Management practices and species interactions drive yield increases through complementarity and selection effects in L. iberica–chickpea intercropping systems

Ensuring food security amid global population growth requires sustainable agricultural practices such as intercropping, which enhances resource efficiency and yield by cultivating multiple species together. This study assessed intercropping performance using key indices, including the Biodiversity Effect (BE), under three irrigation regimes—severe deficit irrigation (I S ), complete irrigation (I 20 ), and moderate deficit irrigation (I 40 )—as well as two sowing dates—autumn (S 1 ) and spring (S 2 )—and two cropping systems: sole system (Ss) versus 50:50 intercropping (Ic). The results showed that the Ic (I 20 S 1 ) treatment achieved maximum productivity, with a LER of 2.43, a monetary advantage index (MAI) of 6565.25, and total land output (TLO) of 3762.3 kg ha −1 . Complementary effects (CE)—driven by chickpea ( Cicer arietinum L.) deeper root system, nitrogen fixation, and spatiotemporal niche differentiation with L. iberica (Lallemantia iberica)—helped mitigate drought stress and improve resource-use efficiency. In the intercropping system, CE outweighed selection effects (SE), with intercropping benefits mainly attributed to CE, which strongly correlated with BE. Chickpea dominated the intercrop (competitive ratio: CRc > CRl), with its yield peaking under conditions of enhanced nitrogen availability through symbiotic fixation and facilitation. Meanwhile, I S S 2 conditions reduced sole system productivity by 45%, but intercropping remained resilient by leveraging nitrogen synergy and reducing intraspecific competition. Autumn sowing enhanced nitrogen uptake and economic returns (RVT: 5.97) by aligning with cooler temperatures and seasonal rainfall. However, the Ic (I S S 2 ) treatment resulted in economic losses (-26.3% TLO) and shifted species interactions towards competition, reducing LER by 45%. These findings highlight intercropping as a sustainable, low-input strategy under optimal irrigation and sowing conditions, offering critical insights for climate-resilient agriculture. Long-term adaptation strategies will be essential to maintaining these synergies amid increasing environmental challenges. • Full irrigation with autumn sowing (I 20 S 1 ) led to the highest yield and efficiency in intercropping. • Biodiversity benefits were mainly driven by complementary resource use, especially nitrogen fixation by chickpea. • Intercropping remained productive even under severe water deficit, unlike sole cropping which showed major yield loss. • Cooler temperatures and seasonal rainfall improved nitrogen uptake and revenue value. • Sustainable intercropping requires ongoing adjustment to climate variability and ecological dynamics.