51. Green technology for keeping soil-water-nutrient fluxes on cultivated steep land and for mitigating the consequences of climate change.

• Authors:
  • Aiyelari, E. A.
  • Oku, E. E.
• Source: Journal of Agriculture and Environment for International Development
• Volume: 108
• Issue: 1
• Year: 2014
• Summary: Use of vetiver as a green technology can address African farmers' ecological problems through protecting farmlands on steep lands. In addition, it offers the opportunity to integrate smallholders into the green economy as it sequesters carbon, keep water and nutrient fluxes within the system, sustain high crop yield with climate change adaptation potentials. This is particularly important as more slopes are converted to agricultural lands due to increase in population density and poverty. Thus, the study investigated the optimal strip width for increases in soil productivity and farmers' preferences for space. The study planted maize and cassava in between vetiver field structures (VFS) installed on the contour at 5, 15, 25 m apart and compared it with Farmers' Practice (FP) on a 45% slope and quantified the amount of soil displaced, water and plant nutrient losses and crop yields. Vetiver installed at 5 m surface interval spacing significantly enhanced carbon sequestration indicating potentials for GHGs mitigation and reduced N, P, Ca, Mg, Na and K losses when compared with FP. Vetiver allowed only 7% rainfall lost as against 29% on FP this demonstrates the climate change adaptation potentials of vetiver. Soil displaced under FP was 68 times higher than the soil loss tolerance limit of 12 t ha -1 yr -1 whereas under VFS at 5, 15 and 25 m it was 21/2, 13 and 12 times higher. Maize grain yield were 35, 23 and 24% higher on the VFS field at 5, 15 and 25 m respectively when compared to FP. The corresponding values for cassava fresh tuber were 43, 32 and 29% higher. Unlike other technologies, vetiver grass contributes to the livelihood of the farmers by providing raw material for house thatching, handicrafts and fodder for livestock during lean seasons.

52. Innovation platforms for sustainable land management in East African landscapes: Stewardship, incentives, and challenges

• Authors:
  • Sanginga, P.
  • Amede, T.
• Source: JOURNAL OF SOIL AND WATER CONSERVATION Pages:
• Volume: 69
• Issue: 4
• Year: 2014

53. How do various maize crop models vary in their responses to climate change factors?

• Authors:
  • Grassini, P.
  • Gayler, S.
  • Sanctis, G. de
  • Deryng, D.
  • Corbeels, M.
  • Conijn, S.
  • Boogaard, H.
  • Biernath, C.
  • Basso, B.
  • Baron, C.
  • Adam, M.
  • Ruane, A. C.
  • Rosenzweig, C.
  • Jones, J. W.
  • Lizaso, J.
  • Boote, K.
  • Durand, J. L.
  • Brisson, N.
  • Bassu, S.
  • Hatfield, J.
  • Hoek, S.
  • Izaurralde, C.
  • Jongschaap, R.
  • Kemanian, A. R.
  • Kersebaum, K. C.
  • Kim, S. H. (et al)
• Source: Global Change Biology
• Volume: 20
• Issue: 7
• Year: 2014
• Summary: Potential consequences of climate change on crop production can be studied using mechanistic crop simulation models. While a broad variety of maize simulation models exist, it is not known whether different models diverge on grain yield responses to changes in climatic factors, or whether they agree in their general trends related to phenology, growth, and yield. With the goal of analyzing the sensitivity of simulated yields to changes in temperature and atmospheric carbon dioxide concentrations [CO 2], we present the largest maize crop model intercomparison to date, including 23 different models. These models were evaluated for four locations representing a wide range of maize production conditions in the world: Lusignan (France), Ames (USA), Rio Verde (Brazil) and Morogoro (Tanzania). While individual models differed considerably in absolute yield simulation at the four sites, an ensemble of a minimum number of models was able to simulate absolute yields accurately at the four sites even with low data for calibration, thus suggesting that using an ensemble of models has merit. Temperature increase had strong negative influence on modeled yield response of roughly -0.5 Mg ha -1 per °C. Doubling [CO 2] from 360 to 720 mol mol -1 increased grain yield by 7.5% on average across models and the sites. That would therefore make temperature the main factor altering maize yields at the end of this century. Furthermore, there was a large uncertainty in the yield response to [CO 2] among models. Model responses to temperature and [CO 2] did not differ whether models were simulated with low calibration information or, simulated with high level of calibration information.

54. Organic matter composition in density fractions of Cerrado Ferralsols as revealed by CPMAS 13C NMR: influence of pastureland, cropland and integrated crop-livestock.

• Authors:
  • Salton, J. C.
  • Knicker, H.
  • Dick, D. P.
  • Conceicao, P. C.
  • Dieckow, J.
  • Bayer, C.
  • Boeni, M.
  • Macedo, M. C. M.
• Source: Web Of Knowledge
• Volume: 190
• Year: 2014
• Summary: Integrated crop-livestock (ICL) is a promising land use system for the Brazilian Cerrado, but little is known about what this system might change in chemical composition of soil organic matter. In three long-term experiments (9-11 years old), located on Cerrado Ferralsols in Dourados, Maracaju and Campo Grande (Mato Grosso do Sul State, Brazil), we assessed the impact of continuous cropland (CC), ICL, and permanent pasture of Brachiaria decumbens (PP) on the C concentration and composition of the free light fraction (FLF), occluded light fraction (OLF) and heavy fraction (HF) of soil in the 0-5 cm layer. CPMAS 13C NMR spectroscopy was used to determine the percentage of alkyl, O-alkyl, aromatic and carboxyl C types. In Dourados and Maracaju, PP had the highest concentrations of organic C in whole soil and physical fractions, while ICL was intermediate and CC lowest. In Campo Grande, soil organic C concentration was similar among management systems. Distribution of organic C across physical fractions was not affected by management nor by experimental site, and on average the FLF, OLF and HF contained 7%, 26% and 67% of the total storage, respectively. Signal peaks of the four main C types appeared in all CPMAS 13C NMR spectra, but at different intensities. O-alkyl was the major C type (about 50%), carboxyl was the minor representative (generally less than 10%) and alkyl and aromatic C were intermediates. From FLF to OLF, the alkyl and aromatic C concentrations increased, possibly due to selective preservation of waxes, resins, cutin, suberin and lignin. The HF had greater O-alkyl and lower aromatic C concentrations than OLF, which might have been related to the accumulation of microbial carbohydrates on mineral surfaces of the HF. Along the sequence CC-ICL-PP, the most evident changes were greater of O-alkyl and lower alkyl C types, practically in all fractions and sites. In FLF and OLF, these changes were attributed to greater biomass input and less seed drill-induced disturbance of soil surface (lower decomposition of residues) in the PP and ICL. Additionally, in OLF, greater O-alkyl concentration in PP and ICL was attributed to physical protection of particulate organic matter derived from grass roots occluded inside soil aggregates. Our results suggest that PP and ICL systems increased or maintained soil organic C concentrations compared to CC, associated with a qualitative increase of the chemically labile O-alkyl C type which was possibly related to greater biomass addition and less soil disturbance.

55. Farm typologies, soil fertility variability and nutrient management in smallholder farming in Sub-Saharan Africa

• Authors:
  • Johnston, A.
  • Snapp, S.
  • Zingore, S.
  • Chikowo, R.
• Source: Nutrient Cycling in Agroecosystems
• Volume: 100
• Issue: 1
• Year: 2014
• Summary: Farm typologies are a useful tool to assist in unpacking and understanding the wide diversity among smallholder farms to improve targeting of crop production intensification strategies. Sustainable crop production intensification will require the development of an array of nutrient management strategies tailored to farm-specific conditions, rather than blanket recommendations across diverse farms. This study reviewed key literature on smallholder farm typologies focusing on three countries (Kenya, Malawi and Zimbabwe), to gain insights on opportunities for crop production intensification, and the importance of developing farm-specific nutrient management practices. Investigations on farm typologies have done well in highlighting the fundamental differences between farm categories, with 3-5 typologies often adequate to represent the wide differences in resource endowment. Resource-endowed farmers have ready access to large quantities of manure and mineral fertilizers, which contribute to higher soil fertility and crop productivity on their farms. Resource-constrained households use little or no manure and mineral fertilizers, and have limited capacity to invest in labour-demanding soil fertility management technologies. These farmers often have to rely on off-farm opportunities for income that are largely limited to selling unskilled labour to their resource-endowed neighbors. The variability in management practices by farmers has resulted in three main soil fertility classes that can be used for targeting soil fertility management technologies, characterized by potential response to fertilizer application as: (1) low-responsive fertile fields that receive large additions of manure and fertilizer; (2) high-responsive infertile fields that receive moderate nutrient applications; (3) poorly responsive degraded soils cultivated for many years with little or no nutrient additions. The main conclusions drawn from the review are: (1) resource constrained farmers constitute the widest band across the three countries, with many of the farmers far below the threshold for sustainable maize production intensification and lacking capacity to invest in improved seed and fertilizer, (2) farm sizes and livestock ownership were key determinants for both farmer wealth status and farm productivity, and (3) soil organic carbon and available P were good indicators for predicting previous land management, that is also invariably linked to farmer resource endowment.

56. Ecophysiological performance of maize, sorghum and brachiaria under water deficit and rehydration.; Desempenho ecofisiologico de milho, sorgo e braquiaria sob deficit hidrico e reidratacao.

• Authors:
  • Lima, J. R. S.
  • Antonino, A. C. D.
  • Falcao, H.
  • Santos, O. O.
  • Lustosa, B. M.
  • Santos, M. G.
• Source: Bragantia
• Volume: 73
• Issue: 2
• Year: 2014
• Summary: The present study evaluated the ecophysiological performance of species Zea mays (maize), Sorghum bicolor (sorghum) and Brachiaria decumbens (Brachiaria) under water deficit conditions in a greenhouse. The leaf water potential, gas exchange, chlorophyll a fluorescence and biochemical variables of photosynthetic metabolism were assessed at maximum stress and rehydration. At 90 days after emergence and under 21 days under suspension of irrigation the maize showed the highest reduction of leaf water potential (248%), stomatal conductance (87%) and photosynthesis (53%) when compared to well watered plants. Sorghum decreased by 212%, 42% and 26%, while the brachiaria showed lower values in 105%, 36% and 31%, respectively for the same parameters. However, two days of water supply were enough for all species recover the values showed by the respective controls. The species with the smallest decrease related to the variables evaluated was sorghum, which reduced 4 among 14 variables evaluated, while brachiaria and maize decreased 9 variables when under drought. The present study highlights that beyond economics, decision making by small farmers and technicians, about which species should be used under low availability of technology and high risk of water shortages should take into account also the ecophysiological performance.

57. Contemporary land use/land cover types determine soil organic carbon stocks in south-west Rwanda

• Authors:
  • Smaling, E. M. A.
  • Tumwesigye, W.
  • Rwamukwaya, B. M.
  • Groen, T. A.
  • Wasige, J. E.
  • Jetten, V.
• Source: Nutrient Cycling in Agroecosystems
• Volume: 100
• Issue: 1
• Year: 2014
• Summary: Soil organic carbon (SOC) constitutes a large pool within the global carbon cycle. Land use change significantly drives SOC stock variation. In tropical central and eastern Africa, how changes in land use and land cover impact on soil C stocks remains unclear. Variability in the existing data is typically explained by soil and climate factors with little consideration given to land use and management history. To address this knowledge gap, we classified the current and historical land cover and measured SOC stocks under different land cover, soil group and slope type in the humid zone of south-west Rwanda. It was observed that SOC levels were best explained by contemporary land cover types, and not by soil group, conversion history or slope position, although the latter factors explained partly the variation within annual crop land cover type. Lack of the influence of land use history on SOC stocks suggests that after conversion to a new land use/land cover, SOC stocks reached a new equilibrium within the timestep that was observed (25 years). For conversion to annual crops, SOC stocks reach a new equilibrium at about 2.5 % SOC concentration which is below the proposed soil fertility threshold of 3 % SOC content in the Eastern and central African region. SOC stock declined under transitions from banana-coffee to annual crop by 5 % or under transitions from natural forest to degraded forest by 21 % and increased for transitions from annual crops to plantation forest by 193 %. Forest clearing for agricultural use resulted in a loss of 72 %. Assuming steady states, the data can also be used to make inferences about SOC changes as a result of land cover changes. We recommend that SOC stocks should be reported by land cover type rather than by soil groups which masks local land cover and landscape differences. This study addresses a critical issue on sustainable management of SOC in the tropics and global carbon cycle given that it is performed in a part of the world that has high land cover dynamics while at the same time lacks data on land cover changes and SOC dynamics.

58. Sorption of organic carbon compounds to the fine fraction of surface and subsurface soils

• Authors:
  • Gisladottir, G.
  • Zinn, Y. L.
  • Mayes, M. A.
  • Jagadamma, S.
  • Russell, A. E.
• Source: Article
• Volume: 213
• Year: 2014
• Summary: Dissolved organic carbon (DOC) transported from the soil surface is stabilized in deeper soil profiles by physicochemical sorption processes. However, it is unclear how different forms of organic carbon (OC) compounds common in soil organic matter interact with soil minerals in the surface (A) and subsurface (B) horizons. We added four compounds (glucose, starch, cinnamic acid and stearic acid) to the silt- and clay-sized fraction (fine fraction) of A and B horizons of eight soils from varying climates (3 temperate, 3 tropical, 1 arctic and 1 sub-arctic). Equilibrium batch experiments were conducted using 0 to 100 mg C L-1 of C-14-labeled compounds for 8 h. Sorption parameters (maximum sorption capacity, Q(max) and binding coefficient, k) calculated by fitting sorption data to the Langmuir equation showed that Q(max) of A and B horizons was very similar for all compounds. Both Q(max) and k values were related to sorbate properties, with Q(max) being lowest for glucose (20-500 mg kg(-1)), highest for stearic acid (20,000-200,000 mg kg(-1)), and intermediate for both cinnamic acid (200-4000 mg kg(-1)) and starch (400-6000 mg kg(-1)). Simple linear regression analysis revealed that physicochemical properties of the sorbents influenced the Q(max), of cinnamic acid and stearic acid, but not glucose and starch. The sorbent properties did not show predictive ability for binding coefficient k. By using the fine fraction as sorbent, we found that the mineral fractions of A horizons are equally reactive as the B horizons irrespective of soil organic carbon content. (C) 2013 Elsevier B.V. All rights reserved.

59. Uncertainty in simulating wheat yields under climate change

• Authors:
  • Priesack, E.
  • Palosuo, T.
  • Osborne, T. M.
  • Olesen, J. E.
  • O'Leary, G.
  • Nendel, C.
  • Kumar, S. Naresh
  • Mueller, C.
  • Kersebaum, K. C.
  • Izaurralde, R. C.
  • Ingwersen, J.
  • Hunt, L. A.
  • Hooker, J.
  • Heng, L.
  • Grant, R.
  • Goldberg, R.
  • Gayler, S.
  • Doltra, J.
  • Challinor, A. J.
  • Biernath, C.
  • Bertuzzi, P.
  • Angulo, C.
  • Aggarwal, P. K.
  • Martre, P.
  • Basso, B.
  • Brisson, N.
  • Cammarano, D.
  • Rotter, R. P.
  • Thorburn, P. J.
  • Boote, K. J.
  • Ruane, A. C.
  • Hatfield, J. L.
  • Jones, J. W.
  • Rosenzweig, C.
  • Ewert, F.
  • Asseng, S.
  • Ripoche, D.
  • Semenov, M. A.
  • Shcherbak, I.
  • Steduto, P.
  • Stoeckle, C.
  • Stratonovitch, P.
  • Streck, T.
  • Supit, I.
  • Tao, F.
  • Travasso, M.
  • Waha, K.
  • Wallach, D.
  • White, J. W.
  • Williams, J. R.
  • Wolf, J.
• Source: Nature Climate Change
• Volume: 3
• Issue: 9
• Year: 2013
• Summary: Projections of climate change impacts on crop yields are inherently uncertain(1). Uncertainty is often quantified when projecting future greenhouse gas emissions and their influence on climate(2). However, multi-model uncertainty analysis of crop responses to climate change is rare because systematic and objective comparisons among process-based crop simulation models(1,3) are difficult(4). Here we present the largest standardized model intercomparison for climate change impacts so far. We found that individual crop models are able to simulate measured wheat grain yields accurately under a range of environments, particularly if the input information is sufficient. However, simulated climate change impacts vary across models owing to differences in model structures and parameter values. A greater proportion of the uncertainty in climate change impact projections was due to variations among crop models than to variations among downscaled general circulation models. Uncertainties in simulated impacts increased with CO2 concentrations and associated warming. These impact uncertainties can be reduced by improving temperature and CO2 relationships in models and better quantified through use of multi-model ensembles. Less uncertainty in describing how climate change may affect agricultural productivity will aid adaptation strategy development and policy making.

60. Carbon and greenhouse gas mitigation through soil carbon sequestration potential of adaptive agriculture and agroforestry systems

• Authors:
  • Mandi, S. S.
  • Ali, T.
  • Bangroo, S. A.
  • Najar, G. R.
  • Sofi, J. A.
• Source: Range Management and Agroforestry
• Volume: 34
• Issue: 1
• Year: 2013
• Summary: Agriculture together with agro-forestry systems are perceived as a source of significant greenhouse gas (GHG) emissions, with concomitant potentials for mitigation. It is among the economic sectors having the largest GHG mitigation potential. Conversion to invigorating land uses and implementation of recommended management practices (RMP) can enhance soil organic carbon (SOC). The adoption of these alternatives is likely to have considerable benefits for some cropping systems under moderate climate change. The C sequestration potential in soils of terrestrial ecosystems is 3x10(9) tonnes C/year or 0.05% reduction of atmospheric CO2 at the rate of 1 Mg/ha/year by improving C pool by the end of the year 2099. The role of forest and grasslands as a sink for atmospheric CO2 is the subject of active debate. The carbon stock for the period 2006-2030 is projected to increase from 8.79x10(9) tonnes C to 9.75x10(9) tonnes C with forest cover becoming more or less stable, and new forest carbon accretions coming from the current initiatives of afforestation and reforestation programme. With the knowledge and information that is now emerging, the role of agro-forest and plantations in mitigation is becoming more and more important. Over the past decades, national policies of India aimed at conservation and sustainable management of forests have transformed India's forests into a net sink of CO2. Not all improved management practices are suitable to all soils and ecological conditions. Dealing with many barriers to effective adaptation will require a comprehensive and dynamic policy approach covering a range of scales and issues. A crucial component of this approach is the implementation of adaptation assessment frame works that are relevant, robust and easily operated by all stakeholders, practitioners, policymakers and scientists.