Research Article

Effect of Potassium Sources and Soil Calcareous Levels on Sunflower (Helianthus annuus L.) Growth at the Early Stage

Abdul Aleem Memon1*, Inayatullah Rajpar2, Ghulam Murtaza Jamro2, Javaid Ahmed Shah3

1Soil Fertility Research Institute, Agriculture Research Center, Tandojam, Pakistan; 2Department of Soil Science, Faculty of Crop Production, Sindh Agriculture University, Tandojam, Pakistan; 3Soil and Environmental Sciences Division, Nuclear Institute of Agriculture, Tandojam, Pakistan.

Received | February 19, 2023; Accepted | December 10, 2023; Published | December 21, 2023

*Correspondence | A.A. Memon, Soil Fertility Research Institute, Agriculture Research Center, Tandojam, Pakistan; Email: [email protected]

Citation | Memon, A.A., I. Rajpar, G.M. Jamro and J.A. Shah. 2024. Effect of potassium sources and soil calcareous levels on sunflower (Helianthus annuus L.) growth at the early stage. Pakistan Journal of Agricultural Research, 37(1): 13-22.

DOI | https://dx.doi.org/10.17582/journal.pjar/2024/37.1.13.32

Keywords | Calcareous soils, Muriate of potash, Sulphate of potash, K nutrition, Sunflower seedling

Copyright: 2024 by the authors. Licensee ResearchersLinks Ltd, England, UK.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Introduction

Calcareous soils are soils that contain calcium carbonate (CaCO3) in one or more on their horizons, with concentrations ranging from a few to 95% (Weil and Brady, 2017). High amount of CaCO3 affect the physicochemical characteristics of soil, reducing crop productivity due to high soil pH, low nutrient availability and cycling, and reduced microbial activity (Taalab et al., 2019; Babar et al., 2022; Narayanasamy et al., 2023; Wang et al., 2023). The fixation of K and variation in basic cation ratios limit the concentration of K in the soil solution for plant uptake (Wakeel et al., 2017). With the increasing global population demands of agriculture foods are growing and further widening is the gap between agricultural output and food demand, calling for the implementation of smart practices like increased fertilizer use efficiency to lessen the impact of calcareous soils on crop output (Abbasi et al., 2022; Naorem et al., 2023).

Calcareous soils cover roughly about 1.5 billion acres or 30 percent of world land surface, mainly in the arid and semi-arid areas (Leytem and Mikkelsen, 2005; Taalab et al., 2019). Generally, calcareous soils more extensively present in Asian, African, European and American continents, and countries including USA, Iran, Iraq, Jordan, Oman, Lebanon, Sudan, Egypt, Afghanistan, Cyprus, Libya, Qatar, Saudi Arabia, Sudan, Somalia, Bulgaria, Turkey, Syria, India, Bangladesh and Pakistan (FAO, 1973). These soil types are most prevalent in Pakistan’s arid and semi-arid regions (Rashid, 2005; Wakeel et al., 2017). Most of the areas in lower Sindh are also reported as moderately to strongly calcareous in nature (Chohan et al., 2015; Talpur et al., 2016).

Potassium is known as a vital plant nutrient that contributes to sustainability by aiding in the development of plants, enhancing agricultural yield and quality, and enhancing soil health (Wakeel et al., 2017). Potassium plays important roles in photosynthesis, ionic equilibrium, protein synthesis, nutrient translocation, stomatal regulation, water usage, and enzyme activation for the formation of ATP, starch in grains, sugar translocation, photosynthesis, and protein synthesis (Wolde, 2016). There are several ways in which plants can benefit from it, including the improvement in water utilization efficiency, and the increased resistance to biotic and abiotic stressors (Das et al., 2022). K is a crucial macronutrient and osmotically active substance that aids plants in adjusting to reduce water potential during drought stress (Bukhsh et al., 2012). It is possible for plants lacking sufficient potassium to experience stunted growth, low yields, and increased vulnerability to pests and diseases (Das et al., 2022). We might be able to help maintain and protect natural resources for future generations by adopting sustainable agriculture practices that encourage potassium usage.

Besides several other issues (high pH, low N, P and organic matter), the problem of K availability and uptake by plants in calcareous soils has extensively been noticed and reported in the world mainly due to antagonistic relationship with other basic cations i.e., Na+, Ca2+ and Mg2+ present in such soils (Ertiftik and Zengin, 2015; Narayanasamy et al., 2023). The majority of the K in plant tissue is absorbed by roots from the soil solution as a monovalent cation, and the rate of absorption is controlled by environmental and plant factors (Jan and Hussan, 2022). Even though K is typically abundant in calcareous soils, a large amount of soil K is nevertheless unavailable to plants due to imbalances between available Ca2+, Mg2+, and K ions that may result in K deficit through competitive uptake interactions (Weil and Brady, 2017).

Exhaustively cultivated calcareous soils in Pakistan generally get insufficient and or no inputs of K fertilizer despite the fact, plants absorb K significantly (Wakeel et al., 2017). The K status of the soil may possible be adversely affected by intensive farming without K application over time due to the potential mining of indigenous K reserves (Das et al., 2018). Generally, the growers apply fertilizers without following recommended sources, rates, methods and time of application. To some extent the growers apply nitrogenous and phosphatic fertilizers on large scale, however they regret to apply K fertilizers to their field crops with a general perception that K is adequate and enough for field crops to be grown on their soils (Chajjro et al., 2013; Wakeel et al., 2017).

The objective of this research was to assess the impact of potassium fertilizer sources on the growth and development of sunflower seedlings on artificially established calcareous soils with range of CaCO3 levels. Two K sources namely SoP, and MoP were tested in four different artificially prepared CaCO3 levels (<5, 10, 20 and 30%). A successful source of K could improve sunflower seedling growth in high calcareous soils.

Materials and Methods

In order to select the effective K source to improve sunflower growth in developed calcareous soils at early stage this trial was carried out in a wire-house of the Department of Soil Science, SAU, Tandojam, Pakistan under natural sunlight. The growth period was 25th February 2018 to 6th April 2018. The average maximum temperature during the experiment was between 28.6 and 39.5oC, the average lowest temperature was between 20.6 and 28.5oC, and the average relative humidity was between 31 and 49%. In plastic pots measuring 24 cm in diameter and 28 cm deep, five kilograms of soil material was placed. Using 70% of the field capacity of soil in plastic pots, all plants were irrigated every day with tap water.

Preparation of calcareous soil

The technique described by Osman et al. (1978) was used to artificially prepare calcareous soils. The soil used in the experiment (Table 1) was taken from the field of Latif farm. Four CaCO3 levels established for the study were <5, 10, 20, and 30%. The soil of each treatment was taken and properly incorporated with the necessary ratios of pure CaCO3. A steady weight of 5 kg was maintained using sand. In order to achieve equilibrium, the artificial calcareous soils were repeatedly wet and dried. The soil of each treatment was placed in 5 kg plastic pots with drainage holes at bottom. The pots were placed in the wire-house.

Experimental details

A factorial (two factors) Complete Randomized Design (CRD) with four repeats was used for the experiment. In addition to control, treatments consisted of four CaCO3 levels (Slightly calcareous = <5%, moderately calcareous=10%, strongly calcareous = 20% and very strongly calcareous = 30%) and two K fertilizer sources (SoP and MoP).

Plant material and growth conditions

A local sunflower cultivar HO-1 was used in the study. The seed was obtained from Oil Seed Research Institute, Tandojam. Seed was initially surface sterilized with 5% Sodium hypochlorite (NaOCl) solution to improve the seed germination and to prevent the growth of certain microbial contaminants. In each pot, nine sunflower achene were sowed at equally spaced and roughly two centimetres deep. After two weeks of emergence, plants were thinned to obtain five seedlings of almost uniform size in each pot. Regular irrigation with tap water was given to the plants.

Fertilizer application

The suggested dose (140-70 NP kg ha-1) of urea and diammonium phosphate was used, two sources of K, sulphate of potash (SoP) and muriate of potash (MoP), were also applied at the rate of 70 kg ha-1 at the start of the experiment.

 

Table 1: Selected physico-chemical properties of the soil used in the pots.

Parameters	Unit	Values	Categorizations	Reference
Sand	%	30	Medium texture	Bouyoucos method (1962)
Silt	%	24
Clay	%	46
Texture class (USDA)		Silty clay
EC e	(dS m-1)	1.67	Non saline	FAO (USDA)
pH		7.54	Slightly to Mildly alkaline	Rayment and Lyons (2011)
Organic matter content	%	0.65	Low	FAO (1980)
Lime content	%	4.98	Slightly-calcareous	Sahai (2004)
Exchangeable (NH4OAc)	mg kg-1	99	Low	Estefan et al. (2013)
Phosphorus (AB-DTPA)	mg kg-1	1.02	Low	Estefan et al. (2013)
Nitrogen	%	0.030	Low	Estefan et al. (2013)
Soluble Ca	meq L-1	2.70	-	-
Soluble Mg	meq L-1	1.05	-	-
Soluble K	meq L-1	0.42	-	-
K activity ratios	([K+])/√([Ca2+]+[Mg2+])	0.21	-	Basak (2007)
	([K+])/√( [Mg2+])	0.41	-	Basak (2007)
	([K+])/√([Ca2+])	0.25	-	Basak (2007)

 

Seedling growth measurement and analysis

Forty days after emergence two plant samples were uprooted from the pots and used to record the growth parameters using standard procedures.

Root and shoot weight

Shoots were separated from roots and weighted immediately using an electronic balance for fresh weight. Samples were dried at 70°C for 48 hours to attain constant weight. After being cooled to room temperature, their dry weight was measured using an electronic scale.

Measurement of chlorophyll concentration

Fresh leaf samples of sunflower plants were collected. Each sample, which weighed 0.5 g, was cut into minute pieces and homogenised with 80% (v/v) acetone in a pre-cooled mortar and pestle. The Centrifuging of the extract at 3,000 rpm was done for fifteen minutes, prepared up to 25 mL using 80% (v/v) acetone. Using a spectrophotometer (Hitachi-220 Japan), the supernatant’s absorbance was measured at wavelengths of 645, 663, and 480 nm. The concentrations of chlorophylls a and b were calculated using Arnon’s (1949) formulae.

Measurement of K concentration

The K concentration were analysed by the method as suggested by Estefan et al. (2013). The plant tissue samples were washed with distilled water before drying. Each sample remained 48 hours in an oven set at 70 oC. The plant tissue samples were dried, and then powdered in a grinder. Dry ash techniques were used to analyze the K concentration in sunflower plant tissue. Each ground sample weighed 1.0 g, and it was ashed in a muffle furnace for five hours at 550oC. The substance was then dissolved in 2 N HCl, and then made up to a volume of 100 mL using distilled water. The material was then diluted and used for K analyses with a flame photometer (Jenway PFP-7).

Statistical analysis

The data on the growth parameters, chlorophyll concentration and shoot K concentration were analyzed using Minitab® Ver. 17 for analysis of variance (ANOVA). Parameters means were compared at p <0.05.

Results and Discussion

Shoot height

The results of shoot height of sunflower seedlings as influenced by K fertilizer sources on calcareous soils are presented in Table 2. Overall, the both sources of K fertilizer on shoot height were highly significant (p<0.05). Maximum shoot height was obtained with SoP followed by MoP as compared to control. The results exhibited that the effect of CaCO3 levels on shoot height were also highly significant (p<0.05). Shoot height at CaCO3 level (30%) were significantly less than CaCO3 level <5, 10 and 20%. The effect of interaction of sources x CaCO3 levels for shoot height was statistically non-significant (p<0.05). However, as compared to CaCO3 levels shoot height at CaCO3 level (30%) was less than CaCO3 level <5, 10 and 20%. The results concluded that the application of SoP gained greater shoot height (16.33 cm) and CaCO3 level (30%) had minimum (12.83 cm) shoot height on individual basis.

 

Table 2: Effect of K sources and soil calcareous levels on shoot height and root length of sunflower at early growth stage.

Source	CaCO3 (%)
	Shoot height (cm)					Root length (cm)
	<5	10	20	30	Means	<5	10	20	30	Means
without K	15.69	14.90	14.06	11.93	14.14b	5.48	5.18	4.72	4.13	4.88b
SoP	18.24	17.56	15.56	13.97	16.33a	6.60	6.33	5.54	5.01	5.87a
MoP	17.51	17.06	15.91	12.58	15.76 a	6.09	5.90	5.47	4.34	5.45 a
Means	17.14a	16.51ab	15.18b	12.83c	-	6.05a	5.80ab	5.25b	4.49c	-
		K sources	CCL	K sources x CCL
Shoot height (cm)	SED	0.463	0.534	0.925
	LSD	0.781***	0.902***	NS
Root length (cm)	SED	0.193	0.223	0.386
	LSD	0.326***	0.377***	NS

 

Root length

The data on how K fertilizer sources affect the length of sunflower roots on calcareous soils are presented in Table 2. Overall, the both source of K fertilizer on root length were highly significant (p<0.05). In comparison to control, SoP followed by MoP produced the greatest root length. The results showed that the effect of CaCO3 levels on root length were also highly significant (p<0.05). Root length at CaCO3 level (30%) were significantly less than CaCO3 level <5, 10 and 20%. The effect of interaction of sources x CaCO3 levels for root length was statistically non-significant (p<0.05). However, compared to CaCO3 levels root length at CaCO3 level (30%) was less than CaCO3 level <5, 10 and 20%. The results concluded that the application of SoP gained greater root length (5.87 cm) and CaCO3 level (30%) had minimum (4.49 cm) root length on individual basis. However, treatment combination of source SoP x CaCO3 level <5% had more (6.60 cm) root length.

Fresh shoot weight

The data on how two K fertilizer sources on calcareous soils affected the fresh shoot weight of sunflower is shown in Table 3. The effect of SoP and MoP sources of K fertilizer on fresh shoot weight were highly significant (p<0.05). As compared to the control, SoP and then MoP yielded the highest fresh shoot weight. The findings demonstrated that CaCO3 levels had a highly significant (p<0.05) impact on fresh shoot weight. Fresh shoot weight at CaCO3 level (30%) were significantly less than CaCO3 level <5, 10 and 20%. The statistics showed that the interaction between sources and CaCO3 levels had no significant (p <0.05) influence on fresh shoot weight. However, compared to CaCO3 levels fresh shoot weight at CaCO3 level (30%) was less than CaCO3 level <5, 10 and 20%. The results concluded that the application of SoP gained greater fresh shoot weight (8.00) g and CaCO3 level (30%) had minimum (5.69 g) fresh shoot weight on individual basis. However, treatment combination of source SoP x CaCO3 level <5% had more (9.32 g) fresh shoot weight.

Dry shoot weight

The result pertaining of dry shoot weight of sunflower (Table 3) indicated that the effect of K sources and CaCO3 levels was highly significant (p<0.05), but the interaction of sources x CaCO3 levels was non-significant at (p<0.05). Dry shoot weight decreased with increasing CaCO3 levels. Maximum dry shoot weight was observed in CaCO3 level <5 and 10%. However dry shoot weight was decreased by 28.84% over CaCO3 level <5% in CaCO3 level 30%. In case of sources greater dry shoot weight observed in SoP and MoP while lower dry shoot weight was found in control. Between sources under different CaCO3 levels results further indicated that the greater shoot weight (1.22 g) was observed in SoP at CaCO3 level <5% and lowest was observed in control at CaCO3 level 30%.

Fresh root weight

Data regarding fresh root weight of sunflower as influenced by different CaCO3 level and K fertilizer sources are shown in Table 4. The findings showed that the impact of CaCO3 levels and K sources was highly significant (p<0.05) for fresh root weight. However, CaCO3 levels x K sources interaction was non-significant at (p<0.05). Fresh root weight of

 

Table 3: Effect of K sources and soil calcareous levels on fresh shoot weight and dry shoot weight of sunflower at early growth stage.

Source	CaCO3 (%)
	Fresh shoot weight (g)					Dry shoot weight (g)
	<5	10	20	30	Means	<5	10	20	30	Means
without K	6.72	6.52	6.15	5.26	6.16b	0.88	0.85	0.80	0.68	0.80b
SoP	9.32	8.87	7.54	6.27	8.00a	1.22	1.13	1.00	0.82	1.04a
MoP	7.87	7.50	7.01	5.55	6.98b	1.03	0.98	0.91	0.73	0.91b
Means	7.97a	7.63a	6.90 a	5.69b	-	1.04a	0.98a	0.90a	0.74b	-
		K sources	CCL	K sources x CCL
Fresh shoot weight	SED	0.399	0.460	0.797
	LSD	0.673***	0.777***	NS
Dry shoot weight	SED	0.049	0.057	0.098
	LSD	0.083***	0.096***	NS

 

Table 4: Effect of K sources and soil calcareous levels on fresh root weight and dry root weight of sunflower at early growth stage.

Source	CaCO3 (%)
	Fresh root weight (g)					Dry root weight (g)
	<5	10	20	30	Means	<5	10	20	30	Means
without K	0.64	0.58	0.54	0.44	0.55b	0.30	0.25	0.21	0.18	0.23c
SoP	0.75	0.69	0.60	0.53	0.64a	0.33	0.29	0.25	0.21	0.27a
MoP	0.70	0.65	0.60	0.46	0.60a	0.32	0.28	0.24	0.18	0.25b
Means	0.70a	0.64b	0.58c	0.48d	-	0.32a	0.27b	0.23c	0.19d	-
		K sources	CCL	K sources x CCL
Fresh root weight	SED	0.018	0.021	0.037
	LSD	0.031***	0.036***	NS
Dry root weight	SED	0.006	0.006	0.011

 

Table 5: Effect of K sources and soil calcareous levels on chlorophyll a and chlorophyll b concentration of sunflower at early growth stage.

Source	CaCO3 (%)
	Chlorophyll a concentration (mg g-1 fw)					Chlorophyll b concentration (mg g-1 fw)
	<5	10	20	30	Means	<5	10	20	30	Means
without K	0.988	0.824	0.739	0.587	0.785b	0.534	0.416	0.369	0.264	0.396c
SoP	1.252	1.074	0.882	0.700	0.977a	0.937	0.786	0.660	0.434	0.704a
MoP	1.105	0.928	0.828	0.656	0.879b	0.708	0.545	0.439	0.324	0.504b
Means	1.115a	0.942b	0.816c	0.648d	-	0.727a	0.582b	0.489b	0.341c	-
		K sources	CCL	K sources x CCL
Chlorophyll a concentration	SED	0.040	0.047	0.081
	LSD	0.068***	0.079***	NS
Chlorophyll b concentration	SED	0.031	0.035	0.061

 

sunflower was high (0.64 g) in SoP source of K and less (0.55 g) in control. In K sources under different CaCO3 levels greater fresh root weight was found in SoP at CaCO3 level <5% while less (0.44) in case of control at CaCO3 level 30%. In overall CaCO3 levels, fresh shoot weight decreased with increasing CaCO3%. Between sources highest fresh shoot weight (0.64 g) was observed in SoP followed by MoP (0.60 g) and the control (0.55 g).

Dry root weight

Statistical analysis of data for sunflower dry root weight presented in Table 4 showed that the effect of CaCO3 levels as well as K sources differed significantly (p<0.05), while interaction of CaCO3 levels x K sources interaction was non-significant at (p<0.05). Greater dry root weight (0.27 g) was significantly produced from SoP followed by MoP (0.25 g) as compared to control which produced (0.23 g). with respect to CaCO3 levels, CaCO3 <5% attained larger dry root weight (0.32 g) then decreased by 14.49%, 26.77% and 40.35 in CaCO3 10%, 20% and 30%, respectively. Between sources under different CaCO3 levels results further indicated that the greater dry root weight (0.33 g) was observed in SoP at CaCO3 level <5% and lowest was observed in control at CaCO3 level 30%.

Chlorophyll concentration

Tables 5, 6 summarize the results of the influence different CaCO3 level and K fertilizer sources on chlorophyll a, b and total concentration of sunflower seedlings. With increasing percentages of CaCO3, chlorophyll a, b and total concentration decreased progressively (p<0.05) in comparison to controls. Significant increases of the chlorophyll a, b and total concentration of sunflower seedlings (p<0.05) were detected in both the sources of K. The primary leaves of sunflower were significantly affected by CaCO3 levels, which resulted in a decline of chlorophyll a, b and total concentration. Presence of 30% CaCO3 levels resulted in a significant decrease of chlorophyll (a, b and total). Beyond that concentration, decrease of chlorophyll a, b concentration was observed with elevated concentration level of CaCO3. When sunflower leaves were exposed to 30% CaCO3 levels, the amount of chlorophyll a, b reached a minimum value. Chlorophyll concentration of seedlings produced from CaCO3 levels with 10, 20 and 30% CaCO3 were decreased by 15.54, 26.80 and 41.92%, respectively, compared to the CaCO3 level (<5%) seedlings (p<0.05). CaCO3 stress caused a significant reduction in chlorophyll a and b concentration of the sunflower seedlings. Application of potash in the form of SoP improved the Chlorophyll concentration by 24.52% and 12.06% with MoP compared with the control.

Shoot K concentration

K concentration in shoot of sunflower seedlings as influenced by different CaCO3 level and K fertilizer sources are shown in Table 6. The results indicated the effect of CaCO3 levels and K sources was highly significant (p<0.05), but the interaction of CaCO3 levels x K sources was non-significant at (p<0.05). There was a decreasing trend in K accumulation in shoots by increasing CaCO3 levels. Maximum K was observed in where level of CaCO3 was <5%. However, K accumulation was decreased by 30.44% over CaCO3 <5% in CaCO3 30%. The effect of sources for K concentration in shoot was significant (p<0.05). Application of K sources caused increase in shoot K content. The shoot K content was increased by 31.14% with SoP and 13.92% with MoP compared with the control.

In this study, two K fertilizer sources SoP and MoP were tested by conducting pot experiment. This study was to find out the effective K source under different levels of CaCO3 (<5, 10, 20, and 30%) which improved sunflower growth at early stage. The results revealed that both sources of K fertilizer significantly enhanced the growth, chlorophyll content, and shoot K concentration parameters of sunflower seedlings grown in pots with varying levels of calcareousness. Regardless of the two sources of K fertilizer, K application increased shoot height, root length, fresh and dry shoot weight, fresh and dry root weight, Chlorophyll concentration and shoot K concentration. Potassium used as SoP demonstrated a greater improvement in growth parameters, chlorophyll concentration and shoot K concentration in sunflower seedlings. Comparatively, potassium applied as MoP performed lower in growth and other parameters. These results are related to the earlier findings of Zhang et al. (2017) in which it was found that addition of potassium fertilizer enhanced the chlorophyll concentration in leaves of Brassica oleracea. These results are also in accordance with those provided by Kapourchal et al. (2011) and Arshadullah et al. (2014) but results are contradictory to those Ayub et al. (1999) and Bakht et al. (2010). The inconsistent results could have been caused by variations in the CaCO3 levels or chloride (Cl-) contents of the soil (Hussain et al., 2015).

The findings also demonstrated that increasing CaCO3 level in the soil decreased the growth parameters, chlorophyll concentration and shoot K concentration in sunflower seedlings. Higher the values for all the growth parameters, chlorophyll and shoot K concentration parameters recorded at slightly calcareous level <5% CaCO3 level and lowest at strongly calcareous level of 30% CaCO3. High calcium levels in the soil solution may decrease K uptake by

 

Table 6: Effect of K sources and soil calcareous levels on total chlorophyll concentration and shoot K concentration of sunflower at early growth stage.

Source	CaCO3 (%)
	Total chlorophyll concentration (mg g-1 fw)					Shoot K concentration (%)
	<5	10	20	30	Means	<5	10	20	30	Means
without K	1.620	1.287	1.137	0.876	1.230b	2.80	2.67	2.49	2.09	2.5b
SoP	2.053	1.678	1.357	1.045	1.533a	3.88	3.59	3.14	2.56	3.29a
MoP	1.811	1.451	1.274	0.981	1.379ab	3.26	3.08	2.85	2.25	2.86b
Means	1.828a	1.472b	1.256c	0.967d	-	3.31a	3.12ab	2.83b	2.30c	-
		K sources	CCL	K sources x CCL
Total chlorophyll concentration	SED	0.066	0.076	0.132
	LSD	0.112***	0.129***	NS
Shoot K concentration	SED	0.059	0.084	0.119
	LSD	0.123***	0.139***	NS

 

the crop (Wakeel et al., 2017). Chohan et al. (2015) indicated that high amount of lime can be one of the major factors responsible for lowering K availability in these soils. Generally, low soil K availability limits plant growth and decreases sunflower yield (Li et al., 2014). CaCO3 in soil solution disturbs soil properties associated to the growth of plant including availability of plant nutrient, soil crusting and soil water relations (Wahba et al., 2019). Plants in calcareous soils experience reduced K availability, which causes much more severe problems than K deficiencies (Alghamdi et al., 2023). The K requirement of a sunflower crop and the need for fertilizer K may vary significantly
depending on soil and climatic conditions (Li et al., 2018). Though it may not be the always same for all crops, the uptake of K by crops is also considerable affected by other cations (Amo et al., 2023).

This study was conducted in an artificial environment which may not accurately represent natural conditions. A limited sample size, a single cultivar of sunflower seedlings, and fertilizer nutrient K source, artificially prepared calcareous soils may have contributed to the results of the study. There may have been an absence of consideration of the interactions between soil nutrients, weather conditions, pests and diseases, or the potential long-term effects on the soil and environment that may have been overlooked in this study. A further limitation of the study may be that it was conducted over a short period of time and was not replicated in other places. In future studies, the sample size could be increased, investigate the interaction between K fertilizers with nitrogen, phosphorus, and micronutrients such as boron, to use zinc in a broader range of calcareous soil types, environmental factors could be taken into account, and multiple cultivars of sunflower seeds may be used. Moreover, research studies could be conducted over a longer period of time to gain a better understanding of the potential fertilizer K effects on sunflower seedlings under various calcareous soil conditions.

Conclusions and Recommendations

It is concluded that under calcareous soil conditions, potassium fertilization either in the form of SoP or MoP could more effectively promote sunflower seedling growth. Application of SoP in calcareous soils is recommended for better early growth. It would be evaluated further to confirm our findings.

Novelty Statement

The findings of study confirmed that increasing the CaCO3 level in the soil decreased the growth parameters, chlorophyll concentration, and shoot K concentration in sunflower seedlings. The results showed that both SoP and MoP K fertilizer sources improved the growth, chlorophyll content, and shoot K concentration parameters of sunflower seedlings grown in pots with varying levels of calcareousness in the soil.

Author’s Contribution

Abdul Aleem Memon: Conceived the idea, designed the study, did chemical analysis, wrote abstract, introduction, methodology, data collection, data entry in minitab and analysis, results and discussion, conclusion, and references.

Inayatullah Rajpar: Conceptualization, designed the study, supervision, elaborated the intellectual content and modifies the manuscript.

Ghulam Murtza Jamro: Conceptualization, designed the study, supervision, elaborated the intellectual content and, reviewed, proof reading, manuscript revision, plagiarism check.

Javeed Shah: Reviewed proof reading, manuscript revision and modify the manuscript.

Conflict of interest

The authors have declared no conflict of interest.

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