131. How is CO2 affecting yields and technological progress? A statistical analysis

• Authors:
  • Attavanich,Witsanu
  • McCarl,Bruce A.
• Source: Climatic Change
• Volume: 124
• Issue: 4
• Year: 2014
• Summary: This paper analyzes the impact of climate, crop production technology, and atmospheric carbon dioxide (CO2) on current and future crop yields. The analysis of crop yields endeavors to advance the literature by estimating the effect of atmospheric CO2 on observed crop yields. This is done using an econometric model estimated over pooled historical data for 1950-2009 and data from the free air CO2 enrichment experiments. The main econometric findings are: 1) Yields of C3 crops (soybeans, cotton, and wheat) directly respond to the elevated CO2, while yields of C4 crops (corn and sorghum) do not, but they are found to indirectly benefit from elevated CO2 in times and places of drought stress; 2) The effect of technological progress on mean yields is non-linear; 3) Ignoring atmospheric CO2 in an econometric model of crop yield likely leads to overestimates of the pure effects of technological progress on crop yields of about 51, 15, 17, 9, and 1 % of observed yield gain for cotton, soybeans, wheat, corn and sorghum, respectively; 4) Average climate conditions and climate variability contribute in a statistically significant way to average crop yields and their variability; and 5) The effect of CO2 fertilization generally outweighs the effect of climate change on mean crop yields in many regions resulting in an increase of 7-22, 4-47, 5-26, 65-96, and 3-35 % for yields of corn, sorghum, soybeans, cotton, and wheat, respectively.

132. Greater Sensitivity to Drought Accompanies Maize Yield Increase in the US Midwest

• Authors:
  • Hammer, G..
  • Rejesus, R.
  • Little, B.
  • Braun, N.
  • Schlenker, W.
  • Roberts, M.
  • Lobell, D.
• Source: Science
• Volume: 344
• Issue: 6183
• Year: 2014
• Summary: A key question for climate change adaptation is whether existing cropping systems can become less sensitive to climate variations. We use a field-level data set on maize and soybean yields in the central United States for 1995 through 2012 to examine changes in drought sensitivity. Although yields have increased in absolute value under all levels of stress for both crops, the sensitivity of maize yields to drought stress associated with high vapor pressure deficits has increased. The greater sensitivity has occurred despite cultivar improvements and increased carbon dioxide and reflects the agronomic trend toward higher sowing densities. The results suggest that agronomic changes tend to translate improved drought tolerance of plants to higher average yields but not to decreasing drought sensitivity of yields at the field scale.

133. Evaluation of three field-based methods for quantifying soil carbon.

• Authors:
  • Rappaport, A. G.
  • Mitra, S.
  • Francis, B.
  • Harris, R.
  • Thomson, A. M.
  • Reeves, J. B.
  • Ebinger, M. H.
  • Wielopolski, L.
  • Rice, C. W.
  • Izaurralde, R. C.
  • Etchevers, J. D.
  • Sayre, K. D.
  • Govaerts, B.
  • McCarty, G. W.
• Source: PLOS ONE
• Volume: 8
• Issue: 1
• Year: 2013
• Summary: Three advanced technologies to measure soil carbon (C) density (g C m -2) are deployed in the field and the results compared against those obtained by the dry combustion (DC) method. The advanced methods are: (a) Laser Induced Breakdown Spectroscopy (LIBS), (b) Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS), and (c) Inelastic Neutron Scattering (INS). The measurements and soil samples were acquired at Beltsville, MD, USA and at Centro International para el Mejoramiento del Maiz y el Trigo (CIMMYT) at El Batan, Mexico. At Beltsville, soil samples were extracted at three depth intervals (0-5, 5-15, and 15-30 cm) and processed for analysis in the field with the LIBS and DRIFTS instruments. The INS instrument determined soil C density to a depth of 30 cm via scanning and stationary measurements. Subsequently, soil core samples were analyzed in the laboratory for soil bulk density (kg m -3), C concentration (g kg -1) by DC, and results reported as soil C density (kg m -2). Results from each technique were derived independently and contributed to a blind test against results from the reference (DC) method. A similar procedure was employed at CIMMYT in Mexico employing but only with the LIBS and DRIFTS instruments. Following conversion to common units, we found that the LIBS, DRIFTS, and INS results can be compared directly with those obtained by the DC method. The first two methods and the standard DC require soil sampling and need soil bulk density information to convert soil C concentrations to soil C densities while the INS method does not require soil sampling. We conclude that, in comparison with the DC method, the three instruments (a) showed acceptable performances although further work is needed to improve calibration techniques and (b) demonstrated their portability and their capacity to perform under field conditions.

134. Altered precipitation regime affects the function and composition of soil microbial communities on multiple time scales.

• Authors:
  • McGowan, A.
  • Lindsley, A.
  • Arango, M.
  • Rice, C. W.
  • Jumpponen, A.
  • Bottomley, P. J.
  • Zeglin, L. H.
  • Mfombep, P.
  • Myrold, D. D.
• Source: ECOLOGY
• Volume: 94
• Issue: 10
• Year: 2013
• Summary: Climate change models predict that future precipitation patterns will entail lower-frequency but larger rainfall events, increasing the duration of dry soil conditions. Resulting shifts in microbial C cycling activity could affect soil C storage. Further, microbial response to rainfall events may be constrained by the physiological or nutrient limitation stress of extended drought periods; thus seasonal or multiannual precipitation regimes may influence microbial activity following soil wet-up. We quantified rainfall-driven dynamics of microbial processes that affect soil C loss and retention, and microbial community composition, in soils from a long-term (14-year) field experiment contrasting "Ambient" and "Altered" (extended intervals between rainfalls) precipitation regimes. We collected soil before, the day following, and five days following 2.5-cm rainfall events during both moist and dry periods (June and September 2011; soil water potential=-0.01 and -0.83 MPa, respectively), and measured microbial respiration, microbial biomass, organic matter decomposition potential (extracellular enzyme activities), and microbial community composition (phospholipid fatty acids). The equivalent rainfall events caused equivalent microbial respiration responses in both treatments. In contrast, microbial biomass was higher and increased after rainfall in the Altered treatment soils only, thus microbial C use efficiency (CUE) was higher in Altered than Ambient treatments (0.700.03 >0.460.10). CUE was also higher in dry (September) soils. C-acquiring enzyme activities (beta-glucosidase, cellobiohydrolase, and phenol oxidase) increased after rainfall in moist (June), but not dry (September) soils. Both microbial biomass C:N ratios and fungal: bacterial ratios were higher at lower soil water contents, suggesting a functional and/or population-level shift in the microbiota at low soil water contents, and microbial community composition also differed following wet-up and between seasons and treatments. Overall, microbial activity may directly (C respiration) and indirectly (enzyme potential) reduce soil organic matter pools less in drier soils, and soil C sequestration potential (CUE) may be higher in soils with a history of extended dry periods between rainfall events. The implications include that soil C loss may be reduced or compensated for via different mechanisms at varying time scales, and that microbial taxa with better stress tolerance or growth efficiency may be associated with these functional shifts.

135. Drought impact on crop production and the soil environment: 2012 experiences from lowa

• Authors:
  • Robertson, A. E.
  • Mallarino, A. P.
  • Lenssen, A. W.
  • Hodgson, E. W.
  • Helmers, M. J.
  • Hart, C. E.
  • Hanna, H. M.
  • Guzman, J. G.
  • Elmore, R. W.
  • Al-Kaisi, M. M.
  • Sawyer, J. E.
• Source: Journal of Soil and Water Conservation
• Volume: 68
• Issue: 1
• Year: 2013

136. Plastic mulching in agriculture-Friend or foe of N 2O emissions?

• Authors:
  • Gebauer, G.
  • Kettering, J.
  • Kim, Y. S.
  • Berger, S.
• Source: Web Of Knowledge
• Volume: 167
• Year: 2013
• Summary: Polyethylene (PE) mulching is a very common method in agriculture worldwide because the use of PE films can improve product quality and yield by mitigating extreme weather changes, optimizing growth conditions and extending the growing season. Other than the problem with disposal of the plastics hardly any other of its effects on the environment are known. To determine whether covering fields with PE films affects N 2O emission, we conducted two experiments: first, comparing N 2O emissions of furrows and PE-mulched ridges of a radish field which had received different amounts of N fertilizer and second, assessing whether PE mulching increases N 2O emissions from PE-mulched ridges in comparison to non-PE-mulched ridges and furrows of a non-fertilized field. To achieve those aims we took comparative closed chamber measurements in conjunction with a photoacoustic infrared trace gas analyzer during the growing seasons of 2010 and 2011 at a radish and soy bean field site in South Korea. For the radish field site we found significant differences between the N 2O emitted by furrows and PE-mulched ridges and found extraordinarily low N 2O fluxes from those spots of the ridges which were totally PE-mulch-covered between plant hole openings. At the soy bean field we observed that plant holes of PE-mulched ridges showed only 68% of the emission measured of soils around soy bean plants of non-PE-mulched ridges, implying that PE mulching may decrease N 2O emissions. Since our result is contrary to very recent findings we consider the extremely low soil moisture at our sites as explanation for the differences. Because knowledge on how PE mulches affect production and emissions of greenhouse gases is very limited, our study contributes greatly to understanding N 2O emission behavior of PE-mulched, poor sandy soils in a temperate monsoon climate.

137. Implications of inorganic fertilization of irrigated corn on soil properties: lessons learned after 50 years.

• Authors:
  • Blanco-Canqui, H.
  • Schlegel, A. J.
• Source: Web Of Knowledge
• Volume: 42
• Issue: 3
• Year: 2013
• Summary: Inorganic fertilizers are widely used for crop production, but their long-term impacts on soil organic carbon (SOC) pools and soil physical attributes are not fully understood. We studied how half a century of N application at 0, 45, 90, 134, 179, and 224 kg ha -1 and P application at 0, 20, and 40 kg ha -1 (since 1992) affected SOC pools and soil structural and hydraulic parameters in irrigated continuous corn ( Zea mays L.) under conventional till on an Aridic Haplustoll in the central Great Plains. Application of 45, 90, 134, 179, and 224 kg N ha -1 increased the SOC pool by 4.6, 6.8, 7.6, 7.9, and 9.7 Mg ha -1, respectively, relative to nonfertilized plots in the 0- to 45-cm depth. Application of 20 kg P ha -1 increased the SOC pool by 2.9 Mg ha -1 in the 0- to 30-cm depth. The highest N rate increased the SOC pool by 195 kg ha -1 yr -1. The C gains may be, however, offset by the C hidden costs of N fertilization. Application of >45 kg N ha -1 reduced the proportion of soil macroaggregates (>0.25 mm) in the 7.5- to 30-cm depth. Fertilization did not affect hydraulic properties, but application of ≥90 kg N ha -1 slightly increased aggregate water repellency. An increase in SOC concentration did not increase the mean weight diameter of wet aggregates ( r=0.1; P>0.10), but it slightly increased aggregate water repellency ( r=0.5; P<0.005). Overall, long-term inorganic fertilization to irrigated corn can increase SOC pool, but it may reduce soil structural stability.

138. Modern maize hybrids in Northeast China exhibit increased yield potential and resource use efficiency despite adverse climate change.

• Authors:
  • Zhang, F. S.
  • Yuan, L.X.
  • Yang, X. L.
  • Gao, Q.
  • Chen, Y. L.
  • Chen, F. J.
  • Chen, X. C.
  • Mi, G. H.
• Source: Global Change Biology
• Volume: 19
• Issue: 3
• Year: 2013
• Summary: The impact of global changes on food security is of serious concern. Breeding novel crop cultivars adaptable to climate change is one potential solution, but this approach requires an understanding of complex adaptive traits for climate-change conditions. In this study, plant growth, nitrogen (N) uptake, and yield in relation to climatic resource use efficiency of nine representative maize cultivars released between 1973 and 2000 in China were investigated in a 2-year field experiment under three N applications. The Hybrid-Maize model was used to simulate maize yield potential in the period from 1973 to 2011. During the past four decades, the total thermal time (growing degree days) increased whereas the total precipitation and sunshine hours decreased. This climate change led to a reduction of maize potential yield by an average of 12.9% across different hybrids. However, the potential yield of individual hybrids increased by 118.5 kg ha -1 yr -1 with increasing year of release. From 1973 to 2000, the use efficiency of sunshine hours, thermal time, and precipitation resources increased by 37%, 40%, and 41%, respectively. The late developed hybrids showed less reduction in yield potential in current climate conditions than old cultivars, indicating some adaptation to new conditions. Since the mid-1990s, however, the yield impact of climate change exhibited little change, and even a slight worsening for new cultivars. Modern breeding increased ear fertility and grain-filling rate, and delayed leaf senescence without modification in net photosynthetic rate. The trade-off associated with delayed leaf senescence was decreased grain N concentration rather than increased plant N uptake, therefore N agronomic efficiency increased simultaneously. It is concluded that modern maize hybrids tolerate the climatic changes mainly by constitutively optimizing plant productivity. Maize breeding programs in the future should pay more attention to cope with the limiting climate factors specifically.

139. Closing the yield gap could reduce projected greenhouse gas emissions: a case study of maize production in China.

• Authors:
  • Chen, X. P.
  • Zhang, F. S.
  • Li, S. Q.
  • Zhang, Q.
  • Yang, Z. P.
  • Wu, L.
  • Meng, Q. F.
  • Wang, G. L.
  • Yue, S. C.
  • Cui, Z. L.
• Source: Global Change Biology
• Volume: 19
• Issue: 8
• Year: 2013
• Summary: Although the goal of doubling food demand while simultaneously reducing agricultural environmental damage has become widely accepted, the dominant agricultural paradigm still considers high yields and reduced greenhouse gas (GHG) intensity to be in conflict with one another. Here, we achieved an increase in maize yield of 70% in on-farm experiments by closing the yield gap and evaluated the trade-off between grain yield, nitrogen (N) fertilizer use, and GHG emissions. Based on two groups of N application experiments in six locations for 16 on-farm site-years, an integrated soil-crop system (HY) approach achieved 93% of the yield potential and averaged 14.8 Mg ha -1 maize grain yield at 15.5% moisture. This is 70% higher than current crop (CC) management. More importantly, the optimal N rate for the HY system was 250 kg N ha -1, which is only 38% more N fertilizer input than that applied in the CC system. Both the N 2O emission intensity and GHG intensity increased exponentially as the N application rate increased, and the response curve for the CC system was always higher than that for the HY system. Although the N application rate increased by 38%, N 2O emission intensity and the GHG intensity of the HY system were reduced by 12% and 19%, respectively. These on-farm observations indicate that closing the yield gap alongside efficient N management should therefore be prominent among a portfolio of strategies to meet food demand while reducing GHG intensity at the same time.

140. Short- and long-term labile soil carbon and nitrogen dynamics reflect management and predict corn agronomic performance.

• Authors:
  • Green, J. M.
  • Snapp, S. S.
  • Culman, S. W.
  • Gentry, L. E.
• Source: Agronomy Journal
• Volume: 105
• Issue: 2
• Year: 2013
• Summary: Labile soil organic matter plays an extremely important role in crop nutrient acquisition, but quantifying this pool can be prohibitively expensive to farmers. A better understanding of rapid and inexpensive measures of labile organic matter could lead to new tools for predicting soil N supply and crop performance. Toward this end, we quantified several simple measures of labile C and N over the course of the corn ( Zea mays L.) growing season in a long-term systems trial to determine:(i) the temporal dynamics of these measures, (ii) the long-term response of these measures to management, and (iii) the capacity of these measures to predict corn agronomic performance. We found that all labile soil measures (permanganate oxidizable carbon [POXC], C mineralization, N mineralization, and soil inorganic N) varied temporally and responded to long-term differences in management. Corn grain and vegetative biomass also responded to long-term treatment differences and these differences were strongly related to the measured labile soil C and N fractions. The history of crop rotation had a greater influence than management regime on all soil measures, with the exception of POXC. Of all the measures, C mineralization was the best predictor of agronomic performance both individually ( r=0.61-0.78, depending on corn stage), and when modeled with multiple indicators (six out of nine models). The results presented here demonstrate the strong relationship between crop growth and labile organic matter dynamics, and provide further evidence that C mineralization is an inexpensive, but sensitive predictor of corn agronomic performance.