Optimal combination of potassium coupled with water and nitrogen for strawberry quality based on consumer-orientation

The quality of strawberry fruits is a key factor in consumer choice. This study investigated the effect of potassium coupled with water and nitrogen on multiple strawberry fruits quality categories over two growing seasons (from August 2021 to April 2022 and August 2022 to April 2023) in China, to aid in the determination of water and fertilizer decisions based on consumer-orientation. In particular, a composite quadratic orthogonal rotation design with three factors and five levels was adopted to characterize volume water content (W), nitrogen (N) and potassium (K). Twelve quality indicators at three harvest stages were measured respectively. The indicators related to commodity quality, flavor quality and nutritional quality of strawberry fruits were assigned weights based on consumer orientation using analytic hierarchy process. Total soluble solid was regarded as the most important quality indicator with the weight value of 0.1387, followed by single fruit weight (0.1183). All the quality indicators of strawberry fruits were systematically evaluated based on grey relational analysis, and the response model of the comprehensive quality to the combined application of W, N and K was established for each harvest stages. The response trends of consumer-oriented quality were shown as negative parabolas basically to W, N and K in all the three harvests, except a negative linear trend to W in the third harvest and an increased linear to K in the second harvest. Notably, the low level of K supply limited the quality of strawberries, regardless of the input amount of W and N. And the coded values of the optimal combinations for W, N and K were (−0.728, 0, 0.512), (−0.440, 0, 1.682) and (−1.682, 0, 0.834) for the three harvest stages, respectively. By weighting the comprehensive quality based on the corresponding yield of strawberry for the three harvest stages over the two study seasons, the optimal application interval of W, N and K for the entire growth period was determined as: 55.05–76.45%, 3.32 – 4.49 g N/plant and 4.06 – 5.47 g K2O/plant, respectively. The results of this experiment provide a theoretical basis for water and fertilizer management, as well as the in-depth research of strawberry.