HC&RI, Periyakulam A field experiment was conducted in B deficient soil (0.37 mg kg¹) to assess the frequency and level of B application for increasing crop yields in maize - sunflower cropping system, fate of B pools in soils system and to monitor the changes in soil fertility and productivity due to different levels and frequency of B application under continuous cropping system at Tamil Nadu Agricultural University, Coimbatore since 2012. The analysis of initial soil samples indicated that experimental soil was neutral in soil pH and free from salinity with sandy clay in texture. The grain and stover yield of maize crop varied from 5.51-8.38 and 5.16 to 8.00 t ha¹, respectively and significantly differed with rate of B application. Among the B levels application of B @ 1.0 kg ha¹ registered the maximum grain and stover yield of 7.55 and 7.00 t ha¹, respectively and was followed by application of 1.5 kg ha¹, however they were on par with each other. After the harvest of maize crop, sunflower was raised and harvested and the grain and stalk yields were recorded. Among the B levels, application of B @ 1.0 kg ha¹ registered the maximum seed yield of 2.33 t ha¹ respectively and was followed by application of 0.5 kg ha¹. The interaction between the rate of B application and frequency significantly differed with grain and stalk yield. Among the frequency levels, application of B to maize crop alone every year (F3) registered the maximum seed yield as compared to others. The interaction effect revealed that application of B @ 0.5 kg ha¹ to all crop registered the highest seed yield of 2.79 t ha¹ respectively. Boron fractions like available boron, specifically adsorbed B, oxide B, organically bound B, residual B status and total boron contents were analysed after the harvest of second crop. The results revealed that the available B status varied from 0.277 to 1.940 mg kg¹, specifically adsorbed B ranged from 0.190 to 1.332, oxide bound B status in soil varied from 0.127 to 0.89 mg kg¹, organically bound B status in soil varied from 0.235 to 1.644 mg kg¹, residual fraction of B varied from 41.61 to 291.8 and total boron varied from 42.44 to 297.6 mg kg¹. Boron application resulted in significant increase in maize yield as first crop and sunflower as residual crop, respectively. Among the B fractions the order was residual B >organically bound > specifically adsorbed > oxide bound B. Application of B @ 2.0 kg ha¹ significantly registered the highest available B in soil (1.038 mg kg¹) and among the frequencies, application of B to all crops registered the highest available B (1.32 mg kg¹). The actual fraction of B fertilizer removed by the crops is only 1-2% of the total applied fertilizer through soil.
Boron is a non-metallic element and the only non-metal in Group 13 of the periodic table. It is an essential micronutrient for crops. More than 90% of boron (B) in plants is found in cell walls, and its most important role is associated with cell wall formation.
Boron is involved in the reproduction of plants and the germination of pollen spikelets (Bolanos et al., 2004). It plays a direct or indirect role in several physiological and biochemical processes during plant growth. Boron deficiency causes reduction in cell enlargement in growing tissues due to its structural role. Its deficiency is also responsible for male sterility and floral abnormalities (Sharma, 2006).
The range between the toxic level and adequate level of boron is narrower than for other nutrient elements (Mortvedt and Woodruff, 1993). Boron availability in soil and irrigation water is an important determinant of agricultural production (Tanaka and Fujiwara, 2007) due to its low sufficiency level in soil.
Boron exists in the soil in five fractions. Zerrari et al. (1999) reported these fractions as:
The amount of these different fractions depends on soil properties, and the availability levels of these fractions vary. Ellis and Knezek (1972) stated that boron is more strongly adsorbed by soil compared to other anions like Cl⁻ and NO₃⁻. This adsorption occurs through inorganic substances such as Fe and Al oxides, hydroxides, clay minerals (especially mica-type clay), Mg(OH)₂, and organic matter.
A field experiment was conducted at Tamil Nadu Agricultural University (TNAU), Coimbatore, under the All India Coordinated Research Project on "Micronutrients, Secondary Nutrients, and Polluted Elements in Soils and Plants." The objectives of the experiment were:
The results obtained from the 2012–2014 study are discussed in this paper.
To assess the frequency and level of B application for increasing crop yields in maize sunflower -cropping system, fate of B pools in soil system and to monitor the changes in soil fertility and productivity due to different levels and frequency of B application under continuous cropping system, a field experiment was conducted in Periyanaickenpalayam soil series (Field No.75, Eastern block, TNAU Farm situated at 11° 00 N Latitude and 76° 93 E Longitude) at Tamil Nadu Agricultural University, Coimbatore. Totally twenty treatment combinations were replicated thrice in a split plot design using main treatment as frequency of B application (F1: One time application to maize crop in I year), F2: Alternate years (Ist, 3rd 1 5th year - maize crop alone), F3: Every year (maize crop alone) and F4: All crop (Every year maize and sunflower crops) and levels of B as sub plots (5 levels viz.,0,0.5,1.0,1.5 and 2.0 kg ha¹) First crop as maize and residual crop as sunflower was raised. Recommended dose of fertilizers 250:75:75 for maize and 60:90:60 NPK kg ha¹ for sunflower was followed, common fertilizer borax was used and harvested the crop at maturity. The analysis of initial soil samples indicated that experimental soil was neutral in soil pH and free from salinity with sandy clay in texture. The soil was low in available nitrogen (269.7 kg ha 1), medium in available P (16.2 kg ha¹) and K (265.3 kg ha¹) and high in available S (38.2 mg kg-1). The DTPA extractable Fe and B was deficient (3.30 and 0.39 mg kg-1) and Mn, Zn and Cu were sufficient (5.1, 1.52 and 1.54 mg kg¹, respectively). Post harvest soil samples were analysed for B fractions by spectrophotometric technique using a colorimetric reaction with azomethine-H and hot water and 0.5 M HCI as extractants. Boron fractions like available boron, specifically adsorbed B, oxide B, organically bound B, residual B status and total boron contents were analysed after the harvest of second crop by adopting the sequential extraction procedure given by Raza et al., (2002).
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.
| 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 |
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.
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 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 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.
Boron (B) is a unique micronutrient required for normal plant growth and optimum yield of crops. Its deficiency is widespread in alkaline/calcareous, coarse-textured, and low organic matter soils in many countries of the world.
Prevention and/or correction of B deficiency in crops on B-deficient soils can have a dramatic effect on yield. The source, rate, formulation, time, and method of B fertilizer application, along with the proper balancing of B with other nutrients in the soil, will all affect crop yield on B-deficient soils.
Soil-applied B leaves a residual effect for years on succeeding crops grown on B-deficient soils in the same field.
In the present study, boron application resulted in a significant increase in yield in maize as the first crop and sunflower as the residual crop.
Among the B fractions, the order of availability was:
Residual B > Organically Bound B > Specifically Adsorbed B > Oxide Bound B.
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