Effect of Boron Application on Maize and Sunflower Yield
The grain yield of maize crop due to varied frequency and doses of boron application ranged from 5.51 – 8.38 t ha⁻¹ and significantly differed with the rate of B application. Among the B levels, the application of B @ 1.0 kg ha⁻¹ registered the maximum grain yield of 7.55 t ha⁻¹, followed by 1.5 kg ha⁻¹, though both were on par with each other.
Boron plays a major role in cell wall formation, transport of sugars, pollen formation, and seed set, which might be the reason for obtaining a higher yield in the treatments. Similar results were reported by Mishra and Shukla (1986) in maize.
After the harvest of the maize crop, sunflower was raised and harvested, and the grain yield was recorded. Among the B levels, application of B @ 1.0 kg ha⁻¹ registered the maximum seed yield of 2.33 kg ha⁻¹, followed by 1.5 kg ha⁻¹ (Table 1).
The interaction between the rate of B application and frequency significantly differed. Among the frequency levels, application of B to maize crop every year alone (F3) registered the maximum seed yield compared to others. The interaction effect revealed that application of B @ 0.5 kg ha⁻¹ to all the crops registered the highest seed yield of 2.79 kg ha⁻¹.
Table 1. Effect of Frequency and Rate of Boron Application on Yield of Maize and Sunflower
| Treatments |
Levels of Boron (kg ha⁻¹) |
Maize Grain Yield (t ha⁻¹) |
Sunflower Seed Yield (t ha⁻¹) |
| F₁ - once |
0 |
5.56 |
1.57 |
| |
0.5 |
5.81 |
1.81 |
| |
1.0 |
6.78 |
1.87 |
| |
1.5 |
7.07 |
2.12 |
| |
2.0 |
7.35 |
2.37 |
| F₂ - alternate years |
0 |
5.51 |
1.59 |
| |
0.5 |
5.88 |
1.82 |
| |
1.0 |
6.84 |
1.91 |
| |
1.5 |
7.09 |
2.15 |
| |
2.0 |
7.42 |
2.39 |
| F₃ - maize crop alone |
0 |
5.51 |
1.61 |
| |
0.5 |
7.07 |
2.15 |
| |
1.0 |
8.38 |
2.71 |
| |
1.5 |
8.11 |
2.61 |
| |
2.0 |
6.98 |
2.56 |
| F₄ - all crops |
0 |
5.52 |
1.62 |
| |
0.5 |
7.89 |
2.79 |
| |
1.0 |
8.21 |
2.47 |
| |
1.5 |
7.72 |
2.26 |
| |
2.0 |
6.69 |
2.01 |
CD (P=0.05)
- F: 0.76 | 0.93
- T: 0.94 | 0.84
Boron Fraction Studies
Boron fractions like available boron, specifically adsorbed B, oxide-bound B, organically bound B, and residual B were analyzed after the harvest of the second crop. Boron may bind with organic matter or with carbohydrates released during humification. Boron associated with humic colloids is the principal B pool for plant growth in most agricultural soils (Jones, 2003).
The results revealed that the available B (Hot Water Soluble Boron – HWSB) status in soil increased due to different frequency and doses of boron application, varying from 0.277 to 1.940 mg kg⁻¹ (Fig.1). The initial HWSB content was 0.37 mg kg⁻¹, and it showed a declined status due to removal, whereas the treated soil maintained and increased its status after crop removal. Similar findings were in accordance with Bandit Jena et al. (2017).
Readily soluble boron (HWSB and non-specifically adsorbed B) is the boron fraction present in the soil solution and weakly adsorbed by various soil particles. This form is mostly available for plant uptake.
Specifically Adsorbed Boron in Soil
The second most plant-available form is specifically adsorbed boron (sp.B). It may be adsorbed onto clay surfaces or associated with organic matter in soil.
Organically Bound B in Soil
Organically bound boron is present in soil as complexed forms with humic substances. The organically bound fractions of B in soil after the harvest of the sunflower crop revealed that the application of B @ 2.0 kg ha⁻¹ registered the highest oxide B in soil (0.879 mg kg⁻¹), which significantly differed from other B application levels (Fig. 4).
The organically bound B status in soil varied from 0.235 to 1.644 mg kg⁻¹. Among the varied frequencies of B application, the application of B to all crops registered the highest organically bound B in soil, and there was a significant difference between the frequency of B application and their levels.
The interaction effect revealed that application of 2.0 kg of B to every crop (F4) registered the highest organically bound B in soil (1.644 mg kg⁻¹). Similar findings were reported by Bandit Jena et al. (2017).
Residual B Status in Soil
Residual boron is the major form of boron in soil, accounting for nearly 87 to 99% of the total boron in soil. The residual fraction of B status in soil, due to varied frequencies and doses, significantly differed, varying from 41.61 to 291.78 mg kg⁻¹.
Among the varied B levels, the application of B @ 2.0 kg ha⁻¹ registered the highest residual fraction of B in soil (81.2 mg kg⁻¹). The interaction effect revealed that application of 2.0 kg of B to every crop (F4) registered the highest residual B in soil (291.7 mg kg⁻¹) (Fig. 5).
Residual boron is associated with the structures of primary and secondary minerals. Russell (1973) reported that the equilibrium status between the soil solution and adsorbed boron exists in the soil in five fractions. Zerrari et al. (1999) reported that these fractions are easily soluble, adsorbed, oxide-bound, organic matter-bound, and residual (these are in silicate minerals and cannot be used by plants).
It has also been specified that the amount of these different fractions depends on the soil properties, and the availability levels of these fractions differ. Diana and Beni (2006) determined that in soils, water-soluble and adsorbed B fractions represented only a small proportion of the total soil B content (0.66-1.21% of total soil B). However, in most soils, the residual B fraction accounted for 86.3 to 88.2% of the total soil B.
Boron concentration in soil increased with the application of increased doses of boron and was distributed to various labile and non-labile pools in soil, thus maintaining the availability to increase crop yields of both maize and sunflower.
