Despite the potential to provide N to crops, the rapid incorporation of green manure nutrients into stable fractions of organic matter in the soil (SOM) may reduce the efficiency of green manuring. Thus, the objective of this work was to characterize the changes of C and N stocks in fractions of SOM cultivated with coffee (Coffea arabica L.) and fertilized with sunn hemp (Crotalaria juncea) and ammonium sulfate. To study the changes in organic C (OC) and total N (TN) in soil and fractions of SOM over time, soil samples were collected in the 0-5 and 5-10 cm layers, with the initial sampling done prior to the application of sunn hemp residues and ammonium sulfate. Five samples were collected every 2 months after the application of the legume and ammonium sulfate. The soil samples were submitted to densimetric and granulometric fractionation, obtaining the free light organic matter (F-LOM), particulate organic matter (POM), and organic matter associated with minerals (MAM). OC and TN stocks were then determined in soil and the SOM fractions. The changes in the stocks of OC (ΔStcC) in the soil in relation to time zero were positive in the evaluations carried out in the two layers. The fractions of SOM showed positive ΔStcC at almost all of the evaluated times. The N supplied to the soil in the form of mineral and organic fertilizer promoted an increase of 0.24 Mg ha -1 of N in the 0-5 cm layer until after 60 days. Of this total, 0.03 Mg ha -1 was associated with F-LOM, 0.07 Mg ha -1 with POM, and the remainder was associated with MAM. Nearly 60% of the N that was supplied to the soil was drawn to the stable fractions of the SOM, indicating a rapid stabilization of this nutrient in the most recalcitrant organic compartments. Despite that, the variations in N stocks of MAM became smaller over time, and eventually became negative, in relation to time zero. This indicates the mineralization of N of this compartment. In the 5-10 cm layer, no effect of time was observed in the soil TN, N-POM, or N-MAM stocks. Additionally, under the conditions of this experiment, the majority of the N supplied to the soil was rapidly incorporated into the most stable fraction of SOM, and this might can reduced the efficiency of the green manuring. ResumoApesar do potencial para fornecer N aos cultivos, a rápida incorporação dos nutrientes do adubo verde em frações estáveis da matéria orgânica do solo (MOS) pode reduzir a eficiência da adubação verde. Portanto, objetivou-se com este trabalho caracterizar as alterações temporais dos estoques de C e N em frações da matéria orgânica de solo cultivado com cafeeiro (Coffea arabica L.) e adubado com crotalária (Crotalaria juncea) e sulfato de amônio. Para estudar o comportamento do C orgânico (CO) e N total (NT) no solo e nas frações da MOS ao longo do tempo, foram coletadas amostras de solo nas camadas de 0-5 e 5-10 cm, sendo a primeira amostragem antes da aplicação dos resíduos de crotalária e sulfato de amônio. Outras cinco amostras foram coletadas a cada dois meses após a aplicação ...
Volatilization of nitrogen ammonia (N-NH 3 ) and rapid incorporation of mineralized nitrogen (N) into soil organic matter fractions can reduce the efficiency of green manuring. The objective of this study was to characterize N-NH3 loss through volatilization and the changes in carbon (C) and N stocks in soil fertilized with Crotalaria juncea and ammonium sulfate during coffee plant cultivation. The N-NH 3 collectors were installed and evaluated at 1, 2, 3, 4, 5, 6, 9, 12, 15, 18, 25, 32, 67 and 123 days after their installation. Total organic carbon (TOC) and total nitrogen (TN) in the 0-5-and 5-10-cm soil layers were evaluated at 0, 60, 120, 180, 240, and 300 days after fertilization. After 9 days, 20.83 kg ha -1 (N-NH 3 ) had volatilized from the 41.88 kg haobserved at the end of the evaluation period. The TOC stock in both soil layers was 5.81 Mg ha -1 , and after 300 days, the stocks were 8.84 and 8.36 Mg ha -1 for the 0-5 and 5-10 cm layers, respectively. The TN stock in the 0-5 cm layer increased from 1.74 to 1.98 Mg ha -1 over 60 days, and then decreased. There was no time dependency in the TN stock in the 5-10 cm layer. Volatilization of N-NH 3 was rapid but low. The increase in TOC stocks was not followed by an increase in TN stocks.Key words: ammonium; green manure; organic matter N-NH 3 volatilizado e estoques de N e C de solo após adubação verde de cafeeiro RESUMO: A volatilização de N-NH 3 e a rápida incorporação do N mineralizado em frações da matéria orgânica do solo podem reduzir a eficiência da adubação verde. O objetivo do trabalho foi caracterizar as perdas por volatilização de N-NH 3 e as modificações nos estoques de C e N em solo cultivado com cafeeiro e adubado com Crotalaria juncea e sulfato de amônio. Foram instalados coletores de N-NH 3 , procedendo-se com avaliações aos 1, 2, 3, 4, 5, 6, 9, 12, 15, 18, 25, 32, 67 e 123 dias após a sua instalação. Os estoques de carbono orgânico total (COT) e nitrogênio total (NT) do solo foram avaliados, nas camadas de 0-5 e 5-10 cm, aos 0, 60, 120, 180, 240 e 300 após as adubações, sendo a primeira amostragem antes das adubações. Aos nove dias já haviam sido volatilizados (N-NH3) 20,83 kg ha -1 dos 41,88 kg ha -1 observados no final do período de avaliação. O estoque de COT em ambas as camadas era de 5,81 Mg ha -1 e após 300 dias os estoques foram de 8,84 e 8,36 Mg ha -1 , respectivamente para as camadas 0-5 e 5-10 cm. Já o estoque NT na camada 0-5 cm aumentou até os 60 dias, passando de 1,74 para 1,98 Mg ha -1 , e em seguida apresentou redução. Não houve efeito do tempo no estoque de NT na camada 5-10 cm. A volatilização de N-NH 3 é rápida, porém é baixa. O aumento nos estoques de COT não foi acompanhado por aumentos nos estoques de NT. Palavras-chave: amônia; adubo verde; matéria orgânicaVolatilized N-NH 3 , N, and C stocks in soil after green manuring of coffee crops Rev. Bras.
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