An Analysis of the Effects of Phosphorus Solubilizing Bacteria (PSB) on Phosphorus Intake to Increase Groundnut Productivity

Groundnut (Arachis hypogaea L.) is a self-pollinated, auto-tetraploid legume crop with 2n=40 chromosomes and belongs to the family Fabaceae. Groundnut is an important food and oilseed crop. Groundnut, also known as “the poor man’s nut” or “the king of vegetable oilseeds” appears to have originated in South America, i.e. the northwest of Brazil andits secondary cultivation centre is in Africa. Groundnut is an important oilseed crop in India, where it ranks first in terms of area and second in terms of output after soybean. It covered around 26.4 million ha worldwide with a total production of 37.1 million metric tonnes (Faldu et al., 2018). China produces the most groundnuts (17.57 million metric tonnes), followed by India (6.73 million metric tonnes), Nigeria (4.45 lakh metric tonnes), Sudan (2.83 million metric tonnes) and the United States of America (2.49 million metric tonnes), which accounted for 36.01, 13.79, 9.12, 5.80 and 5.11 percent of total world production (48.80 million metric tonnes) in 2019-20. Groundnut is grown mainly in Hoshiarpur district in the Punjab state and is grown in a very small area, i.e. nearly 1.2 thousand hectares. The productivity of groundnut in Punjab was 816 kg per hectare in 1990-91, which increased to 1739 kg per hectare in 2012-13 and then to 1920 kg per hectare in 2016-17 (Anonymous, 2022).
       
Phosphorus, a macronutrient, ranks second in plant requirements after nitrogen and is involved in a variety of plant metabolic processes. Because phosphorus is fixed in soil layers, it is sometimes lacking in the soil. (Khan et al., 2009). Phosphorus-solubilizing soil microbes gaining significance due to their ability to mineralize complex compounds (Wani et al., 2005). The release of various organic acids by these microorganisms causes acidification of microenvironments (Maliha et al., 2004) and, as a result, the substitution of P ions with cations, which is referred to as “phosphorus solubilization” (Trivedi and Sa, 2008). Phosphorus is important in plants because it is a component of nucleoproteins, phytins andphospholipids, as well as an essential component of a number of enzymes and a key component in energy transfer.
       
The influence of interactions with phosphorus and rhizobium inoculation helps plant establishment. The plant with the highest flower count was where the application of phosphorus was balanced. According to Praveen et al., (2012) and later, as cited by Ganesh et al., (2015) meaningfully improved flower count was observed with the application of phosphorus fertilizer, which also speeds up the meristem tip activity. As reported by Keba et al., (2014) for the flower count per plant, phosphorus was very important for the essential reproductive organs, like the flowers or sinks, on which yield is mainly dependent and was responsible for higher yields. By applying phosphorus fertilizer, the vegetative growth of the plant is influenced in a positive way. Shiyam (2010) reported that different levels of phosphorous had a negative effect on plant height. According to Slave and Gunjal (2011), with the change in phosphorus concentration, a significant change in plant height was found. According to Zafar et al., (2013), with improved root arrangement, phosphorus provides better contact between roots and soil, resulting in the absorption of phosphorus and other important nutrients. It has been reported that by a few specified times, phosphorus remaining in the soil as a key constituent and poorly resolvable mineral phosphate were formed andthey were basically not available to the plant (Marschner and Marschner, 2012). Phosphorus is crucial for various aspects of plant growth, including nitrogen fixation, nutrient absorption androot development. Phosphorus fertilizers are essential for promoting concentrated, fibrous root growth and enhancing the overall health of plants, as highlighted by Niu et al., (2012).
       
In groundnuts (peanuts), phosphorus plays a significant role in supporting root and lateral root formation, which is essential for optimal vegetative growth. This aspect has been noted in the findings of Ganesh et al., (2015), who emphasized the acceleration of meristem tip activity.
       
According to Bajya et al., (2023), Mepiquat chloride (MC) is an important growth retardant inhibits vegetative growth and accelerates the development of reproductive parts by reducing plant height, thereby decreasing the distance between the source and sink, resulting in better translocation of photosynthetic into developing pods, which is expected to improve groundnut harvest index. Hence the present study, was conducted on three groundnut genotypes viz. TG37A, J87 and SG99 to observed the difference of growth retardant mepiquat chloride, water spray.
       
According to Bajaya et al., (2022), During survey, maximum collar rot incidence was observed in Jaipur (28.85%) and minimum in Bikaner (21.04%) district while overall mean disease incidence of eight districts was 22.99 per cent covering 200 fields of major groundnut growing districts of Rajasthan. Among six levels of seed rate (80, 85, 90, 95, 100 and 105 kg/ha), higher disease reduction with increased pod yield was observed with seed rate of 105 kg/ha as compared to standard recommended seed rate (80 kg/ha). As reported by Meena et al., (2021), On the basis of experimental finding, it can be concluded that the application of PEC @4 t/ha + Zn @ 4 kg/ha alongwith the recommended dose of fertilizer results in significantly higher yield and protein content of blackgram under Typic Haplustepts soil of sub-humid southern plain of Rajasthan.

Field experiments were conducted at the research farm of oilseeds section, Department of Plant Breeding and Genetics, Punjab Agricultural University Ludhiana in design during Kharif season 2020-2021. The experimental site is located at 30°54'N latitude and 75°48'E longitude and at an altitude of 247 meters above the mean sea level. Microbial inoculant Azotobacter (Azotobacter chroococcum), Bacillus (Bacillus subtilus) and Pseudomonas (Pseudomonas sps.) were applied @ 250 g/acre. Consortium comprised of 3 microbial inoculants/strain @ 166.0 each for 500 g per acre.
 
Phenological traits
 
The data consisted of the number of days from the date of sowing the crop to the appearance of the first flower. Number of days elapsed from the date of sowing to the date of first flower opening in 50 per cent plant was recorded on the plot basis. Completion of flowering was recorded by counting the number of days required for physiological maturity i.e. when plants under go leaf senescence and all pods from the plants turn green to yellow.
 
Physiological parameters
 
Chlorophyll content was estimated in 4^th leaf from the top (fully expended leaflet) with the help of chlorophyll meter (SPAD502 plus). Readings measured in 10 plants per plot at flowering and podding stages. Chlorophyll content is expressed in terms of Soil Plant Analysis Development (SPAD) units.
 
Yield and yield attributes
 
Pods from the net plot area were washed and cleaned to remove the soil adhering to the pods, Impurities and immature pods. The developed pods were dried completely (up to 8% moisture level) and weighed. On the basis of pod yield net plot^-1 the pod yield ha^-1 was calculated.
 
Statistical analysis
 
The data were analysed by method of Analysis of Variance obtained by Panse and Sukhatme (1978). The recorded data in the experiment was statistically analysed by two factorial randomized block design. Significance was tested by F value at 5 per cent level of probability. Critical differences were worked out for the effects which were significant.

Effect on microbial count in soil
 
The total rhizospheric bacterial, fungal, actinomycetes, phosphate-solubilizing and diazotrophic bacterial population was enumerated of before and after sowing soil samples of groundnut. The soil adhering to the plant roots was collected, brought to the laboratory, serially diluted up to 10-6 and plated on nutrient agar, potato dextrose agar, yeast malt extract agar, modified Pikovskayas agar and Jensen’s agar for enumerating bacterial, fungal, actinomycetes, phosphate-solubilizing and diazotrophic bacterial populations, respectively. The Petri plates were incubated in triplicates at 28°C for 48 h for total bacterial and diazotrophic bacterial count, 3-5 days for fungal and phosphate-solubilizing bacterial count and for 5-7 days for actinomycetes count. The results were expressed as colony forming units (CFU) per gram of soil. CFU: Colony Forming Units Value in parenthesis indicate log₁₀ CFU/g.
       
Soil sample collected before sowing consisted of 2.5×10⁵ CFU of Actinomycetes and 2.5×10⁵ CFU of PSB and 3.4×10³ CFU of fungi from 0-15 cm soil depth however variation existed.
       
Soil sample collected before sowing from 15-30 cm soil depth consisted of 1.8×10⁵ CFU of Actinomycetes and 2.8×10³ CFU of PSBs and 3.3×10² CFU of fungi however variation existed.
       
Soil sample collected after harvesting, control recommended dose of only P₂O₅ consisted 2.83×10⁸, 2.0×10⁴, 4.2 ×10⁶, 3.8 ×10⁶ and 1.20×10⁷ CFU of Bactria, fungi, Actinomycetes, PSB and diazotrophs from 0-15 cm soil depth however variation existed. Whereas with control double dose consisted 3.38×10⁸, 2.2×10⁴, 4.4×10⁶, 4.0×10⁶ and 3.67×10⁷ CFU of Bactria, fungi, Actinomycetes, PSBs and diazotrophs.
       
Similarly, from soil sample collected at 15-30 cm depth control recommended dose of only P₂O₅ consisted of 2.43×10⁶, 3.75×10², 3.3×10⁴, 3.0×10⁴ and 1.2×10⁴ CFU of Bactria, fungi, Actinomycetes, PSB and diazotrophs from 0-15 cm soil depth however variation existed. Whereas with control double dose consisted 3.12×10⁶, 3.2×10², 3.4×10⁴, 3.9×10⁴ and 2.0×10⁴ CFU of bacteria, fungi, Actinomycetes, PSBs and diazotrophs. Whereas with application of PSBs, bacteria, fungi, Actinomycetes, PSBs and diazotrophs ranged from 1.67×10⁸ to 9.2×10⁷ with recommended dose and bacteria, fungi, Actinomycetes, PSB and diazotrophs with double dose ranged from 2.11×10⁶  to 9.2×10⁷ (Table 1).
 

       
An increase in microbial count was observed with the treatments at 0-15 cm depth (Table 1 and 2). The bacterial count increased from the initial count of 2.5×10⁷ (taken at the start of the experiment) to 1.67-5.17×10⁸ with the highest count observed with the treatment Consortium double dose. Likewise, the fungal count increased from an initial count of 3.4×10³ to 2.0-3.6×10⁴ CFU/g. Similarly, count of actinomycetes increased from 2.5×10⁵ to 7.2×10⁷, PSBs from 2.5×10⁵  to 8.3×10⁶ and diazotrophs from 1.3×10⁶ to 9.6×10⁷. Microbial count decreased with increase in soil depth. However, different treatments had no effect on the microbial count in the soil samples taken from 15-30 cm.
 

       
For in depth studies field experiment on PSBs along with two doses of P₂O₅ were carried out during two consecutive Kharif season in 2020 and 2021 on SG99.The data pertaining to the effect of different treatments on days to initiation flowering, 50% flowering, completion of flowering and days to maturity are presented in Table 3. Results revealed that the different treatments of recommended dose and double dose of PSBs exerted their significant effect on initiation of flowering, 50% flowering, completion of flowering and days to maturity (Table 3). Days to initiation of flowering was non-significant during kharif 2020-2021 and for interaction of the year. Whereas days to 50% flowering significantly varied from 30.8 to 37.0 days and 30.8 to 36.7 during kharif 2020 and kharif 2021, respectively. The results showed that days to 50% flowering significantly declined after PSBs treatment and maximum reduction observed with Consortium recommended dose (DP1) (30.0 days and 30.8 days) during kharif 2020 and kharif 2021, respectively. Pooled mean showed that day to 50% flowering varied from 30.4 to 36.8 days and minimum days to 50% flowering recorded with Consortium recommended dose (DP1) i.e. 30.4 days (Table 3).
 

       
Completion of flowering differed significantly among the recommended dose and double dose of PSBs during kharif 2020 and kharif 2021 than the recommended dose and double dose of only P₂O₅. During kharif 2020, completion of flowering varied from 42.0 to 47.0 days and during kharif 2021 ranged from 41.4 to 46.9 days. Maximum days to completion of flowering observed with Consortium double dose (DP2) (47.0 days) during kharif 2020 and kharif 2021, respectively. Pooled means showed that among the different PSBs maximum days to completion observed with Consortium double dose (DP2) i.e. 47.0 days (Table 3). A previous study documented that effect of phosphorous fertilizer on groundnut and showed the significant effect of on plant height, leaf count, number of branches, days to 50% flowering, number of pods/plant, 100 seeds weight, total yield and biomass with the application of 60 kg P ha^-1 (Ibrahim et al., 2019).
       
Days to maturity significantly varied from 119.0 to 121.5 days and 119.8 to 122.2 days) during kharif 2020 to kharif 2021 respectively. The minimum days to maturity observed with Pseudomonas recommended dose (CP1) (119.0 days) during 2020 and Pseudomonas double dose (CP2) i.e. 119.8 days during 2021. Pooled mean showed that Azotobacter double dose (AP2) showed minimum days to maturity i.e.120.8 days (Table 3).

SG99 treated with microbial inoculants at the time of sowing to test their ability to mobilize phosphorous uptake in order to enhance yield. Treatments comprising of recommended and double dose of PSB significantly reduced days to initiation of flowering, 50%, completion flowering and days to maturity. SPAD values enhanced by 19.2% and RWC content by 15.6 % with Azotobacter double dose over control.

There is no conflict of interest in this article.