Crop development based assessment framework for guiding the conjunctive use of fresh water and sewage water for cropping practice—A case study

• We proposed a crop-specified evaluation framework for managing sewage irrigation.
• The framework composes of crop nutrition diagnosis test and phytotoxicity bioassays.
• Sewage irrigation deriving phytotoxicity and nutrition input are evaluated simultaneously.
• Formulated fertilization and sewage dilution ratio are suggested by cropping stages.
• The framework was proved practically feasible with a case study.

Sewage dilution and formulated fertilization are cost-effective to avoid sewage-deriving phytotoxicity stress and excess fertilizer application in agricultural sewage irrigation practice. However, it is hard for us to fix the parameters of sewage dilution ratio (SDR) and fertilization formula exactly for the best management of sewage irrigation practice according to those published guidelines. This paper presented such an assessment framework. The assessment tools in the framework consist of four consecutive sewage irrigation experiments, which include germination test, seedling test and cropping test for assessing sewage-deriving phytotoxicity stress in different crop development stages, and DRIS test for diagnosing crop nutrient deficiency. The framework is further verified with crop kale (Brassica oleracea L. var. acephala D.C.) under different pre-set SDR values. The results of germination, seedling and cropping tests can significantly reflect the change of sewage-deriving phytotoxicity with both SDR gradient and crop development stages. Furthermore, the results of DRIS test show that sewage irrigation causes the deficiency of N and P nutrients relative to K nutrient in crop kale. Finally, according to these test results, SDR values and fertilization formula are optimized for guiding the conjunctive use of sewage and fresh water in cropping practice. The framework is thus a best management tool supplementary for those published guidelines to enhance the efficiency and feasibility of agricultural sewage reuse.

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