Effects of boron application rate on double-low rapeseed yield and quality

Objectives The main winter oilseed rape production areas in China are generally deficient in boron (B), which seriously affects rapeseed yield and quality. This study analyzed the effects of different borax application rates on the yield and quality of rapeseed.

Methods Field experiments were conducted in Chizhou of Anhui, Wanzhou of Chongqing, and Nanchang of Jiangxi from 2020 to 2021. The soil in the three experimental sites was B-deficient, and the tested rapeseed cultivars were low in erucic acid and sulfur glycosides. Four borax (B 10%) application rates were set up, including 0, 4.5, 9.0, and 13.5 kg/hm², and denoted as B0, B4.5, B9.0, and B13.5. The yield, seed boron concentration, main quality indexes, and fatty acid fractions of rapeseed were determined, and the correlations among the factors were analyzed.

Results Compared with B0, B13.5 recorded the highest yields in Chizhou, Wanzhou, and Nanchang, with 296, 818, and 715 kg/hm² increase, corresponding to 20.7%, 42.6% and 38.3%, respectively. However, the yields among the three B treatments were not (P>0.05) different. The yield increase was attributed to the increased pod number per plant and the seed number per pod. Compared with B0, B4.5, B9.0, and B13.5 (P<0.05) increased the pod number by 20.0%, 20.4%, and 35.0%; increased seed number per pod by 7.3%, 13.1%, and 11.1%, respectively. B13.5 treatment was recorded 30.5% higher harvest density in Nanchang, and B9.0 treatment was recorded 7.4% higher 1000-seed-weight in Wanzhou. All the B treatments (P<0.05) increased the oil, oleic, and linolenic acid contents in rapeseed, with a maximum increase of 10.3%, 15.8%, and 22.7%, respectively. Similarly, a maximum reduction of 19.4%, 36.1% and 14.1% in linoleic, palmitic, and stearic acid contents were recorded. The rapeseed protein content was increased by 19.1% in Nanchang, but the oil and protein yield (P<0.05) increased significantly, reaching a maximum of 53.4% and 53.2%, respectively. B application showed the risk of increasing erucic acid and sulfur glycosides. Compared to B0, B4.5 increased erucic acid and sulfur glycosides by 19.1% and −3.0% on average, while the increase by B13.5 were 57.3% and 35.8%. Nevertheless, the contents were within the designated thresholds by the national standards for edible rapeseed oil and forage cake meal for double-low rapeseed (13.5 kg/hm²). Boron application increased rapeseed B content, with the highest increase of 56.9%, 26.3%, and 33.8% in Wanzhou, Chizhou, and Nanchang, respectively. Rapeseed B content was (P<0.05) positively correlated with oil, protein, oleic, and linolenic acid and negatively correlated with linoleic and palmitic contents. Rapeseed B content indirectly increases the oil or protein yield by increasing yield and oil content.

Conclusions Boron application effectively enhances the yield of double-low oilseed rape by increasing the plant’s productivity. Further, it improves the quality and quantity of oilseed derived from the plant, which enhances protein yield. Considering the linoleic and palmitic acid risk, the recommended boron application rate is 4.5−9.0 kg/hm².