In continuously-flooded paddies, the small, fast-growing aquatic plant duckweed ( Lemna minor L.) considered to compete with rice for nitrogen, thereby having a negative impact on early rice growth. While duckweed overpopulation was known can be effectively overcome through field water management, the influence of such management on the N fate and its use efficiency in rice-duckweed systems is poorly documented. Accordingly, a three-year (2020-2022) field experiment was conducted to examine the combined impact on rice yield, as well as N loss and utilization, of two water management approaches (flood irrigation, FI vs . alternate wetting and drying irrigation, AWD), factorially combined with two rice production systems (rice-duckweed, +D, vs. duckweed-free rice, -D). In AWD+D fields, the density of duckweed generally remained below 250 g m( - 2) (about 85 % coverage), whereas in FI+D fields it reached 100 % coverage (300 g m - 2 ) within 5 days after transplanting, with individual duckweeds overlapping one another. Following AWD irrigation, duckweed performed as a nitrogen cache, akin to a split fertilizer application, with the first of several splits occurring at the rice crop's early tillering stage. Within the first 2 days of a specific wet -dry cycle, duckweed can store 0.5-1.5 g N m( - 2) , and then, within a further 3 days, release 0.3-1.0 g N m( - 2) . In contrast, in FI+D paddies, this caching function occurred once under midseason drainage, with further N being stored in the duckweeds during the remaining rice production season. As a result, at harvest the 0-0.10 m soil layer's N level increased significantly ( p <0.05) in both FI+D (8.5-16.8 %) and AWD+D (14.9-20.8 %) compared to FI-D and AWD-D, respectively. Due to the coverage and storage -release function of duckweed, apparent N loss decreased in rice-duckweed system by 1.4-12.5 % in the FI field and 22.1-31.3 % in the AWD field compared to their respective duckweed-free systems. In FI fields, except for a 10 % relative reduction in nitrogen recovery efficiency (NRE) in 2020, duckweed didn't significantly affect rice yield or NRE. The yield reduction (3.5-6.7 %) and the NRE increase (0.8-7.4 %) under AWD-D ( vs . FI-D) was, in the presence of duckweed, compensated for and overrun, resulting in a greater yield (5.3-6.7 %) and NRE (5.4-28.9 %) in the AWD+D vs. AWD-D field. When duckweed was present, AWD irrigation improved the by-path nitrogen cycling through duckweed, making the AWD+D system more beneficial for rice cultivation and the agroecosystem's environment health. The AWD+D system offers a promising measure for building an efficient and sustainable rice-duckweed agroecosystem.

The increasing energy required to synthesize inorganic fertilizers warrants more sustainable soil amendments that produce comparable crop yields with less environmental damage. Duckweed, a prolific aquatic plant, can not only sequester carbon dioxide through photosynthesis, but also hyperaccumulate nutrients from its environment and upcycle them into valuable bioproducts. In this study, dried duckweed, grown on treated wastewater treatment plant effluent, was utilized as a fertilizer for a variety of crops (beet, tomato, kale, and sorghum). Comparative experiments examined the effect of duckweed, inorganic fertilizer, and a 40-60 mix of both on crop yield and nutrient fate in the plants, soil, and leachate. Comparable yields of beet, tomato, and sorghum were generated with duckweed and inorganic fertilizer. Duckweed significantly enhanced phosphorus (P) uptake in sorghum, exhibiting a P use efficiency level of 18.48%, while the mix treatment resulted in the highest P use efficiencies in beet and tomato. Duckweed-amended beet and kale systems also increased residual soil N (0.9% and 11.1%, respectively) and carbon (4.5% and 16.6%, respectively). Linear regression models developed using the data collected from all crops confirmed that duckweed can be used as a substitute for inorganic fertilizer without negative effects to food yield or nutritional quality.