Effect of foliar spraying of organic and inorganic selenium fertilizers during different growth stages on selenium accumulation and speciation in rice

Aims Most crops are supplemented with selenium (Se) through the exogenous addition of inorganic Se fertilizer. There is a lack of in-depth research on organic Se fertilizers. Meanwhile, the dosage range between human Se deficiency and Se toxicity is narrow, so the Se content of agricultural products needs to be controlled within a reasonable interval. Methods Se accumulation and speciation in rice were analyzed and compared during three different growth stages (late tillering stage, initiate heading stage, and full heading stage) using three Se fertilizers: selenite, fermented Se, and potassium selenocyanoacetate (Se-AAF) via the foliar application. Results The Se content in rice sprayed with organic Se fertilizer was controlled in the relatively safe range and met the human Se supplement requirement compared to the sprayed sodium selenite, which was too high of a dose. The percentage of organic Se and protein Se in brown rice was found to be similar in all three Se fertilizers. The highest organic Se content of 91.57% was found in the grain of rice at the full heading stage by spraying Se-AAF. The main Se species in the grain was selenomethionine (SeMet), which reached 80% of the total Se. Se-methyl selenocysteine(SeMeCys) was found only in Se-AAF. The grain quality showed that all three Se fertilizers increased the consistency of gelatinization. Conclusions Appropriately delaying the spraying time and selecting organic Se fertilizer as the Se source can help to produce green and safe selenium-rich rice.