31. Understanding and Assessing Climate Change: Implications for Nebraska

• Authors:
  • Bathke, D. J
  • Oglesby, R. J.
  • Rowe, C. M.
  • Wilhite, D. A.
• Year: 2014
• Summary: The goal of this report is to inform policy makers, natural resource managers, and the public about the state of the science on climate change, current projections for ongoing changes over the twenty-first century, current and potential future impacts, and the management and policy implications of these changes. Hopefully, this report will lead to a higher degree of awareness and the initiation of timely and appropriate strategic actions that will enable Nebraskans to prepare for and adapt to future changes to our climate.

32. Projected climate impacts to South African maize and wheat production in 2055: a comparison of empirical and mechanistic modeling approaches.

• Authors:
  • Ruane, A. C.
  • Oppenheimer, M.
  • Debats, S. R.
  • Bradley, B. A.
  • Beukes, H.
  • Estes, L. D.
  • Schulze, R.
  • Tadross, M.
• Source: Global Change Biology
• Volume: 19
• Issue: 12
• Year: 2013
• Summary: Crop model-specific biases are a key uncertainty affecting our understanding of climate change impacts to agriculture. There is increasing research focus on intermodel variation, but comparisons between mechanistic (MMs) and empirical models (EMs) are rare despite both being used widely in this field. We combined MMs and EMs to project future (2055) changes in the potential distribution (suitability) and productivity of maize and spring wheat in South Africa under 18 downscaled climate scenarios (9 models run under 2 emissions scenarios). EMs projected larger yield losses or smaller gains than MMs. The EMs' median-projected maize and wheat yield changes were -3.6% and 6.2%, respectively, compared to 6.5% and 15.2% for the MM. The EM projected a 10% reduction in the potential maize growing area, where the MM projected a 9% gain. Both models showed increases in the potential spring wheat production region (EM=48%, MM=20%), but these results were more equivocal because both models (particularly the EM) substantially overestimated the extent of current suitability. The substantial water-use efficiency gains simulated by the MMs under elevated CO 2 accounted for much of the EM-MM difference, but EMs may have more accurately represented crop temperature sensitivities. Our results align with earlier studies showing that EMs may show larger climate change losses than MMs. Crop forecasting efforts should expand to include EM-MM comparisons to provide a fuller picture of crop-climate response uncertainties.

33. Conservation tillage systems: a review of its consequences for greenhouse gas emissions

• Authors:
  • Smith, P.
  • Williams, M.
  • Forristal, D.
  • Lanigan, G.
  • Osborne, B.
  • Abdalla, M.
  • Jones, M. B.
• Source: Soil Use and Management
• Volume: 29
• Issue: 2
• Year: 2013
• Summary: Conservation tillage (CT) is an umbrella term encompassing many types of tillage and residue management systems that aim to achieve sustainable and profitable agriculture. Through a global review of CT research, the objective of this paper was to investigate the impacts of CT on greenhouse gas (GHG) emissions. Based on the analysis presented, CT should be developed within the context of specific climates and soils. A number of potential disadvantages in adopting CT practices were identified, relating mainly to enhanced nitrous oxide emissions, together with a number of advantages that would justify its wider adoption. Almost all studies examined showed that the adoption of CT practices reduced carbon dioxide emissions, while also contributing to increases in soil organic carbon and improvements in soil structure.

34. 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.

35. Mitigation potential of greenhouse gases under different scenarios of optimal synthetic nitrogen application rate for grain crops in China

• Authors:
  • Zhang, Y.
  • Wu, L.
  • Wang, H.
  • Liu, L.
  • Huang, L.
  • Niu, Y.
  • Chai, R.
• Source: Nutrient Cycling in Agroecosystems
• Volume: 96
• Issue: 1
• Year: 2013
• Summary: Proper management of synthetic nitrogen (N) fertilizer can reduce direct N2O emission from soil and indirect CO2 emission from production and transportation of synthetic N. In the late 1990s, the average application rates of synthetic N were 212, 207 and 207 kg ha(-1), respectively, for rice, wheat, and maize in China's croplands. But research suggests that the optimal synthetic N application rates for the main grain crops in China should be in the range of 110-150 kg ha(-1). Excessive application of synthetic N has undoubtedly resulted in massive emission of greenhouse gases. Therefore, optimizing N application rates for grain crops in China has a great potential for mitigating the emission of greenhouse gases. Nevertheless, this mitigation potential (MP) has not yet been well quantified. This study aimed at estimating the MP of N2O and CO2 emissions associated with synthetic N production and transportation in China based on the provincial level statistical data. Our research indicates that the total consumption of synthetic N on grain crops in China can be reduced by 5.0-8.4 Tg yr(-1) (28-47 % of the total consumption) if the synthetic N application rate is controlled at 110-150 kg ha(-1). The estimated total MP of greenhouse gases, including direct N2O emission from croplands and indirect CO2 emission from production and transportation of synthetic N, ranges from 41.7 to 70.1 Tg CO2_eq. yr(-1). It was concluded that reducing synthetic N application rate for grain crops in China to a reasonable level of 110-150 kg ha(-1) can greatly reduce the emission of greenhouse gases, especially in the major grain-crop production provinces such as Shandong, Henan, Jiangsu, Hebei, Anhui and Liaoning.

36. Re-evaluating the biophysical and technologically attainable potential of topsoil carbon sequestration in China's cropland

• Authors:
  • Pan, G.
  • Smith, P.
  • Nayak, D.
  • Zheng, J.
  • Cheng, K.
• Source: Soil Use and Management
• Volume: 29
• Issue: 4
• Year: 2013
• Summary: To assess the topsoil carbon sequestration potential (CSP) of China's cropland, two different estimates were made: (i) a biophysical potential (BP) using a saturation limit approach based on soil organic carbon (SOC) accumulation dynamics and a storage restoration approach from the cultivation-induced SOC loss, and (ii) a technically attainable potential (TAP) with a scenario estimation approach using SOC increases under best management practices (BMPs) in agriculture. Thus, the BP is projected to be the gap in recent SOC storage to either the saturation capacity or to the SOC storage of uncultivated soil, while the TAP is the overall increase over the current SOC storage that could be achieved with the extension of BMPs. The recent mean SOC density of China's cropland was estimated to be 36.44t/ha, with a BP estimate of 2.21 Pg C by a saturation approach and 2.95 Pg C by the storage restoration method. An overall TAP of 0.62 Pg C and 0.98 Pg C was predicted for conservation tillage plus straw return and recommended fertilizer applications, respectively. This TAP is comparable to 40-60% of total CO2 emissions from Chinese energy production in 2007. Therefore, carbon sequestration in China's cropland is recommended for enhancing China's mitigation capacity for climate change. However, priority should be given to the vast dry cropland areas of China, as the CSP of China is based predominantly on the dry cropland.

37. Impacts of conservation agriculture on total soil organic carbon retention potential under an irrigated agro-ecosystem of the western Indo-Gangetic Plains

• Authors:
  • Saad, A. A.
  • Das, S.
  • Sharma, A. R.
  • Bhattacharyya, R.
  • Das, T. K.
  • Pathak, H.
• Source: European Journal of Agronomy
• Volume: 51
• Year: 2013
• Summary: Sequestration of C in arable soils has been considered as a potential mechanism to mitigate the elevated levels of atmospheric greenhouse gases. We evaluated impacts of conservation agriculture on change in total soil organic C (SOC) and relationship between C addition and storage in a sandy loam soil of the Indo-Gangetic Plains. Cotton (Gossypium hirsutum L.) and wheat (Triticum aestivum L.) crops were grown during the first three years (2008-2011) and in the last year, maize (Zea mays L), wheat and green gram (Vigna radiate L.) were cultivated. Results indicate the plots under zero tillage with bed planting (ZT-B) and zero tillage with flat planting (ZT-F) had nearly 28 and 26% higher total SOC stock compared with conventional tillage and bed planting (CT-B) (similar to 5.5 Mg ha(-1)) in the 0-5 cm soil layer. Plots under ZT-B and ZT-F contained higher total SOC stocks in the 0-5 and 5-15 cm soil layers than CT-B plots. Although there were significant variations in total SOC stocks in the surface layers, SOC stocks were similar under all treatments in the 0-30 cm soil layer. Residue management had no impact on SOC stocks in all layers, despite plots under cotton/maize + wheat residue (C/M+W RES) contained similar to 13% higher total SOC concentration than no residue treated plots (N RES; similar to 7.6 g kg(-1)) in the 0-5 cm layer. Hence, tillage and residue management interaction effects were not significant. Although CT-B and ZT-F had similar maize aboveground biomass yields, CT-F treated plots yielded 16% less maize biomass than CT-B plots. However, both wheat and green gram (2012) yields were not affected by tillage. Plots under C/M + W RES had similar to 17, 13, 13 and 32% higher mean cotton, maize, wheat and green gram aboveground biomass yields than N RES plots, yielding similar to 16% higher estimated root (and rhizodeposition) C input in the 0-30 cm soil layer than N RES plots. About 9.3% of the gross C input contributed towards the increase in SOC content under the residue treated plots. However, similar to 7.6 and 10.2% of the gross C input contributed towards the increase in SOC content under CT and if, respectively. Thus, both ZT and partial or full residue retention is recommended for higher soil C retention and sustained crop productivity. (c) Elsevier B.V. All rights reserved.

38. Litterfall production and associated carbon and nitrogen fluxes of seven woody species grown in indigenous agroforestry systems in the south-eastern Rift Valley escarpment of Ethiopia

• Authors:
  • Starr, M.
  • Negash, M.
• Source: Nutrient Cycling in Agroecosystems
• Volume: 97
• Issue: 1-3
• Year: 2013
• Summary: We compared the litterfall production and associated carbon (C) and nitrogen (N) fluxes for seven woody species grown in three agroforestry systems practiced on the slopes of the south eastern Rift Valley escarpment of Ethiopia. Five of the species were native (Coffea arabica L., Cordia africana Lam., Croton macrostachyus Del., Erythrina brucei Schweinf. and Millettia ferruginea (Hochst.) Bak) and two were non-native fruit tree species (Mangifera indica L. and Persea americana Mill.). Together, these species accounted 85 % or more of the crown area of each agroforestry system: the Enset system (occurring at 2,100-2,400 m asl), the Enset-Coffee system (1,900-2,200 m asl), and the Fruit-Coffee system (1,500-1,900 m asl). Enset or false banana [Ensete ventricosum (Welw.) Cheesman] is a staple food crop in this region of Ethiopia and coffee and fruit trees are grown as cash crops. Monthly litterfall was collected from 4 to 6 trees of each species during 2010 and dry mass, carbon and nitrogen contents determined. The annual litterfall production per unit area of crown decreased in the order: C. macrostachyus (1,014 g m(-2)), E. brucei (929), C. africana (917), P. americana (809), M. indica (807), C. arabica (446) and M. ferruginea (362). The simple linear regression equation using breast height diameter explained 95 % of the variation in the litterfall production of M. ferruginea, but only 55 % for C. africana. The annual litterfall production of the seven species combined per unit area of land was the highest for the Fruit-Coffee system (average 12,938 kg ha(-1)), followed by the Enset-Coffee system (10,187) and the Enset system (7,430). The associated annual C fluxes (kg ha(-1)) were 5,145 (Fruit-Coffee system), 3,928 (Enset-Coffee system) and 2,803 (Enset system), and corresponding N fluxes 278 (kg ha(-1)), 257 and 190. The combined litterfall production of the seven species in our study was higher than has been reported for other agroforestry systems and tropical forests.

39. Moldboard plowing effects on soil aggregation and soil organic matter quality assessed by 13C CPMAS NMR and biochemical analyses.

• Authors:
  • Berns, A. E.
  • Knicker, H.
  • Panettieri, M.
  • Murillo, J. M.
  • Madejon, E.
• Source: Agriculture, Ecosystems & Environment
• Volume: 177
• Year: 2013
• Summary: The impact on soil aggregates status of two tillage practices (moldboard plowing, TT, and chisel plowing, RT) applied to a farm previously cultivated under no-tillage (NT) was studied. The experiment was carried out on a Leptic Typic Xerorthent soil at the "Las Navas" dryland experimental farm located in Jerez de la Frontera (Cadiz, SW Spain). Several organic C pools such as total organic carbon (TOC), water soluble carbon (WSC), permanganate oxidizable carbon (POxC), and microbial biomass carbon (MBC) were analyzed, together with two enzymatic activities related to soil organic matter (SOM) oxidization metabolism: dehydrogenase activity (DH) and beta-glucosidase activity (beta-Glu). 13C cross polarization magic angle spinning nuclear magnetic resonance ( 13C CPMAS NMR) spectroscopy was used to characterize the composition of the SOM and its degradation status. Two years after the implementation of the new management practices, analysis of the aggregate distribution of the topsoil (0-10 cm) showed that, even after a short term, TT enhanced aggregate disruption. The apparent reduction in soil quality of TT plots was evident from the lower contents of total organic carbon (TOC), permanganate oxidizable carbon (POxC) and microbial biomass carbon (MBC) if compared with RT and NT. Moreover, TT soil showed also a lower beta-glucosidase activity. As confirmed by 13C CPMAS NMR, the SOM of the TT fractions revealed higher alkyl C to O-alkyl ratios than their RT and NT counterparts. Also signals commonly referred to lignin structures were absent in the spectra of the TT fractions, but were still present in those of the larger fractions of the NT treatment. After a short term evaluation, RT samples did not show the same declining trend as observed for the TT treatment. For this reason, chisel plowing seems to offer a viable occasional management option when required during long-term NT.

40. Biochar an alternate option for crop residues and solid waste disposal and climate change mitigation.

• Authors:
  • Govindaraj, M.
  • Prabukumar, G.
  • Arunachalam, P.
  • Kannan, P.
• Source: African Journal of Agricultural Research
• Volume: 8
• Issue: 21
• Year: 2013
• Summary: Atmospheric rise of CO 2, N 2O and CH 4 over years, accelerated increase in global temperature, has led to uncertainty in monsoon rainfall and also leading to recurrence of drought, which in turn is severely affecting crop productivity and livelihood security of the farmers in Semi Arid Tropics. Agriculture contributes considerable amount of CO 2, N 2O and CH 4 emission into the atmosphere through different soil and crop management practices. Nevertheless agricultural activities contribute to global warming. The medium of crop production, soil is one of the major sinks of global warming gaseous and it helps to sequester more carbon and cut the N 2O emission by adopting smart soil and crop management techniques. Biochar is one of the viable organic amendments to combat climate change and sustain the soil health with sustainable crop production. It is an anaerobic pyrolysis product derived from organic sources and store carbon on a long term basis in the terrestrial ecosystem and also capable of reducing greenhouse gases (GHG) emission from soil to the atmosphere. Biochar application improved the soil health, increase the carbon capture and storage, reduce the GHG emission and enhance the crop yield with sustained soil health, which enables to meet out the food grain needs of the ever growing population.