880 research outputs found
Full chain analysis of nitrogen use efficiency in rice-livestock systems in Uruguay: identifying opportunities for optimizing N management.
No full textHaefele, Stephan M. - Associate SupervisorTraditionally the rice crop in Uruguay rotates with pastures for direct livestock
grazing. This rotation has allowed a constant rice yield increase of 90 kg ha⁻¹
yr⁻¹ over the past 50 years, with yields averaging 8.4 Mg ha⁻¹ in the last decade.
Relatively little nitrogen (N) fertilizer is added (80 kg ha⁻¹ yr⁻¹) and the system
shows no sign of soil degradation. By contrast, the livestock component is
conducted extensively with mostly (75-80%) unimproved pastures, with low
animal productivity (100 kg liveweight ha⁻¹ yr⁻¹). This thesis is concerned with how
the system N balance is sustained at regional and national scales and if it can be
maintained in the future. The objectives were to quantify the N balance (all N
inputs – outputs), N surplus (all N inputs – N removed in food products) and N
use efficiency (NUE = N in food products / all N inputs) of different rice-livestock-
pasture rotations across Uruguay over time. Because historical records of N
inputs and outputs are available at regional and national scales, it was possible
to assess the whole system in the long term at a farm-gate level. The DNDC
model was parameterised with data from a rice long-term experiment and used
to compliment the regional N balance data. Results showed a very high average
NUE (55–60%) with N balances around neutrality (-6 to +5 kg N ha⁻¹ yr⁻¹) and low
N surplus (20 kg N ha⁻¹ yr⁻¹). These values were worse where pastures have been
replaced by other cash-crops or rotations shortened. However, there is an
opportunity to intensify the system, maintaining the good N balance by improving
the livestock component with improved pastures and higher stocking rates to
improve N cycling. Results showed the rice-livestock system of Uruguay is a
model mixed farming system with several decades of integration.PhD in Environment and Agrifoo
Biochar amendment techniques for upland rice production in Northern Laos 1. Soil physical properties, leaf SPAD and grain yield
No full textAbstract not availableHidetoshi Asai, Benjamin K. Samson, Haefele M. Stephan, Khamdok Songyikhangsuthor, Koki Homma, Yoshiyuki Kiyono, Yoshio Inoue, Tatsuhiko Shiraiwa, Takeshi Hori
sj-pdf-1-oag-10.1177_00307270211045410 - Supplemental material for Revisiting strategies to incorporate gender-responsiveness into maize breeding in southern Africa
No full textSupplemental material, sj-pdf-1-oag-10.1177_00307270211045410 for Revisiting strategies to incorporate gender-responsiveness into maize breeding in southern Africa by Jill E Cairns, Frédéric Baudron, Kirsty L. Hassall, Thokozile Ndhlela, Isaiah Nyagumbo, Steve P. McGrath and Stephan M Haefele in Outlook on Agriculture</p
Dry spectral diagnostic tools and methods for precise fertilizer application
No full textCorstanje, Ronald - Associate Supervisor
Haefele, Stephan M. - Associate Supervisor, Rothamsted Research
Kebede, Fassil - Associate Supervisor, UM6P, MoroccoThis study explores the potential of soil spectroscopy to enhance fertilizer
decision-making by providing cost-effective, portable instruments for farm-level
soil property prediction. The study focused on assessing the performance of
various spectrometers, including low-cost near-infrared (NIR) devices, compared
to mid-infrared (MIR) bench-top instruments, using a case study on maize
productivity in East Africa and soil data from Morocco’s semi-arid rainfed wheat-
growing regions. The overall aim was to determine whether these spectroscopic
methods could generate reliable predictions of key soil properties for nitrogen,
phosphorus and potassium fertilizer recommendations.
The results indicate that NIR spectroscopy, despite being the most affordable and
portable option, demonstrated sufficient accuracy for predicting key soil
properties such as soil pH, organic carbon, and exchangeable potassium, with
concordance correlation coefficients (CCCs) ranging from 0.77 to 0.96. However,
the prediction of phosphorus (Olsen P) showed considerable uncertainty,
particularly for values above 15 mg P kg⁻¹, where deviations from measured
values increased. Comparatively, the MIR spectrometer showed better prediction
accuracy for phosphorus, though its higher cost and complexity limit its
applicability in resource-limited settings. The NIR spectrometer, with a prediction
accuracy suitable for nitrogen fertilization (deviation between -8 to 8 kg N ha⁻¹),
emerged as a promising tool for cost-effective and rapid nutrient
recommendations in developing countries.
Furthermore, this research demonstrated that integrating spectroscopic data into
crop models like QUEFTS for nutrient management enhances decision-making
by considering both soil supply and crop response to nutrients. The findings
underscore the necessity of developing region-specific calibration models to
improve prediction reliability, with spatial autocorrelation analysis of soil spectra
suggesting that proper calibration sample selection can improve prediction
performance, especially for phosphorus and other key properties.
Ultimately, this thesis contributes to the ongoing development of soil spectral
libraries and highlights the potential of low-cost, field-friendly spectrometers to
improve nutrient management and crop productivity in regions with limited soil
data.OCP Group of MoroccoPhD in Environment and Agrifoo
A soil organic carbon indexing and measurement system
No full textSoil organic carbon (SOC) is an important component of soils for the various goods and
services that soils perform. But SOC stocks have declined significantly in soils around
the world over many years due to poor land management. To enable land managers and
policy makers to manage SOC better, simple guideline values and measures of SOC
concentration are needed. An index based on the SOC to clay concentration ratio as
related to soil structural conditions was tested for soils across England and Wales using
data from the National Soil Inventory (NSI). Threshold values of SOC/clay equal to 1/8,
1/10 and 1/13 indicated Very Good, Good, Moderate and Degraded levels of SOC.
Land use was a driver of SOC/clay ratio, with 38% of arable soils classed as Degraded
compared with < 7% of permanent grass or woodland soils. To examine how SOC/clay
ratios have been changing over time, I analysed data from resampled sites in the NSI
(mean interval of 15 years). The Very Good class was particularly vulnerable to losses
compared with other classes. This finding agrees with SOC protection being limited by
soil clay concentration. Long-term experiments on soils of contrasting clay
concentration showed that the index was sensitive to management activities. In further
work I explored the use of dry soil spectral analysis to measure SOC and clay
concentrations. I compared dry spectral and conventional wet laboratory analyses of
soils in the NSI and in the US National Soil Survey Center-Kellogg Soil Survey
Laboratory spectral library (NSSC-KSSL). The NSSC-KSSL results, and to a lesser
extent the NSI results (which used older, less-accurate wet laboratory analyses), showed
that the technique is suitable for assigning soils to Very Good, Degraded, or
Good/Moderate ranges. The index provides quantitative guideline concentrations for
SOC with a functional basis and scope for rapid assessment.Haefele, Stephan M. (Associate)PhD in Environment and Agrifoo
Degradability of black carbon and its impact on trace gas fluxes and carbon turnover in paddy soils
No full textAbstract not availableChristian Knoblauch, Arina-Ann Maarifat, Eva-Maria Pfeiffer and Stephan M. Haefel
Climate change and unfavorable rice environments: overview of approaches to assess trends and future projections
No full textThe likely impacts of climate change on rice-based agroecosystems in Asia are uncertain, especially for rainfed rice systems in theunfavorable environments that are vulnerable to precipitation changes. Regional impacts of climate change are typically assessedquantitatively through spatially downscaling a global circulation model (GCM), but this approach is inherently biased through the GCMselected, which is typically not more than one. In this paper, we pursue a different approach that is based on an ensemble analysisof several GCMs. In the first section, the ensemble analysis is illustrated by using two rainfed rice environments (in eastern India andBangladesh) as examples. Although the different GCMs showed a similar overall trend of declining precipitation, major discrepancieshave occurred in seasonal aspects of climate change. The spatial downscaling of predicted changes in precipitation projected thatthe changes are varying throughout the months and regions, probably further increasing the severity and the areas already plaguedby floods and droughts. The second section of the paper assesses the potential and constraints of seasonal forecasting as a meansto alleviate losses in rice production. Drought is a major production constraint in rainfed rice, so that forecasts on drought occurrencecan be used to alleviate losses. In a broader sense, short-term and long-term climate projections could be a key for achieving rising productivity in unfavorable rice environments.Kay Sumfleth and Stephan M. Haefel
Agricultural residue gasification for low-cost, low-carbon decentralized power: an empirical case study in Cambodia
No full textAbstract not availableJohn L. Field, Paul Tanger, Simon J. Shackley, Stephan M. Haefel
A survey: potential impact of genetically modified maize tolerant to drought or resistant to stem borers in Uganda
No full textMaize production in Uganda is constrained by various factors, but especially drought and stem borers contribute to significant yield losses. Genetically modified (GM) maize with increased drought tolerance and/or Bt insect resistance (producing the Bacillus thuringiensis Cry protein) is considered as an option. For an ex ante impact analysis of these technologies, a farmer survey was carried out in nine districts of Uganda, representing the major farming systems. The results showed that farmers did rate stem borer and drought as the main constraints for maize farming. Most farmers indicated a positive attitude towards GM maize, and 86% of all farmers said they would grow GM maize. Farmer estimated yield losses to drought and stem borer damage were on average 54.7% and 23.5%, respectively, if stress occurred. Taking the stress frequency into consideration (67% for both), estimated yield losses were 36.5% and 15.6% for drought and stem borer, respectively. According to the ex-ante partial budget analysis, Bt hybrid maize could be profitable, with an average value/cost ratio of 2.1. Drought tolerant hybrid maize had lower returns and a value/cost ratio of 1.5. Negative returns occurred mainly for farmers with non-stressed grain yields below 2 t·ha−1. The regulatory framework in Uganda needs to be finalized with consideration of strengthening key institutions in the maize sector for sustainable introduction of GM maize.Isaac M. Wamatsembe, Godfrey Asea and Stephan M. Haefel
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