1. Introduction
Sesame (
Sesamum indicum L.), a popular health food, has been growing in Asia and Africa for over 7,500 years. Sesame seed contains oil (46–64%), protein (15–25%), carbohydrates (20–25%) and micronutrients. Nutritionally, sesame seeds are rich in oil with high levels of unsaturated fatty acids, mainly oleic and linoleic, protein, especially high levels of methionine, and micronutrients such as minerals, lignans, tocopherol and phytosterol; thus, sesame is known as the ‘queen of oilseeds’ [
1]. However, due to the pronounced antioxidant activity of its seed oil, sesame offers a high shelf life and is also known as the ‘seed of immortality’ [
1]. Owing to the high nutritional and therapeutic values, sesame is also used extensively in confectionaries and baked goods globally [
2]. In India, sesame is grown over an area of 1.85 million ha and 0.83 million tonnes of sesame grains are produced yearly with an average productivity of 474 kg ha
−1 [
3]. Since sesame yield is influenced by various physiological processes occurring in the plants, it can be further changed by management practices in a given environment [
4].
Inadequate management practices, along with intensive use of fertilizers, have resulted in an imbalance of micronutrients in the fertile regions of Northwest India [
5]. The insufficient availability of a particular essential micronutrient may alter plant growth and thus reduce crop yield [
6]. The essential role of micronutrients in crop productivity has been reported in the literature [
7]. Micronutrients are needed in small quantities by plants; these elements play a crucial role in plant development [
8]. Boron (B) is known as an essential micronutrient required for plant growth and its deficiency is the most globally widespread limit to crop production both quantitatively and qualitatively. It is well known for its role in pollen production and the viability of pollen tubes as well as their germination and growth. The limited supply of B is a major constraint in oil production and impairs its quality [
9]. It is also involved in the synthesis of lignin, which provides strength to the cell walls of biological membranes [
10].
Micronutrient enrichment of crops through agronomic biofortification (in soil or foliar) has been evidenced to ameliorate the adverse effects of micronutrient deficiencies and improve the yield and nutritional parameters of the crops [
11]. Foliar fertilization has gathered much attention in recent years due to the high water solubility of fertilizers. Foliar application is more effective when the absorption of nutrients in the roots is insufficient due to low soil moisture, and foliar fertilization is also a better option when the crop height is greater [
12]. Exogenous supply of nutrients through foliar facilitates a quick regain in a drought situation and also prevents nutrient losses in soil [
13].
The improved oil quality at a B concentration of 30 mg L
−1 has been reported. On the other hand, when using foliar B application at 20 mg L
−1 the maximum results for growth parameters including plant height, plant stem diameter and capsule length were recorded as compared to those of the control or those with treatment using a higher B concentration [
14]. In another report, the highest values of seed and stover yield were recorded using a treatment of 0.15% foliar spray of B in sesame due to fertility improvement and the translocation of photosynthates [
15]. Studies in the literature have demonstrated that the seed yield of sesamum can be increased with an increase in B levels [
16,
17]. For instance, a significant increase of 10.7% in seed yield of sesame has been recorded with 0.15% B application over the control under red laterite soils [
18]. There is also evidence that boron application can improve certain quality parameters of oilseed crops. Furthermore, the oil content of some sunflower cultivars has been found to increase with B application [
19]. In another study, the activity of several antioxidant enzymes in maize [
20] and soybeans [
21] have improved with B application. Thus, the present study was conducted to evaluate the effect of B on sesame yield, B uptake, certain oil quality parameters and the economics of sesame cultivation.
3. Results
3.1. Effect of B on Seed and Stover Yield of Sesame
In both study years, boron application showed a significant impact on seed and stover yield (
Table 3).
The highest increase of 26.75% in seed yield over the control in the two years was recorded in treatment T8 (706.6 kg ha−1) where B was applied at 30 mg L−1 at the flowering and capsule formation stages. The result of treatment T8 was statistically at par with treatments T4 (679.5 kg ha−1) and T7 (662.4 kg ha−1) where B was applied at 30 mg L−1 at the flowering stage and at 20 mg L−1 at the flowering and capsule formation stages, respectively. Likewise, an increase in stover yield was the highest when using treatment T4 (34.51%) as compared to the control. The stover yield of treatment T4 (4420.7 kg ha−1) was statistically at par with treatment T7 (4412.5 kg ha−1) and T8 (4293.5 kg ha−1). The seed and stover yield was associated with the rate of B application. Both the seed and stover yield initially increased with an increasing rate of B application up to 30 mg L−1, it then decreased with an increasing B application rate (T5 and T9). Thus, the results indicated that excessive B application lowered the yield of sesame. Overall, treatments T4, T7 and T8 showed significantly higher results in comparison to the control.
3.2. Effect of B on Its Uptake by Seed and Stover of Sesame
The results of the two-year study showed that B uptake in seed and stover of sesame increased significantly with B application at higher levels as compared to the untreated plants (
Table 4).
The mean of the two years’ worth of data demonstrated that the maximum increase in B uptake by seed (64.08%) and stover (70.07%) were recorded in treatment T8 and T4, respectively. The B uptake by seed in treatment T8 (205.40 g ha−1) was not statistically different from those of treatment T4 (192.94 g ha−1). Thus, B application at 30 mg L−1 applied at the flowering and capsule formation stages showed comparable results. The higher dose of B application (40 mg L−1) in T5 and T9 significantly reduced the B uptake in sesame (180.28 and 177.25 g ha−1, respectively). The water spray in treatment T2 and T6 at the flowering stage and at the flowering and capsule formation stages (131.49 and 133.50, respectively) did not show significant improvement in B uptake compared to the control (125.18 g ha−1). Similar results were observed in the stover of sesame for B uptake. The highest B uptake was recorded in T4 (1726.85 g ha−1), which was not statistically different from those of treatments T7, T8 and T9.
3.3. Effect of B on Certain Quality Parameters of Sesame
The data in
Table 5 revealed that the B application improved certain quality parameters of the sesame seed.
The mean of the two years’ worth of data demonstrated that the AOA of sesame seed recorded significant improvement with B application as compared to the control. The highest AOA was recorded in treatment T8 (69.41%), which was not statistically different from those of treatments T7 (68.65%) and T9 (68.89%). Thus, the rate of B application at similar growth stages did not affect the AOA as the variation observed in treatment T3, T4 and T5 were not significant. Water spray did not affect the AOA as treatments T2 and T6 did not show significant variation as compared to the control.
Boron application improved the TOC of sesame seed to a significant extent as compared to the control. Maximum TOC was recorded in treatment T5 (45.98%), which was significantly at par with treatments T8 (44.35%) and T9 (45.92%). Thus, the rate of B application significantly affected the TOC as significant variation was also observed among the treatments T3, T4 and T5, and likewise in treatments T7, T8 and T9. However, the time of B application did not show a significant effect on the TOC as treatments in which B was applied at the flowering and capsule formation stages showed no significant variation as compared to the treatments in which B was applied at the flowering stage alone at the same rate. Water spray did not affect the TOC as treatments T2 and T6 did not show significant variation as compared to the control. For acid value, the mean of the two years’ worth of data indicated that the effect of B application rate and time of application did not significantly affect the acid value of sesame seed oil.
3.4. Effect of B on Efficiency Indices and Economic Analysis
Foliar application of B improved the boron agronomic efficiency (BAE) and boron crop recovery efficiency (BCRE) as shown in
Figure 1. The highest value of BAE was obtained in treatment T7 (5.25) when B was applied at 20 mg L
−1 at the flowering and capsule formation stages, which was followed by treatment T8 (4.96) and T4 (4.07) when B was applied at 30 mg L
−1 at both the growth stages and at the flowering stage alone, respectively. Likewise, the highest BCRE was recorded in treatment T7 (30.56) followed by T8 (26.11) and T4 (19.48). Thus, treatment T7 showed the maximum increase in boron use efficiency indices over the control and water spray.
The economic analysis demonstrated that the cultivation cost was highest for treatment T9 (US
$359.40) whereas net return was highest for treatment T8 (US
$584.21) in comparison to the control. Thus, B:C was highest in treatment T8 (2.63). Thus, for maximum economic returns of sesame, treatment T8 can be suggested (
Figure 2).
5. Conclusions
The results of the present study reflected the beneficial effect of boron application in improving the agroeconomic indicators of sesame crop. During both the years, foliar-applied B at 30 mg L−1 at the flowering and capsule formation stages in sandy loam soil showed the maximum increase in seed yield, B uptake and B:C ratio. Moreover, certain oil quality parameters including antioxidant activity and oil content were significantly enhanced with B application at 30 mg L−1 at the flowering and capsule formation stages. The efficiency indices viz., BAE and BCRE, were positively affected when B was applied at the rate of 20 and 30 mg L−1 at the flowering and capsule formation stages. However, water spray did not significantly affect the agroeconomic indicators. Thus, application of B at 30 mg L−1 at the flowering and capsule formation stages can be recommended to enhance grain yield, B uptake, certain quality parameters and high economic returns of sesame cultivation on sandy loam soil. In the future, further studies can be performed to optimize the level of B for sesame cultivation on different types of soils.