Aims Increasing the leaf silicification of cereal crops to ameliorate defenses against stresses and improve yield constitutes a major challenge in (sub-)tropical regions with highly desilicated soils.We tested the efficacy of different biochars -as readily available alternatives to commercial fertilizers -to increase leaf silicification and understand subsequent impacts of leaf traits that might benefit crops. MethodsWe compared the application of two biochars (rice-derived biochar with 198 g kg -1 of Si and cotton-derived biochar with 4 g kg -1 of Si) and wollastonite (240 g kg -1 of Si) at two application rates on the leaf silicification patterns and leaf traits of rice growing in pots containing highly desilicated soil (Ferric Lixisol) from Burkina Faso.Results Leaf Si increased from 19.0 to 70.4 g kg -1 with Si addition (control < cotton biochar < wollastonite < rice biochar), resulting in larger epidermal silica deposits. Leaf carbon (C), leaf mass per area (LMA) and leaf arc decreased and were negatively correlated with leaf Si, however, surprisingly, the leaf force to punch and the plant biomass decreased. ConclusionsWe demonstrate the effective use of rice biochar in desilicated environments to improve the Si status of cereal crops and their associated leaf traits. In particular, the decrease in LMA with rice biochar application shows a promising capacity of rice biochar to reduce rice leaf 2 C costs. In situ trials are now needed to investigate whether or not these beneficial effects may result in increased crop yields through resilience against environmental stresses.

RESUMELa baisse de la fertilité des sols agit fortement sur la productivité des cultures et par conséquent, le revenu des agriculteurs. L'utilisation des engrais minéraux permet d'améliorer la productivité des sols mais son accès reste limité aux petits producteurs. L'objectif de la présente étude est d'évaluer l'efficacité agronomique et économique de la microdose selon la toposéquence. Des tests ont été implantés suivant la toposéquence pendant deux ans et des enquêtes ont été menées auprès des ménages pour évaluer la rentabilité de la technologie. Effects of fertilizer microdosing on cowpea, millet and sorghum production as a function of the toposequence ABSTRACT The decline in soil fertility has a strong effect on crop productivity and, consequently, on farmers' incomes. The use of mineral fertilizers improves soil productivity, but access is limited to small-scale producers. The objective of this study was to evaluate the agronomic and economic efficiency of the microdose according to the toposequence. Tests were carried out following the toposequence during two cropping seasons and household surveys were conducted to assess the cost-effectiveness of the technology. NPK (14-23-14) fertilizer was applied on cowpea and sorghum at a rate of 2 g / pit and 3 g /pit for millet pocket (62.5 kg/ha). Urea was applied only on sorghum and millet respectively at a rate of 1 g/pit (31.25 kg/ha) and 1.5 g/pit (46.88 kg/ha). These treatments were compared with the recommended fertilizer rate and an absolute control. Microdose increased grain yields by 143%, 134%, and 155% respectively for sorghum, millet and cowpea compared with the control. Microdose was economically more profitable than the recommended fertilizer rate.

Agriculture in Burkina Faso relies on mineral fertilizers to reach decent crop production. Therefore, there is an urgent need to implement sustainable solutions that improve soil nutrient status while maintaining crop yields. Here we experiment with the recycling of nutrients through the production of biochar from cotton (Gossypium hirsutum L.) stalks and its mixing with compost to improve soil properties of highly weathered Lixisol. The trials included three treatments: conventional compost (COMP-100), co-composted biochar (COMPBI-100), each with recommended fertilization rates [cotton = 16.3 kg N ha -1 , 15.1 kg P ha -1 and 17.4 kg of K ha -1 ; maize (Zea mays L.) = 21.8 kg N ha -1 , 20.1 kg P ha -1 and 23.2 kg K ha -1 ], and co-composted biochar with 75% of recommended NPK fertilizer rate (COMPBI-75).We amended the soil with compost at conventional rates used in Burkina Faso, that is, 2.5 t ha -1 at each crop year (2018 and 2019). We measured the effect of the amendments on cotton and maize yield cropped in rotation using a randomized block design with four replicates for each of the studied treatments. Our results showed that the soil properties and crop yield in COMPBI-75 were not significantly lowered compared to COMPBI-100, which did not differ compared to soil and plant responses in COMP-100. Even not significant, COMPBI-100 and COMPBI-75 tend to have higher grain yields for cotton and maize. Our results highlight that co-composted biochar may be a promising amendment to increase crop productivity parameters in Burkina Faso while decreasing the NPK doses. The reduction of fertilizer rates can have essential implications considering the socio-economic and environmental advantages of reducing by quarter fertilizer doses in the Sudanese climatic region of Burkina Faso.Abbreviations: CEC, cation exchange capacity; COMP-100, conventional compost and 100% of recommended NPK fertilizer dose; COMPBI-75, co-composted biochar and 75% of recommended NPK fertilizer dose; COMPBI-100, co-composted biochar and 100% of recommended NPK fertilizer dose; C org , organic carbon; Ca tot , total calcium; DAS, days after sowing; K tot , total potassium; Mg tot , total magnesium; N tot , total nitrogen; Na tot , total sodium; P tot , total phosphorus.