Assessing the Impacts of Mulching on Vegetable Production Under Drip Irrigation in Burkina Faso

Abstract

Burkina Faso faces chronic food insecurity because of adverse agroclimatic conditions and significant soil degradation. Mulching, the practice of applying organic or synthetic materials to the soil surface, offers a promising avenue for enhancing agricultural production in this challenging agroecological setting. This study utilized the Sustainable Intensification Assessment Framework (SIAF) to evaluate the ecological, economic, and social impacts of mulching on vegetable production in Burkina Faso. Experimental and survey data collected from Sonsongona village in Bobo-Dioulasso were used to compare the production of mulched and non-mulched vegetables (tomato, cabbage, and onion) across the five SIAF domains. A calibrated AquaCrop crop model was also applied with 30-year historical weather data to simulate mulched and non-mulched cabbages for the study site. Our results reveal that mulching conserves soil moisture, suppresses weed growth, and enhances soil fertility, contributing to enhanced vegetable production and long-term sustainability. Economically, adopting mulching positively influences vegetable yields, reduces labor requirements, and increases income for smallholder farmers. These mulching benefits lead to community empowerment, particularly among women farmers. Our findings highlight the multifaceted benefits of mulching, suggesting that it holds promise for increasing agricultural productivity and improving economic stability, ecological sustainability, and social well-being in Burkina Faso. These insights contribute to developing context-specific strategies for sustainable intensification, with applicability across similar agroecological contexts in sub-Saharan Africa and beyond.

1. Introduction

Smallholder farming plays a crucial role in the agricultural production system, food security, and the economy of Burkina Faso. Previously reported statistics indicate that agriculture accounts for more than 85% of employment opportunities and contributes more than 33% of the GDP in this country [1,2]. However, like many sub-Saharan African countries, agricultural production in Burkina Faso is threatened by climate change, land degradation, and population growth [1,3]. Several studies have projected climate change to significantly reduce crop yields, alter growing seasons, and increase severe weather events in sub-Saharan Africa [4]. Furthermore, climate change has been linked to the proliferation of pests and diseases, particularly in vegetable production systems [5]. In the Sahel region, where Burkina Faso is located, land degradation has also emerged as one of the significant environmental threats to agricultural production and food security [6]. Land degradation, mainly characterized by soil erosion, nutrient depletion, salinization, and reduced water availability, has diminished agricultural land in sub-Saharan Africa by about 16%, resulting in significant yield reductions, particularly in vegetable and grain production for smallholder farmers [7]. Such yield reductions annually account for at least a 3% loss in the GDP of sub-Saharan African countries.

Potential strategies to improve the resilience of agricultural production systems to threats of climate change and land degradation in sub-Saharan African countries, particularly among smallholder farmers, have been proposed [8]. Mulching is one strategy that has been widely adopted and reported to have positive economic, social, and ecological impacts on crop production in arid regions [9]. Mulching, defined as the application of organic or synthetic materials to the soil surface to reduce crop water stress throughout the growing season, is particularly relevant in Burkina Faso, a country characterized by erratic rainfall, soil degradation, and resource constraints [9]. Furthermore, Kamga et al. [10] indicated that mulching was a widespread soil and water conservation strategy among smallholder farmers involved in vegetable production in Burkina Faso. Other studies have also supported the positive impacts of mulching in water-scarce regions, as it improves the retention of soil moisture, reduces the need for irrigation, and improves crop yields [11].

While the benefits of mulching, such as moisture conservation, weed suppression, and soil fertility enhancement, have been recognized in sub-Saharan Africa, the comprehensive evaluation of its impacts within the context of sustainable intensification on smallholder farms remains a critical research gap [12]. Kuyah et al. [12] defined sustainable intensification as producing more output from the same land area while reducing the negative environmental impacts and contributing to ecosystem services. The concept of sustainable intensification has gained prominence as a pivotal approach to address the need to double food and fiber production for the growing population in Africa while simultaneously protecting the environment [13,14]. According to Rahman et al. [15], sustainable intensification is now more holistic, adding human and social dimensions to the traditional focus of maximizing agronomic production and profits and ensuring environmental integrity. To reinforce the paradigm shift of evaluating sustainable intensification and provide a comprehensive understanding of sustainability, Musumba et al. [16] developed a sustainable intensification assessment framework (SIAF) for assessing the performance and sustainability potential of interventions in an agricultural production system. The SIAF measures the sustainability of a production system based on indicators from five domains: productivity, economic, environment, human, and social. A domain in the SIAF is a specific area of focus or a distinct category of evaluation that helps assess the sustainability and impact of agricultural intensification intervention or practice of interest. A few studies have applied the SIAF to several crops. For instance, Snapp et al. [13] applied the SIAF to assess the sustainability of a maize–legume cropping system in Malawi. Additionally, Rahman et al. [15] used the SIAF to evaluate the sustainable intensification of groundnut production in northern Ghana.

Limited studies in the literature have applied the current SIAF approach to investigate the sustainability of agricultural systems, particularly for smallholder farms [15]. Thus, this study applies the SIAF to investigate the diverse and interconnected impacts of mulching on vegetable production in Burkina Faso. By utilizing the SIAF framework, this study offers a comprehensive assessment of mulching as a sustainable intensification practice in the context of vegetable production in Burkina Faso. The findings are expected to provide valuable insights into the potential of mulching to enhance agricultural productivity, economic stability, and social well-being while concurrently advancing ecological sustainability. Ultimately, this research contributes to developing context-specific strategies for sustainable intensification that can be replicated and adapted in similar agroecological contexts across sub-Saharan Africa and beyond. Specifically, the main objective of this study was to evaluate the impact of mulching on vegetable production in Sonsongona village in Burkina Faso using the SI assessment framework and the AquaCrop model.

2. Materials and Methods

2.1. Study Area

The data were collected from a solar-powered drip irrigated experiment for vegetables conducted in Sonsongona village (Subarea in Bobo-Dioulasso city), located 20 km from Bobo-Dioulasso city in the Houet province, Burkina Faso (04°16′ W, 11°60′ N) (Figure 1).

2.2. Experimental Design and Data Collection

The experiment was set up as a randomized complete block design, as described in Millogo et al. [1]. Vegetables included in this study were onion (Violet De Galmi), tomato (Cobra), and cabbage (Oxylus). Each crop had two treatments (mulched and non-mulched). Each treatment was planted in a 16 m² plot and replicated four times. All the crops were transplanted to the plots. Onion plots included eight rows of seedlings with inter-row and in-row spacings of 30 cm and 15 cm, respectively. Tomato and cabbage plots had four rows with inter-row and in-row spacings of 60 cm and 45 cm, respectively. The mulching was about 10 cm thick, and the material was straw from the previous rice crop. The plots were irrigated every two days based on the water requirements calculated using the CropWat 8.0 software. Irrigation applications were measured using a flow meter. Measurement of vegetative growth parameters, including the height of the plants, was completed every fifteen (15) days after the date of transplanting. Weeds from each treatment were removed by hoeing and dried to determine their biomass weight. The time to complete different cultural operations for each treatment was also recorded.

2.3. Sustainable Intensification Framework

The Sustainable Intensification Assessment Framework (SIAF Toolkit) developed by the USAID Feed the Future Innovation Lab for Collaborative Research in Sustainable Intensification was used to compare the mulched and non-mulched cabbage, onions, and tomatoes at the study site. The details of the SIAF are described comprehensively in Musumba et al. [16]. Two indicators from each of the five domains in the SIAF framework were used for the assessments. The indicators were selected based on their relevance and the availability of data to assess the performance of mulching on vegetable production in Burkina Faso. The selection of indicators followed the guidelines for using the SIAF toolkit developed by Musumba et al. [16].

Table 1. Domains, selected indicators, and metrics used for the SI assessment.

Domain	Indicator	Metric	Units
Productivity	Yield	Yield cuts on-farm trials	kg/ha
Productivity	Crop Biomass Productivity	Plant height	cm
Economic	Profitability	Gross income	USD/ha
Economic	Labor Requirement	Labor requirement	hours/ha
Environmental	Pest Level	Weed biomass	kg/ha
Environmental	Water Availability	Irrigation water productivity	kg/m3
Human	Nutrition	Protein production	g/ha
Human	Food security	Food production	kCal/ha
Social	Gender Equality	Women who prefer the system	%
Social	Lack of Conflict	Probability of no conflict	probability

below details the five domains and the selected indicators for this study.

Radar charts were generated for the three vegetables to compare the mulched and non-mulched systems.

2.4. Weather Data

The area experiences a southern Sudanian climate with annual rainfall ranging between 800 and 1200 mm [1]. As highlighted by Jha et al. [17], weather data availability in sub-Saharan Africa is limited. For this study, daily weather data were obtained from the Prediction of Worldwide Energy Resource (POWER) Project of the National Aeronautics and Space Administration (NASA), produced by the NASA Langley Research Center. NASA-POWER provides data on a global grid with a spatial resolution of 0.5° latitude by 0.5° longitude (https://power.larc.nasa.gov/data-access-viewer/, accessed on 21 June 2023) [18]. To address the issue of data scarcity, several studies have used this gridded data for modeling crop yields with acceptable accuracy [17,19,20].

Table 2. The 30-year (1993–2022) average temperature and rainfall data for November–April at the study site.

Month	Tmin (°C)	Tmax (°C)	Rain (mm)
November	18.9	33.7	1.0
December	16.2	33.9	2.6
January	16.5	34.6	10.0
February	19.5	37.2	47.7
March	23.3	39.1	3.9
April	25.6	38.9	0.3

T_min is the minimum air temperature; T_max is the maximum air temperature.

presents long-term climatic parameters for the dry season months (November to April) at the experimental site obtained from NASA-POWER.

2.5. Soil Data

The experimental site has sandy loam and clayey soils at shallow and deeper depths, respectively [1]. For AquaCrop simulations, soil data were obtained from SoilGrids1km and HarvestChioce based on the location coordinates of the experimental site [21].

Table 3. Soil parameters at the experimental site.

Layer (m)	Water Content (m3 m−3)			Ksat (mm d−1)
	Sat.	FC	WP
0.00–0.20	0.40	0.27	0.16	135.6
0.20–0.30	0.41	0.30	0.18	91.2
0.30–0.60	0.41	0.31	0.20	69.6
0.60–1.00	0.41	0.31	0.20	69.6
1.00–2.00	0.41	0.30	0.19	84.4

presents the soil water content limits at saturation (Sat.), field capacity (FC), and wilting point (WP), as well as the saturated hydraulic conductivity (K_sat) for different soil layers at the experimental site.

2.6. AquaCrop Model and Application

The AquaCrop model version 7.1, developed by the Food and Agriculture Organization (FAO) was also used to simulate cabbage production under mulched and non-mulched scenarios. The AquaCrop model is a crop growth model that simulates crop yield in response to water supply, agronomic management, and environmental conditions [22]. The underlying principles and main algorithms in AquaCrop are presented in Steduto et al. [22] and Raes et al. [23], respectively. The crop grows in the model by developing a canopy and accumulating biomass (B) and yield in daily time steps [22]. Contrary to other crop modeling approaches that use the leaf area index, AquaCrop utilizes canopy cover (CC) as the most important crop parameter [22]. CC represents the source for actual transpiration (T_r) that is translated in a proportional amount to biomass (B) based on the concept of normalized water productivity (WP*) [22]. Water stress limits or delays the CC development through stress coefficients in the model. These coefficients describe the impact of water stress on canopy development and, ultimately, transpiration. T_r is simulated in the model by using the following equation:

$${\mathrm{T}}_{\mathrm{r}}={\mathrm{K}}_{\mathrm{S}}\left({\mathrm{K}}_{{\mathrm{C}}_{\mathrm{T}\mathrm{r},\mathrm{x}}}{\mathrm{C}\mathrm{C}}^{\mathrm{*}}\right){\mathrm{E}\mathrm{T}}_{\mathrm{o}}$$

(1)

where K_S is the stress coefficient, CC* is the canopy cover adjusted for micro-advective effects, Kc_Tr,x is the crop coefficient for maximum crop transpiration, and ET_o is the reference evapotranspiration.

Biomass is estimated as a product of WP* and the ratio of T_r and ET_o throughout the growing season, as presented by Equation (2) [22].

$$\mathrm{B}={\mathrm{W}\mathrm{P}}^{\mathrm{*}}\times \sum ({\displaystyle \frac{{\mathrm{T}}_{\mathrm{r}}}{{\mathrm{E}\mathrm{T}}_{\mathrm{o}}}})$$

(2)

Finally, the crop harvestable yield (Y) is estimated as a product of B and the harvest index (HI). HI is defined as the ratio of yield to aboveground dry biomass.

$$\mathrm{Y}=\mathrm{B}\times \mathrm{H}\mathrm{I}$$

(3)

Wellens et al. [2] evaluated the performance of the AquaCrop model in simulating cabbage production in the study area. Their results indicated that the model is very reliable for simulating cabbage. Therefore, using long-term historical data, the current study adopted the calibrated AquaCrop model to simulate mulched and non-mulched cabbage for the study area.

Table 4. Calibrated parameters used in the AquaCrop model for cabbage at Sonsongona, Burkina Faso, from Wellens et al. [2].

Parameter	Units	Value
Base temperature	°C	12
Cut-off temperature	°C	35
Canopy cover per seedling at 90% emergence	cm2	6
Canopy growth coefficient	% GDD−1	0.624
Canopy decline coefficient	% GDD−1	0.247
Sowing to emergence	GDD	12
Sowing to maximum canopy cover	GDD	1156
Maximum canopy cover	%	98
Maximum transpiration coefficient (KcTr,x)	unitless	1.10
Sowing to flowering	GDD	502
Length of flowering	GDD	709
Sowing to max rooting depth	GDD	956
Sowing to senescence	GDD	1601
Sowing to maturity	°C	1956
Normalized crop water productivity, WP*	g m−2	35
Canopy expansion function
P-upper	fraction of TAW	0.20
P-lower	fraction of TAW	0.70
Shape	unitless	0
Stomatal closure function
P-upper	unitless	0.75
Shape	unitless	3
Stomatal closure function
P-upper	unitless	0.7
Shape	unitless	3

presents the calibrated AquaCrop parameters for cabbage at Sonsongona (subarea in Bobo-Dioulasso city, Burkina Faso, adopted from Wellens et al. [2]).

The simulated cabbage yields were analyzed for the mulched and non-mulched scenarios over the application period using the analysis of variance (ANOVA) at a significance level of 0.05. Pairwise comparisons among the means were also conducted using Fisher’s least significant difference. The probability of exceedance (PE) for the simulated yield was also calculated by sorting all 30 years of simulated cabbage yield data in descending order at each scenario, following Masasi et al. [24].

3. Results and Discussion

The data for each SI indicator are presented and discussed for the three vegetables. The results are presented visually as radar charts to compare mulched and non-mulched vegetables across the five domains.

3.1. SI Radar Charts

The results are presented visually as radar charts to compare the mulched and non-mulched vegetables across the five domains of sustainable intensification. Two indicators from each domain were used for the assessments. The data showed similar radar charts across the cabbage, onion, and tomato vegetables shown in Figure 2.

3.1.1. Productivity

The productivity domain for the mulched and non-mulched vegetable plots was assessed based on fresh vegetable yield and plant height. The mean yield for mulched plots was 14,750 ± 736, 4188 ± 162, and 6875 ± 548 kg ha⁻¹ for cabbage, onion, and tomato, respectively. The mean yield for non-mulched plots was 8500 ± 736, 1750 ± 162, and 3975 ± 548 kg ha⁻¹ for cabbage, onion, and tomato, respectively. These results indicate a 42, 58, and 42% yield difference between the mulched and non-mulched cabbage, onion, and tomato, respectively. The results demonstrated that mulching positively influences both yield and crop biomass. Mulched vegetable plots showed higher yields compared to non-mulched plots. Similar data were reported by Millogo et al. [25], where mulched treatment showed a positive impact on soil moisture and maize yield. As noted by previous studies, the higher yields of mulched vegetables can be attributed to the moisture conservation properties of mulching, which enhances plant growth and development, particularly during the dry season [26,27,28]. According to Kosterna [27], improved soil moisture retention and reduced evaporation under mulched conditions contribute to a more favorable microenvironment for plants, increasing productivity. Plant height was also monitored for the three vegetables throughout the growing season. Thirty days after planting, the mean height was 8, 32, and 27% larger in mulched compared to non-mulched cabbage, onion, and tomato, respectively. These results are also in agreement with the studies by Ikeh et al. [29], Barche et al. [26], and Hudu et al. [28]. Barche et al. [26] attributed the increased plant height in mulched vegetables to the better availability of soil moisture and optimum soil temperature provided by the mulch.

3.1.2. Economic

Profitability and labor requirement indicators were evaluated for the economic domain. Gross incomes calculated based on the yield and prices at the time of the study were much higher in the mulched treatments for all three vegetables. This indicates that adopting mulching practices can enhance farm profitability for vegetable producers in Burkina Faso. These results agree with the study by Kamga et al. [10], who highlighted that soil and water management techniques, such as mulching in Burkina Faso, increased yields and crop biomass productivity, directly translating into higher revenues. Reducing labor requirements for labor-intensive activities, such as weeding in mulched plots, may further contribute to cost savings, improving farmers’ overall profitability. Additionally, reduced labor for weeding in mulched vegetables can free up farmers’ time and labor for other productive activities, contributing to improved livelihoods. Our results suggest that mulching can improve profitability in vegetable production, but more education and resources are needed to encourage its adoption in Burkina Faso. Furthermore, this study did not consider the cost of the mulching materials and other inputs, and this may be important to assess in future studies. However, the mulched plots are still likely to make more profit due to the higher crop yields. Moreover, most farmers use stover from the previous crops for mulching in smallholder farming systems.

3.1.3. Environmental

Pest level and water availability indicators were evaluated for the environmental domain. The pest level was assessed based on the weed biomass in the mulched and non-mulched plots. The average weed biomass for the three vegetables was 370 and 182 kg ha⁻¹ in the mulched and non-mulched plots, respectively. These results show that mulching effectively suppressed weed growth compared to the non-mulched vegetable plots. The physical barrier created by the straw mulch appeared to reduce weed emergence and competition for resources with vegetable crops. As a result, mulched plots exhibited more than 50% lower weed levels than non-mulched plots, which could have contributed to improved crop performance and higher yields. Awodoyin et al. [30] also demonstrated the effectiveness of mulching for weed control in tomato production in Nigeria. Their study reported weed control efficiencies of mulching above 91%. Awodoyin et al. [30] argued that the high weed control efficiencies in mulched vegetables help reduce herbicide usage and, thus, prevent environmental pollution.

Irrigation water productivity (IWP), defined as the yield produced per unit of irrigation water use, was used to assess the water availability indicator in this study [31]. The IWP values were 4.75, 1.90, and 2.59 kg m⁻³ for mulched cabbage, onion, and tomato, respectively. IWPs for non-mulched plots were 2.74, 0.80, and 1.50 kg m⁻³ for mulched cabbage, onion, and tomato, respectively. These results agree with other studies showing better soil moisture retention in mulched crop production and yield enhancement [32]. Mulching optimizes irrigation water use efficiency by reducing evaporation and improving water retention in the soil [27,33]. In water-scarce regions like Burkina Faso, efficient water use is critical for sustainable agriculture and food security [3,10,34].

3.1.4. Human

The human domain was evaluated by considering the nutrition and food security indicators: protein and calorie supply [35]. Both metrics were computed based on each vegetable’s yield and respective protein and calorie content in mulched and non-mulched plots. The protein and calorie production were 1.7, 2.4, and 1.7 times larger in mulched compared to non-mulched cabbages, onions, and tomatoes, respectively. These results show that the improved yields and crop productivity observed in mulched vegetable plots have essential food security and nutrition implications. Considering the Sahelian region of West Africa, particularly Burkina Faso, remains food insecure and malnourished [36], the increased vegetable production contributes to a diversified and nutritious diet for the farmers and local communities, enhancing food security and reducing malnutrition. Additionally, higher protein production from vegetable crops can address protein deficiencies and improve nutritional outcomes. Previous studies have also reported a positive effect of mulching on yield, quality of biomass, protein, and nutrient content in cabbage and other vegetables [37,38]. These studies attributed the positive effect of mulching to its ability to improve the soil’s microclimate (temperature and moisture) regime. They also argued that mulching improved the soil properties concerning available nutrients, organic carbon, and soil pH, enhancing the quality of the vegetables.

3.1.5. Social

Social equality and lack of conflict were selected for the social domain. Nkwake et al. [39] compared crop and soil management by gender in the Sahel region and found that women significantly utilize mulching compared to men. This might be explained by the reduced labor requirement in mulched plots discussed in previous sections, which has important implications for gender equality in agriculture. Women often shoulder a significant burden of agricultural labor, including weeding. By decreasing the need for manual weeding, mulching can alleviate the workload on women, providing them with more time for other productive activities and potentially empowering them within the agricultural sector. Women’s adoption of mulching may also be driven by other benefits of soil and water conservation, as seen in Burkina Faso and Kenya [10,40]. However, the stalks and straws from previous crops are also used as fodder for livestock, thus competing with their use as mulching in the fields [39]. Berre et al. [41] argued that even though mulching has a direct positive effect on crop productivity, it can lead to conflicts between private interests and communal use of resources, for example, the free grazing of crop residues. However, in this study, we argue that mulching enhances food security and economic stability for farming communities. Hence, adopting this practice can alleviate tensions and competition for agricultural resources, fostering a more harmonious and collaborative environment. For instance, women obtained financial benefits approximately six times the required investment per hectare in mulched plots in Burkina Faso [39]. When mulching is coupled with other agricultural water management practices, such as solar-powered drip systems, as in this case study, women are empowered to grow their crops on their small plots of land and decide what to do with the money earned from the vegetables [42].

3.2. AquaCrop Application—Long-Term Cabbage Yields

The long-term simulations showed less variability of the year-to-year cabbage yields for mulched and non-mulched scenarios (Figure 3), with coefficients of variation (CVs) of 8 and 7%, respectively. Since the same irrigation schedule was used for all thirty years, lower yields were simulated in dry years, as expected. For instance, both scenarios had their lowest cabbage yields in the year 2008, the year the crop received 43 mm of rainfall. Fresh cabbage yields ranged from 11.6 to 17.0 Mg ha⁻¹ for mulched and 6.9 to 9.6 Mg ha⁻¹ for non-mulched simulations. The mean simulated cabbage yields were 14.8 Mg ha⁻¹ for mulched and 8.5 Mg ha⁻¹ for non-mulched simulations. These mean simulated yields agree with the experimental yields at the study site by Millogo et al. [1].

In order to understand the effects of mulching on cabbage production, which in turn helps farmers set realistic yield goals in each season, the probability of exceedance (PE) of the simulated yields was calculated and plotted. PE indicates the probability or likelihood of exceeding a certain yield level in each given year in the future [24]. The analysis of the PE curves showed significantly larger simulated cabbage yields under mulched compared to the non-mulched scenario at all PE values, as expected (Figure 4). The expected yields determined at PE = 0.50 were 14.8 and 8.5 Mg ha⁻¹ for mulched and non-mulched simulations, respectively. These simulated yields agree with the results of the cabbage AquaCrop modeling study in India by Pawar et al. [43]. To better demonstrate the benefits of mulching in vegetable production in Burkina Faso, the cabbage yields expected every year (PE ≈ 0.99) were 11.6 and 6.9 Mg ha⁻¹ for mulched and non-mulched simulations, respectively. These results indicate that mulching can increase cabbage yields by approximately 1.7 times.

4. Conclusions

The results of this study demonstrate the numerous benefits of adopting sustainable agricultural practices. Mulching is a promising technique to enhance yields, crop biomass productivity, profitability, water productivity, and food security for smallholder farmers while reducing labor requirements and weed levels. Moreover, its potential to promote gender equality and mitigate conflicts further reinforces its importance in Burkina Faso’s agricultural development. These findings provide valuable guidance for policymakers, extension services, and farmers to support the widespread adoption of sustainable intensification practices in vegetable production, ultimately contributing to a more resilient and sustainable agricultural sector in Burkina Faso.