No abstract

Throughout the Amazon of Brazil, manioc (Manihot esculenta) is a staple crop produced through slash-and-burn agriculture. Nutrient losses during slash-and-burn can be large and nutrient demand by food crops so great that fields are often abandoned after two years. In recent decades, farmers have reduced the fallow phase from 20 to *5 years, limiting plant nutrient accumulation to sustain crop yields. Improved fallows through simultaneous planting of trees with food crops may accelerate nutrient re-accumulation. In addition, slash-and-mulch technology may prevent loss of nutrients due to burning and mulch decomposition may serve as a slow-release source of nutrients. This study in Pará, Brazil, in a 7-year-old secondary forest following slashing and mulching of the vegetation, involved two main plot treatments (with and without P and K fertilizers) and two sub-plot treatments (with or without a N 2 -fixer Inga edulis). A mixed-culture of trees and manioc was planted in all plots. P and K fertilizer increased tree mortality due to weed competition but growth of surviving trees in four of the five tree species tested also increased as did biomass production of manioc. In the N 2 -fixer treatment trends of greater growth and survival of four of five tree species and manioc biomass were also observed. Fertilization increased the biomass of competing vegetation, but there was a fertilizer by N 2 -fixer interaction as I. edulis caused a reduction in competing biomass in the fertilized treatment. After one year, fertilization increased decomposition of the mulch such that Ca, Mg, and N contents within the mulch all decreased. In contrast, P and K contents of mulch increased in all treatments. No influence of the N 2 -fixer on 0-10 cm soil N contents was observed. Two years after establishment, this agroforestry system succeeded in growing a manioc crop and leaving a well-maintained tree fallow after the crop harvest.

No abstract

The slash-and-burn practice of land preparation that farmers use traditionally in forest-based fallow systems in the humid tropics causes land degradation and human health hazards. As an alternative to slash-and-burn, a mechanized, fire-free method of land preparation was evaluated on smallholdings in the eastern Amazon region. The use of machinery for harvesting fallow vegetation and chopping it for mulch eliminates the need for hard labor and fire for land clearing and increases labor productivity. Four different tractor-propelled choppers with power demand of 50 kW to 122 kW were tested. Their chopping capacity varied between 4.5 Mg and 20 Mg of fresh biomass per hour. The mechanized chop-and-mulch technology can be used in fallow vegetation that is up to 12 years old, which in the study region corresponded to 20 Mg to 150 Mg fresh biomass per hectare. Two additional choppers-a stationary silage chopper and a high-powered crawler tractor with a chopping device-were also tested but both were not suitable for smallholder fallow systems. In the context of the mulch technology, new low-input crop varieties were screened and their response to fertilizer was studied. The mulch technology facilitates extended cropping, to plant crops off-season, and modify crop rotation. Degraded fallow vegetation can be improved by enrichment planting using fast-growing leguminous tree species. Financial analysis of different scenarios revealed that farm income and labor productivity from chop-and-mulch systems can be up to two times greater than from the traditional slash-and-burn system.

The slash-and-burn practice of land preparation that farmers use traditionally in forest-based fallow systems in the humid tropics causes land degradation and human health hazards. As an alternative to slash-and-burn, a mechanized, fire-free method of land preparation was evaluated on smallholdings in the eastern Amazon region. The use of machinery for harvesting fallow vegetation and chopping it for mulch eliminates the need for hard labor and fire for land clearing and increases labor productivity. Four different tractor-propelled choppers with power demand of 50 kW to 122 kW were tested. Their chopping capacity varied between 4.5 Mg and 20 Mg of fresh biomass per hour. The mechanized chop-and-mulch technology can be used in fallow vegetation that is up to 12 years old, which in the study region corresponded to 20 Mg to 150 Mg fresh biomass per hectare. Two additional choppers-a stationary silage chopper and a high-powered crawler tractor with a chopping device-were also tested but both were not suitable for smallholder fallow systems. In the context of the mulch technology, new low-input crop varieties were screened and their response to fertilizer was studied. The mulch technology facilitates extended cropping, to plant crops off-season, and modify crop rotation. Degraded fallow vegetation can be improved by enrichment planting using fast-growing leguminous tree species. Financial analysis of different scenarios revealed that farm income and labor productivity from chop-and-mulch systems can be up to two times greater than from the traditional slash-and-burn system.

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...

Many Amazon soils are naturally fragile and develop under intense rainfall and high temperature climate. Soil structural quality is improvable through vegetation management systems providing abundant soil mulch and little soil disturbance. We tested the effect of the chopping‐and‐mulching systems of secondary forest‐vegetation on selected soil physical properties of a sandy Oxisol, located in the eastern Brazilian Amazon. The treatments consisted of two fallow forest‐vegetation, namely, chop‐and‐mulch of secondary vegetation with a dual vertical‐rotor chopper (VC) and with a horizontal‐rotor chopper (HC) and a control composed of standing secondary forest‐vegetation (SF). Six months after vegetation chopping, we evaluated soil bulk density (BD), degree‐of‐compactness (DC), pore‐size distribution and soil hydraulic properties. Compared with SF, the VC and HC systems did not affect soil BD in surface layer (0·00–0·05 m) but increased BD in subsurface layers. DC in surface layer are below the range of the optimum values for most crops (77%–88%), while for other layers DC was within this optimum range. High macroporosity and sandy granulometry were responsible for high drainable water from soil saturation until field capacity, down to 0·20 m depth in all systems. Pore‐size distribution was influenced by vegetation chopping with increase in smaller pores. These pores represent a small percentage of total porosity and contribute more to water retention and availability. Chopping by VC and HC mechanisms was effective in maintaining soil physical quality, characterized by lower soil bulk density, higher porosity and water retention, build up during growth of secondary vegetation in fallow period between cash crops. Copyright © 2015 John Wiley & Sons, Ltd.

A dinâmica do efluxo de dióxido de carbono (CO 2 ) do solo e seus fatores controladores em sistemas agroflorestais da Amazônia são pouco compreendidas. O objetivo deste estudo foi avaliar a variação temporal do efluxo de CO 2 do solo em sistemas agroflorestais onde a palma de óleo é a cultura principal e sua relação com fatores bióticos (carbono microbiano do solo, carbono total do solo, respiração microbiana do solo, raízes finas do solo, indivíduos componentes dos sistemas agroflorestais (SAFs) ) e abióticos (umidade e temperatura do solo). As medições foram realizadas nos períodos menos chuvoso (dezembro de 2010) e chuvoso (maio de 2011). O efluxo de CO 2 do solo foi mais alto no período chuvoso, provavelmente, devido à maior atividade microbiana nesse período influenciada por fatores climáticos aliados a fatores bióticos. O efluxo de CO 2 do solo se correlacionou positivamente com umidade do solo e carbono da biomassa microbiana e negativamente com temperatura do solo e quociente metabólico, porém as correlações foram fracas. O efluxo de CO 2 do solo foi sensível ao tipo de sistema agroflorestal e a sazonalidade da precipitação. PALAVRAS-CHAVE: Efeito estufa, biomassa microbiana do solo, respiração do solo, umidade do solo, temperatura do solo. Temporal variation of soil CO 2 efflux in oil palm-based agroforestry systems in eastern Amazon ABSTRACTThe soil carbon dioxide (CO 2 ) efflux dynamics and its controlling factors of Amazonian agroforestry systems are poorly understood. The objective of this study was to evaluate the temporal variation of soil CO 2 efflux in oil palm-based agroforestry systems and the relation between efflux and biotic (microbial and total soil carbon, microbial respiration, fine roots, individual components of agroforestry systems (AFS)) and abiotic factors (soil moisture and temperature). The measurements were taken during the less rainy (December 2010) and rainy (May 2011) periods. The soil CO 2 efflux was highest during the rainy season, probably due to increased microbial activity influenced by climatic factors coupled with biotic factors. The soil CO 2 efflux correlated positively with soil moisture and microbial biomass carbon and negatively with soil temperature and metabolic quotient, but these correlations were weak. The soil CO 2 efflux was sensitive to the type of agroforestry system and to rainfall seasonality.