Boron fertilization improves quality and yield of maize (Zea mays L.)

Article history Received: February 10, 2020 Revised: April 29, 2020 Accepted: May 28, 2020 Boron deficiency drastically affects the yield and quality of many crops especially maize. The low availability of boron in soils is one of the major causes of poor quality and low yield of maize in Pakistan. A wirehouse experiment was carried out at Department of Crop Physiology, University of Agriculture, Faisalabad to optimize the dose of boron to increase quality and yield of maize. Two recommended local maize hybrids Monsanto-919 and Monsanto-5219 were evaluated in a randomized complete block design with factorial arrangements. The Boron was applied as borax @ 0, 0.3, 0.6, 0.9, 1.2 and 1.5 kg ha ̄1 at tasseling stage. Although both hybrids showed non-significant differences in yield attributes exogenous boron supply @ 0.6 kg boron ha ̄1 increased grain yield by 27% as compared to control treatment in both the hybrids. It increased grain oil, protein and starch contents by 10%, 12% and 16% respectively.


INTRODUCTION
Maize, commonly known as the king of grain crops, is grown extensively in Pakistan and occupies the third position after wheat and rice. Imbalanced application and improper management of plant essential elements have limited yield potential of crops in the country. Better plant nutrient management is necessary for achieving selfreliance in agriculture (Ahmad and Muhammad, 1998). Boron is one of the most commonly deficient micronutrients in agriculture, with reports of deficiencies in 132 crops and in 80 countries (Shorrocks, 1997). Boron deficiency results in the general stunting of the young plants due to shortening of the internodes; leaves of young plants fail to emerge, and death of growing point may occur (Follett et al., 1981). These deficiencies typically result from boron leaching (Welch, et al., 1991;Mortvedt and Woodruff, 1993;Marschner, 1995). Boron's widespread role within the plant includes cell wall synthesis, sugar transport, cell division, differentiation, membrane functioning, root elongation, and regulation of plant hormone levels (Pilbeam and Kirkby, 1983;Romheld and Marschner, 1991;Marschner, 1995). Many researchers have reported the significance of exogenous boron supply to different crops (Reinbott and Blevins, 1995;Hudson and Clarke, 1997;Ismail, 2003;Garcia et al., 2005). Increase in solution B concentration increased the concentration of B in the ear leaf and root and changed the concentrations of Nitrogen (N), Phosphorous (P), Manganese (Mn), Iron (Fe), Zinc (Zn), and Molybdenum (Mo) in the ear leaf and calcium (Ca), Magnesium (Mg), copper (Cu), Mn, Fe, Zn and Mo in the root (Mozafar, 1989;Adiloglu and Adiloglu, 2006). Soil-applied B rates of 2.8 kg ha¯¹ in a silt clay loam increased soybean yield by 11 % and 13%, respectively, in the first two years with no effect in the third year after application (Reinbott and Blevins, 1995). Keeping in view the above-mentioned facts, the present study was carried out with the objective of evaluating the role of exogenous boron supply to maize hybrids.

MATERIAL AND METHODS
The present study was carried out at the wirehouse of Department of Crop Physiology University of Agriculture, Faisalabad. The Experiment was laid out in a randomized complete block design (RCBD) with factorial arrangements. Two local maize hybrids (Monsanto-919 and Monsanto-5219) were used as experimental crops. Five seeds of each hybrid were sown in plastic pots of 10 kg capacity, however; only two plants were grown till maturity. Soil analysis: Before sowing, soil samples were taken from soil used to fill pots to determine initial soil fertility level. The available B in soil was determined by dilute HCl method (Kausar et al., 1990). Available S in soil was determined by Turbidimetric method (Verma, 1977). Available K in soil was determined with ammonium acetate solution (Richards, 1954). Available P in soil was determined by sodium bicarbonate method (Olsen and Sommers, 1982). Total Nitrogen in soil was determined by the Kjeldahl method. (Bremner and Mulvaney, 1982;Buresh et al., 1982). The soil analysis revealed 0.2 mg kg¯¹ available boron (B), 7.5 mg kg¯¹ available sulphur (S), 175 mg kg¯¹ potassium (K), 1 mg kg¯¹ phosphorous (P) and 0.21% available nitrogen (N) in the soil (Table 1). Borax was used as a source of boron and 1.5, 3.0, 4.5, 6.0 and 7.5 mg of borax, for application of boron @ 0, 0.3, 0.6, 0.9, 1.2 and 1.5 kg ha¯¹ respectively, was mixed separately in 10 kg of soil for each pot after taking soil samples for analysis. All other fertilization and cultural practices were standard and uniform. The plants were harvested at maturity to record various growth, quality and yield attributes by using standard procedures. Quality variables: Total nitrogen in grain was determined by Gunning and Hibbard's method of sulphuric acid digestion and distillation by micro-Kjeldhals method (Jackson, 1962). Seed samples equal to one gram from each pot were taken randomly, ground and subjected to chemical analysis according to Kjeldahl's method to estimate nitrogen content (Jackson, 1962). Nitrogen (%) was then multiplied by a constant factor 6.25 for calculating protein (%) in the grain (Hiller et al., 1948). For oil analysis, the representative samples from each pot were dried and ground. Oil contents in grains were determined by means of Soxhlet fat extraction method (Low, 1990). Grain starch contents were determined by treating the seed sample was with 80 % alcohol to remove sugars and then starch was extracted with perchloric acid. In hot acid, medium starch was hydrolyzed to glucose and dehydrated to hydro methyl furfural. This compound formed a green colour product with anthrone (Thimmaiah, 2004).

Statistical analysis:
The data obtained from different variables were analyzed statistically using Fishers Analysis of Variance Technique and least significant difference test level was used to compare differences among the treatments means (Steel et al., 1997).

Growth variables
The boron application significantly affected various growth attributes of both hybrids. The maximum leaf area (3164 cm²) cm 2 ) was observed where boron was applied @ 0.6 kg ha¯¹ while minimum leaf area (2920 cm²) in control treatment (no boron supply). Among hybrids, Monsanto-5219 attained significantly higher leaf area plant¯¹ (3066) than Monsanto-919 (3029 cm²) however, the interaction was non-significant among hybrids and boron levels ( Table 4). The exogenous boron application significantly increased cob length in both the hybrids. The maximum cob length (17.68 cm) was recorded by the boron application @ 0.6 kg ha¯¹ while the control (0 kg boron ha¯¹) gave minimum cob length (15.21 cm) which was statistically at par with boron applied @ 0.3 kg ha¯¹. Among different hybrids, the maximum cob length (16.58 cm) was recorded in Monsanto-919 and minimum cob length of 16.43 cm was noted in Monsanto-5219 (Table 4). The maximum cob diameter (6.69 cm) was recorded where boron was applied @ 0.6 kg ha¯¹ which was at par with boron application @ 0.9 kg ha¯¹ however, control (0 kg Boron ha¯¹) gave minimum cob diameter (5.95 cm) which was statistically at par with boron applied @ 0.3 kg boron ha¯¹. Among hybrids, significantly higher cob diameter (6.32 cm) was recorded in Monsanto-919 while minimum cob diameter (5.9 cm) was observed in Monsanto-5219 (Table 4). Both hybrids recorded significantly higher cob diameter when they were supplied with 0.6 kg boron ha¯¹. Minimum cob diameter (5.45cm) was recorded in Monsanto-5219 where boron was applied @ 1.2 kg ha -1 . Yield attributes: The maximum number of grains cob¯¹ (527.16) was recorded in plants applied with boron @ 0.6 kg ha¯¹ (Table 3) however, it was at par with all other levels except control which gave the minimum number of grains cob¯¹ (432.23). Both hybrids showed nonsignificant differences for a number of grains cob¯¹. Boron application significantly increased 1000-grain weight. The maximum 1000-grain weight (302.66 g) was recorded with boron application @ 0.6 kg ha¯¹. While minimum 1000-grain weight (236.41 g) was recorded in control treatment (no boron application). The efficiency and effectiveness of different levels of boron application are ultimately determined by the level of grain yield ha ¯¹, which in turn is a function of the cumulative behaviour of all the yield components. Maximum grain yield per plant (175.4 g) was recorded where boron was applied @ 0.6 kg ha¯¹ while minimum grain yield (105.0 g) was recorded in hybrids with no boron application (Table 3). showed that the exogenous boron supply significantly increased the quality variables of maize hybrids ( Table 2). The grain oil contents were increased by 10% with boron application as compared with no boron application (control). The maximum grain oil contents (4.77 %) were recorded where boron was applied @ 0.6 kg ha¯¹. statistically at par with 0.3 kg boron ha¯¹ while minimum grain oil contents (4.46 %) were observed in control treatment (Figure 1). Among hybrids, maximum grain oil contents (4.66%) were observed in Monsanto-919 which was significantly higher than grain oil contents of Monsanto-5219 (4.45%). The exogenous boron application increased grain protein contents by 12%. The maximum value (9.5%) for grain protein contents was recorded in boron application @ 0.6 kg ha¯¹, while minimum grain protein contents (8.28 %) were recorded in control treatment. Hybrids also showed a significant effect with respect to grain protein contents. Among hybrids, maximum protein contents (8.84%) were observed in Monsanto-219, while minimum grain protein contents (8.57%) were recorded in Monsanto-919 ( Figure 2). The interactive effect of hybrids and boron levels was also significant for this variable (Table 2). Both the hybrids gave significantly higher protein contents when they were supplied with @ 0.6 boron kg ha¯¹. Minimum grain protein contents (8.26 %) were recorded in Monsanto-919 where no boron was applied (control).  The significantly higher grain starch contents (71.45 %) were recorded where boron was applied @ 0.6 kg ha¯¹, while minimum grain starch content (61.26 %) was observed where no boron was applied. However, hybrids did not show a significant effect of boron with respect to grain starch content. The interactive effect of hybrids and boron levels was also significant for this variable. Both the hybrids recorded significantly higher starch content when they were supplied with @ 0.6 kg boron ha¯¹. Minimum grain starch contents (61.18 %) were recorded in Monsanto-919 with no Boron application (Figure 3).

DISCUSSION
The increase in leaf area due to exogenous application of boron was probably due to the increase in chlorophyll contents of both the hybrids. These results support the findings of Sayed (1998) who reported that the application of boron increased the chlorophyll contents and relative water contents which increased the leaf area of maize plants. Parkash and Mehra (2006) reported that application of nitrogen (N) and boron (B) significantly increased the plant leaf area production in sunflower. The boron application has been reported to increase ear length and a number of grains spike¯¹ in wheat (Spasovski et al., 1987) which supports the results of this study that exogenous boron application increased cob length, diameter and number of grains cob¯¹ in maize hybrids. Many researchers have also reported the significant role of boron in increasing cob diameter of maize plants (Pasha et al., 2002;Parkash and Mehra, 2006). The increase in 1000-grain weight due to exogenous boron supply has also been reported by Mandal and Das (1988) while 1000grain weight has also been reported to increase by the borax application in wheat (Mishra et al., 1989).
The boron application has been reported to increase grain yield up to 33% in wheat (Gunnes et al., 2003). Rahim et al., 2004 reported increased dry weight plant¯¹, a number of grains cob¯¹ and grain weight cob¯¹ in maize plants which support the findings of the present study that boron application significantly increased various yield attributes of maize hybrids. The significant role of boron in improving the yield of crop plants has been reported by many researchers (Wrobel et al., 2006;Malhi et al., 2007;Misra and Patil, 2008;Tombo et al., 2008). The increase in biological yield is in agreement with Renukadevi et al. (2003) who reported increased biological yield in sunflower with boron application. The exogenous application of boron in soil has been reported to increase the harvest index and seed yield by 23% and 53%, respectively (Naik, 1991). The increase in grain oil content due to exogenous application of boron is in accordance with the findings of Oyinlola (2007)  hydroxyproline-rich proteins in the cell walls of borondeficient bean root nodules compared with those of boron-sufficient controls. The low levels of grain protein contents may be due to the inability of proteins to assemble and resulted in the secretion of proteins under boron deficient conditions as reported by Jackson (1991).

CONCLUSION
The exogenous application of boron significantly affected the growth, yield and quality attributes of both maize hybrids. The application of boron @ 0.6 kg ha¯¹ significantly increased leaf area, cob length and diameter, grain yield, 1000-grain weight and no. of grains cob¯¹. It also significantly increased various quality attributes i.e. grain oil content, grain protein content and grain starch content. It was also observed that application higher doses of boron @1.2 and 1.5 kg ha -¹ significantly reduced grain oil, protein and starch contents.