Nitrogen supply reduces the earthworm-silicon control on rice blast disease in a Ferralsol

Revealing belowground-aboveground relationships (BAR) is essential to drive ecological processes to address agriculture dysfunctions, especially in the management of aboveground plant diseases. Earthworms are one of the most important soil organisms involved in BAR, and silicon (Si) has been identified as a crucial element regulating aboveground plant health. How earthworm-Si interactions induce BAR in poor- and rich-nutrient soil contexts is still poorly understood, despite a growing interest in agricultural sustainability. We investigated the potential of BAR induced by the earthworm-silicon interaction to control the severity of rice blast disease in a Ferralsol in Madagascar, with or without NPK fertilization. We conducted a greenhouse microcosm experiment in which we manipulated the presence of the endogeic earthworm Pontoscolex corethrurus and the fungus Pyricularia oryzae in a Ferralsol supplied or not with Si and fertilized with macronutrients (nitrogen, phosphorus and potassium, i.e., NPK). After eight weeks of growth, plant biomass, nutrition and disease severity were measured. Our results validated the hypothesis that a dual treatment of earthworm inoculation and Si fertilization in a nutrient-poor tropical soil confers a higher tolerance of rainfed rice to P. oryzae, in comparison with treatments with only earthworms or Si, providing the optimal agronomic balance between a gain in biomass (and nutrition) and a reduction in disease severity. The supply of macronutrients altered this positive BAR by favouring the phenomenon of N-induced susceptibility. The aboveground plant C:N ratio of 15 is a threshold below which any increase in N per C unit likely enhances blast disease. The role of belowground interactions to counteract agricultural dysfunctions is supported by our study. To accomplish ecological intensification and provision of ecosystem services such as disease regulation, our findings recommend replacing excessive use of macronutrient fertilizer with sustained agricultural practices promoting the development of earthworm populations, such as organic matter inputs, superficial or no tillage, and the use of cover crops or conservation agriculture

Earthworm Functional Groups, Residue Quality and Management Impact on Upland Rice Growth and Yield – An Experimental Study in the Madagascar Highlands

International audienceAims: In Madagascar, agroecological practices to increase and sustain upland rice productivity are based on an intensification of soil ecological processes. Study Design: The effects of earthworm presence and identity (Pontoscolex corethrurus, Dichogaster saliens, or no earthworms), residue presence and identity [Crotalaria grahamiana (Fabaceae), Desmodium uncinatum (Fabaceae), Stylosanthes guianensis (Fabaceae), Eleusin

Earthworm Functional Groups, Residue Quality and Management Impact on Upland Rice Growth and Yield – An Experimental Study in the Madagascar Highlands

International audienceAims: In Madagascar, agroecological practices to increase and sustain upland rice productivity are based on an intensification of soil ecological processes. Study Design: The effects of earthworm presence and identity (Pontoscolex corethrurus, Dichogaster saliens, or no earthworms), residue presence and identity [Crotalaria grahamiana (Fabaceae), Desmodium uncinatum (Fabaceae), Stylosanthes guianensis (Fabaceae), Eleusin

Does rice breeding affect the ability of plants to interact with earthworms in nutrient-depleted Ferralsols?

International audienceAgroecology is based on the optimization of ecological processes occurring in agrosystems, especially by improving beneficial interactions among organisms. Recent studies have provided evidence that the ability of plants to interact with free-living soil organisms can be influenced by plant breeding. The upland rice breeding programme in the Highlands of Madagascar aims to develop cultivars that are adapted to local climatic, soil fertility and pest constraints. However, it is still unknown whether this genetic improvement alters rice cultivar abilities to interact with free-living soil plant-mutualistic organisms such as earthworms. We assessed in mesocosms the response of six upland rice cultivars commonly used by farmers in the Highlands of Madagascar to the presence of the endogeic earthworm Pontoscolex corethrurus. Plant nutrition and growth-related traits were measured after eight weeks of growth. These traits were significantly improved in the presence of P. corethrurus for all cultivars compared to the control treatment. However, the magnitudes of earthworm effects on plant traits were strongly variable and were dependent on specific rice cultivars. Agronomic and phylogenetic distance matrices were computed using agronomic data and available phylogenetic data of the rice cultivars. We did not detect significant correlations between cultivar responses to earthworm inoculation and agronomic or phylogenetic distances. Our results suggest that (i) the ability of rice to exploit beneficial interactions involving freeliving soil organisms is influenced by its genetic background, but (ii) the loss of earthworm-interactive abilities of rice crops is independent of the genetic distance among cultivars and breeders? agronomic criteria. Our findings are significant for attempts to use rice cultivars that optimize plant-soil interactions within agroecological practices and highlight the need to integrate free-living soil partners as life-long plant partners in future strategies for plant breeding

Development of a multi-criteria evaluation of agroecological practices involving soil biodiversity, agronomic performance and farmer perception

International audienceAn experiment has been designed in the Highlands of Madagascar withthe aim to produce multi-criteria indicators of performance ofagroecological practices. In this experiment, different traditionaland innovative practices were tested in field conditions with theassumption that practices that enhance soil biodiversity and soilecological processes are the one that best promote plant production,yield and sustainability. Both ecological and agronomic performanceswere confronted with socio-economic performance defined by farmers inorder to propose innovative practices adoptable by farmers.A 2-year field experiment with 16 different practices, replicated 4times, was designed in the Highlands of Madagascar with upland riceas the main crop. Many soil and plant parameters were measured: 73parameters to describe soil biodiversity and soil ecologicalprocesses, 19 descriptors to measure rice production, nutrition andyield, and 8 socio-economic descriptors.This study led to the production of a useful indicator allowing toevaluate an agroecological practice on the way it promotes soil healthand especially soil biodiversity, crop yield and socio-economicalrequirements which are the main limits for practice adoption. Wemeasured interesting relations between soil ecological descriptorsand agronomic descriptors