Effect of BioNiK-Phos and Phosphorus-based fertilizers on yield of hybrid sunflower in Northern Uganda

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Introduction
Sunflower (Helianthus annuus L.) is the world`s fourth largest oil seed crop (Adeleke;Babalola, 2020).Global production has been growing steadly in the last 35 years.The largest producers in 2019 were Ukraine, Russia, Argentina and Romania, and the largest producer in Africa was Tanzania (Khondoker et al., 2022).In Uganda, sunflower is an important oil crop.The crop is cultivated in the eastern and northern parts of Uganda.The sunflower sub-sector presents good business opportunities in Uganda (Kamoga, 2011).Land under sunflower production in Uganda is approximately 593,000 acres.
In Uganda, the area under sunflower production has been increasing (Elobu et al., 2013).Sunflower yield, however, has remained low in the country, despite the increase in production.A number of factors have been reported to be responsible for the low yield including poor agronomic practices and lack of high-yielding varieties (Anyanga, 2003).On-station yields of open-pollinated varieties range from 1,500-1,800 kg/ha, while the average on-farm yield ranges from 750-900 kg ha -1 (Anyanga, 2003).Currently, there are a number of high yielding sunflower hybrids in Uganda, but their yields in farmers` gardens are low due to poor agronomic practices and declining soil fertility.
It has been reported that fertilization with phosphorous-based fertilizer increases growth and yield in sunflower (Abbadi et al., 2011;Sadozai et al., 2013).According to Soomro et al. (2018), lack of phosphorous in sunflower causes reduced growth rate, delay in flowering, poor filling of achenes, and reduction oil content.The effect is worse if the phosphorous deficiency occurs at the beginning of the vegetative cycle (Prado et al., 2006).It is, therefore, important to test the soil for phosphorous to guide the amount of phosphorous-based fertilizer to be used in sunflower growing.The application of phosphorous should however, focus on use efficiency (Veneklaas et al., 2012) to reduce the environmental impacts which can result from excessive use of this fertilizer (Godfray et al., 2010).
Phosphorous availability to plants is a key factor for sustainable agriculture (2010).According to McGill (2012), agriculture is highly dependent on phosphorus, a non-renewable resource.Hence, phosphorous use in agriculture should target maximizing efficiency.For Northern Uganda, studies on the response of sunflower hybrid to phosphorous-based fertilizer micro dosing under field conditions is needed.BioNiK-Phos contains biofertilizer microbe/bacterium Acinetobacter spp, with ability to fix atmospheric nitrogen and dissolve phosphate in the soil for plant usage.Thus, we hypothesized that BioNiK-Phos and Di-Ammonium Phosphate fertilization increase sunflower seed yield.

Study area
The study was conducted in 2021b (August to November) and 2022a (April to July) seasons in 3 Sub-counties (locations) in Alebtong District.The 3 Sub-counties were Aloi, Abako and Angeta, Uganda.The three Sub-counties were used in both growing seasons.

Plant materials
Certified seed of hybrid sunflower (PAN 5057) and Di-Ammonium Phosphate (DAP) fertilizer were procured from Agro Wonders input shop in Lira City.In addition, BioNiK-Phos fertilizer was sourced from NARO Holdings Ltd. 200 mL of BioNiK-Phos was added to 20 L of water, mixed well and the mixture was transferred into clean containers.

Experimental design
A randomized complete block design with 3 replications was adopted for the field experiments.Three treatments: 40 kg ha -1 DAP fertilizer, 6.0 L ha -1 of BioNiK-Phos and no treatment with DAP or BioNiK-Phos as a control were randomly assigned to plots within each block.The plot size was 20 m by 10 m and sunflower spacing of 75 cm by 30 cm was used.DAP fertilizer was broadcasted at planting time at the rate of 40 kg ha -1 to represent the micro-dosed plots, BioNiK-Phos was applied evenly on planting holes immediately after planting using a watering can.
One plot in each block was left without DAP micro-dosing or BioNiK-Phos to act as a control.DAP fertilizer broadcast was done between lines of sunflower.The choice to use DAP as a fertilizer for this study didn't result from soil testing, but from the results of cowpeas and groundnut study using DAP in the same region which indicated that phosphorus is a major limiting nutrient in soils within Northern Uganda (Nyamaizi et al., 2020;Abaca et al., 2023).BioNiK-Phos fertilizer was included because it contains biofertilizer bacterium, Acinetobacter species, with ability to fix atmospheric nitrogen and dissolve phosphate in the soil for plant usage.2021b season experiment was planted in April 2021 and 2022b season experiment in August 2018.Recommended agronomic practices were followed.Data was collected on plot yield.Plot yield data was used to estimate yield in kg ha -1 .

Statistical analysis
Data on sunflower yield in kg/ha was analysed by analysis of variance (ANOVA) assuming normal distribution.Data analysis was performed using GENSTAT statistical package 16th edition.The data was subjected to ANOVA, and residual plots were used to check ANOVA assumptions.Hypotheses were rejected at P < 0.05 and means compared by Turkey's test.Mean values of results were presented.

Results
The result of the effect of BioNik-Phos bio-fertilizer and DAP fertilizer micro-dosing is presented in (Table 1).There were significant (P < 0.05) differences in sunflower yields across treatments in all the three locations (Table 1).
Table 1.ANOVA for the effect of BioNik-Phos bio-fertilizer and DAP fertilizer micro-dosing on yield of hybrid sunflower (PAN 5057).
Hybrid PAN 5057 treated with DAP fertilizer yielded 3,524 kg ha -1 , 3,488 kg ha -1 and 3,369 kg ha -1 in Abako, Aloi and Angeta, respectively in 2021.Again in 2022, hybrid PAN 5057 micro-dozed with DAP fertilizer had the highest yield across locations with 3,500 kg ha -1 , 3,607 kg ha -1 and 3,417 kg ha -1 in Abako, Aloi and Angeta, respectively.Bio-NikPhos treatment effect was, however, not significantly different (P < 0.05) from the control across locations ( Note: Bio-fert = BioNiK-Phos fertilizer, DAP = Di-Ammonium Phosphate fertilizer, LSD = Least Significant Difference, CV=Coefficient of variation, NS = Not significant, Control=Not treated with either BioNiK-Phos or Di-Ammonium Phosphate fertilizer. The yield of plants treated with Bio-NikPhos were 1,393 kg ha -1 , 1,333 kg ha -1 and 1,262 kg ha -1 in Abako, Aloi and Angeta respectively in 2021, and 1,500 kg ha -1 , 1,452 kg ha -1 and 1,429 kg ha -1 in Abako, Aloi and Angeta respectively in 2022.The yield performance of untreated control across the three locations in 2021 were 1,250 kg ha -1 , 1,274 kg ha -1 and 1,238 kg ha -1 in Abako, Aloi and Angeta, respectively, and 1,268 kg ha -1 , 1,357 kg ha -1 and 1,286 kg ha -1 respectively in 2022.Overall, The effect of DAP fertilizer micro-dosing on sunflower hybrid (PAN 5057) yield was three folds.There were no significant differences in yield response within locations for BioNiK-Phos, DAP and untreated control.

Discussion
Sunflower yield varied significantly (P < 0.05) across treatments.The highest yield in all the test locations was recorded for DAP fertilizer.The average yield of sunflower hybrid PAN (5057) was 3460 kg ha -1 and 3.508 kg ha -1 in 2021b season and 2022b season, respectively.Application of DAP fertilizer in sunflower hybrid (5057) at a rate of 40 kg ha -1 at planting time increased yield in the three test locations three folds.The increase in yield could be attributed to the release of PO 3-and NH 4+ in the soil.
The increase in yield in crops following P-fertilizer applications has been reported for groundnuts (Abaca et al., 2022) and maize (Murendo;Wollni, 2015).This finding suggests sunflower hybrid PAN 5057 is adapted to these locations, only that its yield was being limited by the soil nutrients including Phosphorous.The implication of this finding is that soil testing, soil fertility management and improvement could be used as a strategy for increasing hybrid sunflower productivity in northern Uganda.Oliveira et al. (2022) described the benefits of Phosphorus fertilization for sunflower.Other studies have also shown that phosphorus application promotes growth and increases sunflower yield (Abaca et al., 2022;Sadozai et al., 2022).Lack of Phosphorus has also been reported to affect growth, delay flowering and cause less filling of the achenes (Padro, 2006;Soomro et al., 2018).There is, therefore, the need to promote the use of P-based fertilizer micro-dosing in sunflower growing in dry areas of Northern Uganda, where declining soil fertility is a major constraint to sunflower production.
The high efficiency of phosphorus use in a low dose (40 kg ha -1 ) in the current study indicates that the hybrid sunflower (PAN 5057) has greater adaptation to conditions of low phosphorus concentration.Plant response to phosphate fertilization is related to its availability in the soil.Applications of large doses of Phosphorous-based fertilizers have been reported to result in sorption, making Phosphorous unavailable to plants.Hence, the need to apply Phosphorous in small doses to make it available to plants.
BioNiK-Phos used in the current study contains bio-fertilizer bacterium, Acinetobacter species, a plant-growth promoting rhizobacteria.Several studies have demonstrated the multiple functional traits of bacteria of the genus Acinetobacter for plant growth promotion including siderophore production, calcium phosphate solubilization, auxin synthesis and antibiosis and (Oliveira-Longatti et al., 2014;Kandel et al., 2017).Velázquez et al. (2008), reported occurrence of Acinetobacter in association with the rhizosphere and as endophytic bacteria of sugarcane

Table 2 .
Table2).Variation in yields of sunflower hybrid (5057) treated with or without DAP and BioNik-Phos fertilizers across locations.