• Authors:
    • Leblanc, H. A.
    • Harmand, J.-M.
    • Fernandez, M. P.
    • Nygren, P.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 94
  • Issue: 2-3
  • Year: 2012
  • Summary: We compiled quantitative estimates on symbiotic N-2 fixation by trees in agroforestry systems (AFS) in order to evaluate the critical environmental and management factors that affect the benefit from N-2 fixation to system N economy. The so-called "N-2-fixing tree" is a tripartite symbiotic system composed of the plant, N-2-fixing bacteria, and mycorrhizae-forming fungi. Almost 100 recognised rhizobial species associated with legumes do not form an evolutionary homologous clade and are functionally diverse. The global bacterial diversity is still unknown. Actinorrhizal symbioses in AFS remain almost unstudied. Dinitrogen fixation in AFS should be quantified using N isotopic methods or long-term system N balances. The general average +/- A standard deviation of tree dependency on N-2 fixation (%Ndfa) in 38 cases using N isotopic analyses was 59 +/- A 16.6 %. Under humid and sub-humid conditions, the percentage was higher in young (69 +/- A 10.7 %) and periodically pruned trees (63 +/- A 11.8 %) than in free-growing trees (54 +/- A 11.7 %). High variability was observed in drylands (range 10-84 %) indicating need for careful species and provenance selection in these areas. Annual N-2 fixation was the highest in improved fallow and protein bank systems, 300-650 kg [N] ha(-1). General average for 16 very variable AFS was 246 kg [N] ha(-1), which is enough for fulfilling crop N needs for sustained or increasing yield in low-input agriculture and reducing N-fertiliser use in large-scale agribusiness. Leaf litter and green mulch applications release N slowly to the soil and mostly benefit the crop through long-term soil improvement. Root and nodule turnover and N rhizodeposition from N-2-fixing trees are sources of easily available N for the crop yet they have been largely ignored in agroforestry research. There is also increasing evidence on direct N transfer from N-2-fixing trees to crops, e.g. via common mycelial networks of mycorrhizal fungi or absorption of tree root exudates by the crop. Research on the below-ground tree-crop-microbia interactions is needed for fully understanding and managing N-2 fixation in AFS.
  • Authors:
    • Craine, J. M.
    • Ramirez, K. S.
    • Fierer, N.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 6
  • Year: 2012
  • Summary: Ecosystems worldwide are receiving increasing amounts of reactive nitrogen (N) via anthropogenic activities with the added N having potentially important impacts on microbially mediated belowground carbon dynamics. However, a comprehensive understanding of how elevated N availability affects soil microbial processes and community dynamics remains incomplete. The mechanisms responsible for the observed responses are poorly resolved and we do not know if soil microbial communities respond in a similar manner across ecosystems. We collected 28 soils from a broad range of ecosystems in North America, amended soils with inorganic N, and incubated the soils under controlled conditions for 1 year. Consistent across nearly all soils, N addition decreased microbial respiration rates, with an average decrease of 11% over the year-long incubation, and decreased microbial biomass by 35%. High-throughput pyrosequencing showed that N addition consistently altered bacterial community composition, increasing the relative abundance of Actinobacteria and Firmicutes, and decreasing the relative abundance of Acidobacteria and Verrucomicrobia. Further, N-amended soils consistently had lower activities in a broad suite of extracellular enzymes and had decreased temperature sensitivity, suggesting a shift to the preferential decomposition of more labile C pools. The observed trends held across strong gradients in climate and soil characteristics, indicating that the soil microbial responses to N addition are likely controlled by similar wide-spread mechanisms. Our results support the hypothesis that N addition depresses soil microbial activity by shifting the metabolic capabilities of soil bacterial communities, yielding communities that are less capable of decomposing more recalcitrant soil carbon pools and leading to a potential increase in soil carbon sequestration rates.
  • Authors:
    • Akinnifesi, F. K.
    • Debusho, L. K.
    • Sileshi, G. W.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 5
  • Year: 2012
  • Summary: Growing maize ( Zea mays L.) in association with legume trees in agroforestry arrangements has been shown to increase yields in many parts of sub-Saharan Africa; however, the stability of crop yields has not been critically analyzed in the various cropping systems that integrate leguminous trees. The objective of this analysis was to compare yield stability in improved cropping systems, namely maize-gliricidia [ Gliricidia sepium (Jacq.) Kunth] intercropping and fertilized monoculture maize, with the de facto practice of resource-poor farmers who grow maize continuously without any external input. Yield stability was determined for three long-term field trials (12-13 consecutive yr) conducted at Makoka Research Station in southern Malawi and Msekera Research Station in eastern Zambia. At Makoka, the most stable yield was recorded in maize-gliricidia intercrops. Average yield was highest for maize-gliricidia intercropping amended with 50% of the recommended N and P fertilizer, and this was comparable with the yield recorded in monoculture maize that received inorganic fertilizer. On the two sites at Msekera, the highest yield was recorded in fertilized monoculture maize, followed by maize-gliricidia intercrops. Yields were more stable, however, in maize-gliricidia intercropping than fertilized maize on both sites at Msekera. It was concluded that maize yields remain more stable in maize-gliricidia intercropping than in fertilized maize monoculture in the long term, although average yields may be higher with full fertilization.
  • Authors:
    • Kanengieter, R. L.
    • Sleeter, R. R.
    • Bennett, S. L.
    • Reker, R. R.
    • Bouchard, M. A.
    • Sayler, K. L.
    • Sleeter, B. M.
    • Sohl, T. L.
    • Zhu, Z. L.
  • Source: AGRICULTURE ECOSYSTEMS & ENVIRONMENT
  • Volume: 153
  • Year: 2012
  • Summary: The Great Plains of the United States has undergone extensive land-use and land-cover change in the past 150 years, with much of the once vast native grasslands and wetlands converted to agricultural crops, and much of the unbroken prairie now heavily grazed. Future land-use change in the region could have dramatic impacts on ecological resources and processes. A scenario-based modeling framework is needed to support the analysis of potential land-use change in an uncertain future, and to mitigate potentially negative future impacts on ecosystem processes. We developed a scenario-based modeling framework to analyze potential future land-use change in the Great Plains. A unique scenario construction process, using an integrated modeling framework, historical data, workshops, and expert knowledge, was used to develop quantitative demand for future land-use change for four IPCC scenarios at the ecoregion level. The FORE-SCE model ingested the scenario information and produced spatially explicit land-use maps for the region at relatively fine spatial and thematic resolutions. Spatial modeling of the four scenarios provided spatial patterns of land-use change consistent with underlying assumptions and processes associated with each scenario. Economically oriented scenarios were characterized by significant loss of natural land covers and expansion of agricultural and urban land uses. Environmentally oriented scenarios experienced modest declines in natural land covers to slight increases. Model results were assessed for quantity and allocation disagreement between each scenario pair. In conjunction with the U.S. Geological Survey's Biological Carbon Sequestration project, the scenario-based modeling framework used for the Great Plains is now being applied to the entire United States.
  • Authors:
    • Tavares Filho, J.
    • Hungria, M.
    • Machado, W.
    • Telles, T. S.
    • Souza, R. A.
    • Guimaraes, M. de F.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 155
  • Year: 2012
  • Summary: Soil microbial biomass represents an important and strategic reservoir of plant nutrients that can be quickly altered due to different soil and crop managements. In this context, the aim of this study was to evaluate the influence of sugarcane harvesting systems, with or without burning, on the chemical and biological properties of the soil. The experiment was conducted on a dystrophic red latosol (Oxisol) soil in 2008, in a commercial area of a sugarcane factory in the municipality of Paraguacu Paulista, Sao Paulo state, Brazil. The treatments included areas previously burned, areas with mechanical harvesting and no burning and native forest. Soil samples were collected immediately after the sugarcane harvest from the treatments at a depth of 0-20 cm. The parameters evaluated were: microbial biomass C and N (MB-C and MB-N), total organic C (TOC), recalcitrant C (R-C), labile-C (L-C), total nitrogen (TN), pH, exchangeable cations (Ca 2++Mg 2+ and K +), exchangeable (Al 3+) and potential (H ++Al 3+) acidity, and P available in the soil. Soil chemical fertility under the sugarcane without burning was better than under sugarcane with burn. The TOC values for native forest and for the harvesting without burn were higher than those under the sugarcane with burn (148% and 54%, respectively). This superiority was also confirmed for TN, L-C and R-C. An even more significant difference was found under natural forest and sugarcane without burn for MB-C, which was 222% higher under native forest and 102% higher under sugarcane without burn than the value under sugarcane with burn, confirming that MB-C could be a reliable indicator of soil quality for monitoring soils under different sugarcane harvesting systems.
  • Authors:
    • Paeth, H.
    • Gaiser, T.
    • Srivastava, A. K.
    • Ewert, F.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 153
  • Year: 2012
  • Summary: This study elucidates the effects of the projected climate variables and CO 2 on yam yield in relation to three major soils in the Upper Oueme basin (Benin Republic) on yam ( Dioscorea alata) yield. The impact of the SRES climate scenarios A1B and B1 based on the output of the GCM ECHAM5 downscaled with the REMO model and the A1B scenario output of the GCM HADC3Q0 downscaled with the RCM s SMHIRCA and HADRM3P were analyzed. The A1B scenario, as expected with highest increase in temperature and extreme decline in rainfall, exhibited a decrease of 33% in yield until 2050 under ambient CO 2 concentration (350 ppmv), while under B1 around 27% decline was registered. Whereas, decline under A1B emission scenario of SMHIRCA and HADRM3P accounted 19% and 18%, respectively. The soil type "Ferruginous soils improverished without concretions" (S1) was most sensitive to climate change registering a decline of 48% in yam yield in the decade 2041-2050 followed by "Ferralitic soils" (S2) and "Raw mineral soils" (S3) showing a decline of 36% and 33%, respectively under A1B scenario derived from REMO model. Analysis of the growth constraints suggest that besides water stress, the indirect effect of reduced rainfall on the release of nitrogen from soil organic matter and hence nitrogen deficiency in the yam crop was the major constraint in the S1soil type.
  • Authors:
    • Cavigelli, M. A.
    • Spargo, J. T.
    • Mirsky, S. B.
    • Teasdale, J. R.
    • Maul, J. E.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 3
  • Year: 2012
  • Summary: There is interest in developing no-tillage systems for organic farming; however, potential limitations include the inability to control weeds and to provide sufficient crop available N. A 3-yr field experiment was conducted on organically certified land to explore roller-crimper technology for terminating a hairy vetch ( Vicia villosa Roth) cover crop in a reduced-tillage compared to a disk-tillage organic corn ( Zea mays L.) production system in Maryland. Within this tillage comparison, factors including the corn planting date and post-plant cultivation were examined for optimizing reduced-tillage organic corn production. Corn yield in roll-killed hairy vetch treatments where corn was planted by mid-June and that received high-residue cultivation was similar or higher than the best treatments with disk-killed hairy vetch. Delayed corn planting dates had little impact on corn yield in either disk- or roll-killed treatments, a result consistent with the similarity in weed biomass after cultivation, fertility, moisture, and radiation across planting dates. In 2 yr with supplemented weed populations, weed biomass was the major driver determining corn yield, which was reduced by 53 to 68% relative to weed-free control plots in the absence of post-plant cultivation, and by 21 to 28% with post-plant cultivation. In a year with low, natural weed populations, weeds had no significant influence on yield. These results demonstrate that organic corn production in a reduced-tillage roll-killed cover crop system can provide similar yields to those in a traditional tillage-based system, but also highlight the importance of maintaining low weed populations to optimize corn yield.
  • Authors:
    • Boe, A.
    • Wimberly, M. C.
    • Tulbure, M. G.
    • Owens, V. N.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 146
  • Issue: 1
  • Year: 2012
  • Summary: The U.S. Renewable Fuel Standard calls for 136 billion liters of renewable fuels production by 2022. Switchgrass (Panicum virgatum L.) has emerged as a leading candidate to be developed as a bioenergy feedstock. To reach biofuel production goals in a sustainable manner, more information is needed to characterize potential production rates of switchgrass. We used switchgrass yield data and general additive models (GAMs) to model lowland and upland switchgrass yield as nonlinear functions of climate and environmental variables. We used the GAMs and a 39-year climate dataset to assess the spatio-temporal variability in switchgrass yield due to climate variables alone. Variables associated with fertilizer application, genetics, precipitation, and management practices were the most important for explaining variability in switchgrass yield. The relationship of switchgrass yield with climate variables was different for upland than lowland cultivars. The spatio-temporal analysis showed that considerable variability in switchgrass yields can occur due to climate variables alone. The highest switchgrass yields with the lowest variability occurred primarily in the Corn Belt region, suggesting that prime cropland regions are the best suited for a constant and high switchgrass biomass yield. Given that much lignocellulosic feedstock production will likely occur in regions with less suitable climates for agriculture, interannual variability in yields should be expected and incorporated into operational planning.
  • Authors:
    • Akiyama, H.
    • Nishimura, S.
    • Uchida, Y.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 156
  • Year: 2012
  • Summary: Factors controlling soil respiration ( RS) are of great interest because RS plays a critical role in determining global atmospheric carbon dioxide (CO 2) concentrations. Substrate availability is one of the most important factors controlling RS. Soil microorganisms consume various substrates ranging from simple sugars supplied by aboveground photosynthesis to complex humic acids in soil organic matter; however, substrate decomposition rates depend on substrate availability. Thus, RS is partly determined by the amount and quality of available substrate. However, accurate quantification of the amount of available substrate is difficult because soil microorganisms utilize carbon (C) substrates of varying quality for RS. Water-soluble C (WSC), hot-water-soluble C (HWSC), and microbial biomass C are known as indicators of the amount of available soil C substrate. We continuously measured RS in two contrasting soils, Andosol and Fluvisol, during the cultivation of soybean and brassica crops with a 6-month fallow period between them. The total annual RS in Andosol and Fluvisol were 37623 and 40849 g CO 2-C m -2, respectively, with no significant difference between them. WSC and HWSC were measured every month during RS measurement. During the soybean growth period, RS and WSC were correlated, and soil type did not affect RS. During the fallow period, RS, HWSC and microbial biomass C in Fluvisol were higher than those in Andosol, despite the total soil C in Andosol being higher than that in Fluvisol. RS during brassica crop growth was not correlated with any of the measured substrate indicators. We therefore concluded that the relationships among the measures of available substrates and RS at the field level could provide vital information on seasonal changes in the interaction between the effects of soil type and plants on RS, thereby leading to a better understanding of belowground C dynamics.
  • Authors:
    • Perales, H. R.
    • Martinez-Meyer, E.
    • Ureta, C.
    • Alvarez-Buylla, E. R.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 3
  • Year: 2012
  • Summary: Climate change is expected to be a significant threat to biodiversity, including crop diversity at centers of origin and diversification. As a way to avoid food scarcity in the future, it is important to have a better understanding of the possible impacts of climate change on crops. We evaluated these impacts on maize, one of the most important crops worldwide, and its wild relatives Tripsacum and Teocintes. Maize is the staple crop in Mexico and Mesoamerica, and there are currently about 59 described races in Mexico, which is considered its center of origin. In this study, we modeled the distribution of maize races and its wild relatives in Mexico for the present and for two time periods in the future (2030 and 2050), to identify the potentially most vulnerable taxa and geographic regions in the face of climate change. Bioclimatic distribution of crops has seldom been modeled, probably because social and cultural factors play an important role on crop suitability. Nonetheless, rainfall and temperature still represent a major influence on crop distribution pattern, particularly in rainfed crop systems under traditional agrotechnology. Such is the case of Mexican maize races and consequently, climate change impacts can be expected. Our findings generally show significant reductions of potential distribution areas by 2030 and 2050 in most cases. However, future projections of each race show contrasting responses to climatic scenarios. Several evaluated races show new potential distribution areas in the future, suggesting that proper management may favor diversity conservation. Modeled distributions of Tripsacum species and Teocintes indicate more severe impacts compared with maize races. Our projections lead to in situ and ex situ conservation recommended actions to guarantee the preservation of the genetic diversity of Mexican maize.