Leaching Characteristics of Exogenous Cl in Rain-Fed Potato Fields and Residual Estimation Model Validation.

Potato ( L.) is a chlorine-sensitive crop. When soil Cl concentrations exceed optimal thresholds, the yield and quality of potatoes are limited. Consequently, chloride-containing fertilizers are rarely used in actual agricultural production. Therefore, two years of field experiments under natural rainfall regimes with three chlorine application levels (37.5 kg ha/20 mg kg, 75 kg ha/40 mg kg, and 112.5 kg ha/60 mg kg) were conducted to investigate the leaching characteristics of Cl in field soils with two typical textures for Northeast China (loam and sandy loam soils). In this study, the reliability of Cl residual estimation models across different soil types was evaluated, providing critical references for safe chlorine-containing fertilizer application in rain-fed potato production systems in Northeast China. The results indicated that the leaching efficiency of Cl was significantly positively correlated with both the rainfall amount and the chlorine application rate ( < 0.01). The Cl migration rate in sandy loam soil was significantly greater than that in loam soil. However, the influence of soil texture on the Cl leaching efficiency was only observed at lower rainfall levels. When the rainfall level exceeded 270 mm, the Cl content in all the soil layers became independent of the rainfall amount, soil texture, and chlorine application rate. Under rain-fed conditions, KCl application at 80-250 kg ha did not induce Cl accumulation in the primary potato root zone (15-30 cm), suggesting a low risk of toxicity. In loam soil, the safe application range for KCl was determined to be 115-164 kg ha, while in sandy loam soil, the safe KCl application range was 214-237 kg ha. Furthermore, a predictive model for estimating Cl residuals in loam and sandy loam soils was validated on the basis of rainfall amount, soil clay content, and chlorine application rate. The model validation results demonstrated an exceptional goodness-of-fit between the predicted and measured values, with R > 0.9 and NRMSE < 0.1, providing science-based recommendations for Cl-containing fertilizer application to chlorine-sensitive crops, supporting both agronomic performance and environmental sustainability in rain-fed systems.