Phosphorus High-rate application through band placement improved cotton productivity under arid climate

Abstract

The plant-available soil phosphorus rate and methods for applying phosphatic fertilizer and soil P-fixation capacity are critical factors for lower cotton productivity in Southern Punjab, Pakistan. Hence, a two-year study was conducted in Central Cotton Research Institute (CCRI), Multan, Pakistan, to examine the effects of various P rates and application methods on cotton crop output during the growing seasons of 2014 and 2015. Phosphorus was applied in four rates (0, 40, 80, and 120 kg ha⁻¹ P₂O₅) using broadcast, band application, and fertigation methods. Results indicated that the impact of P rates was statistically significant on plant height, the number of nodes, monopodial and sympodial branches, leaf area index, harvest index, and seed cotton yield. The greater P application (120 kg P₂O₅ ha⁻¹) had a better effect on cotton productivity than the lower application rates (0, 40, and 80 kg P₂O₅ ha⁻¹). The band application responded better on nodes plant⁻¹, sympodial branches plant⁻¹, boll weight, leaf area index, lint yield, and harvest during the growing season 2015. Therefore, by adopting the band application coupled with 120 kg P₂O₅ ha⁻¹ rather than the conventional method of broadcast, productivity of cotton crops could be increased.

Introduction

Cotton has a 0.6% and 2.4% share in Gross domestic production (GDP) and value-added agriculture in Pakistan, respectively. In Pakistan, it is grown over an area of 2.37 M ha, and 9.86 M bales are collected with an average yield of 710 kg per hectare in 2018–19, significantly less than the production in developed nations. During 2021–22, the cropped area declined to 1937 thousand hectares (6.8%) against last year’s 2079 thousand hectares. Lower cotton productivity in Pakistan might be due to the usage of poor-quality seeds, water stress, severe insect pest attacks, insufficient supply of mandatory nutrients, and inappropriate planting practices^1–3. Cotton crop requires more essential nutrients throughout growth. Among different nutrients, P is a crucial part of ribonucleic acid, phospholipids, and nucleic acids play a critical part in numerous physiological and biochemical activities such as photosynthesis and regulate all energy-demanding metabolic procedures^4,5. It is essential in adequate amounts during cell division and expansion^6,7.

Edaphic conditions such as low fertility, salinity, cause unavailability the nutrients for plant uptake. Thus, nutrients supply is a crucial agronomic practice to afford crop plants by required essential elements⁸. Nutrient fertilization program is one of the key factors that influence crop growth and productivity^9,10. Consequently, to increase production and fiber quality, one must be aware of the P rates necessary for the various varieties in the given local environment. The availability of P in cotton can be improved by adopting appropriate fertilizer application techniques¹¹. In this regard, P fertilizers are usually applied through broadcast techniques at sowing time in Pakistan, boosting the transformation of soluble to insoluble forms and uneven distribution in soils¹². Applying P via band application in heavy-textured alkaline soils with low rainfall effectively improves its uptake^13,14. The band placement technique is effective. Roots are near the P applied in band application, improving efficiency^15,16. If P fertilizer is used with the first irrigation after crop germination, its effectiveness is increased because it quickly becomes accessible to plant roots and has minimal interference with the soil⁴. Thus, the accessibility of P to plants depends upon the method of application P fertilizer. Consequently, to increase production and fiber quality, one must be aware of the P rates necessary for the various varieties in the given local environment¹⁷. In P fertilization programs, various methods and forms (biological, organic and inorganic) could be applied to amend the soil medium for achieving high P uptake and utilization^18–21.

Unfortunately, little research has been done to examine the effects of a fixed rate of P and its application methods on the production of cotton in Multan, Pakistan’s arid climate. Consequently, the main objective of this research was to determine the best P fertilizer rate and application technique to raise BT cotton’s productivity in arid climate.

Materials and methods

Site description

The two-year field study was undertaken at Central Cotton Research Institute (CCRI), Multan, Pakistan (30.1718° N, 71.4413° E). The test site has a dry climate with warm summers and cool winters. The experimental soil was a sandy loam (sand: silt: clay = 65: 21: 14), which had a bulk density of 1.45 g cm⁻³, an electrical conductivity (EC) of 1.2 dSm⁻¹, a pH of 8.2, total nitrogen (N) of 0.13 mg kg⁻¹, organic matter (OM) of 0.86%, available P of 7.2 mg kg⁻¹, and available potassium (K) of 250 mg kg⁻¹ (Table 1).

Table 1.

Physiochemical properties of experimental soil.

Parameters	Units	Values	References
Electrical conductivity	dS m−1	3.20	52
pH	–	8.40	53
Total N	%	0.01	54
Available Phosphorus	mg kg−1	7.66	55
Available potassium	mg kg−1	250	56
Bulk density	g cm−3	1.45	57

Climate conditions

During the growing season, higher precipitations (273.6 mm) were observed as compared to the growing season in 2014 (134.4 mm) (Fig. 1). However, the crop was irrigated with supplementary water; no water shortage was recorded in both growing seasons. The average temperature (37 °C) in both growing seasons remained the same. The maximum temperature (51 °C) was recorded in July in both growing seasons.

Figure 1.

Daily precipitation and maximum (red line), average (green line), and minimum (orange line) temperature in Multan, Pakistan, from January 2014 to December 2015.

Treatments

Cotton was grown under different P levels (P₂O₅), i.e., 0, 40, 80, & 120 kg ha⁻¹; however, fertilizer was applied via band placement, broadcast, and fertigation methods. The BT-Cotton variety CIM-616 was used as test material. The experiment followed a split-plot Randomized Complete Block Design (RCBD) with three replications in two years. The application methods were placed in main plot while P rates in sub-plots. The fertilizer broadcast was carried out by hand before the cotton seed sowing, while band application was placed side by side with seed placement. However, in fertigation, the fertilizer was thoroughly mixed with water in plastic tank and placed in the water channel during the first irrigation.

Field experiment

The experimental plot was tilled at a depth of 30 cm to make raised beds (0.3 m high, 1 m wide, 4 m long). The layout was made in the plots through demarcation, and treatments were applied in a split-plot arrangement where P methods were in main plots, and P rates were in subplots. The seeds of the BT-cotton variety CIM-616 were sown using the dibbler method in May 2014 and 2015. Before sowing, the initial irrigation was applied, and subsequent irrigations were scheduled to the soil moisture level. The recommended dose (145 kg ha⁻¹) of N was applied in three identical splits, i.e., sowing time, the start of blooming, and the boll formation phase. K fertilizer (62 kg ha⁻¹) was applied as a basal dose at sowing time. The P was applied during sowing as per the treatment plan. Weeds and insect pests were controlled by weedicides and pesticide application, respectively. The cotton crop was harvested when bolls were around 60% open. Three cotton pickings were done during the respective growing seasons of September, October, and November. The same practices were repeated in both cotton growing seasons in 2014 and 2015 (Table 2).

Table 2.

P value of main and interaction effect of phosphorus application methods and phosphorus rates on the productivity of cotton during 2014 and 2015.

Factors	Plant height	Nodes plant−1	Monopodial branches plant−1	Sympodial branches plant−1	Boll weight	Leaf area index	Seed cotton yield	Lint yield	Harvest index
Growing season–2014
Phosphorus method (M)	0.790	0.710	0.550	0.260	0.910	0.730	0.530	0.240	0.950
Phosphorus rate (R)	0.380	0.010	0.010	< 0.001	< 0.001	0.000	< 0.001	< 0.001	0< 0.001
M × R	0.960	0.930	0.550	0.990	0.780	0.950	0.990	0.820	0.790
Growing season–2015
Phosphorus method (M)	0.790	0.890	0.370	0.310	0.390	0.200	0.390	0.240	0.160
Phosphorus rate (R)	0.380	0.180	0.140	0.030	0.050	0.030	0.000	0.000	0.580
M × R	0.960	0.690	0.990	0.840	0.630	0.980	0.990	1.000	0.970

Data collection

From 10 tagged plants from each treatment, the height of the plant, node number, monopodial branches, and sympodial branches plant⁻¹ were counted. Seed cotton was manually collected thrice (September, October, and November). The weight of the collected bolls was determined after they had been solar-dried to a moisture content of less than 11%²². To determine the yield of seed cotton and lint, the dried bolls were ginned. The ratio of biological yield to seed cotton yield was used to determine the harvest index. The following equation was used to determine the leaf area index²³:

$$\text{LAI}=\frac{\text{L}\times \text{W}\times \text{N}\times \text{K}}{\text{Land area}\left(\text{cm}\right)\text{ocupied by one plant}}$$

were, L = Length of leaf in cm, W = Width of leaf in cm, N = Number of leaves per plant, K = constant factor (0.774 for cotton).

Statistical analysis

The data on cotton productivity was analyzed using a liner mixed model in R using the “nlme” package^24,25. The phosphorus application technique and P rates were considered fixed effects while the year was random. The least mean square and Tukey multiple tests were performed to separate the means at the probability of < 0.05 by using emmeans package of R software²⁶.

Results

Plant height, number of nodes, monopodial and sympodial branches plant⁻¹

The higher application rate of P (120 kg P₂O₅ ha⁻¹) showed an improved response in comparison to other stages of P application (0,40 and 80 kg P₂O₅ ha⁻¹) in both growing seasons (Table 3). By applying 120 kg P₂O₅ ha⁻¹, plant height increased by 9.60, 4.67, 2.54, 17.50, 9.14, and 7.02% in 2015 as contrasted to 0 and 80 kg P₂O₅ ha⁻¹ in 2014 (Table 3). Overall, plant height was higher in 2014 compared to the 2015 growing season (Table 4). The impact of the P rate was found statistically significant in number of nodes-plant⁻¹ during growing seasons in 2014 (Table 2). The higher P rate showed better results compared to the lower application of the rate on several nodes plant⁻¹. During the growing season in 2014, the increase was 10.47, 5.274, and 2.67% by the application of 40,80 and 120 kg P₂O₅ ha⁻¹ P as compared to 0 kg ha⁻¹ application rates, while in the growing season of 2015, this increase was 10.46, 7.39, and 4.08%, respectively. The band application method showed higher node plant⁻¹ than broadcast and fertigation (Table 4). During the 2014 growing season, the P rate had a statistically significant impact on the monopodial branches of plant⁻¹. In both growth periods of 2014–2015, the P rate had a statistically significant impact on plant⁻¹’s sympodial branches (Table 2). The rate of P showed a better result than other doses. The increase in sympodial branches was 19.44, 28.43 and 28.08% by the application rates 40, 80, and 120 P₂O₅ kg ha⁻¹ comparison to 0 kg P₂O₅ ha⁻¹, respectively, in the growing season 2014, while this increase was 16.04, 22.58, and 20.42% in 2015.

Table 3.

Impact of phosphorus application rates on the productivity of cotton during growing seasons 2014 and 2015.

Phosphorus rates (kg P2O5 ha-1)	Plant height (cm)	Nodes plant−1	Monopodial branches plant−1	Sympodial branches plant−1	Boll weight (g)	Leaf area index (%)
Growing season–2014
0	96.94 ± 12.38a	28.44 ± 1.75a	1.39 ± 0.39b	19.8 ± 1.7a	2.75 ± 0.16a	1.46 ± 0.09a
40	101.51 ± 10.72a	29.2 ± 1.18a	1.01 ± 0.2a	23.65 ± 2.01b	2.92 ± 0.12ab	1.63 ± 0.10b
80	103.62 ± 9.55a	29.94 ± 1.47ab	0.95 ± 0.2a	25.43 ± 1.77b	2.97 ± 0.18b	1.66 ± 0.10b
120	106.25 ± 10.03a	31.42 ± 2.19b	0.89 ± 0.26a	25.36 ± 2.07b	3.03 ± 0.13b	1.67 ± 0.10b
Growing season–2015
0	98.94 ± 12.38a	28.66 ± 2.56a	1.55 ± 0.31a	21.25 ± 4.33a	2.85 ± 0.25a	1.73 ± 0.14a
40	106.51 ± 10.72a	29.83 ± 2.99a	1.32 ± 0.37a	24.66 ± 2.91ab	2.95 ± 0.16ab	1.89 ± 0.10b
80	102.62 ± 9.55a	30.78 ± 2.35a	1.13 ± 0.43a	26.05 ± 2.57b	3.01 ± 0.23ab	1.89 ± 0.10b
120	116.25 ± 10.03a	31.66 ± 3.06a	1.19 ± 0.27a	25.59 ± 2.85b	3.16 ± 0.17 b	1.89 ± 0.12 b

With the growing seasons and phosphorus rates, the same letter (s) value is statistically non-significant. The values are the mean ± standard deviation of three replications.

Table 4.

Impact of phosphorus application methods on the productivity of cotton during growing seasons 2014 and 2015.

Phosphorus application method	Plant height (cm)	Nodes plant−1	Monopodial branches plant−1	Sympodial branches plant−1	Boll weight (g)	Leaf area index (%)
Growing season–2014
Broadcast	103.93 ± 12.4a	29.45 ± 2.31 a	1.08 ± 0.29a	23.1 ± 3.10a	2.91 ± 0.17a	1.61 ± 0.12a
Band application	101.04 ± 9.24a	29.74 ± 1.86 a	0.98 ± 0.30a	24.35 ± 2.88a	2.91 ± 0.24a	1.62 ± 0.13a
Fertigation	101.26 ± 11.31a	30.06 ± 1.82 a	1.11 ± 0.43a	23.22 ± 2.93a	2.93 ± 0.12a	1.59 ± 0.14a
Growing season–2015
Broadcast	103.93 ± 12.4a	30.2 ± 2.98 a	1.39 ± 0.27a	24.08 ± 3.39a	3.00 ± 0.20a	1.81 ± 0.13a
Band application	101.04 ± 9.24a	30.54 ± 2.67 a	1.17 ± 0.40a	25.59 ± 3.36a	3.05 ± 0.21a	1.9 ± 0.08a
Fertigation	101.26 ± 11.31a	29.96 ± 3.17 a	1.33 ± 0.43a	23.49 ± 4.09a	2.92 ± 0.26a	1.84 ± 0.17a

With the growing seasons and phosphorus methods, the value with same letter (s) is statistically non-significant. The values are the mean ± standard deviation of three replications.

Boll weight and leaf area index

Throughout both growing seasons, the impact of the P rate on the boll weight was statistically significant (Table 2). Compared to 0, 40, and 120 kg P₂O₅ ha⁻¹, the boll weight was greater when the P rate of 120 kg P₂O₅ ha⁻¹ was used (Table 3). However, a higher rate of increase was observed in the growing season in 2014 than in 2015. The increase in boll weight was observed by applying (40, 80, & 120 kg P₂O₅ ha⁻¹) was 6.18, 8.00, and 10.18%, %, respectively, in the growing season 2014, while 3.50, 5.71%, and 10.87%in growing season 2015, compared with 0 kg P₂O₅ ha⁻¹, correspondingly. However, band application performed slightly better in the growing season of 2015 than broadcast and fertigation methods.

In both growing seasons, the effect of various P doses on the leaf area index was statistically significant (Table 2). This parameter was higher in 2015 than 2014 (Tables 3 and 4). However, the difference in the P rate was more viable in the growing season 2014. The band application method showed a higher leaf area index than the broadcast and fertigation methods (Table 4). The response of P application methods during the growing season 2015 was better than the growing season 2014.

Seed cotton yield, lint yield, and harvest index

The effect of the P rate on seed cotton yield showed a statistically significant difference during both growing seasons (Table 2). The higher application rate of P showed a better response to seed cotton yield than lower application rates (Fig. 2). Compared to the 0 kg P₂O₅ ha⁻¹ application rate, the P dosages of 40, 80, and 120 kg P₂O₅ ha⁻¹ increased by 29.76, 43.83, and 49.31% in 2014. This rise was 23.68, 39. 34, and 48.12% in 2015. The band application method responded better to seed cotton yield than broadcast and fertigation methods in both growing seasons (Fig. 2). The elevated yield of seed cotton by band application was 5.02 and 2.04% compared to broadcast and fertigation during 2014, while the increase was 8.50 and 7.91% in 2015. Across both growing seasons, the impact of the P rate on the lint yield was statistically significant (Table 2). The treatment with a P rate of 120 kg P₂O₅ ha⁻¹ showed a higher response in lint yield than lower application rates. In the growing season 2014, applying 40, 80, and 120 kg P₂O₅ ha⁻¹ increased lint yield by 55.75, 50.59, and 32.93%, respectively, above 0 kg ha⁻¹. In the growing season 2015, this rise was 52.44, 47.43, and 29.51% (Fig. 2). A greater lint production was seen comparing the band application to broadcast and fertigation. The rise in yield of lint by the band application of P was 9.17 and 7.53% compared to broadcast and fertigation methods in the growing season of 2015. During both growing seasons, the P rate statistically impacted the harvest index (Table 2). Compared to other dosages, the phosphorus application rate of 120 kg P₂O₅ ha⁻¹ in 2015 and 80 kg P₂O₅ ha⁻¹ in the growth season of 2014 produced better results. In comparison to 0 kg ha⁻¹ in 2014, the application of 40, 80, and 120 kg P₂O₅ ha⁻¹ resulted in a wed increase in harvest index of 9.14, 12.83, and 10.24%; this boost was 2.22, 3.99, and 5.25% during the growing season 2015 (Fig. 2).

Figure 2.

Impacts of phosphorus application methods and phosphorus rates on the harvest index, Lint yield, and yield of seed cotton. Within growing seasons and phosphorus application method, the value with the same letters is non-significant at p < 0.05. within the growing seasons, capital letters show the soil application methods are not statistically significant at p < 0.05. The error bars show the three replications’ standard deviation.

Discussion

The study showed that band application and higher P rate perform comparatively better than broadcast and fertigation methods. This may be because adenosine triphosphate and adenosine diphosphate molecules, formed when enough phosphorus is present, play a significant role in energy transmission. The formation of compounds helps photosynthesis^27–29. The other important process, like the utilization of starch and sugar, could not be completed without a reasonable amount of P, as reported in many studies^6,30. Another possible reason for the good productivity of cotton in higher phosphorus rates might be due to good germination and reproduction, as this process is after the limited supply of phosphorus. In addition, an adequate amount of P promoted root development, strong stem elongation, maximum boll, and square formation^31–33. Another possible reason for the improved productivity of cotton at higher phosphorus rates could be attributed to enhanced germination and reproductive success, which often follow a period of phosphorus limitation. Adequate phosphorus levels support robust root development, which in turn facilitates better nutrient and water uptake. This improved root growth leads to stronger stem elongation and increased boll and square formation, ultimately contributing to higher yields. Studies have shown that sufficient phosphorus promotes these critical growth stages, optimizing overall plant health and productivity. The current study showed that decreased application rates had a detrimental effect on the productive qualities of cotton. According to several research, this might be due to low carbon metabolism, photosynthesis processes, or deficient ATP synthesis^34,35. The band application in this study showed a better response than other application methods. The higher and simpler accessibility of applied P to cotton seed may result from the band application of phosphorus. Or the availability of P in band application might be increased the root germination and development as compared to other methods of P application^36,37. The increased root growth could enhance crop growth and yield by drawing more minerals and water from the soil^11,31,38.

In comparison, the lower performance of broadcast and fertigation may be due to less interaction of seed and applied P fertilizers^15,39,40. Further, in fertigation, the nutrients are normally moved away with water run-off and uniformly unavailable to all plants^4,41. The band application of phosphorus improved the leaf area index, possibly due to more P availability to plants and more vigorous growth of plants. Moreover, leaf area directly affects the process of photosynthesis. The higher rate of photosynthesis produces more carbohydrates, which could positively impact other crop growth and yield characteristics and the productivity of crops^42–44. Plant height may also have increased because of band treatment due to the availability of adequate P and robust root growth. The taller plant also promoted the number of nodes and reproductive branches due to a greater uptake of sunlight and catabolism processes^45,46. The findings of this study, which show a rise in the amount of monopodial and sympodial branches because of band application, are consistent with those of⁴⁷, who found an expansion of the number of branches following the band application of phosphatic fertilizer. A higher number of bolls in a field study with band application, possibly due to P’s high uptake and translocation. The lower number of bolls in lower application rates might be due to less P uptake. The low plant uptake could reduce flowering, leading to a low number of nodes⁴⁸. The seed cotton yield reduction with lower application rates also indicates low growth and development of plants under P-scarce conditions⁴⁹. A greater P level may yield better because more P is available^47,50. Higher availability and absorption of P at high P levels and improved growth and yield characteristics could all contribute to an increase in yield caused by higher P levels⁵¹. The variation in seed cotton yield across both years could be attributed to several factors beyond climatic conditions, such as differences in soil fertility, pest and disease incidence, irrigation practices, and farming techniques. Additionally, variations in seed quality, planting density, and nutrient management could have contributed to the observed yield differences.

Conclusion

Compared to broadcast and fertigation techniques and lower phosphorus rate, the band application approach and higher phosphorus rate (120 kg P₂O₅ ha⁻¹) showed greater response (0, 40, and 80 kg P₂O₅ ha⁻¹). Therefore, by adopting the strategy of band application, higher productivity of cotton crops can be achieved under arid climatic conditions of South Punjab, Pakistan. However, long-term field trials are recommended under different climatic conditions to determine the appropriate dose of phosphorus application for adequate cotton production.

Author contributions

Conceptualization; M.I.A; M.N.A.; K.S.; Conducted experiment; S.A.A.; R.D.; S.D.; Formal analysis; M.I.A; M.N.A.; K.S.; Methodology; S.D.; R.D.; M.J.A.; S.A.A; T.A.A; Writing—original draft; S.D.; R.D.; M.J.A.; S.A.A; T.A.A.; Writing—review & editing; M.I.A; M.N.A.; K.S.;

Funding

This project was supported by Researchers Supporting Project number (RSP2025R5) King Saud University, Riyadh, Saudi Arabia.

Data availability

All data generated or analysed during this study are included in this published article.

Competing interests

The authors declare no competing interests.