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

Abstract

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).