundance of 15N and higher levels of total N and soil organic C, and increased organic forms of N-hydrolyzed, when compared to the eucalyptus short-rotation soil. This indicates the increase of labile N-organic forms in the soil for the plants and reduction of humification of soil organic matter (SOM) of acacia. Thus, the crops rotation with acacia after eucalyptus contributed to the increase of organic forms in the soil, important for the nutrition of plants, because they are potential sources of nutrients to the plants in a short-time period.The nutrients nitrogen and one of the most demanded by plant species, and its presence in soil under organic or mineral forms available to plants is linked to quality and quatity of plant residues added to the soil. The study aimed to evaluate the influence of cultivation of eucalyptus and acacia in the composition of organic and inorganic N forms and the natural abundance of 15N in an Ultisol. For this, we collected soil and litter samples in continuous short-rotation eucalypt (Eucalyptus urophylla x Eucalyptus grandis hybrid) (seven years) compared to a rotation system including acacia (Acacia mangium Willd.) after short-rotation eucalypt; and long-rotation eucalypt (24 years). A native vegetation (Atlantic Forest) was used as a reference for the original site condition representative for the northern coast of  Espírito Santo state. To do so, we evaluated the content of total organic C, total N, N-NH4+, N-NO3-, C/N ratio, fractionation of organic N and 15N natural abundance in soil and litter. Among the forms of organic-N hydrolyzed, the N-amino was the fraction with the highest contribution of organic N (39%), followed by the fraction of N-unidentified (27%), the fraction of N-amide (18%) and N-hexosamine (15%). The acacia plantation presented smaller natural abundance of 15N and higher levels of total N and soil organic C, and increased organic forms of N-hydrolyzed, when compared to the eucalyptus short-rotation soil. This indicates the increase of labile N-organic forms in the soil for the plants and reduction of humification of soil organic matter (SOM) of acacia. Thus, the crops rotation with acacia after eucalyptus contributed to the increase of organic forms in the soil, important for the nutrition of plants, because they are potential sources of nutrients to the plants in a short-time period.http://dx.doi.org/10.5902/1980509821121O nitrogênio e um dos nutrientes mais demandados pelas espécies vegetais, sua presença no solo, sob formas orgânicas ou minerais disponíveis para as plantas, está vinculada à qualidade e quantidade dos resíduos vegetais aportados ao solo. O estudo teve o objetivo de avaliar a influência do cultivo do eucalipto e da acácia na composição das formas orgânicas e inorgânicas de N e, na abundância natural de 15N em um Argissolo Amarelo. Para isso, foram coletadas amostras de solo e serapilheira em monocultivos do Eucalyptus urograndis (clone do Eucalyptus urophylla S. T. Blake x Eucalyptus grandis W. Hill ex Spreng) de ciclo curto (sete anos), sistemas de cultivo de rotação de acácia (Acacia mangium Willd.) após monocultivo de eucalipto, monocultivo de eucalipto de ciclo longo (24 anos) e mata nativa (Mata Atlântica) como condição original de solo do litoral Norte do Espírito do Santo. Foram avaliados os teores de C orgânico total, N total, N-NH4+, N-NO3-, relação C/N, fracionamento do N orgânico e abundância natural de 15N no solo e serapilheira. Das formas de N-orgânico hidrolisado, o N- amino foi a fração que apresentou maior contribuição (39%), seguida pela fração de N- não identificado (27%), da fração N-amida (18%) e N-hexosamina (15%). O povoamento de acácia promoveu menor abundância natural de 15N e maiores teores de N total e C orgânico no solo e aumentou as formas orgânicas de N-hidrolisado, quando comparado àqueles de eucalipto de ciclo curto. Isto indica o aumento de formas lábeis de N orgânico no solo para as plantas e redução da humificação da matéria orgânica do solo (MOS) de acácia. Neste sentido, a rotação de cultivos florestais com acácia após eucalipto de ciclo curto contribuiu para o aumento de formas orgânicas no solo, importantes para a nutrição de plantas, por serem potenciais fontes de nutrientes às plantas em curto período de tempo

THE 15N NATURAL ABUNDANCE AND NITROGEN FORMS IN ULTISOL CULTIVATED WITH EUCALYPTUS AND ACACIA

O nitrog\ueanio e um dos nutrientes mais demandados pelas esp\ue9cies vegetais, sua presen\ue7a no solo, sob formas org\ue2nicas ou minerais dispon\uedveis para as plantas, est\ue1 vinculada \ue0 qualidade e quantidade dos res\uedduos vegetais aportados ao solo. O estudo teve o objetivo de avaliar a influ\ueancia do cultivo do eucalipto e da ac\ue1cia na composi\ue7\ue3o das formas org\ue2nicas e inorg\ue2nicas de N e, na abund\ue2ncia natural de 15N em um Argissolo Amarelo. Para isso, foram coletadas amostras de solo e serapilheira em monocultivos do Eucalyptus urograndis (clone do Eucalyptus urophylla S. T. Blake x Eucalyptus grandis W. Hill ex Spreng) de ciclo curto (sete anos), sistemas de cultivo de rota\ue7\ue3o com ac\ue1cia ( Acacia mangium Willd.) ap\uf3s monocultivo de eucalipto, monocultivo de eucalipto de ciclo longo (24 anos) e mata nativa (Mata Atl\ue2ntica) como condi\ue7\ue3o original de solo do litoral Norte do Esp\uedrito do Santo. Foram avaliados os teores de C org\ue2nico total, N total, N-NH4+, N-NO3-, rela\ue7\ue3o C/N, fracionamento do N org\ue2nico e abund\ue2ncia natural de 15N no solo e serapilheira. Das formas de N-org\ue2nico hidrolisado, o N-amino foi a fra\ue7\ue3o que apresentou maior contribui\ue7\ue3o (39%), seguida pela fra\ue7\ue3o de N-n\ue3o identificado (27%), da fra\ue7\ue3o N-amida (18%) e N-hexosamina (15%). O povoamento de ac\ue1cia promoveu menor abund\ue2ncia natural de 15N e maiores teores de N total e C org\ue2nico no solo e aumentou as formas org\ue2nicas de N-hidrolisado, quando comparado \ue0queles de eucalipto de ciclo curto. Isso indica o aumento de formas l\ue1beis de N org\ue2nico no solo para as plantas e redu\ue7\ue3o da humifica\ue7\ue3o da mat\ue9ria org\ue2nica do solo (MOS) de ac\ue1cia. Nesse sentido, a rota\ue7\ue3o de cultivos florestais com ac\ue1cia ap\uf3s eucalipto de ciclo curto contribuiu para o aumento de formas org\ue2nicas no solo, importantes para a nutri\ue7\ue3o de plantas, por serem potenciais fontes de nutrientes \ue0s plantas em curto per\uedodo de tempo.The nutrients nitrogen and one of the most demanded by plant species, and its presence in soil under organic or mineral forms available to plants is linked to quality and quatity of plant residues added to the soil. The study aimed to evaluate the influence of cultivation of eucalyptus and acacia in the composition of organic and inorganic N forms and the natural abundance of 15N in an Ultisol. For this, we collected soil and litter samples in continuous short-rotation eucalypt ( Eucalyptus urophylla x Eucalyptus grandis hybrid) (seven years) compared to a rotation system including acacia ( Acacia mangium Willd.) after short-rotation eucalypt; and long-rotation eucalypt (24 years). A native vegetation (Atlantic Forest) was used as a reference for the original site condition representative for the northern coast of Esp\uedrito Santo state. To do so, we evaluated the content of total organic C, total N, N-NH4+, N-NO3-, C/N ratio, fractionation of organic N and 15N natural abundance in soil and litter. Among the forms of organic-N hydrolyzed, the N-amino was the fraction with the highest contribution of organic N (39%), followed by the fraction of N-unidentified (27%), the fraction of N-amide (18%) and N-hexosamine (15%). The acacia plantation presented smaller natural abundance of 15N and higher levels of total N and soil organic C, and increased organic forms of N-hydrolyzed, when compared to the eucalyptus short-rotation soil. This indicates the increase of labile N-organic forms in the soil for the plants and reduction of humification of soil organic matter (SOM) of acacia. Thus, the crops rotation with acacia after eucalyptus contributed to the increase of organic forms in the soil, important for the nutrition of plants, because they are potential sources of nutrients to the plants in a short-time period

CARBON AND NITROGEN STOCKS IN THE ALFISOL SUBMITTED TO THE Eucalyptus urograndis MONOCULTURE AND Acacia mangium ROTATION

A busca de sistemas sustent\ue1veis de manejo do solo tem levado pesquisadores a desenvolverem novas t\ue9cnicas de cultivo. Dentre elas, destacam-se no Brasil estudos realizados com esp\ue9cies florestais capazes de fixar N2 atmosf\ue9rico e aumentar o estoque de C e N em fra\ue7\uf5es l\ue1beis e est\ue1veis da mat\ue9ria org\ue2nica do solo (MOS). O presente estudo teve por objetivo avaliar as altera\ue7\uf5es nos estoques de C e N em fra\ue7\uf5es das subst\ue2ncias h\ufamicas, da fra\ue7\ue3o leve da MOS e da mat\ue9ria microbiana em solos cultivados com Eucalyptus urograndis em rota\ue7\ue3o curta, eucalipto em rota\ue7\ue3o longa e povoamentos de Acacia mangium que sucederam plantios de eucalipto em rota\ue7\ue3o curta, tendo como refer\ueancia o solo de floresta nativa (Mata Atl\ue2ntica) adjacente. Foram quantificados os estoques de C org\ue2nico total e N total (COT e NT), nas fra\ue7\uf5es das subst\ue2ncias h\ufamicas (fra\ue7\ue3o \ue1cido f\ufalvico-AF, fra\ue7\ue3o \ue1cido h\ufamico-AH e fra\ue7\ue3o humina-H), C e N da fra\ue7\ue3o leve da MOS (C-MOL e N-MOL) e estoque de C e N da mat\ue9ria microbiana (C-BM e N-BM). Os resultados indicaram que o cultivo do eucalipto em rota\ue7\ue3o curta apresentou menores estoques de COT e NT, nas fra\ue7\uf5es das subst\ue2ncias h\ufamicas e, de N na mat\ue9ria microbiana em compara\ue7\ue3o ao solo sob rota\ue7\ue3o com Acacia mangium. O cultivo de Acacia mangium e o aumento do tempo da rota\ue7\ue3o do eucalipto incrementaram os estoques de C e N da maioria das fra\ue7\uf5es l\ue1beis (C-MOL, N-MOL e C-BM) e est\ue1veis (C e N nas subst\ue2ncias h\ufamicas), indicando tend\ueancia de recupera\ue7\ue3o dos seus estoques para valores pr\uf3ximos daqueles originais (mata nativa), sendo superiores aos estoques obtidos na \ue1rea de eucalipto em rota\ue7\ue3o curta.The pursuit of sustainable systems of soil management has led researchers to develop new techniques of cultivation. Among them, studies with forest species able to fix atmospheric N2 and increase C and N stocks in labile and stable soil organic matter (SOM) stand out in Brazil. The study aimed to evaluate changes in stocks of C and N in fractions of humic substances, light fraction of SOM and microbial biomass in soils of short-rotation Eucalyptus \u201curograndis\u201d, long rotation plantations and stands of Acacia mangium which succeeded short rotation eucalyptus monoculture, in comparison to the soil of native forest (Atlantic Forest). It was obtained the total organic carbon (TOC) and total nitrogen (TN) stocks, C and N stocks in the fractions of humic substances (fulvic acid fraction-AF, humic acid fraction-HA and humin fraction-H), C and N in light fraction of SOM (C-LOM and N-LOM) and C and N microbial biomass (CMB and N-MB). The results indicated that the short rotation eucalyptus cultivation reduced total organic carbon stocks, total nitrogen, C and N in the humic substances, and N storage in the microbial biomass compared to Acacia mangium soil. The cultivation of Acacia mangium and the increase of the eucalyptus rotation time increased stocks of C and N of the labile (C-LOM, N-LOM and C-MB) and stable fractions (C and N in humic substances) indicating a significant recovery of their stocks to levels approaching those original (native), and higher than stocks obtained in the soil of short rotation eucalypt

Nitrogen release from urea with different coatings

Coatings or urease inhibitors are designed to reduce losses of ammonia [NH 3(g) ] from urea fertilizers. However, nitrogen (N) release and its effects on soil solution have not previously been evaluated under standardized conditions in soils. In this study, the urea fertilizers were incubated in chambers filled with sandy loam soil, adapted for the collection of NH 3(g) and soil solution by centrifugation. In the fast-release N fertilizers, around 93% and 100% of urea-N applied was recovered within the first hours of incubation. In contrast, in the slow-release N fertilizers, less than 40% of urea-N applied, was recovered at 19 days of incubation. The maximum N release from the fertilizers followed the order: UP1 (106%) ≈ UNBPT (102%) ≈ urea (93%) > USP2 (57%) ≈ USP3 (57%) > USP4 (31%) ≈ USP5 (18%). NH 3(g) volatilization accounted for only 3% of the applied N in the slow-release fertilizers, which corresponded to about 88% less than the NH 3(g) loss from prilled urea. This study demonstrated distinct N release patterns, which changed the N dynamics in the soil. Some coatings effectively delayed urea release from granules and reduced NH 3(g) gas losses, while other were not efficient