• Authors:
    • Orton, T. G.
    • Jones, A. R.
    • Dalal, R. C.
  • Source: Science Article
  • Volume: 216
  • Year: 2016
  • Summary: Enhancing soil organic carbon (SOC) and total nitrogen (N) is considered an important step in mitigating greenhouse gas emissions and improving soil fertility. The loss of SOC and N generally observed during cropping may be reversed by converting such land use to permanent pasture. However, large uncertainties remain around the processes that govern how much C and N may be sequestered from this conversion in soils worldwide. Here, we sampled soils across 10 paddocks on 20-year old grass pasture sites with a chronosequence of cropping history in order to quantify changes in SOC and N after the conversion of long-term cropping to pasture land use in a semi-arid region of southwest Queensland, Australia. The average rate of change in SOC stocks under pasture in the top 0-0.1m soil layer was approximately 0.1tCha-1yr-1, consisting of an increase in SOCC4 (pasture) of 0.2tCha-1yr-1 and a decrease in SOCC3 (pre-pasture) of 0.1tCha-1yr-1. The decrease in SOCC3 was enhanced at sites with greater years under cropping, indicating a reduced potential for SOC sequestration at sites with longer duration under cropping. The loss of total nitrogen (N) under cropping was also partially recovered with the introduction of permanent perennial pastures. A significant, positive correlation between soil aggregation and mineralisable N under cropping suggested that soil structure has a strong influence over N stability in the soil. However, soil aggregation and mineralisable N did not improve under pastures, indicating that the loss of soil fertility and structure under cropping remained a residual effect that was not recovered within 20 years of permanent pastures in this semi-arid subtropical environment. We suggest here that the resilience of ecosystems to recover soil fertility under pastures declines with greater years under cropping. © 2015 Elsevier B.V.
  • Authors:
    • Strzepek, K.
    • Robinson, S.
    • Fant, C.
    • Arndt, C.
  • Source: Climatic Change
  • Volume: 130
  • Issue: 1
  • Year: 2015
  • Summary: Analysis of climate change is often computationally burdensome. Here, we present an approach for intelligently selecting a sample of climates from a population of 6800 climates designed to represent the full distribution of likely climate outcomes out to 2050 for the Zambeze River Valley. Philosophically, our approach draws upon information theory. Technically, our approach draws upon the numerical integration literature and recent applications of Gaussian quadrature sampling. In our approach, future climates in the Zambeze River Valley are summarized in 12 variables. Weighted Gaussian quadrature samples containing approximately 400 climates are then obtained using the information from these 12 variables. Specifically, the moments of the 12 summary variables in the samples, out to order three, are obliged to equal (or be close to) the moments of the population of 6800 climates. Runoff in the Zambeze River Valley is then estimated for 2026 to 2050 using the CliRun model for all 6800 climates. It is then straightforward to compare the properties of various subsamples. Based on a root of mean square error (RMSE) criteria, the Gaussian quadrature samples substantially outperform random samples of the same size in the prediction of annual average runoff from 2026 to 2050. Relative to random samples, Gaussian quadrature samples tend to perform best when climate change effects are stronger. We conclude that, when properly employed, Gaussian quadrature samples provide an efficient and tractable way to treat climate uncertainty in biophysical and economic models.
  • Authors:
    • Islam, K. R.
    • Mahmood, T.
    • Bangash, N.
    • Aziz, I.
  • Source: Pakistan Journal of Botany
  • Volume: 47
  • Issue: 1
  • Year: 2015
  • Summary: There is a global concern about progressive increase in the emission of greenhouse gases especially atmosphere CO2. An increasing awareness about environmental pollution by CO2 emission has led to recognition of the need to enhance soil C sequestration through sustainable agricultural management practices. Conservation management systems such as no-till (NT) with appropriate crop rotation have been reported to increase soil organic C content by creating less disturbed environment. The present study was conducted on Vanmeter farm of The Ohio State University South Centers at Piketon Ohio, USA to estimate the effect of different tillage practices with different cropping system on soil chemical properties. Tillage treatments were comprised of conventional tillage (CT) and No-till (NT). These treatments were applied under continuous corn (CC), corn-soybean (CS) and corn-soybean-wheat-cowpea (CSW) cropping system following randomized complete block design. No-till treatment showed significant increase in total C (30%), active C (10%), and passive salt extractable (18%) and microwave extractable C (8%) and total nitrogen (15%) compared to conventional tillage practices. Total nitrogen increased significantly 23 % in NT over time. Maximum effect of no-till was observed under corn-soybean-wheat-cowpea crop rotation. These findings illustrated that no-till practice could be useful for improving soil chemical properties.
  • Authors:
    • Zhang, B.
    • Yao, S.
    • Bi, L.
  • Source: Soil and Tillage Research
  • Volume: 152
  • Year: 2015
  • Summary: Soil puddlability measures the susceptibility of a soil to puddling, and can influence transplantation and the growth of rice plants. The effects of chemical fertilizers and organic amendments on soil puddlability of paddy soils are poorly understood. This study used two 26-year field experiments (1) to compare the effects of chemical and organic fertilization on soil puddlability by measuring sinkage resistance and hard clod content after puddling, (2) to characterize physical properties of hard clods and (3) to explain the change in soil puddlability. Each of the two experiments consisted of nine treatments of chemical fertilizers alone or in combination with organic amendments. The sinkage resistance and the content of hard clods were higher in the treatments with chemical fertilization alone than in the treatments with organic amendments. The sinkage resistance was positively correlated with the content of hard clods and negatively correlated to content of soil organic C (SOC) and mean weight diameter (MWD). The bulk density, water sorptivity and apparent porosity were similar among individual hard clods from different treatments, suggesting that the hard clods were formed under the same processes. The formation of hard clods was likely attributed to the breakdown of the compacted topsoil by puddling tillage, which formed due to clogging pores by fine particles produced during previous puddling tillage and due to shrinkage upon drying during rice growth period. Compared with the organic amendment treatments, the chemical fertilization treatments contained more and larger hard clods, indicating that the compacted topsoil was thicker due to higher soil dispersibility due to N fertilization and lower SOC content in the chemical fertilization treatments than in the organic amendment treatments. The study also suggests that continuous input of organic C at an annual rate of >2.5Mgha-1 is needed to maintain SOC content and soil structure under chemical fertilization in the study region. © 2015 Elsevier B.V.
  • Authors:
    • Echeverria, H.
    • Rozas, H. S.
    • Calvo, N. I. R.
    • Diovisalvi, N.
  • Source: Agronomy Journal
  • Volume: 107
  • Issue: 2
  • Year: 2015
  • Summary: In-season N applications to spring wheat ( Triticum aestivum L.) may increase profits and improve N fertilizer accuracy. The objectives were to develop a calibration tool employing normalized difference vegetative index (NDVI) and SPAD 502 chlorophyll meter (SPAD) measurements for calculating the differential from the economic optimum N rate (dEONR) at growth stages Z22, Z24, and Z31 to Z39 and provide N rate algorithms for use in applying N fertilizer at a variable rate. Sensing was conducted trials over 3 yr encompassing 10 site-years across Southeastern Buenos Aires Province, Argentina. The relationship between sensor indices and dEONR was evaluated by fitting quadratic plateau (QP) regression models. Statistically significant QP models were determined at the Z24, Z31, and Z39 growth stages. Relative SPAD (rSPAD) and relative NDVI (rNDVI) reduced variation and improved the calibration of measured N stress with the dEONR. For Z31 and Z39, the rSPAD had the best goodness of fit statistics when compared to rNDVI [adjusted R2 (adj R2)=0.67 and 0.57 at Z31 and 0.68 and 0.52 at Z39, respectively]. However, adjustment at Z24 was higher for rNDVI (adj R2=0.53 and 0.61 for rSPAD and rNDVI, respectively). A single QP model to estimate the dEONR with 58% confidence was adjusted for the Z31 and Z39 growth stages. This indicates that the same calibration for N rate determination based on rSPAD or rNDVI values can be used during stem elongation in spring wheat. This model can be used as an N rate algorithm for applying N fertilizer in-season.
  • Authors:
    • Strzepek, K.
    • McCluskey, A.
    • Gebretsadik, Y.
    • Fant, C.
  • Source: Article
  • Volume: 130
  • Issue: 1
  • Year: 2015
  • Summary: Many residents of the Zambezi River Valley are dependent on water-related resources. Greenhouse gas (GHG) emissions may cause a significant change to the climate in the Zambezi Basin in the future, but there is much uncertainty about the future climate state. This situation leaves policy makers at a state of urgency to prepare for these changes as well as reduce the impacts of the changes through GHG mitigation strategies. First and foremost, we must better understand the economic sectors most likely impacted and the magnitude of those impacts, given the inherent uncertainty. In this study, we present a suite of models that assess the effects of climate change on water resources for four countries in the Zambezi basin: Malawi, Mozambique, Zambia, and Zimbabwe. We use information from a large ensemble (6800) of climate scenarios for two GHG emission policies which represent a distribution of impacts on water-related sectors, considering emissions uncertainty, climate sensitivity uncertainty, and regional climate uncertainty. Two GHG mitigation scenarios are used to understand the effect of global emissions reduction on the River Basin system out to 2050. Under both climate polices, the majority of the basin will likely be drier, except for a portion in the north around Malawi and northern Zambia. Three Key Performance Indicators are used-flood occurrence, unmet irrigation demand, and hydropower generation-to understand the impact channels of climate change effects on the four countries. We find that floods are likely to be worse in Mozambique, irrigation demands are likely to be unmet in Mozambique and Zimbabwe, and hydropower generation is likely to be reduced in Zambia. We also find that the range of possible impacts is much larger under an unconstrained GHG emissions case than under a strict mitigation strategy, suggesting that GHG mitigation would reduce uncertainties about the future climate state, reducing the risks of extreme changes as compared to the unconstrained emissions case.
  • Authors:
    • Franco,J. G.
    • King,S. R.
    • Masabni,J. G.
    • Volder,A.
  • Source: Agriculture, Ecosystems and Environment
  • Volume: 203
  • Year: 2015
  • Summary: In natural ecosystems, plant communities composed of functionally diverse species produce more biomass overall than less diverse communities. This increased biomass production is thought to occur due to complementary use of resources such as nutrients and water, and facilitation during sub-optimal environmental conditions. Using the same concept in a crop setting may lead to increased yield (overyielding) in diverse cropping systems when compared to monocultures. Different combinations of peanut, watermelon, okra, cowpea, and pepper planted alone or in various intercropping combinations were investigated over two growing seasons in a low-input system in the peak of summer heat in Texas. Each species was selected to perform a specific function within the system. Results from land equivalent ratio (LER) indicate that the within-row combination with peanut, watermelon and okra ( Wpwo) and peanut, watermelon, okra and cowpea ( Wpwoc) consistently overyielded in 2011 and 2012. LER values were 1.17 each for Wpwo and Wpwoc in 2011 and 1.17 and 1.20 in 2012, respectively. In 2011, watermelon was the dominant crop and was up-regulated in all intercropping combinations while all other component crops were down-regulated. Watermelon per plant production was significantly higher in the combination containing all species ( Wall) when compared to its monoculture, 5.50 and 2.09 kg fruit plant -1, respectively. In 2012, okra was the dominant crop and was up-regulated in all intercropping combinations while watermelon, cowpea, and pepper were down-regulated. Okra per plant production was significantly higher in Wpwoc and Wall than in monoculture, 2.28, 2.46, and 1.13 kg fruit plant -1, respectively. These findings suggest that three and four species intercropping combinations, whereby each crop is selected to perform a specific function within the system, may provide small-scale sustainably-minded producers a model system that can be utilized in suboptimal conditions and allow them to reduce inputs while increasing overall yields.
  • Authors:
    • Aziz, S. A.
    • Gong, P.
    • Hansen, M.
    • Justice, C.
    • Becker-Reshef, I.
    • Herrero, M.
    • Wood-Sichra, U.
    • Thornton, P.
    • Mosnier, A.
    • Havlik, P.
    • Perger, C.
    • Schill, C.
    • Albrecht, F.
    • Duerauer, M.
    • Moltchanova, E.
    • Bun, A.
    • You, L.
    • McCallum, I.
    • See, L.
    • Fritz, S.
    • Cipriani, A.
    • Cumani, R.
    • Cecchi, G.
    • Conchedda, G.
    • Ferreira, S.
    • Gomez, A.
  • Source: Journal Article
  • Volume: 21
  • Issue: 5
  • Year: 2015
  • Summary: A new 1 km global IIASA-IFPRI cropland percentage map for the baseline year 2005 has been developed which integrates a number of individual cropland maps at global to regional to national scales. The individual map products include existing global land cover maps such as GlobCover 2005 and MODIS v.5, regional maps such as AFRICOVER and national maps from mapping agencies and other organizations. The different products are ranked at the national level using crowdsourced data from Geo-Wiki to create a map that reflects the likelihood of cropland. Calibration with national and subnational crop statistics was then undertaken to distribute the cropland within each country and subnational unit. The new IIASA-IFPRI cropland product has been validated using very high-resolution satellite imagery via Geo-Wiki and has an overall accuracy of 82.4%. It has also been compared with the EarthStat cropland product and shows a lower root mean square error on an independent data set collected from Geo-Wiki. The first ever global field size map was produced at the same resolution as the IIASA-IFPRI cropland map based on interpolation of field size data collected via a Geo-Wiki crowdsourcing campaign. A validation exercise of the global field size map revealed satisfactory agreement with control data, particularly given the relatively modest size of the field size data set used to create the map. Both are critical inputs to global agricultural monitoring in the frame of GEOGLAM and will serve the global land modelling and integrated assessment community, in particular for improving land use models that require baseline cropland information. These products are freely available for downloading from the http://cropland.geo-wiki.org website.
  • Authors:
    • Chen, N.
    • Ti, C.
    • Gao, J.
  • Source: Science Journal
  • Volume: 10
  • Issue: 1
  • Year: 2015
  • Summary: Straw is considered to be a renewable resource for bioenergy and biomaterial. However, about 70% of straw is burned in fields, which causes serious air pollution in China. In this study, a life cycle assessment (LCA) model, together with emergy evaluation, was built to compare four straw applications after harvest vs. direct burning, including bioethanol (BE), combined heat and power plant (CHP), corrugated base paper (CP), and medium-density fiberboard (MDF). The results showed that BE and MDF would avoid greenhouse gas (GHG) emissions by 82% and 36%, respectively, while CHP and CP would emit 57% and 152% more GHG, respectively, compared with direct straw burning. Bioethanol had the highest renewability indicator (RI) of 47.7%, and MDF obtained the greatest profit of 657 Yuan.bale(-1). The applications CHP and CP had low RI (< 10.3%) and profit (< 180 Yuan.bale(-1)). Due to water recycling and electrical power as a coproduct, BE had the lowest value (3 x 10(11) sej.Yuan(-1)) of EmPM (emergy per unit money profit); the EmPM value of CP was 18.6 times higher than that of BE. The four straw applications would also greatly reduce particles emission (57 to 98%) to air. BE was judged to be the most environmentally friendly application among the four straw applications. Imposing a carbon tax would encourage investment in BE, but discourage the applications CHP and CP.
  • Authors:
    • Li, Z.
    • Chen, G.
    • Wang, L.
    • Zhang, L.
    • Yang, Y.
    • Sheng, H.
    • Zhou, C.
    • Han, K.
  • Source: Agronomy Journal
  • Volume: 107
  • Issue: 1
  • Year: 2015
  • Summary: Increasing water and N use efficiency and lowering environmental pollution are primary concerns for both agricultural production and environmental quality in northwestern China. A 2-yr field experiment was conducted to assess and model the effects of irrigation, N, and plant density on maize ( Zea mays L.) when N fertilizer and irrigation were separated in an alternating furrow irrigation system. Regression modeling (a ternary quadratic equation) showed that N fertilization positively affected yield, water use efficiency, N uptake, soil NO 3-N, and NH 3 volatilization. Irrigation improved yield, N uptake, and increased soil NO 3-N in the deeper soil layer (0.6-2.0 m) but reduced water use efficiency, NH 3 volatilization, and soil NO 3-N in the 0- to 0.6-m soil layer. Planting density positively affected yield, water use efficiency, and N uptake but negatively influenced NH 3 volatilization and soil NO 3-N. The combination of 255 kg N ha -1 N fertilizer, 100 mm of irrigation water, and 59,467 plants ha -1 in 2010 and 245 kg N ha -1 N fertilizer, 98 mm of irrigation water, and 58,376 plants ha -1 in 2011 resulted in maximum income for maize yield (7245 kg ha -1 in 2010 and 6972 kg ha -1 in 2011). However, environmental and agronomic objectives did not match. Specifically, the combination of N, irrigation rate, and plant density with maximum yield increased N leaching and NH 3 losses, whereas the combination lowering environmental pollution due to N losses caused a reduction in yield. Therefore, the trade-off in management of N, irrigation, and planting density was emphasized for both environmental and agronomic benefits in our study.