What drives management decisions and grain yield variability in Mesoamerican maize cropping systems? Evidence from small-scale farmers in southern Mexico

Small-scale cropping systems face enormous challenges in obtaining efficient, stable and predictable responses to grain yields due to their great biophysical, management and socioeconomic complexity. In Mesoamerica, traditional managements have incorporated modern agricultural practices; however, the efficacy of these tools on grain yield and systems´ sustainability is unknown. We explored biophysical, agronomic and socioeconomic drivers determining the maize cropping system and grain yield in Southern Mexico. The specific objectives were i) to investigate the effects of geopedologic soil characteristics on maize grain yield, ii) characterise tropical maize cropping systems and model how agronomic factors determine grain yield variability and iii) identify underlying socioeconomic drivers, which determine the agronomic ones and, consequently, the maize cropping systems. On-field interviews and soil data from geopedologic unit maps from maize cropping systems in a Mesoamerican region, Chiapas, Mexico, were used. Structural equation modelling (SEM) and quantitative and qualitative analyses were used to explore the data set. We found that cropping systems are differentiated into conventional (CS) and traditional (TS). Soils determined grain yield variability independently from the cropping systems. The most common agronomic inputs expected to positively impact grain yield were not effective in any cropping system. In CS, neither pesticides nor fertilisation determined the crop grain yield; plant density explained 72% of crop grain yield variation. In TS, grain yield was negatively related to plant density, while the fallow period slightly explained grain yield. We identified that cultural practices acquired by the farmers in their birthplace determine the type of the current maize cropping system. We highlight inconsistent modern agronomic management of the studied maize cropping systems where agrochemical inputs (fertilisers and pesticides) do not translate into higher grain yields or systems' sustainability. New theoretical models for small-scale maize cropping systems incorporating socioeconomic and cultural drivers might be necessary to predict better maize grain yield.