• Authors:
    • Rusinamhodzi, L.
    • Matemba-Mutasa, R.
    • Thierfelder, C.
  • Source: SOIL & TILLAGE RESEARCH
  • Volume: 146
  • Issue: Pt. B
  • Year: 2015
  • Summary: The effect of different conservation agriculture (CA) systems on maize grain yield was studied across four countries in southern Africa. Maize yield data was obtained from plots under no-tillage as well as from conventionally tilled plots. Crop residues were retained in no-till plots, whereas they were removed from conventional tillage plots in line with current farmer practices. Rotations or intercropping systems with grain legumes were introduced at all sites. Fertiliser treatments were uniform across tillage treatments at each trial location but varied across countries, based on local fertilizer recommendations. Focus group discussions were conducted with farmers in the study sites to understand the constraints related to the successful integration of CA into the farming systems and to document farmers' perceptions about CA. In the majority of cases (80%), yield responses from a range of CA systems were greater than those of the conventional control plot at the respective site. In 20% of the cases there was a negative response to CA, due to lack of experience by farmers in the initial year, slow increase in soil fertility at the respective site and waterlogging in some years with too much rainfall. Yield advantages on two manual CA systems, planted with a dibble stick with sole maize and maize-legume intercropping in Malawi were 1152kgha-1 and 1172kgha-1, respectively. Animal traction CA systems had slightly smaller yield benefits (458kgha-1 on a ripline seeded system and 761kgha-1 on an animal traction direct seeding systems) as compared to a ploughed control treatment. Yield benefits increased with increasing years of practicing CA, highlighting the need to gain experience to master critical management steps such as timely planting, weeding, fertiliser application and crop harvest residue management. Yields from CA system responded better to increasing clay and silt content in the top soil and were more resilient to seasonal rainfall variability than conventional control treatments. Results suggest that the niche for CA in southern Africa is larger than expected although rainfalls regimes below 600mm are challenging to sustain large maize biomass production to provide effective soil cover in CA systems. The success of CA implementation will largely depend on addressing critical challenges observed in the field, which will need adaptation of CA system to the site and farmer circumstances.
  • 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:
    • Quenea, K.
    • Mutema, M.
    • Muller-Nedebock, D.
    • Mchunu, C.
    • Everson, C.
    • Dlamini, P.
    • Darboux, F.
    • Bourennane, H.
    • Alexis, M.
    • Abdalla, K.
    • Chaplot, V.
    • Thenga, H.
    • Chivenge, P.
  • Source: Journal
  • Volume: 203
  • Issue: 1
  • Year: 2015
  • Summary: The impact of agricultural practices on CO 2 emissions from soils needs to be understood and quantified to enhance ecosystem functions, especially the ability of soils to sequester atmospheric carbon (C), while enhancing food and biomass production. The objective of this study was to assess CO 2 emissions in the soil surface following tillage abandonment and to investigate some of the underlying soil physical, chemical and biological controls. Maize ( Zea mays) was planted under conventional tillage (T) and no-tillage (NT), both without crop residues under smallholder farming conditions in Potshini, South Africa. Intact top-soil (0-0.05 m) core samples (N=54) from three 5*15 m 2 plots per treatment were collected two years after conversion of T to NT to evaluate the short-term CO 2 emissions. Depending on the treatment, cores were left intact, compacted by 5 and 10%, or had surface crusts removed. They were incubated for 20 days with measurements of CO 2 fluxes twice a day during the first three days and once a day thereafter. Soil organic C (SOC) content, soil bulk density (rho b), aggregate stability, soil organic matter quality, and microbial biomass and its activity were evaluated at the onset of the incubation. CO 2 emissions were 22% lower under NT compared with T with CO 2 emissions of 0.90.10 vs 1.10.10 mg C-CO 2 gC -1 day -1 under NT and T, respectively, suggesting greater SOC protection under NT. However, there were greater total CO 2 emissions per unit of surface by 9% under NT compared to T (1.150.03 vs 1.050.04 g C-CO 2 m -2 day -1). SOC protection significantly increased with the increase in soil bulk density ( r=0.89) and aggregate stability (from 1.70.25 mm to 2.30.31, r=0.50), and to the decrease in microbial biomass and its activity ( r=-0.59 and -0.57, respectively). In contrast, the greater NT CO 2 emissions per m 2 were explained by top-soil enrichment in SOC by 48% (from 12.40.2 to 19.10.4 g kg -1, r=0.59). These results on the soil controls of tillage impact on CO 2 emissions are expected to inform on the required shifts in agricultural practices for enhancing C sequestration in soils. In the context of the study, any mechanism favoring aggregate stability and promoting SOC allocation deep in the soil profile rather than in the top-soil would greatly diminish soil CO 2 outputs and thus stimulate C sequestration.
  • 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:
    • Wambua, J. M.
    • Mungube, E. O.
    • Njiru, E. N.
    • Gatheru, M.
    • Gichangi, E. M.
    • Wamuongo, J. W.
  • Source: Article
  • Volume: 130
  • Issue: 2
  • Year: 2015
  • Summary: A study was conducted to investigate the intra-seasonal climate variability and change in semi-arid eastern Kenya and also assessed the ability of the households to discern trends in climate and how the perceived trends converge with actual long term weather observations. The study utilised long term climatic data and data collected through interviews of 200 households using a structured questionnaire. The survey data was analysed through descriptive statistics using the Statistical Package for Social Sciences (SPSS) version 12.0. The results of long term climatic data indicated high year-to-year variation in seasonal rainfall with 49.0% and 58% negative anomalies observed in the long and short rainfall seasons respectively. No discernible increasing or decreasing trend in the long- seasonal rainfall was observed over the period of study. However, Long-term temperature data showed high year-to-year variation in annual mean maximum and minimum temperatures with maximum temperature increasing during the period. Long term rainfall data (51 years) showed that 31.4 and 35.3% of the long rains would be classified as good and failed seasons respectively, with the remaining percentage classified as moderate seasons. For the short rains, 15.7 and 43.1 % would be classified as good and failed seasons respectively, with the remaining percentage classified as moderate seasons. Farmers interviewed were able to recollect the past seasons fairly accurately especially the 'good' and 'failed' seasons which corroborated well with the meteorological records. Indigenous knowledge on weather forecasting was reported by 81% of farmers to be helpful in farming decision making especialy on the types of crops to be planted. A better understanding of farmers' perceptions of climate change, ongoing adaptation measures, and the decision-making process would important to inform policies aimed at promoting sustainable adaptation of the agricultural sector.
  • Authors:
    • Enders, A.
    • Thies, J. E.
    • Lehmann, J.
    • Guerena, D. T.
    • Karanja, N.
    • Neufeldt, H.
  • Source: Biology and Fertility of Soils
  • Volume: 51
  • Issue: 4
  • Year: 2015
  • Summary: Studies document increases in biological nitrogen fixation (BNF) following applications of biochar. However, the underlying mechanisms for this response remain elusive. Greenhouse experiments were conducted to test the effects of biochar mineral nutrients, pH, and volatile matter (VM) on BNF in common beans ( Phaseolus vulgaris L.). Biochars were produced from seven feedstocks pyrolyzed at either 350 or 550°C. Biochars were treated with acid to reduce mineral nutrient contents, with acetone to remove acetone-soluble VM, with steam to reduce both the mineral and VM contents, or left untreated. The biochar additions at a rate of 15 t ha -1 resulted in an average 262% increase in shoot biomass, 164% increase in root biomass, 3575% increase in nodule biomass, and a 2126% increase in N derived from atmosphere (Ndfa) over the control. Simple mineral nutrients and soil acidity amelioration from the biochar were only to a minimal extent responsible for these increases ( r2=0.03; P=0.0298, n=201). Plant growth and Ndfa were significantly correlated with plant P uptake ( r2=0.22; P0.05). Improved P nutrition resulted from 360% greater mycorrhizal colonization with biochar additions. Removal of acetone-soluble VM increased plant growth and Ndfa, and VM extracted from the biochar produced at 350°C reduced the growth of rhizobia in yeast extract mannitol agar (YMA) medium. In contrast, acetone-soluble VM extracted from seven biochars produced at 550°C increased the growth of rhizobium in the YMA compared to an acetone-residue control, suggesting differential effects of VM forms on rhizobia.
  • Authors:
    • Strzepek, K.
    • Schlosser, A.
  • Source: Article
  • Volume: 130
  • Issue: 1
  • Year: 2015
  • Summary: Projections of regional changes in surface-air temperature and precipitation, in response to unconstrained emissions as well as a climate mitigation policy, for the Zambezi River Basin (ZRB) are presented. These projections are cast in a probabilistic context through a hybrid technique that combines the projections of the MIT Integrated Global System Model (IGSM) to pattern-change kernels from climate-model results of the Coupled Model Intercomparison Project (CMIP). Distributional changes of precipitation and surface-air temperature averaged over the western and eastern ZRB are considered. Overall, the most significant response to climate policy is seen in the spring. Frequency distributions of precipitation change for the unconstrained emission scenario indicate a majority of the outcomes to be drier by 2050, although the distribution spans both increased and decreased precipitation. Through climate policy, the distributions' total range of outcomes collapses considerably, and perhaps more importantly, the mode of the distribution aligns with zero precipitation change. For surface-air temperature, climate policy consistently reduces the modal value of warming, and this reduction is strongest for the western ZRB. Climate policy also considerably abates the occurrence of the most extreme temperature increases, but the minimum warming in the distributions is less affected.
  • Authors:
    • Rubenstein, D.
    • Notenbaert, A.
    • Beringer, T.
    • Thornton, P. K.
    • Estes, L.
    • Searchinger, T. D.
    • Heimlich, R.
    • Licker, R.
    • Herrero, M.
  • Source: Article
  • Volume: 5
  • Issue: 5
  • Year: 2015
  • Summary: Do the wet savannahs and shrublands of Africa provide a large reserve of potential croplands to produce food staples or bioenergy with low carbon and biodiversity costs? We find that only small percentages of these lands have meaningful potential to be low-carbon sources of maize (1/42%) or soybeans (9.5-11.5%), meaning that their conversion would release at least one-third less carbon per ton of crop than released on average for the production of those crops on existing croplands. Factoring in land-use change, less than 1% is likely to produce cellulosic ethanol that would meet European standards for greenhouse gas reductions. Biodiversity effects of converting these lands are also likely to be significant as bird and mammal richness is comparable to that of the world's tropical forest regions. Our findings contrast with influential studies that assume these lands provide a large, low-environmental-cost cropland reserve. © 2015 Macmillan Publishers Limited. All rights reserved.
  • Authors:
    • Vicca, S.
    • Davidson, E.
    • Trumbore, S.
    • Sierra, C.
    • Janssens,I.
  • Source: Journal of Advances in Modeling Earth Systems
  • Volume: 7
  • Issue: 1
  • Year: 2015
  • Summary: The sensitivity of soil organic matter decomposition to global environmental change is a topic of prominent relevance for the global carbon cycle. Decomposition depends on multiple factors that are being altered simultaneously as a result of global environmental change; therefore, it is important to study the sensitivity of the rates of soil organic matter decomposition with respect to multiple and interacting drivers. In this manuscript, we present an analysis of the potential response of decomposition rates to simultaneous changes in temperature and moisture. To address this problem, we first present a theoretical framework to study the sensitivity of soil organic matter decomposition when multiple driving factors change simultaneously. We then apply this framework to models and data at different levels of abstraction: (1) to a mechanistic model that addresses the limitation of enzyme activity by simultaneous effects of temperature and soil water content, the latter controlling substrate supply and oxygen concentration for microbial activity; (2) to different mathematical functions used to represent temperature and moisture effects on decomposition in biogeochemical models. To contrast model predictions at these two levels of organization, we compiled different data sets of observed responses in field and laboratory studies. Then we applied our conceptual framework to: (3) observations of heterotrophic respiration at the ecosystem level; (4) laboratory experiments looking at the response of heterotrophic respiration to independent changes in moisture and temperature; and (5) ecosystem-level experiments manipulating soil temperature and water content simultaneously.
  • Authors:
    • Lobell, D.
    • Abelleyra, D.
    • Veron, S.
  • Source: Article
  • Volume: 130
  • Issue: 2
  • Year: 2015
  • Summary: Understanding regional impacts of recent climate trends can help anticipate how further climate change will affect agricultural productivity. We here used panel models to estimate the contribution of growing season precipitation (P), average temperature (T) and diurnal temperature range (DTR) on wheat, maize and soy yield and yield trends between 1971 and 2012 from 33 counties of the Argentine Pampas. A parallel analysis was conducted on a per county basis by adjusting a linear model to the first difference (i.e., subtracting from each value the previous year value) in yield and first difference in weather variables to estimate crop sensitivity to interannual changes in P, T, and DTR. Our results show a relatively small but significant negative impact of climate trends on yield which is consistent with the estimated crop and county specific sensitivity of yield to interannual changes in P, T and DTR and their temporal trends. Median yield loss from climate trends for the 1971-2012 period amounted to 5.4 % of average yields for maize, 5.1 % for wheat, and 2.6 % for soy. Crop yield gains for this time period could have been 15-20 % higher if climate remained without directional changes in the Pampas. On average, crop yield responded more to trends in T and DTR than in P. Translated into economic terms the observed reductions in maize, wheat, and soy yields due to climate trends in the Pampas would equal $1.1 B using 2013 producer prices. These results add to the increasing evidence that climate trends are slowing yield increase.