This research used the participatory “Mother and Baby trials” approach (Snapp, 2002). It has two steps which are central (Mother) and on-farm (Baby) trials. The central trial is conducted in a village with a leader and innovative farmer or in a nearby research station. On-farm trials are farmers’ individual tests conducted by themselves under the research team’s supervision (Rusike et al., 2004; Gonsalves et al., 2005). Each farmer is a replication and linked to the central trial in order to compare a subset of innovations from the central trial (Snapp, 2002; Gonsalves et al., 2005). This approach allows farmers to evaluate the innovations that are most appropriate for their production system and resource endowment. It is an approach that initiates dialogue and collaboration between farmers, extension workers, policymakers, and researchers. In this way, rapid transformation and dissemination of the innovation are achieved through the snowball effect (Snapp, 2002).

In 2018 - 2019, prior to the start of the experiment, a baseline survey with 250 farmers in the same four communes was conducted on fodder production in crop-livestock systems. A reasoned and stratified sampling approach was used regarding these criteria: (i) farmers’ willingness to conduct food-feed trials on at least 0.1 ha, (ii) farm accessibility, (iii) a minimum of three sheep availability for fattening trials, and (iv) gender with at least 30% of women participation. Based on the results of this study, 30 farmers (20 men and 10 women) were selected for a second survey on the evaluation of their preferences for crop species, cultivars, cropping systems, and fodder conservation methods (Sanfo et al., 2020). Following the results of these surveys, the same 30 farmers were chosen for this participatory research on food-feed crop production based on improved cultivars of sorghum and cowpea in intercropping systems.

The choice of cultivars was done according to the farmers’ preferences (Sanfo et al., 2020) and included improved cultivars of sorghum (Sariaso16 and Ponta Negra) and cowpea (KVx745-11P and Tiligré). These cultivars were released by INERA (Institut de l’Environnement et de Recherches Agricoles) and EMBRAPA (Brazil) research. The INERA cultivars are the ones currently being promoted in Burkina Faso (Zampaligré et al., 2021). These cultivars are described in Table 2 (MRSI, 2014; Palé, 2017; Ramdé, 2019 ; Zampaligré et al., 2021).

The on-station trials were laid out as a completely randomized block design with eight treatments and four replications: two sorghum cultivars, two cowpea cultivars, and two cropping systems (monocultures versus intercropping). The size of each subplot was 35 m² (7 m x 5 m). Below are the treatments:

(T1) Sorghum Ponta Negra only; (T2) Sorghum Sariaso16 only; (T3) Cowpea Tiligré only;

(T4) Cowpea KVx745-11P only; (T5) Sorghum Ponta Negra intercropped with cowpea Tiligré;

(T6) Sorghum Ponta Negra intercropped with cowpea KVx745-11P;

(T7) Sorghum Sariaso16 intercropped with Cowpea Tiligré; and

(T8) Sorghum Sariaso16 intercropped with Cowpea KVx745-11P.

The on-farm trials involved 30 farmers with 0.1 ha as individual plot size. The farmers were all trained on farm agricultural practices and management on 14 and 15 June 2019 at Saria and Kokologo, respectively. Then, they were provided with seed, fertilizer, and pest control products by the research team. Trial implementation was facilitated by a team of extension workers (crop and livestock agents) under the supervision of the research team. Three treatments/options were selected from the on-station trial and tested by 10 farmers per treatment, each farmer representing a replicate for each option:

(T1) Sorghum Sariaso16 only;

(T4) Cowpea KVx745-11P only; and

(T8) Sorghum Sariaso16 intercropped with Cowpea KVx745-11P.

The study was done during two consecutive rainy seasons in 2019 and 2020 on-farm and on-station.

Grain yield (GY) was evaluated at sorghum panicle and cowpea pod maturity stages using the yield square method in 1m². Three yield squares were placed along the diagonal of each plot; sorghum panicles and cowpea pods were harvested separately and sun-dried for 10 days before being shelled/threshed and winnowed. The obtained grains were further sun-dried to constant weight and then weighed using a small scale (2 kg ± 5 g) to get grain yield for each crop. The fodder biomass was evaluated right after grain harvest (same day) using the same three yield squares. Fresh fodder weight in each square was taken using a 10 kg ± 10 g sensitive scale; a sample of 500 g from each square was collected and oven-dried at 105°C for 24 hours to determine fodder biomass on a dry matter basis (kg DM/ha).

Three (03) parameters were used to assess the intercropping efficiency: (i) Weed Control (WC) based on Weed Density (WD) and Weed Biomass (WB), (ii) Land Equivalent Ratio (LER), and (iii) System Productivity Index (SPI).

WD was assessed at 70-80 DAS using three (03) yield squares of 1m² in each plot along the diagonal and all weeds within the square were counted.

➢WB was evaluated using the same three yield squares and all the weeds in the square were collected and weighed. Then, samples were oven-dried at 105°C for 24 h. After dry matter determination, weed biomass was calculated by extrapolation (kg DM/ha).

➢LER is the relative land area under sole crops required to produce the yield achieved in intercropping and determined by the following formula (Wiley, 1979 in N’Goran et al., 2011):

Ya and Yb are the yields of sorghum and cowpea in intercropping, respectively. YA and YB are also the yields of sole cultures of sorghum and cowpea on a similar unit area, respectively.

SPI is the standardization of the yields of the secondary crop “b” into those of the main crop “a” in intercropping according to the formula (Agegnehu et al., 2008; Khan et al., 2020): =

Rs and Rc are the average yields of sorghum and cowpea in monoculture, respectively. Ys and Yc are also the average yields of sorghum and cowpea in intercropping, respectively.

The indexes WC, LER, and SPI were used to identify the relative advantages of intercropping, and their appropriate spatial arrangement is described in Table 3 .

Two composite samples of 500 g of the whole plant (stems + leaves) were taken in each plot replication from the three yield squares on the same day of fodder biomass and grain yield assessment. Samples were pre-dried and then shade-dried and ground at 1 mm size. The Near Infrared Spectrometry (NIRS) method was used for nutritive value analysis. Sample spectra were collected using the NIRS FOSS DS 2500 F and the International Livestock Research Institute (ILRI) Global Mixed Feed calibration was used to predict the nutritional quality. Nutritive value parameters assessed were: Dry Matter (DM), ash, Crude Protein (CP), Neutral Detergent Fiber (NDF), Acid Detergent Fiber (ADF), Acid Detergent Lignin (ADL), Metabolizable Energy (ME), and In Vitro Organic Matter Digestibility (IVOMD).

On-station (mother trial) data analysis of variance (ANOVA) showed that the cultivar effect was significant for fodder biomass, weed density, and biomass of cowpea, while it was only significant for grain yield and fodder biomass of sorghum ( Table 4 ). The cropping system effect was significant for grain yield and fodder biomass for cowpea and sorghum but was significant for only weed density and biomass for sorghum ( Table 4 ).

For the on-farm trial, only the cropping system effect was significant for sorghum grain yield and fodder biomass ( Table 4 ).

Low weed density (12 plants/m²) and low weed biomass (36.2 kg DM/ha) were obtained with cowpea KVx74511P in monoculture ( Table 5 ). In addition, regardless of sorghum cultivar, weed density and biomass were lower in the intercropping system than in monoculture except for Sariaso16 weed biomass in its intercropping with Tiligré ( Table 5 ).

Sorghum Sariaso16 had the greatest grain yield for the on-station trial (4415 kg/ha) and also had a high yield in the on-farm trials (3458 kg/ha) across two rainy seasons (2019 and 2020) ( Table 6 ). Ponte Negra had the highest fodder biomass yield (10051 kg DM/ha). For cowpea cultivars in the on-station trials, KVx745-11P and Tiligré had similar grain yield (2116-2169 kg/ha), while KVx745-11P fodder biomass (4721 kg DM/ha) was higher than Tiligré (3283 kg DM/ha). In the on-station trials, greater fodder biomass was obtained for monoculture of sorghum cultivars compared to intercropping with cowpea. This appeared to repeat for the on-farm trials but was not significant because of large farm-to-farm variability. For intercropping in the on-station trial, the fodder biomass of Ponte Negra was greater than for Sariaso16 regardless of cowpea cultivars used, but Sariaso16 had greater grain yield regardless of cowpea cultivars. For cowpea cultivars tested on-station, grain yield and fodder biomass were greater in monoculture than for intercropping. However, no significant differences were found between the two cultivars for grain yield and fodder biomass in intercropping.

LER and SPI were used to assess land use, grain yield, and fodder biomass efficiencies regarding cropping systems ( Table 7 ). Sorghum and cowpea intercropping LERs for fodder biomass (1.01-1.37) and grain yield (1.02-1.65) were greater than one. Sorghum Sariaso16 intercropped with cowpea Tiligré had the greatest LER for fodder biomass, while the highest LER was obtained for Ponta Negra intercropped with Tiligré for grain yield.

Intercropping SPIs were higher than those of the corresponding sorghum cultivar (main crop) monoculture evaluated. The highest SPI values for fodder biomass were obtained by Ponta Negra intercropped with either cowpea cultivar (10539 and 12587). In terms of grain yield, Sariaso16 intercropped with cowpea had the highest index (4517 - 5438) regardless of the cowpea cultivar.

Sariaso16 had greater fodder DM, NDF, and ADL, and lower fodder ME and IVOMD compared to Ponta Negra regardless of the cropping system (monoculture and intercropping) and cowpea cultivar used in intercropping ( Table 8 ). Nevertheless, the two sorghum cultivars had similar CP (4.1 – 5.1%) concentrations regardless of the cropping system and cowpea cultivar used in intercropping. There were differences between the nutritive value of sorghum fodder in monoculture and intercropping. Sariaso16 intercropped with cowpea KVx745-11P had lower fodder ADF compared to Sariaso16 in monoculture. Ponta Negra intercropped with Tiligré had greater ME than in monoculture.

Cowpea fodder ME and IVOMD were lower in intercropping than their monoculture regardless of sorghum cultivar used for the intercropping. Cowpea Tiligré fodder ash, ADF, and ADL were greater in intercropping than in monoculture regardless of the companion sorghum cultivar in intercropping ( Table 9 ). Cowpea KVx745-11P intercropped with sorghum Sariaso16 had greater fodder CP than in monoculture, while Tiligré intercropped with Ponta Negra had lower CP compared to monoculture. For cowpea cultivars, KVx745-11P had greater ash (10.6-12.5%) and CP (17-20%) regardless of the cropping system.

Cowpea and sorghum intercropping reduced weed density and biomass compared to sorghum monocultures. KVx745-11P was the most effective cowpea cultivar to improve weed control. Cowpea Tiligré was less effective, possibly because it is a semi-erect plant that also exhibits defoliation in the later stages of the reproductive period. This cultivar may be more sensitive to dry spells explaining the loss of leaves unfavorable to the process of smothering weeds (Ekeleme et al., 2019). Both sorghum cultivars were effective in controlling weeds, but Ponta Negra was somewhat more effective in relation to its great capacity to produce aerial biomass with large and long leaves that could play the role of smothering weeds. Allelopathy associated with competition for light, water, and mineral elements would influence weed photosynthesis, inducing a decrease in their growth (Kruk et al., 2006; Cordeau et al., 2015). Crop shading also creates unfavorable conditions for weed seed germination (Barro et al., 2016; Benider, 2018). Other authors also showed that cowpea intercropping with sorghum or maize reduced weed density and biomass compared to cereal monocultures and manual weeding (Bybee and Ryan, 2018; Ekeleme et al., 2019). Better weed control would lead to increased grain yield and fodder biomass and save time for plot weeding (Odhinambo and Ariga, 2001; Muhammad et al., 2013). Intercropping could therefore be an acceptable biological weed control approach in cropping systems instead of using chemical weed management strategies.

Sorghum Sariaso16, being a genetically improved grain type, had the greatest grain yield as expected. By comparison, Ponta Negra being a forage-type sorghum had the greatest fodder biomass. Those cultivars were selected as the best bet for this experiment based on prior research in Burkina Faso (Zampaligré et al., 2021). For cowpea, KVx745-11P and Tiligré had similar grain yield, while KVx745-11P fodder biomass was greater than for Tiligré, which is consistent with its spreading vegetative growth habit (Ramdé, 2019). The results are influenced by the combined effect of genetic, agro-climatic factors and various steps of crop management (Coulibaly et al., 2012; Alidu et al., 2013; Coulibaly et al., 2020; Ouédraogo et al., 2021). Some authors identified Sariaso16 and Ponta Negra as the best cultivars performing well in the North Sudan zone of Burkina Faso respectively for grain yield and fodder biomass even though yields were lower compared to the results presented in this study (Zampaligré et al., 2021).

These results highlight that the choice of cultivar by farmers would depend on their primary production objective (grain or biomass). Sariaso16 and cowpea KVx745-11P cultivars were locally developed at Saria (North Sudan zone of Burkina Faso) by INERA for food and food-feed purposes, respectively, even though Sariaso16 has acceptable fodder biomass (Kondombo, 2001; Palé, 2017; Zampaligré et al., 2021). Sorghum Ponta Negra (EMBRAPA-Brazil) and cowpea Tiligré (INERA) cultivars were released for fodder production and grain purposes, respectively, with more or less intermediate performances for food (Palé, 2017; Zampaligré et al., 2021).

This study was performed in the 2019 and 2020 cropping seasons which were wet years (rainfall deviating from the 1990-2020 series) ( Figure 3 ). The genetic effect and pedo-climatic conditions influenced crop cultivar performance. Indeed, water and soil fertility which were the most limiting factors of crop production affected crop genetic potential (Alidu et al., 2013; Lalsaga and Drabo, 2017). Greater grain yield and fodder biomass were associated with rainy years, moderate temperatures, and normal rainfall distributions with better soil fertility conditions (Ishiyaku and Aliyu, 2013; Kihindo et al., 2015; Obulbiga et al., 2015). Hence, location-specific characteristics and production objectives were important in cultivar selection and recommendation (Zampaligré et al, 2021).

Sorghum and cowpea intercropping LERs for fodder biomass and grain yield were usually greater than one. This showed an advantage in terms of total production for intercropping. The capacity production of one sorghum stand grown with cowpea was higher than the one of sorghum or cowpea stands grown in monoculture. Thus, sorghum and cowpea intercropping would save 1 to 65% of land use for the overall production (grain and biomass) compared to the monoculture of each crop. This would lead to an increase in grain yield and fodder biomass in the same order of magnitude (Obulbiga et al., 2015; Akanza & N’guessan, 2017; Diatta et al., 2019). The SPI values for sorghum-cowpea intercropping were also higher than those of the corresponding sorghum monocultures in the intercropping (main crop). Then, the conversion of grain yield and fodder biomass of the secondary crop (cowpea) to the main crop (sorghum) in the intercropping are all higher than those of the corresponding sorghum monocultures. The best fodder biomass indexes (10539 and 12587) were obtained by the intercropping of Ponta Negra and KVx745-11P, respectively; Ponta Negra and Tiligré. For grain yield, the best values of SPI (4517 and 4883) are recorded respectively by the intercropping of Sariaso16 and KVx745-11P; Sariaso16 and Tiligré. These results showed the advantages of grain yield and fodder biomass production with sorghum-cowpea intercropping and were corroborated by other authors (Agegnehu et al., 2008; Khan et al., 2020). These comparative advantages can be explained by the beneficial relationships of complementarity between the two associated crops for the use of nitrogen resources, space (very different aerial architectures), and growth peaks (Justes et al., 2014; Barro et al., 2016; Louarn et al., 2016). Shifting the sowing date between the two associated crops reduces the interspecific competition (Mbaye et al. (2014). Indeed, the symbiotic fixation of atmospheric nitrogen by cowpeas limits its competition with sorghum, which uses mineral nitrogen in the soil. In addition, a greater interception of radiation and a reduction in weed incidence by intercropping could further explain these advantages (Muhammad et al., 2013). Sorghum and cowpea intercropping is a very efficient and appropriate cropping system to optimize fodder biomass production and grain yield for crop-livestock farmers.

Sorghum Sariaso16 fodder content of two anti-nutritional factors NDF and ADL was greater than those of Ponta Negra, implying a slightly better nutritive value for Ponta Negra. Sariaso16 and Ponta Negra both had similar CP regardless of the cropping system. The fodder of Ponta Negra had higher IVOMD than Sariaso16, regardless of the cropping system, confirming its higher nutritive value. In addition, fodder of sorghum Ponta Negra intercropped with Tiligré had greater ME content. For cowpea cultivars, KVx745-11P had the greatest content of ash and CP regardless of cropping systems. Intercropping also differentially affected cowpea fodder’s nutritive value for ash, ME, CP, and IVOMD. Finally, on-farm sorghum Sariaso16 and cowpea KVx745-fodder concentration in ash and ADF were greater than those on-station with the lowest content being ME. These results could be explained by the combined effect of genetic, agro-climatic factors and cropping systems (Cesar et al., 2009; Python and Boessinger, 2012; Mehdadi et al., 2013; Schlegel and Wyss, 2013; Louarn et al., 2016).

Cowpea KVx745-11P has better stay-green attributes at pod maturity with low leaf losses, resulting in greater CP content than many cultivars, which do not have these genetic characteristics (Obulbiga et al., 2015; Simian, 2017). Many cultivars of sorghum fodder showed variation of their CP content with ranges between 4.3 to 10.2%, (Simian, 2017; Zampaligré et al., 2021). This variability is mostly correlated to the harvest period; better CP concentration occurs during the heading phase and the CP begins to decline as the grains continue their maturation process (Simian, 2017). However, fodder cultivars such as Sariaso16 are more lignified with high concentrations of ADF and ash (Cesar et al., 2009). Some authors have shown that agro-ecological conditions and the duration time between fodder sample collection at farms and their pre-drying or drying would influence ash and crude cellulose content (Python and Boessinger, 2012; Mehdadi et al., 2013; Schlegel and Wyss, 2013). It has also been shown that cereal-legume intercropping would improve their total fodder quality in terms of protein and energy (Louarn et al., 2016). Sorghum fodder cultivars with CP concentration lower than 7% can be intercropped with cowpea in order to obtain an improved diet for livestock. Sorghum Ponta Negra intercropped with cowpea KVx745-11P would be the most appropriate cropping system for agro-pastoralists in Burkina Faso (livestock production as the main goal); whereas for crop-livestock farmers, it would be sorghum Sariaso16 intercropped with cowpea KVx745-11P (food production as the main goal).

For the extension of quality and quantity fodder production based on food-feed crops to meet human and livestock needs in Burkina Faso northern Sudan zone, we suggested emphasizing sorghum cultivar Ponta Negra and cowpea cultivar KVx745-11P intercropping and adoption of best fodder conservation technics in order to preserve fodder nutritive value for dry season utilization in Burkina Faso.