Identification of phosphorus use efficiency of different sunflower genotypes at Tandojam-Pakistan

A field study, phosphorus use efficiency ratio of eight sunflower genotypes (Samsung 20, Mehran 2, HO-1, Melabour, Samsung 30, Valugur, Chinika and Sputnik) was determined. The control and treatment plots were fertilized with NP at100-50 kg ha and 100-90 kg ha respectively in randomized completer block design. Results revealed that the overall trend of all genotypes has shown that all agronomic traits and yield parameters were significantly influenced and increased when P level increased. Treatment and genotypes and the interactive effect of increased P level and genotype were also significantly affected seed and leaf P-uptakes (P<0.05). The sunflower crop in treatment and control plots produced plant height 184.39 and 177.69 cm, stem girth 6.45 and 6.22 cm, head diameter 18.85 and 15.72 cm, head weight 1959.8 and 1786.7 g, shoot dry weight 30.13 and 19.11 g, seeds head 2048.8 and 1588.5, seed yield kg ha 17451 and 1887.9 kg ha, leaf P-uptake 0.259 and 0.113%, seed P-uptake 0.252 and 0.109%, respectively. The HO-1 surpassed all the sunflower genotypes for agronomic traits with highest values for seeds head (2153.5), shoot dry weight (29.82 g), plant height (199.97 cm), head diameter (21.10 cm), head weight head weight (2279.1 g), stem girth (7.13 cm) and seed yield (2463 kg ha). The HO-1 showed higher P-use efficiency ratio than rest of the genotypes. It was observed that sunflower genotypes responded positively to increase rate of P fertilizer; however, there was significant variation in genotypes for response towards P use efficiency ratio.


Introduction
Sunflower (Helianthus annuus L.) is one of the four most important oil crops in the world [1,2].Because of its moderate cultivation requirements and high oil quality, its acreage has increased in both developed and developing countries [3].Sunflower oil contains high percentage of poly-unsaturated fatty acids that reduces cholesterol in blood and prevents heart diseases [4].Sunflower oil is quite palatable and contains soluble vitamins A, D, E and K [5-7].In Pakistan, sunflower has the potential to bridge up the gap between demand and supply of edible oil and it is well adapted to existing agro-ecological conditions.There are many factors which are responsible for low yield; management of fertilizers may be of much importance [8,9].The balanced nutrient application for crop production is essential and their imbalance use reduces crop yields.All sources of nutrients may be applied to crops and advocated that foliar fertilization is widely used practice to correct nutritional deficiencies in plants caused by improper supply of nutrients to roots [10].Phosphorus (P) is an essential nutrient both as a part of several key plant structure compounds and as a catalysis in the conversion of numerous key biochemical reactions in plants [11].The amounts, forms and associated dynamics of soil P are influenced by a number of factors including soil type and environmental conditions, as well as landuse and management practices [10].Phosphorus is involved in controlling key enzyme reactions and in the regulation of metabolic pathways [12].According to different researchers, almost 90% of soils in Pakistan are deficient in P at different severity levels and hence, to apply P is inevitable [13].Furthermore, its deficiency trims down the yield from 10 to 15% [14].Reliance on the increased use of chemical fertilizers and associated hazards put attention on organic sources which are effective in promoting health and productivity of the soil.Integrated management of chemical fertilizers and organic wastes may be an important strategy for sustainable production of crops [15].Sunflower in terms of P use efficiency in nutrient solution and the growth of both species responded strongly to increasing P supply.Sunflower is more efficient in terms of P uptake and utilization at optimal and sub-optimal P levels as compared to other oil seed crops.Pakistani soils are calcareous, generally deficient in P and its deficiency can reduce the yield of crops upto 15 percent [16,17].Kumar et al. [18] conducted an experiment and declared that in various P doses, 60 and 90 kg P ha -1 emerged to be the ideal as for the vegetative growth of plants.In other study [19] conveyed that growth and yield are significantly affected by P rate.There are different views of scientists about role of phosphorus on oil percentage of crops.Lickfett et al. [20] revealed that plant height was enhanced by phosphorus fertilizer.The present study was undertaken on the identification of P use efficiency of different sunflower genotypes.

Materials and methods
The present study was conducted on the identification of phosphorus use efficiency of sunflower genotypes at the experimental fields of oil seeds section, Agriculture Research Institute Tandojam Pakistan during 2016.The experimental land was prepared in offseason and soaked.After soaking dose when land came in condition, the seedbed was prepared as per recommendations.Having a good seed bed, the main plot was divided into three main plots in the RCBD and of these three plots each was divided into eight sub-units of 3.0 m × 5.0 m (15.0 m 2 ).In all, 24 sub-plots were prepared in three replicates of eight treatments.The seeds of eight sunflower genotypes i.e.Mehran 2, Valugur, Samsung 20, Samsung 30, Chinika, Sputnik, HO-1 and Melabour were sown by drilling, after emergence of seedling, thinning was performed to maintain the recommended plant population with 45 cm plant to plant and 60 cm row to row spacing.

Soil analysis
Soil samples were collected at two depths i.e. 0-15 cm and 15-30 cm and these samples were brought to the laboratory of Plant Nutrition, Department of Soil Science, Faculty of Crop Production, Sindh Agriculture University, Tandojam for some basic physico-chemical properties Texture, electrical conductivity, pH, organic matter % and AB-DTPA extractable P. Leaf/Seed P The sunflower leaves and seeds were taken from experimental field for the determination of leaf/seed P content from both sunflower genotypes treatments.Diagnostic leaf and sunflower seed samples were digested with nitric and perchloric acid mixture (1:2).The samples were analysed for P content by developing vanadomolybdo phosphoric acid yellow colour method.

P-Use efficiency Ratio
The P-use efficiency ratio was calculated according to the formula suggested by Brar et al. [21].

Statistical analysis
The data thus collected were statistically analysed using Students Statistical Software Package (Statistix ver.8.1).The ANOVA was derived to examine the significance of treatment effect; while the LSD test was applied to compare the mean values for assessing significance of effect among treatments.

Soil physic-chemical properties
The data related to physic-chemical properties of soil used in this experiment.The soil was clay loam in texture, slightly alkaline, non-saline in nature, low in organic matter and available P at both soil depths i.e. 0-15 and 15-30 cm.

Plant height (cm)
The results (Table 1) showed that increased P level had significant impact among sunflower genotypes, which showed significant variation (P<0.05) in their plant height.The interactive effect of treatments and genotypes was also found significant (P<0.05).The increased rate of P 90 kg ha -1 increased sunflowers plant height 184.39 cm as compared to those in control plots with recommended P level of 50 kg ha -1 (177.69 cm).The increase in plant height in plots given P at increased rates was 3.77% over control.The varietal response showed that sunflower variety HO-1 produced maximum plants height (199.97 cm), followed by Mehran 2, Chinika and Sputnik with average plant height of 190.09, 186.44 and 182.76 cm respectively.However, the minimum plant height (169.01 cm) was recorded in genotype Valugur.Sunflower genotypes Melabour and Samsung 20 showed similarity in plant height; while Samsung 30, Valugur and Sputnik also showed more or less (P>0.05)plant height.The interactive effect showed that the maximum plant height 213.61 was found in variety HO-1 when treated with increased P level (90 kg); while genotype Samsung 30 in control showed lowest plant height (168.67cm).

Stem girth (cm)
The effect of P level was significant on the stem girth of sunflower (P<0.05) and presented in (Table 1).It showed variation (P<0.05)due to different genotypes as well as interactive effect of P treatments and genotypes.The increased P level (90 kg ha - 1 ) produced sunflower plants with thicker stems (6.45 cm) as compared to those in control plots with recommended P level of 50 kg ha -1 (6.22 cm).The increased P rate also enhanced stem girth (3.70%) over control.Among the genotypes, The HO -1 possessed maximum stem girth 7.13 cm, followed by Mehran 2, Sputnik and Chinika with average stem girth of 7.10, 6.67 and 6.26 cm, respectively.However, the minimum stem girth 5.98 cm was measured in genotype Valugur.Rest of the genotypes Samsung 20, Melabour and Valugur were more or less equal in stem girth (P>0.05).

Shoot dry weight (g)
The results regarding shoot dry weight is given in (Table 2) and showed that the effect of applied P on shoot dry weight was significant (P<0.05) and eight genotypes variation were also significant (P<0.05).However, interactive effect of treatments and genotypes was insignificant on shoot dry weight (P>0.05).The increased rate of P (90 kg ha -1 ) resulted in higher shoot dry weight (30.13 g) as compared to control.The results showed that the shoot dry weight under lower P application rate of 50 kg ha -1 (Control), were declined (19.11 g).The increase in shoot dry weight in treatment plots was 57.67 percent over control.The varietal response showed that HO-1 produced maximum shoot dry weight (29.82 g), followed by genotypes Mehran 2, Sputnik and Chinika with average shoot dry weight of 27.29, 26.01 and 24.37 g, respectively.However, the lowest shoot dry weight (22.19 g) was recorded in genotype Melabour.Sunflower genotypes Melabour and Valugur as well as Samsung 20 and Samsung 30 showed similarity (P>0.05) for shoot dry weight.The interactive effect showed that the highest shoot dry weight (36.44 g) was noted in variety HO-1 when treated with increased P level (90 kg); while genotype Melabour remained least for shoot dry weight (17.15 g).

Seed head -1
The results about seed head -1 have been summarized in (Table 2).The data showed that the significant variation in the number of seeds head -1 due to treatment effect and for genotypes of diversified origin (P<0.05); while insignificant interactive effect of treatment and genotype (P>0.05).The treatment comprised of increased rate of P (NP @100-90 kg ha -1 ) resulted in an increased number of seeds (2048.8 head -1 ) over control (NP @100-50 kg ha -1 ) where the number of seeds declined to 1588.5 head -1 .The increase in seeds head -1 in treatment plots was 28.98 percent over control.The varietal response showed that HO-1 produced maximum number of seeds (2153.5 head -1 ), followed by genotypes Mehran 2, Sputnik and Chinika with 2000.2,1911.0 and 1827.2 seeds head -1 , respectively.However, the lowest number of seeds (1647.7 head -1 ) was recorded in genotype Valugur.Sunflower genotypes Samsung 20, Melabour, Samsung 30 and Valugur showed similarity (P>0.05) in number of seeds head -1 .The interactive effect showed that the highest number of seeds (2373.4 head -1 ) was recorded in variety HO-1 when treated with increased P level (90 kg); while genotype Melabour in control remained least for number of seeds (1429.8 head -1 ).

Seed yield (kg ha -1 )
The results showed in this (Table 2) related to the data on sunflower seed yield kg ha -1 that increased P level resulted in a significant effect on seed yield kg ha -1 (P<0.05); and the seed yield kg ha -1 varied significantly in sunflower genotypes used in this study (P<0.05);whereas the interactive effect of treatments and genotypes was insignificant (P>0.05) on seed yield kg ha - 1 .It is suggested that increased P level.Produced higher sunflower yields (17451 kg ha -1 ) as compared to those in control plots with recommended P level of 50 kg ha -1 (1887.9kg ha -1 ).The treatment plots increased 15.55 percent seed yield kg ha -1 over control plots.In variety, HO-1 produced higher seed yields (2463 kg ha -1 ), followed by genotypes Sputnik, Mehran 2, and Chinika with average seed yield of 2179, 2153 and 2053 kg ha -1 , respectively.However, the lowest seed yield (1846 kg ha - 1 ) was recorded in genotype Melabour.The genotypes Samsung 20, Melabour, Samsung 30 and Valugur showed similarity for seed yield kg ha -1 (P>0.05); and Mehran 2, Sputnik and Chinika also showed negligible difference in seed yield (P>0.05).The treatment interaction showed that the maximum seed yield (2463 kg ha -1 ) was recorded in variety HO-1, when it was treated with increased P level; while genotype Melabour remained lowest in seed yield (1846 kg ha-1 ) when sown in control plot.

Leaf P-uptake (%)
The results showed in this (Table 2) for the data on leaf P-uptake described that the effect of higher rate of P application, genotypes as well as treatment and genotype interaction was significant on leaf P-uptake (P<0.05).thefurther results showed that the increased rate of P (90 kg ha -1 ) resulted in higher leaf P-uptake (0.259 %) as compared to control 0.113 % leaf P-uptake recorded in crop given lower P.A high significant difference has been recorded for in treatment plots where 129.20 percent leaf P uptake was higher over control.The varietal effect showed that the leaf P-uptake was higher in genotype Sputnik 0.335%, followed by genotypes Chinika, Valugur and HO-1 with average leaf P-uptake of 0.267, 0.224 and 0.188 percent, respectively.However, the lowest leaf P-uptake (0.093 %) was determined in genotype Samsung 20.The treatment and genotype interaction showed that the highest leaf P-uptake (0.564 %) was examined in genotype Sputnik when treated with increased P level (90 kg ha -1 ); while the minimum leaf P-uptake (0.076 %) was determined in genotype Samsung 20 in control.

Seed P-uptake (%)
The results in (Table 3) showed that the analysis of variance for the data on seed P-uptake indicated that the effect of increased P rate, genotypes as well as interactive effect of treatments and genotypes was significant on seed P-uptake (P<0.05).The data indicated that the increased rate of P (90 kg ha -1 ) resulted in higher seed P-uptake (0.252 %) as compared to 0.109 % (control) seed Puptake recorded in crop given lower P (50 kg ha -1 .The seed P-uptake in treatment plots was 131.19 percent higher over control.The varietal effect showed that the seed P-uptake was higher in genotype Chinika (0.337%), followed by genotypes Sputnik, Melbour and Samsung 30 with average seed P-uptake of 0.323, 0.308 and 0.292 percent, respectively.However, the lowest seed Puptake (0.181 %) was determined in genotype Samsung 20.The treatment and genotype interaction showed that the highest seed P-uptake (0.409 %) was determined in genotype Chinika when treated with increased P level (90 kg ha -1 ); while the minimum seed P-uptake (0.109 %) was recorded in genotype Samsung 20 in control.

P-Use efficiency Ratio
The results regarding P-use efficiency ratio has been summarized in (Table 3) and showed that the effect of increased phosphorus level on different sunflower genotypes.asignificant impact on P-use efficiency ratio of different sunflower genotypes with increasing P application rates have been observed.

Discussion
Sunflower genotypes of diversified origin were evaluated against increased phosphorus level (NP @100-90 kg ha -1 ) and agronomic as well as seed/leaf P-uptake was compared with recommended dose of fertilizers (NP @100-50 kg ha -1 ) which was considered as control.The results are discussed as under: The findings of the study showed that values for all the agronomic traits as well as seed/leaf P-uptakes were significantly influenced by increasing the P level over the control (P<0.05).observed similar results.They evaluated that higher phosphorus at the rates of 0, 30, 45, 60 kg ha -1 has increased plant height, stem girth, head diameter, seeds head -1 , seed weight head -1 , seed index, and seed yield.In another study, Sadozai et al.

Table 3 . Effect of P level on the growth and yield parameters of sunflower genotypes Seed P-uptake (%) S. No. Genotypes Control(NP @100-50 kg ha -1 ) Treatment(NP @100-90 kg ha -1 ) Mean for genotypes
[33]zynski et al. [25]argued that the soil has become deficient of P and needs additional P supply for achieving desired crop production.Poonia[26]found that 40 kg ha -1 P gave an economic seed yield of 2373 kg ha -1 in sunflower.In many another studies in various parts of the world the other researchers [ 27, 28] evaluated and suggested that 40-80 kg P ha -1 can be used for achieving economically higher values for head diameter (13.71 cm), 100-seed weight (5.88 g) and seed yield (998 kg ha -1 ) and crop yields in sunflower.In most of the findings, similar results were obtained by many researchers while [29] recommended 120 kg P2O5 for achieving desired sunflower yields as compared to recommended 75 kg ha -1 P2O5.In other study,[30]argued that phosphorus up to 40 kg ha -1 was not adequate while 80 kg P2O5 ha -1 resulted in higher crop performance in sunflower.[29]Thavaprakashetal. achieved highest sunflower seed yield (3554 kg) with 120 kg P2O5 ha -1 over control.Bono et al. [31]obtained greatest sunflower yield (3750 kg ha -1 ) with 100 kg ha -1 phosphorus applied in addition to recommended rates of N fertilizers.Our results are accordance with the results of [32], who reported that when phosphorus level increases the sunflower yield also increases.Sidiqi et al.[33]