Climate change is expected to intensify water stress even in historically overall water-abundant countries like Germany, where expanding irrigation depicts an effective adaptation strategy. Such path-dependent irrigation growth—here referred to as an irrigation trap—can lock farmers into high and potentially unsustainable water use, heightening trade-offs between food, water, and energy (FWE) sector policy objectives. However, no comprehensive assessment of future policy impacts and cross-sector trade-offs within the FWE nexus exists for Germany. This study evaluates six sectoral policies for their effects on the future irrigation demand of eight major field crops and related FWE indicators, using a hybrid modeling framework that links hydrological and machine learning models with a hydro-economic multi-agent system. Farmers’ adaptive decisions are simulated for each policy under four SSP–RCP scenarios until 2098. The policies show divergent effects on the FWE nexus. Water sector policies—such as abstraction limits and pricing—can curb the projected growth of irrigation demand by up to 61% until 2069-2098, with only marginal profit losses if implemented early. In contrast, bioenergy policies, while increasing farmer profits, can further raise irrigation demand and energy use up to fourfold. Drought compensation schemes weaken incentives to adapt to climate change, and irrigation efficiency subsidies do not deliver net water savings. Our ex-ante policy assessment under multiple SSP-RCP scenarios shows that unregulated and long-term irrigation expansion triggers increasingly steep trade-offs between FWE objectives. Avoiding this irrigation trap requires timely and coordinated cross-sector policies to balance competing demands under growing climatic and socioeconomic pressure.