Using the DSSAT Model to Support Decision Making Regarding Fertilizer Microdosing for Maize Production in the Sub-humid Region of Benin

Fertilizer microdosing is being widely promoted across sub-Saharan Africa, yet all recommendations regarding this technology are derived from short-term studies. Such studies are insufficient to properly assess the production risk caused by climatic variability. To address this issue while avoiding costly long-term experiments, a common and well accepted strategy is to combine results from short-term experiments with validated dynamic crop models. However, there have been few documented attempts so far to model fertilizer microdosing under sub-humid tropical conditions. The objective was therefore to evaluate the potential of the DSSAT model for simulating maize response to fertilizer microdosing, and to use the validated model to assess the effects of inter-annual rainfall variability on maize productivity and economic risk. The model was calibrated and validated against data from a 2-year on-station experiment (2014 and 2015) with 2 levels of hill-placed manure and five mineral fertilization options including broadcast and fertilizer microdosing. Model simulations were in good agreement with the observed grain and biomass yields for conventional broadcast fertilization, with relative RMSE and d-values of 12% and 0.96 for grain and 8% and 0.97 for biomass, respectively. For fertilizer microdosing, the N stress coefficient needed to be adjusted to avoid occurrence of large N stresses during simulation. After optimization, the model adequately reproduced grain yields for fertilizer microdosing, with relative RMSE of 10%. Considering the long-term scenario analysis, the use of the validated model showed that the application of 2 g of NPK15−15−15 fertilizer + 1 g urea per hill (equivalent to 23.8 kg N ha−1, 4.1 kg P ha−1 and 7.8 kg K ha−1) improved both the minimum guaranteed yield and the long-term average without increasing inter-annual variability and the economic risk compared to unfertilized plots. Even though combining microdosing with manure (1–3 t ha−1) was economically slightly riskier than microdosing alone, this risk remained low since a value-cost ratio of 2 could be achieved in almost 100% of the years. Furthermore, combined application consistently reduced the inter-annual yield variability. Considering this as well as the other benefits of manure for soil health, combining microdosing with small quantities of manure would be recommended to increase the sustainability of the system

Variability in maize yield and profitability following hill-placement of reduced mineral fertilizer and manure rates under smallholder farm conditions in northern Benin

Whereas the decision to promote a given agricultural intensification technology has hitherto been largely based on its average agronomic or economic performance, it is increasingly being recognized that the variability in the performance must also be taken into account in order to develop more meaningful and flexible recommendations. This is true in particular for microdose fertilization which is being actively promoted in sub-Saharan Africa as a means to increase crop productivity, profitability and fertilizer use efficiency. To this end, a total of 51 onfarm maize trials were carried out in northern Benin in 2014 and 2015. The performance of two microdose fertilization options (MD1=23.8 kg N, 4.1 kg P, and 7.8 kg K ha−1; MD2=33.1 kg N, 8.2 kg P, and 15.6 kg K ha−1) applied alone or combined with hill-placed manure (FYM) at 3 t ha−1 was compared to an unfertilized control and a broadcast fertilizer treatment at the recommended rate (RR; 76 kg N, 13.1 kg P, and 24.9 kg K ha−1). On average, microdose fertilization alone increased maize grain yields by 1145 kg ha−1 (+105%), compared to the unfertilized control (1096 kg ha−1). There was no significant difference in yields between MD1, MD2 and RR in both years. Combining microdose fertilization with manure further increased yields by 848 kg ha−1 (+40%) on average. There was a large variability in yields among farmers, from 420 to 1687 kg ha−1, 1419 to 3418 kg ha−1 and 1834 to 4475 kg ha−1 for the control, sole microdose (MD1 and MD2) and microdose+FYM treatments, respectively. Variability tended to be lowest in the control treatment. Absolute yield response to microdose fertilization tended to decrease with increasing yields in the control plots and was well explained by the combination of some measured soil parameters (clay and/or silt, total carbon, exch-Mg, pH) and weed pressure. Based on the value-cost ratio (VCR), the economic performance of the RR treatment was less than that of the microdose treatments (alone or combined with manure) despite the higher labor cost associated with the latter treatments. MD1 should be favored over MD2 because yields were not significantly different yet the risk of achieving low VCRs was lower in MD1. Despite the greater variability compared to the control, the risk of no return on investment was nearly nil for MD1 (6%) and MD1+FYM (2%) as a result of the strong increase in yield. Despite the overall good performance of fertilizer microdosing, more effort is needed to better understand crop response to microdose fertilization for a broader range of environmental conditions in Benin in order to fine tune recommendation domains

Using the DSSAT Model to Support Decision Making Regarding Fertilizer Microdosing for Maize Production in the Sub-humid Region of Benin

Fertilizer microdosing is being widely promoted across sub-Saharan Africa, yet all recommendations regarding this technology are derived from short-term studies. Such studies are insufficient to properly assess the production risk caused by climatic variability. To address this issue while avoiding costly long-term experiments, a common and well accepted strategy is to combine results from short-term experiments with validated dynamic crop models. However, there have been few documented attempts so far to model fertilizer microdosing under sub-humid tropical conditions. The objective was therefore to evaluate the potential of the DSSAT model for simulating maize response to fertilizer microdosing, and to use the validated model to assess the effects of inter-annual rainfall variability on maize productivity and economic risk. The model was calibrated and validated against data from a 2-year on-station experiment (2014 and 2015) with 2 levels of hill-placedmanure and fivemineral fertilization options including broadcast and fertilizer microdosing. Model simulations were in good agreement with the observed grain and biomass yields for conventional broadcast fertilization, with relative RMSE and d-values of 12% and 0.96 for grain and 8% and 0.97 for biomass, respectively. For fertilizer microdosing, the N stress coefficient needed to be adjusted to avoid occurrence of large N stresses during simulation. After optimization, the model adequately reproduced grain yields for fertilizer microdosing, with relative RMSE of 10%. Considering the long-term scenario analysis, the use of the validated model showed that the application of 2 g of NPK15−15−15 fertilizer + 1 g urea per hill (equivalent to 23.8 kg N ha−1, 4.1 kg P ha−1 and 7.8 kg K ha−1) improved both the minimum guaranteed yield and the long-term average without increasing inter-annual variability and the economic risk compared to unfertilized plots. Even though combining microdosing with manure (1–3 t ha−1) was economically slightly riskier than microdosing alone, this risk remained low since a value-cost ratio of Tovihoudji et al. Simulating Maize Response to Microdosing 2 could be achieved in almost 100% of the years. Furthermore, combined application consistently reduced the inter-annual yield variability. Considering this as well as the other benefits of manure for soil health, combining microdosing with small quantities of manure would be recommended to increase the sustainability of the system

Combining hill-placed manure and mineral fertilizer enhances maize productivity and profitability in northern Benin

Throughout much of Sub-Saharan Africa (SSA), maize production is characterized by low productivity due to the scarce availability and use of external inputs and recurrent droughts exacerbated by climate variability. Within the integrated soil fertility management (ISFM) framework, there is thus a need for optimizing the application of fertilizers and manure to better use the limited nutrient resources and increase crop yield and farmer income. An on-station experiment was conducted in Northern Benin over a 4-year period to evaluate the effect of hill placement of mineral fertilizer and manure on maize yields and soil chemical properties. The treatments consisted in the combination of three rates of manure (0 (NM), 3 (3M) and 6 (6M) Mg ha−1) and three levels of fertilizer (0% (NF), 50% (50F) and 100% (100F) of the rate recommended by extension (76 kg N + 13.1 kg P + 24.9 K ha−1)). On average across the fertilizer rates, hill-placement of manure significantly improved soil organic carbon content, available P and exchangeable K after 4 years by up to 124, 166 and 77%, respectively, compared to the initial values. As a result of the nutrient inputs and improved soil properties, yields increased steadily over time for all manure and fertilizer combinations. Value-cost ratios and benefit–cost ratios were >2 and generally as good or even better for treatments involving 50F compared to NF or 100F. Although applying half the recommended rate of fertilizer without manure as currently done by many farmers appears to make economic sense, this practice is unlikely to be sustainable in the long term. Substituting 50F for 3M or complementing 50F with 3M are two possible strategies that are compatible with the precepts of ISFM and provide returns on investment at least as good as the current practice. However, this will require greater manure production, made possible in part by the increased stover yields, and access to means of transportation to deliver the manure to the fields

Evaluation of cover crop contributions to conservation agriculture in northern Benin

Context or problem: Conservation agriculture is a sustainable farming system designed to enhance agroecosystem productivity, adaptability, and the conservation of natural resources and biodiversity, while reducing production costs. In the context of northern Benin, understanding the role of cover crops in biomass production and soil improvement is crucial for promoting and adopting conservation agriculture practices. Objective or research question: This study aimed to contribute valuable insights into the growth performance and impact of 10 cover crop species in the Okpara and five in Angaradebou regions of northern Benin. Methods: The study employed a split-block design to assess cover crop growth during the rainy season of 2018. Plant density, height, aboveground biomass, and grain productivity were measured. In the subsequent season, the experimental setup was transformed into a strip-split plot design to evaluate how soil cover management, specifically mulched cover (M) or standing cover (L), influenced soil ground cover, water infiltration, soil moisture, and weed density. Results: The findings of the study indicated that Sesbania rostrata and Mucuna pruriens produced the tallest plants in the Okpara region, while Crotalaria juncea, Brachiaria ruziziensis, and Crotalaria retusa were the tallest in the Angaradebou region. Brachiaria ruziziensis, Crotalaria juncea, Crotalaria ochroleuca, and Sesbania rostrata exhibited the highest biomass production. In terms of yield components, Crotalaria ochroleuca and Crotalaria juncea performed well in seed production per pod, while Mucuna pruriens and Cajanus cajan had the highest seed weight. Regarding ground cover, Brachiaria ruziziensis demonstrated the highest performance, with 60% and 89% ground cover as mulch and standing cover, respectively, followed by Stylosanthes guianensis. Plots with better ground cover exhibited higher soil moisture retention (7–13%) and hydraulic conductivity (0.0015 cm² s−1 - 0.002 cm² s−1), as well as lower weed densities (55–69 weeds m−2). Stylosanthes guianensis and Sesbania rostrata showed the best soil moisture retention (11% and 13%, respectively), followed by Crotalaria juncea, Mucuna pruriens, and Brachiaria ruzisiensis (13%). Conclusions: The study highlighted the agronomic performance of 10 cover crops under conservation agriculture and their potential to positively impact soil physical properties and weed dynamics in northern Benin. Implications or significance: These cover crops have the potential to diversify cotton-based cropping systems in the region, thereby enhancing their sustainability. However, further investigation is needed to explore the effects of these cover crop species on intercrop combinations and crop and cover crop sequences under the specific agroecological conditions of northern Benin.</p

Hill-placement of manure and fertilizer for improving maize nutrient- and water-use efficiencies in the northern Benin

Optimizing the use of organic and mineral fertilizer in rain-fed maize production is crucial for sustainable food production in sub-Saharan Africa. This study investigates the effect of hill-placement of two nutrient sources (farmyard manure and synthetic fertilizer) on nutrient- and water-use efficiencies of maize crops i.e. recovery efficiency (NUEre), internal utilization efficiency (NUEie) and water use efficiency (WUE). A four-year trial was conducted in the tropical sub-humid zone of the northern Benin with a factorial combination of farmyard manure at three levels (0, 3 and 6 t ha−1, hereafter NM, 3M and 6M, respectively) and three levels of fertilizer [0% (NF), 50% (50F) and 100% (100F) of the recommended rate (76 kg N + 13.1 kg P + 24.9 kg K ha−1) by the national center for agricultural research. The NUEre decreased with increasing rate of manure and/or fertilizer, but the decreasing rate was lower under combined manure and fertilizer application. However, the NUEie increased with the increasing manure and fertilizer amounts. The WUE was significantly higher in 3M and 6M treatments than in NM treatment, and higher in 50F and in 100F than in NF treatments. The combination of 3000 kg ha−1 farmyard manure with half recommended fertilizer rate (100 kg ha−1) could be suggested as an optimal nutrient management practice for maize production in the Northern Benin. Future studies should target the other agro-ecological zones in Benin, and also consider other widely cultivated crops in the study area for reducing yield gaps and promote food security