Browsing by Author "Verhulst, N."

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  • Conservation agriculture and soil carbon sequestration: Between myth and farmer reality
    Govaerts, Bram; Verhulst, N.; Castellanos-Navarrete, A.; Sayre, Ken D.; Dixon, John; Dendooven, L. (Taylor & Francis, 2009)
    Improving food security, environmental preservation and enhancing livelihood should be the main targets of the innovators of today's farming systems. Conservation agriculture (CA), based on minimum tillage, crop residue retention, and crop rotations, has been proposed as an alternative system combining benefits for the farmer with advantages for the society. This paper reviews the potential impact of CA on C sequestration by synthesizing the knowledge of carbon and nitrogen cycling in agriculture; summarizing the influence of tillage, residue management, and crop rotation on soil organic carbon stocks; and compiling the existing case study information. To evaluate the C sequestration capacity of farming practices, their influence on emissions from farming activities should be considered together with their influence on soil C stocks. The largest contribution of CA to reducing emissions from farming activities is made by the reduction of tillage operations. The soil C case study results are not conclusive. In 7 of the 78 cases withheld, the soil C stock was lower in zero compared to conventional tillage, in 40 cases it was higher, and in 31 of the cases there was no significant difference. The mechanisms that govern the balance between increased or no sequestration after conversion to zero tillage are not clear, although some factors that play a role can be distinguished, e.g., root development and rhizodeposits, baseline soil C content, bulk density and porosity, climate, landscape position, and erosion/deposition history. Altering crop rotation can influence soil C stocks by changing quantity and quality of organic matter input. More research is needed, especially in the tropical areas where good quantitative information is lacking. However, even if C sequestration is questionable in some areas and cropping systems, CA remains an important technology that improves soil processes, controls soil erosion and reduces production cost. (CabAbstracts)
  • Conservation agriculture, improving soil quality for sustainable production systems?
    Verhulst, N.; Govaerts, Bram; Verachtert, E.; Castellanos-Navarrete, A.; Mezzalama, M.; Wall, P.; Chocobar, A.; Deckers, Jozef; Sayre, Ken D. (Boca Raton, FL: CRC Press, 2010)
    This chapter presents a detailed definition of conservation agriculture and its influence on soil quality. In a time when food security is becoming an increasingly important issue, the manner in which farmers manage their crops can have huge implications for crop productivity. Where conventional farming practices have always been used, it is evident that soil health is declining. Being aware of the physical, chemical, and biological aspects of soil quality can help researchers and developers maintain and improve soil quality and increase crop production.
  • The effect of tillage, crop rotation and residue management on maize and wheat growth and development evaluated with an optical sensor
    Verhulst, N.; Govaerts, Bram; Nelissen, V.; Sayre, Ken D.; Crossa, J.; Raes, D.; Deckers, Jozef (Elsevier B.V., 2011)
    Crop growth and development as well as yield are the result of the efficiency of the chosen agricultural management system within the boundaries of the agro-ecological environment. End-of-season yield results do not permit the evaluation of within-season management interactions with the production environment and do not allow for full understanding of the management practice applied. Crop growth and development were measured during the 2004, 2006 and 2008 crop cycles with an optical handheld NDVI sensor for all plots of the different management treatments of a long-term (since 1991) sustainability trial in the highlands of Mexico. Cropping systems varying in (1) tillage (conventional vs. zero tillage); (2) residue management (retention vs. removal); (3) rotation (monocropping vs. a maize [Zea mays L.]/wheat [Triticum aestivum L.] rotation) were compared. The NDVI-handheld sensor was evaluated as a tool to monitor crop growth and development and was found to be an excellent tool for this purpose. There was a strong relation between NDVI and biomass accumulation of maize and wheat. The measurement with the handheld sensor was non-destructive and fast so that a representative plot area could be measured easily and time-efficiently. Zero tillage induced different crop growth dynamics over time compared to conventional tillage. Zero tillage with residue retention is characterized by a slower initial crop growth, compensated for by an increased growth in the later stages, positively influencing final grain yield. Also crop rotation influenced early crop growth, with lower NDVI values for crops sown after wheat than crops after maize. Zero tillage with residue removal had low NDVI values throughout the growing season. Zero tillage with retention of crop residues results in time efficient use of resources, as opposed to conventional tillage, regardless of residue management, and zero tillage with residue removal. The results indicated that different tillage, rotation and residue management practices influence crop growth and development. It is important to monitor and understand crop growth under different management systems to select the right varieties and adjust timing and practice of input supply (fertilizer, irrigation etc.) in a holistic way in each cropping system. (CAB Abstract)
  • Using NDVI and soil quality analysis to assess influence of agronomic management on within-plot spatial variability and factors limiting production
    Verhulst, N.; Govaerts, Bram; Sayre, Ken D.; Deckers, Jozef; François, I. M.; Dendooven, L. (2008)
    This study uses remote sensing technology to map the spatial variability of crop performance within trial fields using conservation agriculture practices. Using zero tillage and residue removal, it is discovered that crop performance is unevenly distributed within the field with lower elevations offering higher performance. However, retaining soil cover allows for uniform distribution of crop performance. Subsequently, the article concludes that maintaining soil moisture is the most important element of the production system and recommends retention of cover for best performance throughout the field.
  • Wheat yield and tillage-straw management system × year interaction explained by climatic co-variables for an irrigated bed planting system in northwestern Mexico
    Verhulst, N.; Sayre, Ken D.; Vargas, M.; Crossa, J.; Deckers, Jozef; Raes, D.; Govaerts, Bram (Elsevier B.V., 2011)
    Wheat is an important food and income source and estimated demand for wheat in the developing world is projected to increase substantially. The objectives of this study were to gain insight into (i) the effect of tillage-straw system on yield and yield components (number of grains per meter squared and thousand kernel weight), (ii) the relation between climatic conditions and yield and yield components, (iii) the explanation of tillage-straw system × year interaction for yield and yield components by climatic co-variables. Wheat grain yield and yield components were measured in a long-term trial established in 1992 under irrigated, arid conditions in northwestern Mexico. Five tillage-straw management systems (conventionally tilled raised beds [CTB] with straw incorporated and permanent raised beds [PB] with straw burned, removed, partly retained or fully retained) were compared for a wheat-maize rotation. Daily climatic data were averaged over six periods corresponding approximately to advancing wheat growth stages. The PB-straw retained and PB-straw removed had the highest yields (average yield of 7.31 and 7.24 t ha-1, respectively) and grains per m2. The PB-straw burned had the lowest yield (average yield of 6.65 t ha-1) and grains per m2, but the highest thousand kernel weight. Maximum temperature was positively correlated to final grain yield during tillering and head differentiation, but was negatively correlated to thousand kernel weight during grain-filling. For the tillage-straw system year interaction, three groups of management systems were distinguished for yield and grains per m2: PB-straw burned, CTB-straw incorporated and PB where straw is not burned. The CTB-straw incorporated had a positive interaction with year in favorable years with high radiation and evapotranspiration. The PB-straw burned was relatively more affected by excess water conditions and showed positive interactions in years with high relative humidity. The PB-straw retained was the most stable in different climatic conditions, indicating that this management system could contribute to maintaining wheat yield in a changing climate scenario. (Cab Abstracts)