RESUMOO sucesso da produção de palma de óleo (Elaeis guineensis Jacq.) em sistemas agroflorestais (SAFs) na Amazônia está condicionado ao manejo sustentável do solo, em especial dos atributos químicos e microbiológicos. Nosso objetivo foi avaliar o impacto de SAFs com palma de óleo sobre os teores de nitrogênio (N) mineral e microbiano do solo, em função da sazonalidade pluviométrica. Avaliamos diferentes formas de N do solo (N microbiano, nitrato, amônio), além da concentração de carbono (C) do solo, em SAFs com baixa e alta diversidade de espécies cultivadas, os quais foram comparados com uma floresta secundária adjacente de 13 anos de idade. Para a maioria das variáveis analisadas (N total, relação C:N, N microbiano, relação N microbiano:N total, amônio) houve diferença significativa somente entre as épocas de amostragem. A concentração média de C no solo sob o SAF com alta diversidade (15,6 mg g -1 ) foi maior do que na floresta (13 mg g -1 ). Na época chuvosa a concentração de nitrato no SAF com alta diversidade foi 5,1 mg (N) kg -1 (solo), maior do que nos demais tipos de vegetação, resultando em menor concentração média de amônio no solo sob esse SAF, cujo valor foi 9,6 mg (N) kg -1 (solo). A mineralização do N no SAF com baixa diversidade, na época seca, foi 0,1 mg (N) kg -1 (solo) dia -1, menor do que nos demais tipos de vegetação. As variáveis analisadas foram mais sensíveis à sazonalidade da precipitação pluviométrica do que à conversão de floresta secundária em SAFs com palma de óleo. PALAVRAS-CHAVE: amônio, dendezeiro, Elaeis guineensis, nitrato Soil mineral and microbial nitrogen in oil palm-based agroforestry systems in eastern Amazon ABSTRACTThe success of oil palm (Elaeis guineensis Jacq.)-based agroforestry systems (oil palm-AFS) depends on sustainable soil management, especially of soil chemical and microbiological characteristics. Our objective was to evaluate the impact of oil palm-AFS on soil mineral and microbial nitrogen (N) in contrasting rainfall seasons. We evaluated different soil nitrogen (N) forms (microbial-N, nitrate, ammonium) and soil carbon concentration in oil palm-AFS with low and high diversity of species planted, which were compared with an adjacent 13-yr-old secondary forest. Most variables (total N, C:N ratio, microbial-N, microbial-N:total N ratio, ammonium, and net nitrification rate) varied only in response to rainfall seasonality. Soil C was significantly higher in the high diversity AFS (15.6 mg g -1 ) than in the secondary forest (13.0 mg g -1 ). In the rainy season, nitrate concentration (5.1 mg N kg -1 soil) was higher in the high diversity AFS than in other vegetation types; consequently, the average soil ammonium concentration (9.6 mg N kg -1 soil) was significantly lower in the high diversity AFS. Net N mineralization in the low diversity AFS (0.1 mg N kg -1 soil day -1 ) in the dry season was significantly lower than in other vegetation types. The soil variables were more sensitive to the rainfall seasonality than to the conversion of secondary forest to oil p...

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The impact of substituting forests for smallholder agricultural production systems on soil carbon (C) stocks is not well understood in Brazilian Amazonia. Most surveys of soil C stocks are restricted to the top 30 cm of soil and do not include measurements of litter and root stocks. Here, we quantify the stocks of C in soil (0–100 cm depth), aboveground litter and coarse roots of traditional (slash‐and‐burn) and alternative (Schizolobium amazonicum‐planted forest and silvopastoral system) smallholder agricultural systems, which were compared with a reference area (forest regrowth) in the eastern Amazonia. The soil C stocks in the 0–100 cm layer were larger in the forest regrowth treatment (156.8 ± 15.5 Mg/ha) than in the other treatments (S. amazonicum = 85.3 ± 6.5, silvopastoral = 108.0 ± 4.4 Mg/ha) but did not differ from the soil C stock in the slash‐and‐burn treatment (127.2 ± 6.1 Mg/ha). The soil C stocks at the 0–30 cm layer, which represented 33–50% of the total C of the 0–100 cm layer, did not differ among the treatments. The litter C stocks were ranked in the following order: silvopastoral > forest regrowth > S. amazonicum > slash‐and‐burn. The forest regrowth treatment had a greater coarse root C stock (0.84 ± 0.10 Mg/ha) than the other treatments (silvopastoral = 0.28 ± 0.03, S. amazonicum = 0.18 ± 0.03, slash‐and‐burn = 0.27 ± 0.04 Mg/ha). Soil, litter and root C stocks were negatively impacted by the conversion of forest regrowth to cultivation systems.

Physalis angulata L. (Solanaceae), popularly known as ‘camapu’, has high pharmacological and agroindustrial potential. However, because it essentially is a wild species, studies on the physiological quality of its seeds are still scarce. In this sense, the objective was to evaluate the physiological performance of P. angulata seeds as a function of pre-germination treatments with chemical promoters. For this, germination, first germination count, germination speed index and seedling emergence tests were performed. The substrate was previously moistened with solutions of gibberellic acid - GA3 (0.00, 0.02, 0.04, 0.06 and 0.08%), potassium nitrate - KNO3 (0.0, 0.2, 0.4, 0.6, 0.8 and 1.0%) and Stimulate® (0.00, 0.25, 0.50, 0.75, 1.00, 1.25 and 1.50%). Each chemical promoter constituted an independent experiment, in a completely randomised design, with four replicates of 25 seeds each. The three chemical promoters enhanced the physiological performance of P. angulata seeds, and the concentrations of 0.05% GA3, 0.4% KNO3 and 1.0% Stimulate® were most suitable.