• Authors:
    • Lynch, J. P.
    • Zhan, A.
  • Source: Article
  • Volume: 66
  • Issue: 7
  • Year: 2015
  • Summary: Suboptimal nitrogen (N) availability is a primary constraint for crop production in developing countries, while in developed countries, intensive N fertilization is a primary economic, energy, and environmental cost for crop production. We tested the hypothesis that under low-N conditions, maize ( Zea mays) lines with few but long (FL) lateral roots would have greater axial root elongation, deeper rooting, and greater N acquisition than lines with many but short (MS) lateral roots. Maize recombinant inbred lines contrasting in lateral root number and length were grown with adequate and suboptimal N in greenhouse mesocosms and in the field in the USA and South Africa (SA). In low-N mesocosms, the FLphenotype had substantially reduced root respiration and greater rooting depth than the MS phenotype. In low-N fields in the USA and SA, the FLphenotype had greater rooting depth, shoot N content, leaf photosynthesis, and shoot biomass than the MS phenotype. The FLphenotype yielded 31.5% more than the MS phenotype under low N in the USA. Our results are consistent with the hypothesis that sparse but long lateral roots improve N capture from low-N soils. These results with maize probably pertain to other species. The FLlateral root phenotype merits consideration as a selection target for greater crop N efficiency.
  • Authors:
    • Lehmann, J.
    • Lamers, J.
    • Bationo, A.
  • Source: Article
  • Volume: 102
  • Issue: 1
  • Year: 2015
  • Authors:
    • Buerkert, Andreas
    • Bruentrup, Michael
    • Lamers, John P. A.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 102
  • Issue: 1
  • Year: 2015
  • Summary: Low concentrations of phosphorus (P) also limit crop production on the acid, sandy soils in Sudano-Sahelian West Africa (SSWA). An increased P-use is thus a key leverage for enhancing food security and alleviating poverty. Therefore, P-imports into the predominating agro-pastoral farming systems are indispensable, but most smallholders are cash-poor and risk averse, face labor-constraints, and P-fertiliser responses are site-specific. Key to the adoption of any new technology is a high financial performance with low risk levels of failure, low demands of labor and cash, and adaptation to the prevailing farming systems. Financial performances were assessed from nine, annually applied fertilising practices during 4 years in five SSWA zones. Information about the farming systems, labor demands, and input-output prices stem from secondary sources. The profitability largely depended on rainfall and location-specific soil conditions, but those of annually repeated mineral and organic P-strategies increased over time. Several P-fertilisations were profitable on a per land unit basis, but could not compete with farmers' practices on a per labor unit basis. Mulching with and without P (13 kg P ha(-1)) were not financially superior, but the broadcast application of 13 kg P ha(-1) became profitable over time. Hill-placed P (4 kg P ha(-1)), also known as micro-dosing, was a profitable alternative to farmers' practices particularly in the intermediate rainfall zone. The results showed the importance of recommendations following rainfall zones, which are of interest across a spectrum of users including policy makers, land use practitioners, private firms, NGOs and research for development implementers.
  • Authors:
    • Louw,E. L.
    • Hoffman,E. W.
    • Theron,K. I.
    • Midgley,S. J. E.
  • Source: South African Journal of Botany
  • Volume: 99
  • Year: 2015
  • Summary: Rising temperatures associated with global climate change may alter the physiology and phenology of Protea species and cultivars. Protea species are assumed to be well adapted to warm summers characteristic of their natural Mediterranean-type habitat, but their plasticity in responding to higher growth temperatures is not known. Using infrared lamps, a greenhouse-based temperature gradient was constructed, with temperatures ranging from ambient to ambient + 3.1°C. Potted plants of Protea 'Pink Ice' ( P. compacta R. Br * P. susannae Phill.) were grown at five positions along this gradient for 12 months under irrigation. Simultaneously, a field verification experiment in a nearby commercial 'Pink Ice' orchard was conducted under ambient temperature and ambient + 2.9°C. Increased sclerophylly (leaf dry weight per unit area) with increasing temperature indicated leaf structural changes. While leaf area based gas exchange (net CO 2 assimilation rate, stomatal conductance and dark respiration rate) did not differ across the temperature gradient, leaf weight based CO 2 assimilation rate and dark respiration rate decreased significantly towards the upper end of the temperature range. The optimum temperature for net CO 2 assimilation rate (T opt) showed seasonal adjustments, but increased in response to experimental warming only in the field experiment. Significant temperature elevation resulted in an earlier onset of spring bud break, but warming extended inflorescence initiation from the spring flush to the summer flush, leading to delayed flowering. Aboveground biomass allocation shifted from inflorescences to leaves and to a lesser degree to stems, with elevated temperatures, whereas root growth was stimulated in the middle of the warming range. The results of this study suggest that elevated temperature may prolong the vegetative growth period in some Protea cultivars where water is not limiting, at the expense of flower production. This could have significant economic and marketing consequences for commercial cut flower production systems. The findings are also of significance to ecologists studying the responses of Proteaceae to climate change.
  • Authors:
    • Oluwole,O. S. A.
  • Source: Climatic Change
  • Volume: 131
  • Issue: 2
  • Year: 2015
  • Summary: Konzo epidemics occur during droughts in East, Central, and Southern Africa, where the population depends almost exclusively on poorly processed cassava. Warm phases of El Nino-Southern Oscillation (ENSO) and Pacific decadal Oscillation (PDO) are associated with droughts in these areas of Africa, but with increase rainfall in South America. To further understanding of the relationship of droughts, cassava production, and konzo epidemics, this study was done to determine if there is coherence of spectra of ENSO, PDO and cassava production. Annual time series of cassava production in Tanzania and Brazil, multivariate ENSO index (MEI), and the Pacific Decadal Oscillation index (PDO) from 1961-2013 were compared. Wavelet and cross wavelet analyses of cassava production, ENSO, and PDO were performed. Warm phases of ENSO and PDO were associated with high cassava production in Tanzania, but with low cassava production in Brazil. Spectrogram of cassava showed significantly high production at periodicities of 3-9 years in Tanzania, but with significantly low production at periodicities of 2-6 years in Brazil. Cross wavelet spectrograms showed coherence of cassava production, ENSO and PDO in Tanzania and Brazil. Time-varying cyclical cassava production in Tanzania and Brazil are coupled to ENSO and PDO modes. Occurrence of droughts, high cassava production, and konzo epidemics in Tanzania are attributable to the impact of climate variability, which should be the focus of public health policies to control konzo epidemics.
  • Authors:
    • Hachigonta, S.
    • Crespo, O.
    • Zinyengere, N.
    • Tadross, M.
  • Source: AGRICULTURE ECOSYSTEMS & ENVIRONMENT
  • Volume: 197
  • Year: 2014
  • Summary: Climate change impact assessments on agriculture in Southern Africa are mostly carried out at large spatial scales, risking missing out on local impacts and adaptation potential that reflect the range of multiple and unique bio-physical and agronomic conditions under which farmers in the region operate. This study investigated how climate change may affect yields of various major food crops in specific locations in the region; maize and sorghum (Mohale's Hoek - Lesotho and Big Bend - Swaziland), maize and groundnut (Lilongwe - Malawi). Using statistically downscaled climate projections from nine GCMs and the DSSAT crop model and simulating selected agronomic strategies practiced in each location, the study confirmed that impacts of climate change on crop yields in Southern Africa vary across locations and crops. Despite various uncertainties associated with such assessments, the results showed that crop yields were predominantly projected to decline in Big Bend (maize (-20%); sorghum (-16%)) and Lilongwe (maize (-5%); groundnut (-33%)). However, crop yields in Mohale's Hoek, located in a high altitude region historically prone to cold related crop yield losses were on average projected to increase (maize (+8%) and sorghum (+51%)). The geographical variation of yield projections highlights the importance of location specific climate change impact assessments. The exploration of local agronomic management alternatives revealed prospects for identifying locally relevant adaptation strategies, which cannot easily be captured at larger scales.
  • 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.
  • Authors:
    • Bonsch, M.
    • Dietrich, J. P.
    • Popp, A.
    • Lotze-Campen, H.
    • Krause, M.
  • Source: Land Use Policy
  • Volume: 30
  • Issue: 1
  • Year: 2013
  • Summary: Conservation of undisturbed natural forests, which are important for biodiversity, carbon storage, and other ecosystem services, affects agricultural production and cropland expansion. We analyze the economic impacts of undisturbed natural forest conservation programs on agriculture and the magnitude of avoided deforestation and avoided carbon emissions in the tropics. We apply a global agricultural land use model to estimate changes in agricultural production costs for the period 2015-2055. Our forest conservation scenarios reflect two different policy goals: either maximize forest carbon storage or minimize impacts on agricultural production. In all the scenarios, the economic impacts on agriculture are relatively low. Production costs would increase due to forest conservation by a maximum of 4%, predominantly driven by increased investments in agricultural productivity increase. We also show regional differences in Latin America, Sub-Saharan Africa, and Southeast Asia, due to different growth rates in food demand, land availability and crop productivity. The area of avoided deforestation does not exceed 1.5 million ha yr(-1) in the period 2015-2055, while avoided carbon emissions reach a maximum of 1.9 Gt CO2 per year. According to our results on the potential changes in agricultural production costs, undisturbed natural forest conservation appears to be a low-cost option for greenhouse gas emission reduction. (C) 2012 Elsevier Ltd. All rights reserved.
  • Authors:
    • Thorburn, P.
    • Ruane, A.
    • Marin, F.
    • Jones, M.
    • Singels, A.
  • Source: An International Journal of Sugar Crops and Related Industries
  • Volume: 115
  • Issue: 1380
  • Year: 2013
  • Summary: Future climate change is expected to have important consequences for sugarcane production, and reliable predictions of crop response to climate change are necessary to plan adaptation strategies. The objective of this study was to assess the use of global climate models (GCMs) and a crop simulation model for predicting climate change impacts on sugarcane production. The Canegro model was used to simulate growth and development of sugarcane crops under typical management conditions at three sites (irrigated crops at Ayr, Australia; rainfed crops at Piracicaba, Brazil and La Mercy, South Africa) for current and three future climate scenarios. The baseline scenario consisted of a 30-year time series of historical daily weather records and atmospheric CO2 concentration ([CO2]) set at 360 ppm. Future climate scenarios were derived from three GCMs for the A2 greenhouse gas emission scenario and [CO2] set at 734 ppm. The three GCMs were chosen to represent the uncertainty in projected rainfall changes. Future cane yields are expected to increase at all three sites, ranging from +4% for Ayr, to +9% and +20% for Piracicaba and La Mercy. The uncertainty of these predictions correlates with the magnitude of the predicted yield increase. Canopy development was accelerated at all three sites by increased temperature, which led to increased interception of radiation, increased transpiration, and slight increases in drought stress at rainfed sites. For the high potential sites (Ayr and Piracicaba), yield increases were limited by large increases in maintenance respiration which consumed most of the daily assimilate when high biomass was achieved. A weakness of the climate data used was the assumption of no change in rainfall distribution, solar radiation and relative humidity-variables that are crucial in determining the water status of rainfed sugarcane. Crop model aspects that need refinement include improved simulation of (1) elevated [CO2] effects on crop photosynthesis and transpiration, and (2) high temperature effects on crop development, photosynthesis and respiration.
  • Authors:
    • Reinhardt, C. F.
    • Bezuidenhout, S. R.
    • Whitwell, M. I.
  • Source: Weed Research
  • Volume: 52
  • Issue: 2
  • Year: 2012
  • Summary: No information is available on the effect of cover crops on weed growth in maize production in KwaZulu-Natal, South Africa. In a field experiment, the influence of two preceding cover crops, stooling rye and annual ryegrass, on the growth of maize and the weed Cyperus esculentus were compared with herbicides and weed control by hoeing. Maize emergence and early growth were delayed in the presence of physical residues of both cover crop species, especially annual ryegrass. Growth of C. esculentus was significantly inhibited in the inter-row maize planting lines by the cover crops for the first 16 days after maize emergence, but this effect had diminished by day 28. In a pot experiment, the influence of the same two cover crops on maize and C. esculentus growth was evaluated together with oats and two additional annual ryegrass cultivars. Here, the growth of maize and C. esculentus were suppressed, especially by the root residues of the annual ryegrass, in particular the cultivar Midmar. Chemical analysis of the leachate of the root residues indicated the presence of phenolic acids and benzoxazolin-2(3 H)-one. To achieve effective weed control, a weed management strategy combining the mulch retained on the soil surface, with a possible reduction in the type and amount of herbicide, should be implemented.