Eutrophication and ecosystem damage result from phosphate pollution. Competing ions make extracting trace phosphate under 2.0 mg/L from treated wastewater difficult. However, if the phosphate could be sustainably recovered or reused in agriculture, considerable savings in fertilizer could be made. On the other hand, agricultural waste, which is a menace, contains a significant amount of cellulose that finds interesting applications as a biodegradable material. This study synthesized a cellulose-based adsorbent with iron hydroxide nanoparticles from nano-fibrillated cellulose (CNF) from agricultural waste and carboxymethyl cellulose (CMC). It selectively removed phosphate from secondary treated wastewater. Fe(OH)3@CNF/CMC (FCC) removed 3 mg/g phosphate. The hydrogel-like material quickly absorbed 40 g/g of water and slowly released it for a week when dry. Soil burial test indicates microorganisms biodegraded 80 % of the hydrogel in 3 months. After these findings, we delivered plant nutrients using the phosphate-rich exhausted FCC adsorbent. Results showed that phosphate-rich FCC improved seed germination and plant growth. Phosphate-loaded FCC adsorbent promoted better plant growth than single super-phosphate and control samples. This study creates a circular economy-based slowrelease fertilizer from agricultural waste and secondary-treated wastewater. This approach uses the 3 R rule-recycle, recover, and reuse-to benefit society ecologically and economically.

Cropping systems depend on external nitrogen (N) to produce food. However, we lack metrics to account for society's fertilizer dependency, although excessive increases in N application damage human and environmental health. The objective of this study is to propose a novel indicator, N fertilizer dependency, calculated as the ratio between human-controllable external inputs and total N inputs. Nitrogen fertilizer dependency has a solid mathematical base being derived from closing the nitrogen use efficiency (NUE) equation. This study also tests the value of the N fertilizer dependency concept at the cropping system (plant-soil) scale and at different spatial scales, from field to country, as a complementary indicator to promote sustainable production. The field experiments conducted with grain cereals as a main crop showed that when replacing the barley precedent crop with a legume, N fertilizer dependency accounted for soil legacy and was reduced by 15% in fertilized treatments. In a farm population, N fertilizer dependency ranged from 47 to 95% and accounted for the relevance of biological fixation and irrigation water N inputs, adding pertinent information to performance indicators (i.e., NUE). At the country scale, N fertilizer dependency showed different temporal patterns, depending mainly on the relevance of biological atmospheric N fixation. Nitrogen fertilizer dependency of global cropping systems has risen to approximate to 83% in the last five decades, even though the N exchange among regions has increased. Nitrogen fertilizer dependency has great potential to monitor the achievements of efforts aiming to boost system autonomy, and within similar agricultural systems, it can be used to identify practices that lead to a reduction of fertilizer needs. In summary, N fertilizer dependency is a new indicator to evaluate the agroenvironmental sustainability of cropping systems across the scales and provides a complementary dimension to the traditional indicators such as NUE, N output, and N surplus.