Person: Govaerts, B.
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Govaerts
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Govaerts, B.
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0000-0002-6109-7286 5 results
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- Nitrogen use efficiency and optimization of nitrogen fertilization in conservation agriculture(CIMMYT, 2014) Verhulst, N.; Francois, I.; Grahmann, K.; Cox, R.; Govaerts, B.The world population increases and diets change to include more meat. Since livestock mostly have a cerealbased diet, this means global cereal yields have to double by 2050 to meet the demands of the increasing population and dietary changes. Over the past 50 years, N fertilizer application has increased 20-fold, and its application is projected to increase to 180 million tons by 2030. Also, the N fertilizer prices have climbed more than 2.5-fold over the past decade. The use and efficiency of N fertilizers is very different for different types of environment: For high-input environments, an efficient and nonpolluting approach to mineral fertilizer use is essential to prevent excessive N fertilization. Excesses may cause NO3-N leaching which results in eutrophication (excessive plant growth or decay due to extra nutrients in the water) of water bodies and the destruction of water ecosystems. Over-application of N fertilizer also increases environmentally harmful NOx/N2O emissions. Worldwide, N use efficiency (NUE, see below) averages 33% in cereals, indicating substantial potential for improvement. In low yielding, rainfed environments where fertilizer use is marginal and cereal grain yields are low, the focus should be on yield and quality increase by moderate and efficient N fertilizer application rather than over-application. Small grain quality is mainly determined by grain N concentration. The higher the N concentration, the higher the farmers’ profits will be, on the condition that farmers are remunerated for higher quality, which is not always the case. Conservation agriculture (CA) has been proposed as a combination of management principles to improve water use efficiency, reduce soil erosion and conserve resources such as farmers’ time, labor and fossil fuels. It is based on three key components: (1) minimal soil movement, so less or no tillage operations (2) partial retention of residues of the crops as a soil cover (3) economically viable crop rotations. Conservation agriculture has been found to change physical, chemical and biological soil quality components compared to conventional practices involving tillage and thus affects N cycling in the soil (see also the material Conservation agriculture, improving soil quality for sustainable production systems?). Therefore, it is likely that N fertilization will have a different effect on the crops growing under CA-conditions and hence, the fertilization will have to be adjusted in CA-based cropping systems.
Publication - Evaluation of three field-based methods for quantifying soil carbon(Public Library of Science, 2013) Izaurralde, R.C.; Rice, C.; Wielopolski, L.; Ebinger, M.H.; Reeves III, J.B.; Thomson, A.; Harris, R.; Francis, B.; Mitra, S.; Rappaport, A.G.; Etchevers, J.D.; Sayre, K.D.; Govaerts, B.; Mccarty, G.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 Maíz y el Trigo (CIMMYT) at El Batán, 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.
Publication - Conservation agriculture toward sustainable and profitable farming(CIMMYT, 2005) Govaerts, B.; Sayre, K.D.Global agriculture faces major challenges. In large areas, soil erosion and the loss of fertility progressively reduce crop yields and can lead to land being abandoned and turning to desert. Households, industries, and growing urban areas compete with agriculture for increasingly scarce water supplies. Rising fuel and fertilizer prices hike up production costs. Conservation agriculture (CA) provides sustainable ways to address these and other challenges. CA crop management systems are based on three principles: (1) minimum soil movement (for example, no soil inversion by tillage), (2) a soil surface cover of crop residues and/or living plants, and (3) use of crop rotations to avoid build-ups of pests and diseases. The principles of CA appear to have wide adaptation, and CA systems are used for numerous crops in diverse soil types and environments. Nevertheless, the techniques to apply the principles depend heavily on local conditions: climate, soil characteristics, and farmer’s circumstances such as wealth, land size, the availability of labor or a tractor, to name several factors. Expected benefits from CA include: Reduced frequency/intensity of moisture stress: CA increases infiltration; cuts run-off and evaporation from the soil surface. Savings in irrigation water and energy for pumping. Reduced erosion. Higher, more stable crop yields. Reduced labor/tractor use for land preparation, saving fuel, cutting costs. Increased soil organic matter content, resulting in better soil structure, higher cation exchange capacity and nutrient availability, and greater water-holding capacity. Improved biological soil fertility and pest control.
Publication - The normalized difference vegetation index (NDVI) Greenseeker(TM) handheld sensor: toward the integrated evaluation of crop management part B - user guide(CIMMYT, 2010) Verhulst, N.; Govaerts, B.
Publication - The normalized difference vegetation index (NDVI) Greenseeker(TM) handheld sensor: toward the integrated evaluation of crop management part A: concepts and case studies(CIMMYT, 2010) Govaerts, B.; Verhulst, N.Reflectance is the ratio of energy that is reflected from an object to the energy incident on the object. Spectral reflectance of a crop differs considerably in the near infrared region (λ = 700-1300 nm) and in the visible red range (λ = 550-700 nm) of th
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