Modeling the contribution of ecological agriculture for climate change mitigation in cote d'Ivoire

The use of crop models is motivated by the prediction of crop production under climate change and for the evaluation of climate risk adaptation strategies. Therefore, in the present study the performance of DSSAT 4.6 was evaluated in a cropping system involving integrated soil fertility management options that are being promoted as ways of adapting agricultural systems to improve both crop yield and carbon sequestration on highly degraded soils encountered throughout middle Côte d’Ivoire. Experimental data encompassed two seasons in the Guinea savanna zone. Residues from the preceding vegetation were left to dry on plots like mulch on an experimental design that comprised the following treatments: (i) herbaceous savanna-maize, (ii)10 year-old of the shrub Chromolaena odorata fallow-maize (iii) 1 or 2 year-old Lalab pupureus stand-rotation, (iv) the legume L. pupureus -maize rotation; (v) continuous maize crop fertilized with urea; (vi) continuous maize crop fertilized with triple superphosphate; (vii) continuous maize crop, fertilized with both urea and triple superphosphate (TSP); (viii) continuous maize cultivation. The model’s sensitivity analysis was run to figure out how uncertainty of stable organic carbon (SOM3) can generate variation in the prediction of soil organic carbon (SOC) dynamics during the monitoring period of two years, within the first soil layer and to estimate the most suitable value. The observed variations were of 0.05 % in total SOC within the short-term and acceptable dynamics of changes were obtained for 0.80% of SOM3. The DSSAT model was calibrated using data from the 2007-2008 season and validated against independent data sets of yield of 2008-2009 to 2011-2012 cropping seasons. After the default values for SOM3 used in the model was substituted by the estimated one from sensitivity analysis, the model predicted average maize yields of 1 454 kg ha-1 across the sites versus an observed average value of 1 736 kg ha-1, R2 of 0.72 and RMSE of 597 kg ha-1. The impact of fallow residues and cropping sequence on maize yield was simulated and compared to conventional fertilizer and control data using historical climate scenarios over 12 years. Improving soil fertility through conservation agriculture cannot maintain grain yield in the same way as conventional urea inputs, although there is better yield stability against high climate variability according to our results

Conventional versus agro-ecological intensification: assessing the effect of conservation agriculture in maize cropping systems with the DSSAT model in Côte d’Ivoire (West Africa)

Integrated soil fertility management options are being promoted as ways of adapting agricultural systems to sustain yields on highly degraded and poor soils encountered throughout West Africa. The efficiency of these practices may be affected by high variability and uncertainty associated with seasonal rainfall, especially for areas such as Côte d’Ivoire, where intra-seasonal rainfall has been observed to change from 1 year to another. The DSSAT crop simulation model was used in this study as a tool to evaluate the impacts of soil improvement options including inorganic fertilizer and conservation agriculture generating higher carbon sequestration and crop yield in maize agro-ecosystems. The model was calibrated using agronomic data for three cropping seasons from 2009 to 2010 in Goulikao (Center-West Côte d’Ivoire) and Ahérémou 2 (Central Côte d’Ivoire), respectively and validated against independent datasets of yield of 2003–2004 seasons in the buffer zone of the Lamto Natural Reserve, Central Côte d’Ivoire. The model predicted average maize yields of 1454 kg ha−1 across the sites versus an observed average value of 1736 kg ha−1, R2 of 0.72, and RMSE of 597 kg ha−1 after the default values for stable soil organic matter fraction used in the model were substituted by the estimated one. For the validation, the predicted higher maize yield was consistently related to fallow biomass inputs and different rates of fertilizer, thus generating a RMSE of total aboveground biomass and grain yield of 606 kg ha−1 and 350 kg ha−1, respectively. The impact of fallow residues and cropping sequence on subsequent maize yield was simulated and compared with conventional fertilizer and control data using 12 years historic climate time series. We conclude that soil fertility improvements through conservation agriculture can sustain grain yield at the same level as conventional inputs of urea against larger climate variability. However, this system may be substituted by conventional agriculture when climate forecast reveals a dry cropping season year

Comparative study of earthworm communities, microbial biomass, and plant nutrient availability under 1-year Cajanus cajan (L.) Millsp and Lablab purpureus (L.) Sweet cultivations versus natural regrowths in a guinea savanna zone

In tropical savannas where soils are generally sandy and nutrient poor, organic farming associated with enhanced soil biological activity may result in increased nutrient availability. Therefore, legumes have been introduced in the humid savanna zone of Côte d’Ivoire, owing to their ability to fix atmospheric N and to continually supply soil with great quantity of organic materials in relatively short time. The main objective of this study was to assess the influence of two legume (Cajanus cajan and Lablab purpureus) cultivations on earthworm communities and P and N availability. Trials were carried out under farmers' field conditions; C. cajan was planted on savanna soils (trial 1) while L. purpureus was established on new Chromolaena odorata-dominated fallow soils (trial 2). Native vegetations were considered as controls. Changes in soil properties (earthworm abundance and diversity, microbial biomass carbon (MBC), and plant available P and N) were assessed using the biosequential sampling. After 1 year, both the legume stands showed a significantly higher density of earthworms, compared with the respective controls. This trend was linked to an increase in the abundance of the detritivores Dichogaster baeri Sciacchitano 1952 and Dichogaster saliens Beddard 1893, and the polyhumic Stuhlmannia zielae Omodeo 1963. Equally, legume had beneficial impacts on the average number of earthworm species, the Shannon–Weaver index of diversity and MBC in savanna (trial 1). Available P and ammonium significantly increased under both legume cultivations and were significantly and concurrently linked to litter quality and earthworm activities as shown by multiple regressions. As a result, legumes could improve nutrient availability in the sandy soils of central Côte d’Ivoire by positively affecting soil biological activity and this could bring farmers to cultivate crops on savanna lands

Comparative study of earthworm communities, microbial biomass, and plant nutrient availability under 1-year Cajanus cajan (L.) Millsp and Lablab purpureus (L.) Sweet cultivations versus natural regrowths in a guinea savanna zone

In tropical savannas where soils are generally sandy and nutrient poor, organic farming associated with enhanced soil biological activity may result in increased nutrient availability. Therefore, legumes have been introduced in the humid savanna zone of Cte d'Ivoire, owing to their ability to fix atmospheric N and to continually supply soil with great quantity of organic materials in relatively short time. The main objective of this study was to assess the influence of two legume (Cajanus cajan and Lablab purpureus) cultivations on earthworm communities and P and N availability. Trials were carried out under farmers' field conditions; C. cajan was planted on savanna soils (trial 1) while L. purpureus was established on new Chromolaena odorata-dominated fallow soils (trial 2). Native vegetations were considered as controls. Changes in soil properties (earthworm abundance and diversity, microbial biomass carbon (MBC), and plant available P and N) were assessed using the biosequential sampling. After 1 year, both the legume stands showed a significantly higher density of earthworms, compared with the respective controls. This trend was linked to an increase in the abundance of the detritivores Dichogaster baeri Sciacchitano 1952 and Dichogaster saliens Beddard 1893, and the polyhumic Stuhlmannia zielae Omodeo 1963. Equally, legume had beneficial impacts on the average number of earthworm species, the Shannon-Weaver index of diversity and MBC in savanna (trial 1). Available P and ammonium significantly increased under both legume cultivations and were significantly and concurrently linked to litter quality and earthworm activities as shown by multiple regressions. As a result, legumes could improve nutrient availability in the sandy soils of central Cte d'Ivoire by positively affecting soil biological activity and this could bring farmers to cultivate crops on savanna lands