Elemental homeostasis and soil microbiota of forage grasses under drought and irrigation

Aims Perennial forage systems in tropical regions are predominantly rainfed; however, increasing drought frequency associated with climate change has accelerated the adoption of irrigation. Selecting forage species capable of maintaining elemental balance and favorable plant-soil interactions is essential to sustain productivity. This study evaluated the drought tolerance of Mavuno and Zuri grasses under tropical field conditions, focusing on their responses to subsurface drip irrigation, plant carbon (C), nitrogen (N) and phosphorus (P) stoichiometry, and soil microbial dynamics. Methods A field experiment was conducted under rainfed and irrigated conditions, assessing forage biomass production, plant water status, leaf C, N, and P concentrations, and indicators of soil microbial activity and composition in rhizosphere and non-rhizosphere compartments. Results Under rainfed conditions, both grasses exhibited reductions in biomass production; however, Mavuno maintained greater elemental homeostasis and higher soil microbial activity, suggesting greater tolerance to seasonal water deficit. Irrigation restored plant water status, improved C:N:P ratios, and increased the abundance of key microbial groups, including sporulating bacteria, yeasts, and actinomycetes. Forage yield increased by approximately 10 Mg ha⁻¹ of dry matter under irrigation for both species. Under irrigated conditions, Zuri grass was associated with higher microbial biomass C and total soil organic C, indicating enhanced soil C inputs. Conclusion These findings demonstrate species-specific responses to water availability and show that irrigation modulates plant nutrient stoichiometry and soil microbial processes. The choice of forage species with stable elemental composition and favorable plant-soil interactions plays a key role in sustaining productivity.