Unravelling the causes of variability in crop yields and treatment responses for better tailoring of options for sustainable intensification in southern Mali

Abstract

Options that contribute to sustainable intensification offer an avenue to improve crop yields and farmers' livelihoods. However, insufficient knowledge on the performance of various options in the context of smallholder farm systems impedes local adaptation and adoption. Therefore, together with farmers in southern Mali we tested a range of options for sustainable intensification including intensification of cereal (maize and sorghum) and legume (groundnut, soyabean and cowpea) sole crops and cereallegume intercropping during three years on on-farm trials. There was huge variability among fields in crop yields of unamended control plots: maize yielded from 0.20 to 5.24 t ha −1 , sorghum from 0 to 3.53 t ha −1 , groundnut from 0.10 to 1.16 t ha −1 , soyabean from 0 to 2.48 t ha −1 and cowpea from 0 to 1.02 t ha −1. This variability was partly explained by (i) soil type and water holding capacity, (ii) previous crop, its management and the nutrient carry-over and (iii) inter-annual weather variability. Farmers recognized three soil types: gravelly soils, sandy soils and black soils. Yields were very poor on gravelly soils and two to three times greater (depending on the crop) on black soils. Yields were also poor at the end of the typical crop rotation, i.e., after sorghum and millet, and 1.3-1.7 times greater (depending on the crop) after the fertilized crops maize and cotton. We diagnosed a number of cases of technology failure where no improvement in yield was observed with hybrid varieties of maize and sorghum and rhizobial inoculation of soyabean. Regardless of soil type and previous crop, mineral fertilizer improved yields by 34-126% depending on the crop. Targeting options to a given soil type and/or place in the rotation enhanced their agronomic performance: (i) the biomass production of the cowpea fodder variety was doubled on black soils compared with gravelly soils, (ii) the additive maize/cowpea intercropping option after cotton or maize resulted in an average overall LER of 1.47, no maize grain penalty, and 1.38 t ha −1 more cowpea fodder production compared with sole maize. Soil type and position in the rotation, two indicators easy to assess by farmers and extension workers, allowed the identification of specific niches for enhanced agronomic performance of legume sole cropping and/or intercropping.

Trajectories of agricultural change in southern Mali

“…The statistical analysis confirmed farmers' perception and showed that (i) maize, soyabean and groundnut grain yields and maize partial Land Equivalent Ratio (pLER) in intercropping were higher after cotton and maize (the fertilised crops) compared with after sorghum or millet (the un-fertilised crops), (ii) sorghum and soyabean grain yields and cowpea fodder yields were greater on black soils compared with sandy and gravelly soils. Due to pest attacks, cowpea grain yields were not affected by soil type (see Falconnier et al (2016) for more detailed results). As a result, soil type and previous crop defined niches where diversification with legumes without extra input yielded best results (Figure 3).…”

“…Access to subsidised fertiliser for cotton and maize is guaranteed by the Compagnie Malienne pour le Développement des Textiles (CMDT), and the nutrients carried-over benefit the following crops (Falconnier et al, 2016;Ripoche et al, 2015). This carry-over is the backbone of the niches identified for maize/cowpea intercropping and soyabean production ( Figure 3) (Falconnier et al, 2016).…”

“…Access to subsidised fertiliser for cotton and maize is guaranteed by the Compagnie Malienne pour le Développement des Textiles (CMDT), and the nutrients carried-over benefit the following crops (Falconnier et al, 2016;Ripoche et al, 2015). This carry-over is the backbone of the niches identified for maize/cowpea intercropping and soyabean production ( Figure 3) (Falconnier et al, 2016). As the maintenance of a functional cotton sector is uncertain due to world price fluctuations (Coulibaly et al, 2015;Falconnier et al, 2015b), the viability of the farm reconfigurations depends on the development of sustainable alternatives.…”

“…In order to explain yield variability, a statistical analysis was carried out using linear mixed models with treatment, farmeridentified covariates and season as fixed factors and the trial as a blocking random factor. Treatments included fertilisation, intercropping pattern, variety and inoculation and farmer-identified covariates included soil type and previous crop in the rotation (a detailed description of the analysis is given in Falconnier et al (2016)). For further analysis in Step 3, yields were averaged per level of treatment/covariate in case of a significant effect and otherwise were averaged across the levels and covariates were used to define niches where diversification with legumes yielded best results.…”

“…Therefore, maize with current farmer practice was simulated as impacted by rainfall variability and ranged from 840 to 2290 kg ha -1 for HRE-LH, HRE and MRE farms (with a fertilizer application of 60 kg N ha -1 ) and from 790 to 1680 kg ha -1 for LRE farms (with a fertilizer application of 40 kg N ha -1 ) ( Table 2). For maize/cowpea intercropping, cowpea fodder production was assumed to equal 1.38 t DM/ha, independently of rainfall (Falconnier et al, 2016), and the simulated maize yield was multiplied by 1.08, i.e. the maize partial Land Equivalent Ratio for intercropping when cotton is the previous crop (Falconnier et al, 2016).…”