Mitigating nitrate accumulation in potato tubers under optimum nitrogen fertilization with K-humate and calcium chloride

Producing safe food under excessive fertilization strategies is a serious issue; thus, this study introduced a novel approach combining K-humate and calcium chloride under nitrogen (N) fertilization for maximizing potato (Solanum tuberosum L.) yield and improving quality by reducing nitrate (NO3-) accumulation in tubers. A two-season field experiment during the 2017 and 2018 growing seasons was conducted in a farm field with a sandy loam texture. The experiment followed a modified Box-Behnken design with 13 treatments, which combined ammonium sulfate (N-AS), K-humate (KH) and calcium chloride (CC) alternately using their maximum rates (370 kg N ha(-1) for Z, 8.0 kg kH ha(-1) for X, and 1.20 kg Ca ha(-1) for Y) and subdividing. A three-level, three-variable central composite model (TCCM), integrated with regression modeling, was interpreted to illustrate the combined effects of AS, KH and CC on all the variables under investigation. The results indicated a remarkable increment in tuber yield and nitrate accumulation with the N-AS inputs, while KH and CC had minor impacts; however, the later decreased the nitrate concentration to some extent. The maximum soil N content (25 mg kg(-1)), tuber N content (18 g kg(-1)) and nitrate accumulation (450.5 mg kg(-1)), which exceeds the acceptable limit (200 mg kg(-1)) for human consumption, was recorded under the application of 370 kg N ha(-1) as the ammonium sulfate fertilizer with the conventional farming practices used. The response surface combined with regression models showed that the N rate (246 kg N ha(-1)), when combined with KH (1.33 kg ha(-1)) and CC (0.2 kg ha(-1)) representing T8 (66.6% N-AS + 16.6% KH + 16.6% CC), could reduce the NO3- content in tubers to an acceptable level (170 mg kg(-1)) and at the same time resulted in the highest tuber yield (58.8 Mg ha(-1)). The regression models accurately predicted the changes in nitrate accumulation in tubers, soil N and plant attributes under different N rates as related to KH and CC. Generally, when using these models under similar soil conditions worldwide, it can be concluded that using 222, 2.5, and 0.2 kg ha(-1) of ammonium sulfate, potassium humate, and calcium chloride, respectively, would achieve a proximal yield (56 Mg ha(-1)) while simultaneously decreasing nitrate accumulation in tubers to a very safe level (160 mg kg(-1)). (C) 2020 Published by Elsevier Ltd.