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Dossou-Yovo E.R.,University Of Cape Coast | Dossou-Yovo E.R.,University Abomey Calavi | Bruggemann N.,Julich Research Center | Ampofo E.,University Of Cape Coast | And 4 more authors.
Soil and Tillage Research | Year: 2016

Agricultural management practices are frequently non conservative and can lead to substantial loss of soil organic carbon and soil fertility, but for many regions in Africa the knowledge is very limited. To study the effect of local agricultural practices on soil organic carbon content and to explore effective ways to increase soil carbon storage, field experiments were conducted on an upland rice soil (Lixisol) in northern Benin in West Africa. The treatments comprised two tillage systems (no-tillage, and manual tillage), two rice straw managements (no rice straw, and rice straw mulch at 3 Mg ha-1) and three nitrogen fertilizer levels (no nitrogen, 60 kg ha-1, 120 kg ha-1). Phosphorus and potassium fertilizers were applied to be non-limiting at 40 kg P2O5 ha-1 and 40 kg K2O ha-1 per cropping season. Heterotrophic respiration was higher in manual tillage than no-tillage, and higher in mulched than in non-mulched treatments. Under the current management practices (manual tillage, with no residue and no nitrogen fertilization) in upland rice fields in northern Benin, the carbon added as aboveground biomass and root biomass was not enough to compensate for the loss of carbon from organic matter decomposition, rendering the upland rice fields as net sources of atmospheric CO2. With no-tillage, 3 Mg ha-1 of rice straw mulch and 60 kg N ha-1, the soil carbon balance was approximately zero. With no other changes in management practices, an increase in nitrogen level from 60 kg N ha-1 to 120 kg N ha-1 resulted in a positive soil carbon balance. Considering the high cost of inorganic nitrogen fertilizer and the potential risk of soil and air pollution often associated with intensive fertilizer use, implementation of no-tillage combined with application of 3 Mg ha-1 of rice straw mulch and 60 kg N ha-1 could be recommended to the smallholder farmers to compensate for the loss of carbon from organic matter decomposition in upland rice fields in northern Benin. © 2016 Elsevier B.V.

Eyshi Rezaei E.,University of Bonn | Webber H.,University of Bonn | Gaiser T.,University of Bonn | Naab J.,West African Science Service Center on Climate Change and Adapted Land Use Competence Center | Ewert F.,University of Bonn
European Journal of Agronomy | Year: 2014

Increased climate variability and higher mean temperatures are expected across many world regions, both of which will contribute to more frequent extreme high temperatures events. Empirical evidence increasingly shows that short episodes of high temperature experienced around flowering can have large negative impacts on cereal grain yields, a phenomenon increasingly referred to as heat stress. Crop models are currently the best tools available to investigate how crops will grow under future climatic conditions, though the need to include heat stress effects has been recognized only relatively recently. We reviewed literature on both how key crop physiological processes and the observed yields under production conditions are impacted by high temperatures occurring particularly in the flowering and grain filling phases for wheat, maize and rice. This state of the art in crop response to heat stress was then contrasted with generic approaches to simulate the impacts of high temperatures in crop growth models. We found that the observed impacts of heat stress on crop yield are the end result of the integration of many processes, not all of which will be affected by a “high temperature“ regime. This complexity confirms an important role for crop models in systematizing the effects of high temperatures on many processes under a range of environments and realizations of crop phenology. Four generic approaches to simulate high temperature impacts on yield were identified: (1) empirical reduction of final yield, (2) empirical reduction in daily increment in harvest index, (3) empirical reduction in grain number, and (4) semi-deterministic models of sink and source limitation. Consideration of canopy temperature is suggested as a promising approach to concurrently account for heat and drought stress, which are likely to occur simultaneously. Improving crop models' response to high temperature impacts on cereal yields will require experimental data representative of field production and should be designed to connect what is already known about physiological responses and observed yield impacts. © 2014 Elsevier B.V.

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