• Authors:
    • Lin, X. M.
    • Hubbard, K. G.
    • Liu, Z. J.
    • Yang, X. G.
  • Source: Global Change Biology
  • Volume: 19
  • Issue: 11
  • Year: 2013
  • Summary: Northeast China (NEC) accounts for about 30% of the nation's maize production in China. In the past three decades, maize yields in NEC have increased under changes in climate, cultivar selection and crop management. It is important to investigate the contribution of these changing factors to the historical yield increases to improve our understanding of how we can ensure increased yields in the future. In this study, we use phenology observations at six sites from 1981 to 2007 to detect trends in sowing dates and length of maize growing period, and then combine these observations with in situ temperature data to determine the trends of thermal time in the maize growing period, as a measure of changes in maize cultivars. The area in the vicinity of these six sites accounts for 30% of NEC's total maize production. The agricultural production systems simulator, APSIM-Maize model, was used to separate the impacts of changes in climate, sowing dates and thermal time requirements on maize phenology and yields. In NEC, sowing dates trended earlier in four of six sites and maturity dates trended later by 4-21 days. Therefore, the period from sowing to maturity ranged from 2 to 38 days longer in 2007 than it was in 1981. Our results indicate that climate trends alone would have led to a negative impact on maize. However, results from the adaptation assessments indicate that earlier sowing dates increased yields by up to 4%, and adoption of longer season cultivars caused a substantial increase in yield ranging from 13% to 38% over the past 27 years. Therefore, earlier sowing dates and introduction of cultivars with higher thermal time requirements in NEC have overcome the negative effects of climate change and turned what would have otherwise been a loss into a significant increase in maize yield.
  • Authors:
    • Wang, H.
    • Desjardins, R.
    • Neilsen, D.
    • Huffman, T.
    • Gameda, S.
    • Jong, R. de
    • Qian, B. D.
    • McConkey, B.
  • Source: Canadian Journal of Soil Science
  • Volume: 93
  • Issue: 2
  • Year: 2013
  • Summary: The Canadian agricultural sector is facing the impacts of climate change. Future scenarios of agroclimatic change provide information for assessing climate change impacts and developing adaptation strategies. The goal of this study was to derive and compare agroclimatic indices based on current and projected future climate scenarios and to discuss the potential implications of climate change impacts on agricultural production and adaptation strategies in Canada. Downscaled daily climate scenarios, including maximum and minimum temperatures and precipitation for a future time period, 2040-2069, were generated using the stochastic weather generator AAFC-WG for Canadian agricultural regions on a 0.5° * 0.5° grid. Multiple climate scenarios were developed, based on the results of climate change simulations conducted using two global climate models - CGCM3 and HadGEM1 - forced by IPCC SRES greenhouse gas (GHG) emission scenarios A2, A1B and B1, as well as two regional climate models forced by the A2 emission scenario. The agroclimatic indices that estimate growing season start, end and length, as well as heat accumulations and moisture conditions during the growing season for three types of field crops, cool season, warm season and over-wintering crops, were used to represent agroclimatic conditions. Compared with the baseline period 1961-1990, growing seasons were projected to start earlier, on average 13 d earlier for cool season and over-wintering crops and 11 d earlier for warm season crops. The end of the growing season was projected on average to be 10 and 13 d later for over-wintering and warm season crops, respectively, but 11 d earlier for cool season crops because of the projected high summer temperatures. Two indices quantifying the heat accumulation during the growing season, effective growing degree days (EGDD) and crop heat units (CHU) indicated a notable increase in heat accumulation: on average, EGDD increased by 15, 55 and 34% for cool season, warm season and over-wintering crops, respectively. The magnitudes of the projected changes were highly dependent on the climate models, as well as on the GHG emission scenarios. Some contradictory projections were observed for moisture conditions based on precipitation deficit accumulated over the growing season. This confirmed that the uncertainties in climate projections were large, especially those related to precipitation, and such uncertainties should be taken into account in decision making when adaptation strategies are developed. Nevertheless, the projected changes in indices related to temperature were fairly consistent.
  • Authors:
    • Katterer, T.
    • Arvidsson, J.
    • Kainiemi, V.
  • Source: Biology and Fertility of Soils
  • Volume: 49
  • Issue: 5
  • Year: 2013
  • Summary: Reduced tillage is proposed as a method of C sequestration in agricultural soils. However, tillage effects on organic matter turnover are often contradictory and data are lacking on how tillage practices affect soil respiration in northern Europe. This field study (1) quantified the short-term effects of different tillage methods and timing on soil respiration and N mineralisation and (2) examined changes in aggregate size distribution due to different tillage operations and how these relate to soil respiration. The study was conducted on Swedish clay soil (Eutric Cambisol) and compared no-tillage with three forms of tillage applied in early or late autumn 2010: mouldboard ploughing to 20-22 cm and chisel ploughing to 12 or 5 cm depth. Soil respiration, soil temperature, gravimetric water content, mineral N and aggregate size distribution were measured. The results showed that respiration was significantly higher (P < 0.001) in no-till than in tilled plots during the 2 weeks following tillage in early September. Later tillage gave a similar trend but treatments did not differ significantly. Soil tillage and temperature explained 56 % of the variation in respiration. In the early tillage treatment, soil respiration decreased with tillage depth. Mineral N status was not affected by tillage treatment or timing. Soil water content did not differ significantly between tillage practices and therefore did not explain differences in respiration. The results indicate that conventional tillage in early autumn may reduce short-term soil respiration compared with chisel ploughing and no-till in clay soils in northern Europe.
  • Authors:
    • Giltrap, D.
    • Hernandez-Ramirez, G.
    • Kim, D.-G.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 168
  • Issue: March
  • Year: 2013
  • Summary: Rising atmospheric concentrations of nitrous oxide (N2O) contribute to global warming and associated climate change. It is often assumed that there is a linear relationship between nitrogen (N) input and direct N2O emission in managed ecosystems and, therefore, direct N2O emission for national greenhouse gas inventories use constant emission factors (EF). However, a growing body of studies shows that increases in direct N2O emission are related by a nonlinear relationship to increasing N input. We examined the dependency of direct N2O emission on N input using 26 published datasets where at least four different levels of N input had been applied. In 18 of these datasets the relationship of direct N2O emission to N input was nonlinear (exponential or hyperbolic) while the relationship was linear in four datasets. We also found that direct N2O EF remains constant or increases or decreases nonlinearly with changing N input. Studies show that direct N2O emissions increase abruptly at N input rates above plant uptake capacity. The remaining surplus N could serve as source of additional N2O production, and also indirectly promote N2O production by inhibiting biochemical N2O reduction. Accordingly, we propose a hypothetical relationship to conceptually describe in three steps the response of direct N2O emissions to increasing N input rates: (1) linear (N limited soil condition), (2) exponential, and (3) steady-state (carbon (C) limited soil condition). In this study, due to the limited availability of data, it was not possible to assess these hypothetical explanations fully. We recommend further comprehensive experimental examination and simulation using process-based models be conducted to address the issues reported in this review. (C) 2012 Elsevier B.V. All rights reserved.
  • Authors:
    • Mihailovic, D. T.
    • Eitzinger, J.
    • Lalic, B.
    • Thaler, S.
    • Jancic, M.
  • Source: The Journal of Agricultural Science
  • Volume: 151
  • Issue: 6
  • Year: 2013
  • Summary: One of the main problems in estimating the effects of climate change on crops is the identification of those factors limiting crop growth in a selected environment. Previous studies have indicated that considering simple trends of either precipitation or temperature for the coming decades is insufficient for estimating the climate impact on yield in the future. One reason for this insufficiency is that changes in weather extremes or seasonal weather patterns may have marked impacts. The present study focuses on identifying agroclimatic parameters that can identify the effects of climate change and variability on winter wheat yield change in the Pannonian lowland. The impacts of soil type under past and future climates as well as the effect of different CO2 concentrations on yield formation are also considered. The Vojvodina region was chosen for this case study because it is a representative part of the Pannonian lowland. Projections of the future climate were taken from the HadCM3, ECHAM5 and NCAR-PCM climate models with the SRES-A2 scenario for greenhouse gas (GHG) emissions for the 2040 and 2080 integration periods. To calibrate and validate the Met&Roll weather generator, four-variable weather data series (for six main climatic stations in the Vojvodina region) were analysed. The grain yield of winter wheat was calculated using the SIRIUS wheat model for three different CO2 concentrations (330, 550 and 1050 ppm) dependent on the integration period. To estimate the effects of climatic parameters on crop yield, the correlation coefficient between crop yield and agroclimatic indices was calculated using the AGRICLIM software. The present study shows that for all soil types, the following indices are the most important for winter wheat yields in this region: (i) the number of days with water and temperature stress, (ii) the accumulated precipitation, (iii) the actual evapotranspiration (ETa) and (iv) the water deficit during the growing season. The high positive correlations between yield and the ETa, accumulated precipitation and the ratio between the ETa and reference evapotranspiration (ETr) for the April-June period indicate that water is and will remain a major limiting factor for growing winter wheat in this region. Indices referring to negative impact on yield are (i) the number of days with a water deficit for the April-June period and (ii) the number of days with maximum temperature above 25 degrees C (summer days) and the number of days with maximum temperature above 30 degrees C (tropical days) in May and June. These indices can be seen as indicators of extreme weather events such as drought and heat waves.
  • Authors:
    • Marfo, J.
    • Man, R.
    • Dang, Q.-L.
    • Li, J.
  • Source: Forest Ecology and Management
  • Volume: 298
  • Issue: June
  • Year: 2013
  • Summary: CO2 elevation stimulates plant growth, which in turn demands more nutrients to sustain. Since the increase of demand for nitrogen (N), phosphorus (P) and potassium (K) may be in different proportions, the optimal N-P-K ratios at elevated [CO2] are likely different from those at the ambient [CO2]. This study investigated the effects of various N supply levels with constant and variable (constant P and K concentrations) N-P-K ratios under ambient and elevated [CO2] on black spruce (Picea mariana Mill. BSP) seedlings. One-year-old seedlings were exposed to two [CO2] (370 vs. 720 mu mol mol(-1)), two nutrient ratio regimes (constant vs. variable N/P/K ratios) and six N concentrations (10, 80, 150, 220, 290 and 360 mu mol mol(-1)) in four environmentally controlled greenhouses for 3.5 months. Growth response to N varied with [CO2] and N/P/K ratios: under the elevated [CO2], height growth increased with increasing N supply when P and K concentrations were kept constant across different N levels, but it only increased when increasing N from 10 to 150 mu mol mol(-1), and started to decline with further increase in N supply when N/P/K ratios were kept constant at different N levels; at the ambient [CO2], height growth was greatest at 150 mu mol mol(-1) N and was generally greater at 220-360 than at 10 and 80 mu mol mol(-1) N in both nutrient ratio treatments. The foliage to root ratio, shoot mass ratio and total biomass generally increased with increasing N supply but root mass ratio decreased. The smallest specific leaf area occurred at the lowest N supply when N/P/K ratios were kept constant but at 220 mu mol mol(-1) N when P and K concentrations were kept constant across different N supplies. The results of leaf nutrient concentrations suggest that the elevated [CO2] increased demand for N, P and K and the increase for N was greater than P and K, altering the relationship between growth and nitrogen supply. Under the elevated [CO2], high N supplies resulted in growth suppression by critical toxicity content only in the constant N/P/K ratios treatment but low N supplies led to growth suppression by critical deficiency content in both nutrient ratio treatments. At the ambient [CO2], in contrast, N/P/K ratio treatments did not affect growth suppression by critical deficiency or critical toxicity content. Because elevated CO2 causes unequal increases in N, P and K demands, N-P-K ratios should be considered when modeling plant growth responses to elevated CO2. (C) 2013 Elsevier B.V. All rights reserved.
  • Authors:
    • Jiang, M.
    • Lu, X.-G.
    • Zhang, Y.
    • Dong, G.-H.
    • Liu, X.-H.
  • Source: CLEAN – Soil, Air, Water
  • Volume: 41
  • Issue: 4
  • Year: 2013
  • Summary: Based on the estimation of greenhouse gases (GHG) emissions and carbon sequestration of the total conversion of marshlands (TMC), marshlands conversion to paddy fields (MCPFs) and marshlands conversion to uplands (MCULs), this study revealed the contribution to the global warming mitigation (CGWM) of paddy fields versus uplands converted from marshlands in the Sanjiang Plain (excluding the Muling-Xingkai Plain on south of Wanda Mountain), Heilongjiang Province, northeast China. The results showed that the total area of MCPFs and MCULs was 504.23x103ha between 1982 and 2005. The CGWM per unit area was 45.53t CO2eq/ha for MCPFs and that was 23.95t CO2eq/ha for MCULs, with an obvious 47.40% reduction. The MCPFs and MCULs ecosystems acted as the carbon sink all of the year. As far as CGWM per unit area is concerned, MCPFs mitigated the greenhouse effect which was greater than MCULs. And it was effective that the implementation of the uplands transformed into paddy fields in Northeast China with regard to marshlands protection and croplands (including paddy fields and uplands) reclamation.
  • Authors:
    • Shang, Z. H.
    • Chen, X. P.
    • Pan, J. L.
    • Dai, W. A.
    • Wang, X. M.
    • Ma, L. N.
    • Guo, R. Y.
  • Source: Chinese Journal of Eco-Agriculture
  • Volume: 21
  • Issue: 11
  • Year: 2013
  • Summary: Soil carbon and nitrogen in vegetable fields are the core elements of soil quality and environmental pollution. The decrease of soil C/N ratio of vegetable fields under greenhouse conditions causes an imbalance in soil carbon and nitrogen content. An effective way of adjusting soil carbon and nitrogen conditions in vegetable fields has been by improving soil quality and decreasing environmental pollution. Furthermore, there has been little research on soil carbon and nitrogen mineralization under greenhouse conditions in the Tibetan region. After transformations of alpine meadows and farmlands into solar greenhouse vegetable fields, there was the need to study the characteristics and processes of soil mineralization. In this study therefore, carbon and nitrogen mineralization in soils of alpine grassland, farmland and greenhouse (1-year, 5-year) were analyzed in an indoor incubation experiment. The results showed that soil carbon mineralization in different soil types mainly occurred during the first seven days (0-7 d) after treatment. Soil carbon mineralization was higher under alpine grassland than in farmland and 5-year greenhouse conditions ( P0.05). This was attributed to soil nutrient and soil microbial environment sensitivity to temperature. Soil CO 2-C accumulation in farmland soil was higher than in alpine grassland soil. It was also higher in alpine grassland soil than in the 1-year greenhouse and 5-year greenhouse soils. However, the differences in soil organic carbon mineralization and accumulation among alpine grassland, farmland, 1-year greenhouse and 5-year greenhouse soil conditions were not significant ( P>0.05) at 28 days after treatment. Soil nitrogen mineralization mainly happened in different soil types during the first three days (3 d) after treatment. With delayed incubation, the main process of soil nitrogen mineralization was nitrogen fixation. Soil inorganic nitrogen content in alpine grassland, farmland, 1-year greenhouse and 5-year greenhouse soils at 28 days after incubation were 29.04%, 75.94%, 66.86% and 65.70% of that at 0 day, respectively. The results showed that soil nitrogen mineralization capacity of alpine grassland soil was stronger than farmland, 1-year greenhouse and 5-year greenhouse soils. Soil nitrogen mineralization capacity of farmland was weaker than alpine grassland, 1-year greenhouse and 5-year greenhouse. Also soil nitrogen mineralization capacities of 1-year greenhouse and 5-year greenhouse were similar. Moreover, soil mineralization processes were similar among different soil conditions.
  • Authors:
    • Penttila,T.
    • Minkkinen,K.
    • Ojanen,P.
  • Source: Forest Ecology and Management
  • Volume: 289
  • Issue: February
  • Year: 2013
  • Summary: We estimated the soil CO2 balance of 68 forestry-drained boreal peatland sites in Finland by subtracting the litter input to soil from the CO2 efflux from soil. We also measured soil-atmosphere fluxes of CH4 and N2O and the CO2 sink of the growing tree stand in order to assess the current greenhouse gas impact of the study sites. The soil was, on average, a CO2 source of +190 +/- 70 g m(-2) year(-1) at the fertile Herb-rich and Vaccinium myrtillus type sites, but a CO2 sink of -70 +/- 30 g m(-2) year(-1) at the poor Vaccinium vitis-idaea and Dwarf shrub type sites. The source increased at the fertile and the sink decreased at the poor sites as the water table deepened. The source at the fertile sites also increased by increasing temperature sum, the highest CO2 sources being around +1000 g m(-2) year(-1) at well drained sites in Southern Finland. Both fertile and poor sites had a climate cooling impact. The sink in CO2 equivalents at the fertile sites was -690 +/- 90 g m(-2) year(-1) and at the poor sites -540 +/- 70 g m(-2) year(-1). The greater sink at the fertile sites was due to clearly better tree growth, their tree stand CO2 sink being -880 +/- 60 g m(-2) year(-1) compared to the -490 +/- 60 g m(-2) year(-1) at the poor sites. Ditching-based forestry can be climatically sustainable at nutrient-poor boreal peatlands since the peat soil continues to be a CO2 sink even after drainage. At the fertile sites, forestry will inevitably lead to loss of carbon in the long term, unless the tree biomass is stored after cuttings, for example in wooden buildings or as biochar in agricultural soils. (C) 2012 Elsevier B.V. All rights reserved.
  • Authors:
    • Pearson, M.
  • Source: Dissertationes Forestales
  • Issue: 159
  • Year: 2013
  • Summary: This dissertation investigated the impacts of soil preparation after clearcutting Scots pine ( Pinus sylvestris L.) forest on thick-peated soil from silvicultural and climatic standpoints. Three growing seasons after outplanting, mounding most effectively secured seedling survival, growth, and vitality through improved soil aeration of the planting spot. However, other presumed benefits of mounding to seedlings such as warmer soil temperatures and faster organic matter decomposition were not confirmed here. Regeneration in scalps was unsuccessful due to waterlogged soil. Importantly when scalping, only the humus layer should be scraped off without creating depressions in the peat. Seedling tolerance to desiccated as well as waterlogged peat soil over one growing season was remarkable in controlled conditions as mortality remained low. Drought stress was, however, plainly evident in seedlings as root and shoot growth, fractional colonization of ectomycorrhizal fungi, and root hydraulic conductance were all reduced. Nevertheless, maintenance of rather high photochemical efficiency (F v/F m) especially in current-year needles despite harsh drought seemed to indicate a potential for seedling recovery. Polyamine analysis also revealed that new needles are preferred in protecting the different parts of the seedlings against drought stress. Conversely, wet-stressed seedlings exhibited few signs of suffering. It was also demonstrated how the experimental environment - a controlled versus field setting - influences seedling tolerance to stress. The differing moisture levels within comparable microsites - dry vs. wet scalps and ditch vs. inverted mounds - had little influence on seedling growth and condition although physiological upset (i.e., F v/F m) was evident within scalps. Namely, the wetter the soil was, the lower F v/F m was. The fear of soil preparation accelerating GHG emissions, particularly CO 2, from peat into the atmosphere appears unwarranted at least on nutrient-poor, boreal forestry-drained peatland sites. The overall climatic impacts of mounding and scalping three years after application were neutral compared to leaving soil unprepared. The core findings of this research support mounding as the best alternative on nutrient-poor, drained peatland sites when the goal is to maximize the regeneration success of Scots pine after clearcutting with minimal impact on soil GHG emissions. In the future, development of soil preparation methodology is particularly deserving of further attention. While it may not be the sexiest research topic in the worldwide rat race of the modern day, it is nonetheless of substantial importance in a country highly specialized not only in the utilization but also the rejuvenation of wood resources on drained peatlands.