Growth, Yield, Quality and Insect-Pests in Sugarcane (Saccharum officinarum) as Affected by Differential Regimes of Irrigation and Potash under Stressed Conditions

Abstract

Land productivity and quality were negatively impacted by both unbalanced fertilization and water-stressed conditions, which has arisen as an important topic of research. In the semi-arid tropics, sugarcane is the main source of sugar and ethanol; however, no potash (K) dose is recommended for the deficient sites in the region, which are further responsible for lower recovery. As a result, in order to standardize the K dose for deficient sites, present experiments carried out during plant (2019–2020) and ratoon (2020–2021) seasons. The statistical design was a split-plot design with main plot treatments comprised of I₁ (irrigated) and I₂ (stressed) treatments followed by K₁, K₂, K₃, and K₄ plots fertilized with 0, 40, 80, and 120 kg K₂O ha⁻¹ in subplots. Germination was reported to be 13.7, 25.0 and 32.3% higher during plant and 6.2, 17.3 and 24.4% higher during ratoon season in K₂, K_3, and K₄ plots, respectively. Tiller’s cane⁻¹ was recorded to be significantly affected by potash levels at 241 days after planting (DAP) and 261 and 326 days after harvesting (DAH). Periodic chlorophyll content of the sugarcane leaves was reported not to be affected by irrigation treatments except at 355 DAP and 324 and 357 DAH, where respected values were reported to be 2.06% in the plant season and 1.55 and 2.54% higher in the ratoon season in I₁ plots, respectively. During plant season purity and extraction after the 10th month, respective values were reported to be 1.5% lower and 4.03% higher under I₁ plots, while only Brix (%) was reported as significant and 2.42% higher in I₁ plots during plant season after the 12th month. The incidence of early shoot borer (Chilo infuscatellus) and stalk borer (Chilo auricilius) was reported to be significantly higher under stressed conditions (30.4 and 21.5% lower in I₁ plots) during the plant season, while early shoot borer (Chilo infuscatellus), stalk borer (Chilo auricilius) and top (Scirpophaga excerptalis) incidences were significantly lower in I₁ plots to the tune of 19.6, 22 and 9.73% as compared to the I₂ plots during the ratoon season. The application of 80 kg K₂O ha⁻¹ resulted in significantly higher cane yield and decreased insect-pest occurrence. Even though 120 kg K₂O ha⁻¹ promoted different plant and ratoon sugarcane characteristics, they were all statistically equivalent. In I₁ plots, benefits increased from K₂ to K₃ plots by 26.7% during plant and 155% during ratoon seasons but decreased from K₃ to K₄ plots by 21.0% during plant and 26.1% ratoon seasons. In I₂ plots, however, benefits from K₂ to K₃ plots were reported to be 72.7% during plant and 76.5% during ratoon seasons, which was reduced to 10.5% during plant and 16.7% during ratoon seasons in K₄ plots. Results of a two-year study on plant and ratoon canes revealed that 80 kg K₂O ha⁻¹ at deficient sites significantly improved the performance of both plant and ratoon canes yields, sugar yields, reduced the insect-pests’ incidence, and finally the benefits of the cane farmers under both irrigation regimes.

1. Introduction

In the northern Indian states of Punjab and Haryana, intensive unscientific traditional agricultural practices lead to excessive withdrawal of underground water, which resulted in water-stressed conditions [1,2,3] and poor soil health [4,5]. The GRACE-NASA, the United States gravity mapping satellite has discovered a 30 cm yr⁻¹ decline in underlying water in the 440,000 km² region of North India, which further resulted in 4-cm drop groundwater. In Punjab, India, because of these excessive water withdrawal rates, the underground water table is dwindling at an alarming rate which is due to an enhanced 60% rice area in 2015 against the 6% area of 1960. Furthermore, each year in Punjab, India alone more than 13 lakh ham of irrigation water worth US$39 million is used for irrigation purposes [3].

Among the various crops, sugarcane (Saccharum spp. complex) is a major industrial crop with high sugar concentration grown in tropical and subtropical climates and is famous for its by-products, and ethanol for blending into petrol is among the various crops grown in the region [6,7,8]. Sugarcane was cultivated on an area of 47.3 thousand hectares and the average annual production in India was 376.9 M t, with productivity of approximately 71.5 t ha⁻¹ [9]; however, it is grown on 91,000 ha in Punjab, India, with an average sugarcane yield of 80.25 t ha⁻¹ and a sugar recovery rate of 9.59 percent, both of which are lower than neighboring states [10]. Balanced nutrient management is critical to achieving long-term cane yield, and failure to do so can result in severe yield and quality losses [10,11]. According to one estimate, 100 t of sugarcane crop per hectare requires different nutrients such as nitrogen, phosphorus, potassium, and sulfur in the amounts of 208, 53, 280, and 30 kg ha⁻¹, respectively, with iron, manganese, and copper in the amounts of 3.4, 1.2, and 0.6 kg ha⁻¹ [6]. Hence, K uptake is reported to be higher than N and P, and must be applied sustainably but generally negligently [10], even at deficient sites [11]. Several factors including unbalanced fertilization, upcoming water stress, high insect pests, poor soil fertility, low use of organics, etc. were identified, wherein unbalanced fertilization and water-stressed conditions were recognized as the two most essential factors that must be addressed rapidly to improve sugar recovery in the region.

The upcoming water-stressed conditions are recognized as the second important yield-limiting factor [12,13,14,15] that further affects the cane performance and recovery in the region [16,17,18]. Appropriate moisture conditions are essential for the canes to carry out their various metabolic and physiological activities [19]. For transpiration by which water and nutrients enter the plants through the roots, adequate water conditions are a must, which under stressful conditions is adversely affected so that it finally gets less cane recovery [20,21]. Water stress is an important factor as it results in reduced leaf water potential, which leads to down-regulation of photosynthesis-related genes and reduced CO₂ availability [22]. Hence, adequate water is necessary for sugarcane to report good growth, yield, and quality parameters. Both water stress and K deficient conditions reduce the performance of cane in terms of land yield and quality, and hence the overall benefits to cane growers in semi-arid tropics. Later, K deficient soils must be supplied with a sustainable K dose, which is currently a huge gap for a good recovery like that obtained by neighboring states. As a result, innovative approaches to reduce the water footprint and enhance cane productivity should be developed, evaluated, and recommended to farmers [21,23,24], including covering the bare soil surface with crop residues and planting crops between cane rows, but little success has been recorded in filling the yield gap.

Nitrogen (N), phosphorus (P), and potassium (K) are three macronutrients that play different roles in physiological and metabolic activities [25,26,27]. Most of the K in fertilization schedules may be due to earlier mineral make-ups, which are now reported to have K deficiencies and hence, must be supplied [28,29]. Soil K could be fractioned into different parts, viz. soil solution K, exchangeable K, non-exchangeable K, and mineral matrix K, which further delineates the availability of soil K to plants [30]. Further, K, also known as Policeman nutrient, plays an important role in photosynthesis [31,32,33], translocation of photosynthates [34], and its utilization [35], reduces insect-pests [36] and eyespot disease [37] incidence, improves seed germination [28,29,30], efficient usage of water and other nutrients [31,32,33], regulates stomatal opening [34,35,36,37,38,39] and detoxification of reactive oxygen species [11,40]. Further, K is involved in the activation of more than 60 enzymes [41,42,43,44], protein synthesis [36], phloem transport [45,46,47], cation and anion balance, energy transfer, and stress resistance [48,49]. Hence, K fertilized plots are always reported with significantly improved yields [50,51,52] and improved quality [53,54,55] at deficient sites. K is advised in different sugarcane growing locations ranging from 60 to 120 kg ha⁻¹, due to its role played in different; however, a response of 700 kg ha⁻¹ was found at some inadequate sites [56,57].

Sugarcane is sown as seed and is referred to as a plant crop, while the process of regrowth of a new plant from a harvested plant crop is known as a ratoon crop. The ratoon crop’s land productivity is generally lower than that of the plant crop, with somewhat higher quality. Ratoon canes had a lower cost of cultivation than the plant crop since the costs of the initial plant crop development procedures were completely omitted [6]. Additionally, the sugar factory-crushing schedule is prolonged due to the drying of early tissues and the flushing of nitrogen during the ratoon season [58]. The yields of the ratoon crop, on the other hand, are lower than those of the previous plant crop, which could be attributable to higher bulk density [5,59], injudicious fertilizer use [14,60], and higher rates of sucking pests and diseases. The Indian subtropical region accounts for 57.1 percent of the total cane area in the country. Among different insect-pests top borer, shoot borer, and stalk borer are found predominantly in the region and responsible for yield declines up to 20–25%. Potash translocates the photosynthates from leaves to the whole plant, thereby making leaves comparatively bitter and hence not being preferred by insect pests [8,22,45]. Poor cultivar selection, cold winters, poor irrigation water quality, and weed competition, regardless of these factors, all contribute to lower ratoon yields [61,62]. Furthermore, due to poor traditional irrigation practices and imbalanced use of nutrients, particularly K, the cane recovery both for seed and for the next ratoon cane crop was adversely affected. To date, in the region viz. Punjab, India, no potash dose is recommended, even for the deficient sites under different moisture regimes and the outcome is the lower sugar recovery than in the neighboring states, which had well-established potash fertilization doses in their sugarcane fertilization programs.

Already, attempts being made in the region to standardize the potash dose for deficient regions of Gurdaspur as in plant [63] and ratoon [64] using mid-late sugarcane cultivar viz. CoPb 91 and at Amritsar as in plant [65] and ratoon [66] using early sugarcane cultivar viz. CoPb 92; however, to corroborate these results, the present investigation carried outat PAU-Regional Research Station, Kapurthala, Punjab, India by cultivating mid-late cultivar CoJ 88 across the plant (2019–2020) and ratoon (2020–2021) with the specific objectives of standardizing K dose which to (i) improve sugarcane growth, roots, yields, and quality parameters; (ii) reduces the incidence of insect-pest; and (iii) improved livelihoods of cane farmers in the region under two irrigation regimes.

2. Material and Methods

2.1. Investigational Site

The current investigation was conducted during the spring of 2019–2020 and 2020–2021 at the experimental farm of the PAU-Regional Research Station in Kapurthala, Punjab, India, which is located at 31°23.114′ N longitude and 75°21.561′ E latitude at an elevation of 225 m above average sea level [67].

During 2019–2020 and 2020–2021, maximum and minimum air temperature, rainfall, and evaporation were measured daily at the climatological station located near the experimental site. The rain gauge at the experimental site is used to measure the rainfall. In the course of our investigation during 2019–2020 and 2020–2021, the average maximum and minimum air temperature ranged from 7.8 to 42.4 °C and 10.2–25.1 °C, while during 2020–2021, it ranged between 19.2 and 37.5 °C and 7.0–7.6 °C, respectively (Figure 1A,B); however, during 2019–2020, rainfall and evaporation varied from 0 to 343 mm and 5.9–249 mm with a total of 976.2 and 1198.8 mm, while during 2020–2021, they varied from 0 to 238 mm and 30–236 mm with total values of 969.5 and 1320.50 mm (Figure 1C,D) indicates 121.7 mm higher evaporation with 6.7 mm lower evaporation during the second year of investigation.

2.2. Soil Characteristics

Representative soil samples were collected from the site using a hand trowel as per procedure [28]. The research site was sandy loam in texture (sand 66–69%, clay 11–12%), neutral to slightly alkaline, non-saline, and lower in soil organic carbon percent and potash, while higher inaccessible phosphorus, magnesium, and lower in available calcium, according to soil analysis (

Table 1. Major properties at 0–15 cm soils of investigational location.

Properties of Soil	Values
Percent sand (%)	65.0
Percent clay (%)	11.4
pH (2:1)	8.66
Electrical conductivity (ds m−1)	0.19
Organic carbon (%)	0.32
N available (kg ha−1)	34.8
P available (kg ha−1)	54.1
K (kg ha−1)	135.0
Mg available (ppm)	553.5
Ca available (ppm)	140.0
Bulk density (Mg m−3)	1.64

).

2.3. Underground Water Quality

The depth of the site’s groundwater was about 280 m. In addition, irrigation water used to irrigate the canes was collected in plastic bottles according to the procedure of Bhatt and Sharma [28] and analyzed for several water quality indicators (

Table 2. Irrigation water quality at the experimental site.

Rep. No.	Ca++ + Mg++ (meq l−1)	Cl− (meq l−1)	Residual NaHCO−3	EC (ds m−1)	CO3− − (meq l−1)	HCO−3 (meq l−1)
R1	3.7	0.7	0.0	0.47	0.0	3.7
R2	3.6	0.6	0.0	0.49	0.0	3.9
R3	3.8	0.8	0.0	0.51	0.0	3.7
Mean ± SE	3.7 ± 0.06	0.7 ± 0.06	0.0	0.49 ± 0.01	0.0	3.7 ± 0.07

).

2.4. Treatments

Irrigation plots viz. I₁ (irrigated) and I₂ (stressed) pertain to the main treatments while potash doses viz. 0, 40, 80, and 120 kg K₂O ha⁻¹ are applied through muriate of potash fertilizer in the sub-plots as K₁, K₂, K_3, and K₄, respectively at the time of planting during 2019–2020 and resprouting of harvested canes during ratoon 2020–2021. On the whole, present replicated experiment equipped with 24 plots. Under I₂ treatment, irrigation was suspended after a 3-week interval at germination, tillering, and grand growth stage, respectively while I₁ plots received normal irrigation through open channels under flood irrigation. Experiments were initiated with 27 m² plots using mid-late sugarcane cultivar CoJ 88 planted at a spacing of 0.75 m row spacing on 20 March 2019 as per recommendations [10] and harvested on 3 March 2020, and extended up to spring season 2020–2021 with a ratoon crop which was harvested on 8 March 2021.

2.5. Collection of Data and Calculations

The following parameters were collected during 2019–2020 (plant cane crop) and 2020–2021 (ratoon cane crop) during the experimentation period after tagging five representative plants from each plot, excluding germination and number of millable sugarcane (NMC), to evaluate the effect of different doses of irrigation and potash at the deficient sites.

2.5.1. Morphological Features

After 45 (days after planting) DAP during plant season (2019–2020) and 35 (days after harvesting) DAH during ratoon season (2020–2021), the germination and resprouting percentage of the canes were manually counted in each sub-plot under various treatment plots. Tiller populations were manually counted at 87, 225, and 241 DAP and 188, 261, and 326 DAH by counting the total number of shoots from five distinct representative plants from each plot and calculating the average used for individual plant tillers. NMC stalks was recorded at 325 DAP and 290 DAH. Well matured canes fit for milling were counted from the net plot area and expressed in thousands per hectare. During the plant season, the cane height of five randomly selected tagged sugarcane stalks was measured at 155, 209, 241, and 272 DAP and 158, 239, 261, and 291 DAH from tagged five plants from each plot, using a ruler to measure from the soil surface and the growing point of the shoot during ratoon season, and the values were expressed as meters (m). Using a vernier caliper, cane diameter was recorded at 155, 207, 248, 275, and 307 DAP during plant season while at 158, 173, 203, 264, and 294 DAH during ratoon season from representative tagged five healthy plants of each plot. The mean value of the top, middle, and bottom diameters was considered the actual diameter of the cane stalk, and the value was expressed in centimeters (cm). Nodes per stalk were manually counted at 180, 220, 262, 280, 305, and 340 DAP, while after 188, 219, 260, 284, 305, and 336 DAH from the five tagged canes, their average was taken. The SPAD-502 plus meter was used for estimating chlorophyll concentrations in sugarcane leaves after 218, 258, 280, 330, and 355 DAP and 220, 260, 281, 324, and 357 DAH. To measure the density of root length (cm cm⁻³) with a length of 81 cm and a diameter of 5 cm, an iron pipe is used in each plot followed by washing with streams of water, drying in the oven, and then measuring of total root lengths.

2.5.2. Cane Yield and Quality

Cane yield was recorded in different plots at the time of harvesting from the entire area of each plot. The total weight of clean cane stalks for each plot was taken into account for yield data. Sugarcane stalk yield data were expressed in mega-grams per hectare (Mg ha⁻¹) during the plant and ratoon seasons (2019–2020 and 2020–2021).

To judge juice quality, five randomly selected canes on the 10th and 12th months of planting were harvested from each plot during both years. For extracting the cane juice, a cane crusher was used for quality analysis following standard methods. A digital refractometer was used to measure the Brix and sucrose content (%) in the cane juice [67]. Furthermore, for judging the commercial cane sugar (CCS), the following winter carp equation was used:

$$\mathrm{CCS} (\%)=\left[\mathrm{Sucrose}\%-\left(\mathrm{Brix}\%-\mathrm{Sucrose}\%\right)\times 0.4\right]\times 0.74$$

(1)

where 0.4 is multiplication and 0.74 is the crusher factor. From cane yield (t ha⁻¹) and CCS (%), sugar yield (t ha⁻¹) was calculated as per the following equation:

$$\mathrm{Sugar} \mathrm{yield}=\frac{\mathrm{CCS}\times \mathrm{sugarcane} \mathrm{yield}}{100}$$

(2)

2.5.3. Insect-Pest Incidence

Various insect pests of sugarcane were reported in detail over both years, including the early shoot borer (Chilo infuscatellus), top borer (Scirpophaga excerptalis), and stalk borer (Chilo auricilius), all of which harmed both canes yields and quality. To assess the influence of irrigation and potash doses on the incidence of insect-pests on sugarcane, the top borer population was recorded in June, the early shoot borer was counted after 60 DAS in May, and the stalk borer was counted from 100 plants at harvest as per methodology proposed by [68]

$$\mathrm{Percent} \mathrm{incidence} \mathrm{of} \mathrm{early} \mathrm{shoot} \mathrm{borer}=\frac{\mathrm{Total} \mathrm{number} \mathrm{of} \mathrm{dead} \mathrm{heart}\times 100}{\mathrm{Total} \mathrm{number} \mathrm{of} \mathrm{shoots}}$$

(3)

The top borer percent incidence was measured in June, July, and August, and the cumulative incidence was calculated

$$\mathrm{Percent} \mathrm{incidence} \mathrm{of} \mathrm{top} \mathrm{borer}=\frac{\mathrm{Total} \mathrm{number} \mathrm{of} \mathrm{infested} \mathrm{canes} \mathrm{in} 3 \mathrm{m} \mathrm{row} \mathrm{length}}{\mathrm{Total} \mathrm{number} \mathrm{of} \mathrm{canes} \mathrm{observed} \mathrm{in} 3 \mathrm{m} \mathrm{row} \mathrm{length}}\times 100$$

(4)

The percentage incidence of stalk borer was recorded at the time of harvest

$$\mathrm{Percent} \mathrm{incidence} \mathrm{of} \mathrm{stalk} \mathrm{borer}=\frac{\mathrm{Total} \mathrm{number} \mathrm{of} \mathrm{affected} \mathrm{canes}\times 100}{100 \mathrm{canes}}$$

(5)

2.5.4. Benefit-Cost Ratio

The benefit-to-cost ratio (B:C ratio) was computed using the formula after taking into account the cost of the muriate of potash fertilizer and the cane’s minimum support price of sugarcane during both the plant during 2019–2020 and the ratoon during 2020–2021 under consideration [5,59,63,64,65,66], as follows:

$$\mathrm{B}:\mathrm{C} \mathrm{ratio}=\frac{\mathrm{Benefit} \mathrm{due} \mathrm{to} \mathrm{applied} \mathrm{additional} \mathrm{K} \left({\mathrm{Rs} \mathrm{ha}}^{-1}\right)}{\mathrm{Cos}\mathrm{t} \mathrm{of} \mathrm{fertilizer} \left({\mathrm{Rs} \mathrm{ha}}^{-1}\right)}$$

(6)

2.6. Statistical Analysis

The analysis of variance was performed using PROC GLM (SAS software version 9.1, SAS Institute Ltd., Cary, NC, USA) [69] according to the standard procedure given by [70] for measuring the effect of main irrigation and sub-plot potash treatments on different sugarcane growth, insect-pests, yield, and quality variables during 2019–2020 and 2020–2021.

3. Results

3.1. Water-Stress Effects on Sugarcane Performance

Irrigated (I₁) plots were on par with water-stressed (I₂) plots concerning cane germination, NMCs, root length density (RLD), and yields during plant and ratoon season though values were somewhat higher in I₁ plots (

Table 3. Germination, NMCs, RLDs, and yields of sugarcane as a function of irrigation and potash levels.

Treatments	Germination (%)		NMC (000/ha)		RLD (cm cm−3)		Cane Yield (Mg ha−1)
	2019–2020	2020–2021	2019–2020	2020–2021	2019–2020	2020–2021	2019–2020	2020–2021
I1	49.76 a	47.75 a	87.6 a	79.2 a	0.439 a	0.539 a	77.55 a	57.69 a
I2	46.81 a	44.79 a	87.2 a	78.9 a	0.449 a	0.549 a	77.20 a	56.95 a
LSD0.05	NS	NS	NS	NS	NS	NS	NS	NS
K1	40.95 c	41.91 c	77.72 b	69.72 b	0.429 a	0.442 a	76.30 b	55.93 b
K2	46.55 b	44.52 b	82.34 b	75.34 b	0.436 a	0.538 a	76.86 b	56.49 b
K3	51.17 a	49.17 a	94.14 a	86.14 a	0.458 a	0.560 a	77.96 a	58.21 a
K4	54.18 a	52.15 a	95.31 a	87.31 a	0.454 a	0.561 a	78.38 a	58.64 a
LSD0.05	3.1	3.0	9.8	9.8	NS	NS	0.58	1.84
K at same I	NS	NS	18.7	18.7	NS	NS	0.29	NS
I at same K	NS	NS	19.5	19.3	NS	NS	0.30	NS

Different superscript letters within each column indicate significant differences at the 0.05 level. I₁ and I₂ represent the main plot treatments of irrigated and stressed plots, while K₁, K₂, K_3, and K₄ represent subplots treatments where potash applied as 0, 40, 80, and 120 kg K₂O ha⁻¹, respectively; NMC and RLD represent the number of millable canes and root length density.

). Tiller cane⁻¹ counts were significantly higher in I₁ plots in ratoon crops at 261 and 326 DAH (18.8 and 11.9%, respectively), while leaves cane⁻¹ counts were statistically similar during both seed and ratoon seasons (

Table 4. Sugarcane tillers and leaves as a function of irrigation and potash levels.

Treatments	Tillers Cane−1							Leaves Cane−1
	2019–2020			2020–2021				2019–2020				2020–2021
	87 DAP	225 DAP	241 DAP	188 DAH	217 DAH	261 DAH	326 DAH	182 DAP	266 DAP	292 DAP	302 DAP	188 DAH	264 DAH	296 DAH	314 DAH
I1	2.4 a	10.4 a	14.8 a	2.5 a	9.9 a	10.1 a	9.4 a	12.4 a	11.4 a	10.7 a	9.5 a	12.8 a	11.8 a	11.2 a	10.0 a
I2	2.9 a	9.3 a	12.4 b	2.5 a	8.7 a	8.5 b	8.4 b	12.1 a	11.1 a	10.4 a	9.3 a	12.6 a	11.6 a	10.9 a	9.8 a
LSD0.05	NS	NS	2.2	NS	NS	0.5	1.0	NS	NS	NS	NS	NS	NS	NS	NS
K1	2.3 a	9.0 a	12.3 a	3.1 a	9.2 a	9.5 c	8.4 c	11.9 a	10.6 c	9.8 c	8.7 b	12.7 a	11.2 c	10.3 c	10.1 a
K2	2.5 a	9.7 a	14.2 a	3.7 a	8.1 a	10.8 b	7.9 bc	12.2 a	11.2 b	10.4 b	9.5 a	12.6 a	11.7 b	10.9 b	10.0 a
K3	2.8 a	10.2 a	13.6 ab	3.0 a	10.0 a	11.8 a	9.9 a	12.2 a	11.4 ab	11.0 a	9.6 a	13.0 a	12.1 a	11.4 a	9.2 b
K4	3.0 a	10.5 a	14.3 a	3.3 a	9.9 a	10.8 b	9.4 a	12.6 a	11.8 a	11.1 a	9.8 a	12.5 a	11.9 a	11.5 a	10.3 a
LSD0.05	NS	NS	NS	NS	NS	0.61	0.80	NS	0.3	0.7	NS	NS	0.26	0.27	0.54
K at same I	NS	NS	NS	NS	NS	0.96	1.37	NS	NS	NS	NS	NS	0.48	0.44	NS
I at same K	NS	NS	NS	NS	NS	0.88	1.32	NS	NS	NS	NS	NS	0.49	0.42	NS

Different superscript letters within each column indicate significant differences at the 0.05 level. I₁ and I₂ represent the main plot treatments viz. irrigated and stressed plots, while K₁, K₂, K_3, and K₄ represent subplots treatments where potash applied as 0, 40, 80, and 120 kg K₂O ha⁻¹, respectively; DAP indicates days after planting during 2019–2020 and DAH represent days after harvesting during 2020–2021.

). Temporal cane height and diameter were reported to be statistically similar throughout the experiments, except for plants higher after 155 DAP, where irrigated plots had 12.9% higher heights than stressed ones (

Table 5. Cane height (cm) as a function of irrigation and potash levels.

Treatments	2019–2020				2020–2021
	155 DAP	209 DAP	241 DAP	282 DAP	158 DAH	239 DAH	261 DAH	291 DAH
I1	126.9 a	209.8 a	230.1 a	239.9 a	126.0 a	214.0 a	223.2 a	224.2 a
I2	112.4 b	210.5 a	227.2 a	236.9 a	129.8 a	215.0 a	216.9 a	222.2 a
LSD0.05	3.2	NS	NS	NS	NS	NS	NS	NS
K1	120.5 a	210.9 a	227.6 a	235.1 a	128.4 a	210.1 a	210.6 c	212.7c
K2	121.3 a	210.4 a	229.9 a	240.2 a	122.4 a	210.1a	214.9 b	216.7 b
K3	120.9 a	211.1 a	229.2 a	240.1 a	130.1 a	220.3 a	226.0 a	230.1 a
K4	116.2 a	208.0 a	227.8 a	238.1 a	130.1 a	218.3 a	229.0 a	231.2 a
LSD0.05	NS	NS	NS	NS	NS	NS	4.0	2.5

Different superscript letters within each column indicate significant differences at the 0.05 level. I₁ and I₂ represent the main plot treatments of irrigated and stressed plots, while K₁, K₂, K_3, and K₄ represent subplots treatments where potash applied as 0, 40, 80, and 120 kg K₂O ha⁻¹, respectively; DAP indicates days after planting during 2019–2020, and DAH represents days after harvesting during 2020–2021; Interaction reported to be non-significant. Interactions both ways were observed to be had non-significant effects.

and

Table 6. Cane diameter (cm) as a function of irrigation and potash levels.

Treatments	2019–2020					2020–2021
	155 DAP	207 DAP	248 DAP	275 DAP	307 DAP	158 DAH	173 DAH	203 DAH	239 DAH	264 DAH	294 DAH
I1	2.71 a	3.24 a	3.46 a	3.45 a	3.58 a	2.40 a	2.59 a	2.63 a	2.65 a	2.70 a	2.70 a
I2	2.69 a	3.13 a	3.37 a	3.38 a	3.53 a	2.39 a	2.54 a	2.56a	2.62 a	2.60 a	2.70 a
LSD0.05	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS
K1	2.63 a	3.12 a	3.35 a	3.32 a	3.48 a	2.32 a	2.58 a	2.56 a	2.58 a	2.61 b	2.63 b
K2	2.67 a	3.18 a	3.40 a	3.41 a	3.55 a	2.33 a	2.53 a	2.58 a	2.60 a	2.61 b	2.64 b
K3	2.72 a	3.20 a	3.43 a	3.42 a	3.57 a	2.42 a	2.58 a	2.59 a	2.68 a	2.72 a	2.73 a
K4	2.78 a	3.25 a	3.47 a	3.49 a	3.62 a	2.48 a	2.57 a	2.60 a	2.70 a	2.72 a	2.74 a
LSD0.05	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS

Different superscript letters within each column indicate significant differences at the 0.05 level. I₁ and I₂ represent the main plot treatments of irrigated and stressed plots, while K₁, K₂, K₃, and K₄ represent subplots treatments where potash applied as 0, 40, 80, and 120 kg K₂O ha⁻¹, respectively; DAP indicates days after planting during 2019–2020, and DAH represents days after harvesting during 2020–2021; Interactions both ways observed to be had non-significant effects.

). Periodic Brix (%) was observed to be similar throughout the experiment period except in ratoon during 113, 264, 278, and 355 DAH, where I₂ plots had 2.13, 1.85, 4.69, and 4.42% higher Brix than the I₁ plots, respectively (

Table 7. Nodes per cane as a function of irrigation and potash levels.

Treatments	2019–2020						2020–2021
	180 DAP	220 DAP	262 DAP	280 DAP	305 DAP	340 DAP	188 DAH	219 DAH	260 DAH	284 DAH	305 DAH	336 DAH
I1	12.3 a	16.3 a	17.8 b	19.1 a	19.9 a	20.1 a	12.8 a	16.9 a	18.4 b	19.1 a	20.6 b	20.7 b
I2	12.4 a	16.4 a	18.5 a	18.4 a	20.5 a	20.6 a	12.9 a	16.9 a	19.1 a	19.7 a	21.1 a	21.2 a
LSD0.05	NS	NS	0.43	NS	NS	NS	NS	NS	0.40	NS	0.40	0.43
K1	12.8 a	17.1 a	18.8 a	19.2 a	20.4 a	20.5 a	13.3 a	17.7 a	19.1 a	19.8 a	20.9 a	21.1 a
K2	12.6 a	16.3 ab	18.5 a	19.1 a	20.7 a	20.8 a	13.5 a	17.4 ab	19.4 a	19.8 a	21.3 a	21.4 a
K3	12.2 b	15.1 b	17.0 b	17.8 a	19.5 b	19.5 b	12.1 c	15.7 b	17.7 b	18.4 a	20.1 b	20.1 b
K4	11.5 c	16.3 ab	18.4 a	19.1 a	20.4 a	20.7 a	12.8 b	16.9 ab	19.0 a	19.7 a	21.0 a	21.3 a
LSD0.05	0.32	0.90	0.51	0.33	0.80	0.46	0.33	NS	0.53	NS	0.35	0.33
K at the same I	NS	NS	NS	NS	NS	NS	0.48	NS	NS	NS	0.72	0.57
I at same K	NS	NS	NS	NS	NS	NS	0.43	NS	NS	NS	0.82	0.55

Different superscript letters within each column indicate significant differences at the 0.05 level. I₁ and I₂ represent the main plot treatments of irrigated and stressed plots, while K₁, K₂, K_3, and K₄ represent subplots treatments where potash applied as 0, 40, 80, and 120 kg K₂O ha⁻¹, respectively; DAP indicates days after planting during 2019–2020, and DAH represents days after harvesting during 2020–2021; Interaction reported to be non-significant during plant cane season.

). Nodes per cane were significantly lower in I₁ plots, reaching 3.78% at 262 DAP during plant and 3.66, 2.37, and 2.36% at 260, 305, and 336 DAH compared to I₂ plots with similar values during rest periods (

Table 8. Chlorophyll cane content as a function of irrigation and potash levels.

Treatments	2019–2020					2020–2021
	218 DAP	258 DAP	280 DAP	330 DAP	355 DAP	220 DAH	260 DAH	281 DAH	324 DAH	357 DAH
I1	60.4 a	48.8 a	36.7 a	38.9 a	39.7 a	60.9 a	38.8 a	36.7 a	39.4 a	40.3 a
I2	60.3 a	43.3 a	36.1 a	38.3 a	38.9 b	60.9 a	42.7 a	37.2 a	38.8 b	39.3 b
LSD0.05	NS	NS	NS	NS	NS	NS	NS	NS	0.50	0.40
K1	62.3 a	42.8 a	37.6 a	41.3 a	43.1 a	62.8 a	43.2 a	38.1 a	41.8 a	43.7 a
K2	61.8 a	48.8 a	37.1 a	39.6 b	39.6 b	62.3 a	45.9 a	37.6 a	40.1 b	40.1 b
K3	59.2 a	45.4 a	35.6 b	37.1 c	37.4 c	59.6 a	48.0 a	36.1 b	37.5 c	37.9 c
K4	58.4 a	47.4 a	35.4 b	36.5 d	37.0 cd	58.9 a	49.3 a	35.9 b	37.1 d	37.6 d
LSD0.05	NS	NS	0.72	0.55	0.84	NS	3.30	0.50	0.30	0.30
K at same I	NS	NS	NS	NS	NS	NS	8.40	NS	0.60	0.50
I at same K	NS	NS	NS	NS	NS	NS	13.7	NS	0.50	0.50

Different superscript letters within each column indicate significant differences at the 0.05 level. I₁ and I₂ represent the main plot treatments of irrigated and stressed plots, while K₁, K₂, K_3, and K₄ represent subplots treatments where potash applied as 0, 40, 80, and 120 kg K₂O ha⁻¹, respectively; DAP indicates days after planting during 2019–2020, and DAH represents days after harvesting during 2020–2021; Interaction reported to be non-significant during plant cane crop.

). Irrigation treatments did not affect the periodic chlorophyll content of the sugarcane leaves except at 355 DAP (plant season) and 324 and 357 DAH (ratoon season), where its values were reported to be 2.06, 1.55, and 2.54% higher in I₁ plots, respectively (

Table 9. Sugarcane quality parameters at 10th months as a function of irrigation and potash levels.

Treatments	2019–2020					2020–2021
	Brix (%)	Pol (%)	Purity (%)	Extraction (%)	CCS (%)	Brix (%)	Pol (%)	Purity (%)	Extraction (%)	CCS (%)
I1	20.08 a	18.48 a	91.86 a	43.93 a	13.10 a	20.62 a	18.19 a	88.20 a	53.63 a	12.57 a
I2	19.81 a	18.44 a	93.25 a	42.23 b	12.98 a	20.71 a	18.14 a	87.66 a	53.76 a	12.50 a
LSD0.05	NS	NS	NS	1.50	NS	NS	NS	NS	NS	NS
K1	19.17 c	17.62 c	91.91 a	39.82 b	12.41 c	20.15 b	17.74 b	88.07 a	53.82 ab	12.25 c
K2	19.87 b	18.25 b	91.86 a	42.72 a	12.85 b	20.63 b	17.97 b	88.70 a	54.80 a	12.45 bc
K3	20.41 a	18.98 a	93.20 a	43.80 a	13.45 a	21.17 a	18.51 a	87.46 a	52.44 b	12.74 a
K4	20.38 a	19.01 a	93.25 a	44.00 a	13.47 a	21.08 a	18.44 a	87.48 a	53.71 a	12.69 ab
LSD0.05	0.47	0.48	NS	NS	0.41	0.38	0.26	NS	NS	0.21
K at same I	NS	NS	2.44	NS	NS	0.58	NS	NS	NS	NS
I at same K	NS	NS	2.18	NS	NS	0.52	NS	NS	NS	NS

Different superscript letters within each column indicate significant differences at the 0.05 level. I₁ and I₂ represent the main plot treatments of irrigated and stressed plots, while K₁, K₂, K_3, and K₄ represent subplot treatments where potash applied as 0, 40, 80, and 120 kg K₂O ha⁻¹, respectively; CCS (%) is percent commercial cane sugar.

). Purity and extraction were not affected by irrigation treatments during the plant season, with respective values reported as 1.5% lower and 4.03% higher in I₁ plots after the tenth month, respectively, while only Brix (%) was significantly 2.42% higher in I₁ plots after 12th month (

Table 10. Sugarcane quality parameters at 12th months as a function of irrigation and potash levels.

Treatments	2019–2020						2020–2021
	Brix (%)	Pol (%)	Purity (%)	Extraction (%)	CCS (%)	Sugar Yield (t/ha)	Brix (%)	Pol (%)	Purity (%)	Extraction (%)	CCS (%)	Sugar Yield (t/ha)
I1	21.20a	19.18 a	90.48 a	53.33 a	13.42 a	10.39 a	21.19 a	18.90 a	89.19 a	54.63 a	13.13 a	7.67 a
I2	20.70b	19.06 a	92.02 a	51.59 a	13.40 a	10.34 a	20.94 a	18.80 a	89.18 a	54.25 a	13.05 a	7.55 a
LSD0.05	0.45	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS
K1	20.54b	18.65 b	90.85 a	51.63 a	13.07 b	9.97 b	20.58 b	18.44 c	89.57 a	54.25 a	12.83 b	7.18 c
K2	20.74ab	18.89 b	91.16 a	52.44 a	13.25 b	10.18 b	20.67 b	18.74 bc	90.67 a	55.49 a	13.11ab	7.41 bc
K3	21.27a	19.45 a	91.47 a	53.12 a	13.67 a	10.66 a	21.48 a	18.99 ab	88.35 b	54.18 a	13.12ab	7.64 ab
K4	21.29a	19.48 a	91.52 a	53.09 a	13.69 a	10.65 a	21.80 a	19.22 a	88.17 b	53.85 a	13.28 a	7.79 a
LSD0.05	0.46	0.29	NS	NS	0.40	0.28	0.31	0.41	1.08	NS	NS	0.32

Different superscript letters within each column indicate significant differences at the 0.05 level. I₁ and I₂ represent the main plot treatments of irrigated and stressed plots, while K₁, K₂, K_3, and K₄ represent subplots treatments where potash applied as 0, 40, 80, and 120 kg K₂O ha⁻¹, respectively; CCS (%) is percent commercial cane sugar; Interactions both ways observed to be had non-significant effects.

and

Table 11. Percent incidence of insect pests as a function of irrigation and potash levels.

Treatments	2019–2020			2020–2021
	Early shoot Borer	Stalk Borer	Top Borer	Early shoot Borer	Stalk Borer	Top Borer
I1	7.80 b	8.4 b	9.3 a	8.2 b	7.8 b	10.2 b
I2	11.2 a	10.7 a	10.4 a	10.2 a	10.0 a	11.3 a
LSD0.05	0.39	1.77	NS	1.34	0.39	1.02
K1	10.3 a	9.7 a	10.5 a	9.7 a	9.3 a	11.8 a
K2	9.7 ab	9.3 a	10.2 a	9.2 a	8.8 a	10.8 b
K3	8.8 b	9.5 a	9.0 a	8.7 a	8.3 a	9.5 c
K4	9.0 b	9.7 a	9.7 a	9.2 a	9.2 a	10.8 b
LSD0.05	1.14	NS	NS	NS	NS	1.04

Different superscript letters within each column indicate significant differences at the 0.05 level. I₁ and I₂ represent the main plot treatments of irrigated and stressed plots, while K₁, K₂, K_3, and K₄ represent sub-plots treatments where potash is applied as 0, 40, 80, and 120 kg K₂O ha⁻¹, respectively; Interactions both ways observed to be had non-significant effects.

). In the observed insect-pest incidence, early shoot borer and stalk borer incidences were significantly higher under stressed conditions (30.4 and 21.5% lower in I₁ plots) during the plant season, while early shoot borer, stalk borer, and top borer incidences were significantly lower in I₁ plots to the tune of 19.6, 22, and 9.73%, respectively, as compared to the I₂ plots during the ratoon season (

Table 12. Cane response and benefit to cost ratio as a function of irrigation and potash levels.

Treatments	Cost of Fertilizer (Rs ha−1)	Yields (t ha−1)		Response over Control		Benefit due to Applied K (Rs ha−1)		Benefit-Cost Ratio		Trends across Irrigations
		Plant	Ratoon	Plant	Ratoon	Plant	Ratoon	Plant	Ratoon	Plant	Ratoon
I1K1	0	76.48	56.54	0	0	0	0	0	0	--	--
I1K2	1273	77.13	56.91	0.65	0.37	1912	1092	1.5	0.9	1.3	1.3
I1K3	2546	78.15	58.52	1.67	1.98	4915	5829	1.9	2.3	1.9	2.6
I1K4	3800	78.43	58.77	1.94	2.22	5736	6556	1.5	1.7	1.6	2.3
I2K1	0	76.12	55.31	0	0	0	0	0	0
I2K2	1273	76.58	56.05	0.47	0.74	1379	2186	1.1	1.7
I2K3	2546	77.78	57.90	1.66	2.59	4903	7650	1.9	3.0
I2K4	3800	78.33	58.52	2.22	3.21	6542	9470	1.7	2.5

Rate of Muriate of potash was Rs 950 per 50 kg bag, and the price of Sugarcane mid-late cultivar CoJ 88 rate is Rs. 2950 t⁻¹ during the experimentation period. I₁ and I₂ represent the main plot treatments of irrigated and stressed plots, while K₁, K₂, K_3, and K₄ represent sub-plots treatments where potash applied as 0, 40, 80, and 120 kg K₂O ha⁻¹, respectively.

).

3.2. Potash Dose Effects on Sugarcane Performance

3.2.1. Sugarcane Growth and Yield Parameters during the Plant and Ratoon Seasons

A significant effect of potash was found to be evident on growth, yield, insect pest incidence, and ultimately the quality of canes. In K₃ plots, germination, NMCs, and yields were higher than those in K₁ and K₂ plots during the plant and ratoon seasons, with statistically similar values in K₄ plots. As compared to the K₁ plot, germination was higher in K₂, K₃, and K₄ plots, respectively, during plant and ratoon seasons. When shifting from K₂ to K₃ and K₃ to K₄ plots, germination was higher by 9.9 and 6.0% during the plant season and 10.4 and 6.1% during the ratoon season.

As compared to K₁ plots, NMCs were 5.9, 21.1, and 22.6% higher during the plant season and 8.1, 23.6, and 25.2% higher during the ratoon season in K₂, K_3, and K₄ plots, with a jump of 14.3 and 1.2% during the plant season and 14.3 and 1.4% during the ratoon season when shifting from K₂ to K₃ and K₃ to K₄ plots. RLDs, however, were not affected by different K treatments. Cane yields in K₂, K₃, and K₄ plots were 0.73, 2.18, and 2.73% significantly higher during the plant season, and 1.0, 4.1, and 4.9% higher during the ratoon season, respectively, with a 1.4 and 0.5% increase during the plant season and 3.0 and 0.7% during the ratoon season when shifting from K₂ to K₃ and K₃ to K₄ plots. (Table 3).

Tiller’s cane⁻¹ was recorded to be significantly affected by potash levels at 241 DAP and 261 and 326 DAH. Tillers in K₂, K₃, and K₄ plots were 15.5, 10.6, and 16.3% higher during the plant season compared to the K₁ plot, and 13.7, 24.2, and 13.7% higher at 261 DAH and 4.7, 21.0, and 7.0% higher at 326 DAH during 2020–2021. Leaves cane⁻¹ levels were significantly greater in the K₃ plots at 266, 292, and 302 DAP and 264, 296, and 314 DAH than in the K₁ and K₂ plots, which were statistically comparable to the K₄ plots. At 302 DAP during 2019–2020, the K₂, K₃, and K₄ plots were 9.2, 10.3, and 12.6% lower than the K₁ plot, respectively, while at 314 DAH, the K₂, K₃, and K₄ plots were 1.0, 8.9% lower, and 2.0% higher, respectively (Table 4).

Cane height was not affected by different K levels throughout the experiment period, except for 261 and 291 DAH during the ratoon season. While compared to the K₁ plot, 2.0, 7.3, and 8.7%, and 1.9, 8.2, and 8.7% hikes were observed in K₂, K_3, and K₄ plots with a jump of 5.2 and 1.3%, and 6.2 and 0.5%, respectively, when shifting from K₂ to K₃ and K₃ to K₄ plots (Table 5).

Similar trends in cane diameter were reported, except for 264 DAH and 294 DAH during the ratoon season; however, K₂, K_3, and K₄ plots were increased by 0, 4.2, and 4.2%, and 0.4, 3.8, and 4.2% compared to the K₁ plot. The cane diameter had an increase of 4.2 and 0% and 3.4 and 0.4%, respectively, when shifting from K₂ to K₃ and K₃ to K₄ plots (Table 6).

Periodically recorded Brix in the field was not affected by K-level treatments during the plant season; it was, however, affected significantly during the ratoon season except at 355 DAH. As compared to the control plots, K₂, K_3, and K₄ plots reported significantly different Brix values at 173, 203, 264, and 325 DAH during 2020–2021with percent increases of 2.1, 3.6, and 2.1%; 1.6, 4.8, and 0.5%; 5.2, 3.1, and 3.0%; 1.0, 1.9, and 1.9%, respectively. Careful evaluation of the table showed that there was an increase of 2.5, 3.2, and 0.9% when shifting from K₂ to K₃ plots during 113, 239, and 325 DAH during the ratoon crop, which decreased during the shift to K₄ plots.

Nodes cane⁻¹ is an important parameter determining the overall extraction percentage in the canes [63,64,65,66] which differed significantly in both seed and ratoon seasons during 2019–2020 and 2020–2021 except during 280 DAP and 284 DAH. As compared to the control plots, K₂, K_3, and K₄ plots reported significantly different Brix values at 180, 220, 262, 305, and 340 DAP during 2019–2020 with percent decreases of 1.6, 4.7, and 10.2%; 4.7, 11.7, and 4.7%; 1.6, 9.6, and 2.1%; 1.5, 4.4, and 0%; 1.5, 4.9, and 1.0%, respectively (Table 7).

Similarly, nodes in K₁ plots at 188, 219, 260, 305, and 336 DAH during 2020–2021 were changed by 1.5, –9.0, and –3.76%; –1.7, −11.3, and –4.5%; 1.6, –7.3, and –0.5%; 1.9, –3.8, and 0.5%; 1.4, –4.7, and 1.0% as compared to K₂, K₃, and K₄, respectively (Table 7). The contents of chlorophyll were reduced with increasing K dose, which was significantly affected with the exception of 218, 258 DAP, and 260 DAH (Table 8).

However, in comparison with control plots at 280, 330, and 355 DAP, the K₂, K₃, and K₄ plots had 1.3, 5.3, and 5.9%; 4.1, 10.2, and 11.6%; 8.1, 13.2, and 14.2% lower chlorophyll levels due to the role of potash in the transfer photosynthates from leaves to cane stems; however, during the conversion of K₂ to K₃ and K₃ to K₄ plots, chlorophyll content was reduced by 4.0 and 0.6%; 6.3 and 1.6%; 5.6 and 1.1% after 280, 330, and 355 DAP during 2019–2020, respectively (Table 8).

During 281, 324, and 357 DAH, the chlorophyll content in K₂, K₃, and K₄ plots were 1.3, 5.3, and 5.8%; 4.1, 10.3, and 11.2%; 8.2, 13.3, and 14% lower as compared to those of the control plots. Careful evaluation of the data showed that moving from K₂ to K₃ and K₃ to K₄ plots, the respectable chlorophyll content was reduced by 4.0 and 0.6%; 6.5 and 1.1%; 5.5 and 0.8% during 281, 324, and 357 DAH during 2020–2021 (Table 8).

3.2.2. Sugarcane Juice Quality

Among the different sugarcane quality parameters, except for purity, all other factors were significantly affected by differential potash doses during the plant and ratoon seasons (Table 9). Compared with the control K₁ plots, Brix, Pol, Extraction, and CCS in K₂, K_3, and K₄ plots were 3.7, 6.5, and 6.3%; 3.6, 7.7, and 7.9%; 7.3, 10, and 10.5%; 3.6, 8.4, and 8.5% higher, respectively, during the plant season, while 2.4, 5.1, and 4.6%; 1.3, 4.3, and 4.0%; 1.8, −2.6, and 0.2%; 1.6, 4, and 3.6% higher during the ratoon season at 10th month; however, when shifting from K₂ to K₃ and K₃ to K₄, CCS values varied to 4.7 and 0.2% in the plant during 2019–2020, respectively, and 2.3 and –0.4% in the ratoon season during 2020–2021 (Table 9).

Different potash levels did not affect sugarcane quality at the 12th month near harvesting, as purity, and extraction during the plant, while only extraction during ratoon was affected; however, in comparison with the control plots, Brix, Pol, CCS, and sugar yields in the K₂, K₃, and K₄ plots were 1.0, 3.6, and 3.7%; 1.3, 4.3, and 4.5%; 1.4, 4.6, and 4.7%; 2.1, 6.9, and 6.8% higher during the plant season, while 0.4, 4.4 and 6.0; 1.6, 3.0 and 4.2; 2.8, 2.3 and 3.5; 3.2, 6.4 and 8.5% higher during the ratoon season at 12th month (Table 10).

During the ratoon season months, a purity difference of 1.2, −1.4, and −1.6% was also reported with K₂, K₃, and K₄ plots compared to the control plot. Further, the shift from K₂ to K₃ and K₃ to K₄, CCS and sugar yield values varied from 3.2 and 0.2%; to 4.7 and 0.1% during the plant season, while 0.1 and 1.2%; 3.1 and 2.0% during the ratoon season, respectively (Table 10).

3.3. Insect-Pest Incidence

Among the different insect-pest incidences, early shoot borer (Chilo infuscatellus), top borer (Scirpophaga excerptalis), and stalk borer (Chilo auricilius) are very important in sugarcane and are considered in the present study during both plant and ratoon seasons. Investigation of the data revealed that among early shoot borer (ESB), stalk borer (SB), and top borer (TB), only ESB was reported during the plant season (2019–2020) and TB during the ratoon season (2020–2021) with significant decreases (Table 11).

Compared with the K₁ control plots, the incidence of ESB during the plant season while TB during the ratoon season decreases in K₂, K₃, and K₄ to the tune of 5.8, 14.6, and 12.6%; 8.5, 19.5, and 8.5%, respectively. The transition from K₂ to K₃ sub-plots reduced the incidence of ESB in plants during 2019–2020 and TB in ratoon season during 2020–2021, to 9.3% and 12%, respectively, which increased to 2.3 and 13.7% after the transition to K₄ plots from K₃ plots (Table 11). Hence, K₃ plots loaded with 80 kg K₂O ha⁻¹ had the lowest incidence of insect pests.

3.4. Overall Benefit to Cost Ratio

Under the main irrigation plots, K₃ plots loaded with 80 kg K₂O ha⁻¹ had the maximum benefits of 1.9 and 2.3 under the plant and ratoon seasons under irrigated plots (I₁) while 1.9 and 3.0 under stressed plots (I₂), respectively. Over the irrigation treatments, shifting from K₂ to K₃ plots increased profits by 46.2 and 100%, respectively, but decreased to 15.8 and 11.5% upon shifting to K₄ plots. The benefits increased by 26.7% during the plant season and 155% during the ratoon season from K₂ to K₃ plots, which decreased to 21.0% during the plant season and 26.1% during the ratoon season from the K₃ to K₄ plots in the I₁ plots; however, in water_-stressed plots, benefits from K₂ to K₃ plots were reported to be 72.7% higher during the plant while during the next ratoon season during 2020–2021, this enhanced to 76.5%; however, on moving to a higher K dose viz. 120 kg K ha⁻¹ instead of increasing, benefits reduced to 10.5% during plant season during 2019–2020 and 16.7% during ratoon season during 2020–2021, respectively (Table 12). Hence, K₃ plots under both irrigated and stressed treatments had higher benefits compared to the K level treatments.

4. Discussion

4.1. Growth and Yield Performance of Sugarcane under Irrigation Treatments

Irrigation depths of 50 mm were applied to the irrigated and stressed treatment plots, respectively, for a total of 18 and 15 irrigations during the plant (2019–2020) and 16 and 13 irrigations during the ratoon season (2020–2021). In I₁ treatments, water stress compared to a 150 mm irrigation water shortage was projected; however, this stress was mitigated due to receiving 976.2 during plant and 969.5 mm rainfall during ratoon season (Figure 1), which mostly coincided with the missing irrigations. Without the rain, the disparities in different irrigation regimes would likely have been even more pronounced than observed. Cane growth parameters viz. germination, NMCs, RLD, tillers, leaves, and nodes per cane, cane height and diameter, chlorophyll content and yield were all reported to be better, albeit not significantly different, under I₁ irrigated main plot treatment compared toI₂ water-stressed treatment (Table 3, Table 4, Table 5 and Table 6); this could be attributed to higher moisture and nutrient intake [22,70], higher use efficiency [71,72], and improved potassium distribution in I₁ irrigation plots [73,74,75]; however, in I₂ plots, stomatal restriction and conductance, transpiration rate, internal CO₂ concentration, and rate of photosynthesis were reduced [20,76], as well as phosphoenolpyruvate carboxylase and ribulose-1,5-biphosphate carboxylase activity [19], further impairing metabolic and physiological activities in canes and yields by up to 60% [72,77]. Sugarcane is more susceptible to water-stressed conditions particularly during tillering and stem elongation periods [78,79], having stunted stem, leaf rolling, stomatal closure, stalk and leaf growth restriction, and reduced leaf area [19,80], all of which adversely effected both cell division and cell elongation [48,78]. Ratoon crops were found to be more responsive to water stress, with periodic nodes being statistically similar during plant but significantly different during ratoon season (Table 7). Plant and ratoon canes were found to have similar chlorophyll contents under both irrigation regimes, which are further reported to be significantly lower under irrigated conditions due to proper moisture availability, well-developed roots [65,75], and less photosynthesis sensitivity under stressed conditions (Table 8). The reason claimed is due to reduced stem growth under stressed conditions, which channeled assimilated CO₂ to sucrose production and accumulation in the cane stalk [81]. Sugarcane quality metrics except for purity and extraction after the 10th month were not affected by irrigation treatments even after the 10th and 12th months (Table 9 and Table 10), even though values were higher in irrigated plots; this could be due to better moisture availability for metabolic and physiological activities, better nutrient uptake, and movement to cane stem, which is further reported to have higher nitrogen and water usage efficiency [19,78,82]. Sufficient water conditions are required for transpiration, in which water and nutrients enter the plants through the roots, which are badly affected under stressful conditions, resulting in reduced cane recovery [22]. Irrigated plots had significantly lower incidences of early shoot borer and stalk borer during the plant, while early shoot borer, top, and stalk borer during ratoon season compared to stressed plots (Table 11), which could be attributable to insufficient nutrient flow from the leaves to cane stem, comparatively sweater leaves [20,80].

4.2. Sugarcane Growth and Yield Performance under Differential K Doses

Potassium fertilizer is not replenishing Indian soils due to earlier misperception that these alluvial soils are high in K and do not require further K fertilizers [65]. Even if the total K content of the soil is acceptable, the rate at which it is released is frequently insufficient to meet crop requirements [83]. Sugarcane responses to K fertilization are largely governed by the availability of K in the soil, with significant responses occurring only in soils with low available K [29,58,59]. Germination and growth parameters viz. NMCs, yields, tillers, and leaves per cane except for root length density both during plant and ratoon season, improved with potash application compared to rest sub-plots treatments (Table 3 and Table 4); it might be because Potash under both irrigation regimes improved input usage efficiency of applied inputs such as N fertilizers [28,29,30] and water [31,32,33], and also detoxified reactive oxygen species [11,34]. In the plant and ratoon, the yield potential of the ratoon cane was reported to be lower than plant crop yields (Table 3) which might be due to soil compaction [84], decreasing soil fertility with continuous sugarcane cropping, and unbalanced fertilization [85]. Further decreases in temperature in semi-arid regions have been documented because of reduced buds emerging following crop harvest. Unsprouted stubbles create gaps in stubble rows, resulting in a poor initial shoot population and cane output. Several agro-techniques, such as trash mulching, polyethylene mulching, and wheat, tomato, and potato intercropping are generally recommended for profitable sugarcane farming in the region [59,86].

Increased potassium levels resulted in a constant increase in tiller density, which was reduced in the later stages. Following that, plots that received 80 kg K₂O ha⁻¹ had more tillers during both seasons. During the first season, however, there was no significant difference in the increase of tillers provided with 40 kg K₂O ha⁻¹ against those supplied with 80 kg K₂O ha⁻¹. Higher K doses substantially affected the shoot population in the second season, showing the importance of potassium in maintaining water balance in the stubble bud and conferring disease and insect resistance to the plant; this could be due to the synergistic action of K and N and the relatively efficient translocation of photosynthates in plants. Later on, the plots containing 80 kg K₂O ha⁻¹, followed by 40 kg K₂O ha⁻¹, had a higher number of tillers survive (Table 4). These findings are consistent with those obtained by Shukla et al. [9]. K application up to 80 kg K₂O ha⁻¹ substantially increased plant and ratoon cane yield. More vigorous tillers were generated in ratoon cane with 80 K₂O ha⁻¹, resulting in a higher number of millable canes. Sugarcane primary and secondary tillers have a longer time of growth and feeding on stubble, which they produce millable canes with increased length, diameter, and weight when supplemented with sufficient N and K, [87]; however, ratoon cane yields are frequently lower than plant crop yields in the plant and ratoon because of soil compaction [84], decreasing soil fertility with continuous sugarcane cropping, and poor fertilizer application [85].

During plant season both cane height and girth were reported with no difference, which differs in ratoon season canes with higher values for the K₃ plot as compared to the K₁ and K₂ plots, which were further similar to the respected values recorded in the K₄ plots (Table 5 and Table 6) Nutrient uptake may have been aided by a decrease in aggregate stability and an increase in total root surface area after K fertigation [88], allowing the roots to explore a larger volume of soil and gain access to more phosphorus and other mineral nutrients. The sugarcane’s strong root growth, increased photosynthetic rate, and better carbohydrate translocation improved phosphorus uptake. Several researchers observed the effects of K and irrigation on ratoon cane yield and dry matter output [89]. Under field conditions, N and K interactions are common. Proper fertilization is critical for better cane and sugar yield where administration of K causes a decrease in leaf nitrogen and moisture in the sheath. Sufficient K is necessary to use the absorbed N in cane [90].

Lesser the number of nodes, the better the extraction percentage due to more juicy internodes. In our study, K₃ subplots had significantly lower nodes as compared to the other subplots (Table 7), which is due to the potassium role in water balance maintenance [84], translocation of photosynthates [34,80,91], and its utilization [92], enhancing photosynthesis [33], and finally better root growth and development [6,60,93]. The application of fertilizer K to deficient soils can improve both cane productivity and quality [29,33,94]. Potash fertilizer boosts cane yield and sucrose concentration [5,95], as reported in the current study (Table 9 and Table 10). Sustainable use of K at deficient sites resulted in (i) good tillering, increased dry matter accumulation at all development stages, (ii) increased height, diameter, and Brix and nodes, and (iii) increased the number of millable cane both in plant and ratoon canes. Moisture stress reduced yield when K was inadequate but had no effect on yield when K was sufficiently supplied (at 120 kg ha⁻¹) [6,96].

K feeding improves N and P uptake, disease resistance, root elongation and thickness, and root elongation and thickness [97]. Several investigations have shown that K⁺ has a role in product translocation [98]. If a higher amount of K⁺ nutrition leads to a rise in net carbon exchange, phloem loading, transport sinks, and metabolic conversion of sucrose in sink tissues, this promotion will occur. As per available literature, increased K⁺ fertilization of plants enhances net carbon exchange. Low K⁺ appears to impair net carbon exchange by increasing stomatal and mesophyll resistance. K is a cation that travels with the NO₃ anion from the roots to the shoot, where nitrate is reduced to NH₃ and then integrated into amino acids, the building blocks of protein. As a result, it may have boosted NO₃ reductase enzyme activity [14], increasing N absorption and thus N usage efficiency.

Potash also regulated the chlorophyll contents of the cane leaves during the plant, ratoon season, and the later stages. In comparison to control plots, the K₂, K₃, and K₄ plots had 1.3, 5.3, and 5.9; 4.1, 10.2, and 11.6; 8.1, 13.2, and 14.2% lower at 280, 330, and 355 DAP. Similarly, the K₂, K₃, and K₄ plots had 1.3, 5.3, and 5.8; 4.1, 10.3, and 11.2; 8.2, 13.3, and 14% lower chlorophyll contents than the control plots during 281, 324, and 357 DAH for plant and ratoon canes, respectively (Table 8). Mainly due to its role in translocating photosynthate from leaves to cane stem and in activating the ATP synthase enzyme, thus enhancing the photosynthetic efficiency. ATPase performance is optimum and proportionate to the K content of the plant [99]. The photosynthesis rate in plants increased with the higher utilization and export of photo-assimilates. Various studies support the fact that higher potassium doses as in the K₄ sub-plots sufficiency increase the sucrose accumulation in leaves, which further reports higher insect-pest incidences due to reported decreased pyruvate kinase activity and/or increases in invertase activity [100].

Potassium fertilizers levels significantly improved sugarcane quality parameters at ten and twelve months after harvesting the plant crop compared to the control treatment (0 kg K₂O ha⁻¹), as previously indicated by numerous workers [53,54,55,101] (Table 9 and Table 10). Sugarcane juice quality parameters were higher in potash-fertilized plots as compared to the unfertilized plots in deficient experimental plots. Further, K₃ plots were reported with higher quality as compared to K₂ while with similar quality in K₄ plots; this could be because the added potassium promotes better sugarcane root growth and development, which is linked to improved water and nitrogen uptake and use efficiency [5,8,73,96]. Further, due to the quicker absorption of potash through well-developed roots, ratoon canes’ quality was observed to be higher than the plan canes (Table 9 and Table 10) [97,98]. K fertilized plots have consistently reported higher yields (Table 3) and [50,51,52] and quality during the 10th and 12th months for both seasons (Table 9 and Table 10) [53,54,55]. These improvements were up to 80 K₂O ha^−1, which was further reported to be statistically at par with 120 K₂O ha⁻¹ in K₄ plots. Additionally, starch synthase, nitrate reductase, invertase, phosphofructokinase, sucrose phosphate synthase β-amylase, and pyruvate kinase were reduced because of decreased stomatal conductance and increased mesophyll resistance [54,99,100]. Better quality of ratoon canes might be due to applied potash, which regulated stomatal openings [67] through which water is transpired from the leaves to the atmosphere [23,97]. Though deficiency of K under stressed conditions is responsible for wilting, poor photosynthate translocation from leaves to cane stem [100,101], and hence higher insect-pests incidence (Table 11), poor yields, and other growth parameters (Table 3, Table 4 and Table 5). On the other hand, a sustainable supply of K⁺ in both plant and ratoon canes improved the conditions even under stressed conditions [5,8,88], due to clay mineralogy [102], reduced the insect-pest incidence [37] (Table 11), and improved the land and water productivities [36].

In K deficient soils, K-fertilization improved nutrient/photosynthate delivery from the leaves to the entire plant, resulting in comparatively bitter leaves than in control plots, hence reducing preference [71,76] and incidence of the sucking insect pest incidence [68,92]; this could also explain why the K₃ treatment reduced the incidence of key insect pests such as stalk borer, early shoot borer, and top borer (Table 11). Further, potash provides faster growth and hard leaf sheath, which provides resistance to the cane against entering neonates of early shoot borer, as reported by [16,57]; however, in the ratoon crop, treatment K₃ had the lowest percent incidence of early shoot borer due to a well-developed root system and a hard base leaf sheath. As the potash dose (0 to 80 kg ha⁻¹) was increased, the percent incidence of top borer decreased (10.5 to 9.0%), as previously described [5,57,103,104]. In sugarcane ratoon, the lowest crop percent incidence of top borer was significantly recorded at 80 kg K₂O ha⁻¹ than other treatments. Similarly, results obtained by [58,79] showed that the potassium significantly reduced the top borer infestation as compared to the control. During both years of the experiment, 80 kg K₂O ha⁻¹ was identified as a sustainable potash dose, which was further reported to have larger benefits under both irrigation regimes than any other subplot treatment (Table 12).

5. Conclusions

Indian Punjab soils are not fertilized with potassium owing to the misperception that alluvial soils of the region are high in inherent potash and do not require further potash fertilization. At many sites, even though the total K content of the soil is adequate, the rate of release is frequently insufficient to meet sugarcane potash requirements which further results in poor crop growth, yield, and quality parameters. Therefore, K fertilization is a necessity in the deficient soils of the region. The present two-year study concluded that water stress conditions did not affect sugarcane’s growth, yield, or quality indices due to accidentally receiving well-distributed rainfalls during experimentation periods; however, as far as potash (K) standardization is concerned for deficient soils in the region, (i) 80 kg K₂O ha⁻¹ was observed to be a sustainable dose for better sugarcane performance, which also (ii) reduced the spread of insect-pests and the use of chemicals and finally (iii) improved the livelihoods of the cane farmers. Interestingly, the higher dose of 120 kg K₂O ha⁻¹ did have some improvements, but these were statistically similar to those of the 80 kg K₂O ha⁻¹. Hence, our final recommendation revealed that 80 kg K₂O ha⁻¹ dose is associated with the reduced insect-pests occurrence, improved sugarcane growth, yields, and quality of sugarcane in the region.