Closed-loop greenhouse irrigation and nutrient reuse in Shandong’s vegetable clusters, China

Greenhouse vegetables supply a large share of China's offseason produce but face converging constraints from groundwater depletion, nutrient surpluses, and declining soil quality. This study evaluates a closed-loop fertigation system that captures, treats, and reuses greenhouse drainage in major vegetable clusters of Shandong Province, with Shouguang as the representative hub. We integrate official open datasets on climate, cropping intensity, and water use with a two-season before-after panel across twenty grower greenhouses. The intervention combines recirculating irrigation, inline electrical conductivity control, sand and membrane filtration, ultraviolet disinfection, and blending rules to stabilize nutrient concentrations. Outcomes include irrigation water use, drainage nitrate nitrogen, phosphorus in filtrate, fruit yield, water productivity, and nutrient recovery efficiency. Comparative and dynamic analyses are supported by a circularity index that aggregates water and nutrient recovery with yield response. Over two seasons, the system reduced water withdrawals, curtailed nutrient losses, and increased yields while lowering fertilizer purchases, demonstrating a scalable pathway to resource-efficient protected horticulture.

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