Keywords

soil moisture depletion; planting pattern; irrigation; economic benefit; root zone; sugar yield; planting geometry; net field benefit

21.1 Introduction

Sugarcane, one of the most important cash crops, plays a vital role in the national economy of Pakistan. It is an important source of income and employment for farmers, particularly during the winter season. The challenge of increasing sugar from sugarcane has been erratic, and there has been insufficient rainfall distribution to support the entire crop cycle (Pires et al., 2008; Cheavegatti-Gianotto et al., 2011). Sugarcane requires about 1200 mm of annual rainfall equally distributed throughout the entire growing period. The sugarcane crop requires 88–118 kg water/kg cane and 884–1157 kg water/kg sugar to produce plant and ratoon crops (Ashok et al., 2011). In Pakistan, it has been estimated that rain meets only 25% of the water needs of the crop; the remaining 75% of water is met through additional irrigation, but water is not always available in the desired quantities and crops frequently suffer from lack of available soil moisture. The prevalence of drought during the peak growth period of sugarcane results in a considerable reduction in its yield ability. Drought remains a research topic of high priority for agricultural scientists (Medici et al., 2014) causing reduction in growth and development of plants due to the cessation of cell expansion directly related to carbon assimilation and photosynthetic rates (Benesová et al., 2012; Zingaretti et al., 2012). In order to realize the full benefits of the land and environmental resources, it is necessary to place the plants in the field in such a pattern that there is the least competition among them for essential growth factors.

Proper orientation of plants in the field plays a significant role in the development and functioning of vital plant organs. Planting geometry provides the right direction of plants in the field in the form of multi-row strips, which facilitate efficient and expeditious intercultural operations, conserve irrigation water with saving in labor, and permit systematic planting and handling of intercrops. Plant spacing accordingly affects the number of plants, plant height, plant health, and plant canopy, which are directly associated with plant yield. The present study, therefore, was designed to investigate the impact of soil moisture depletion and planting geometry on the yield and quality of sugar cane under arid climatic conditions in Pakistan on two soils: silty clay and sandy loam.

21.2 Methodology

Sugarcane (Saccharum officinarum L.) is a tropical crop of long duration and requires abundant water. Increasing urban growth and environmental concerns are limiting the amount of water available for agricultural use. In Pakistan, especially in Punjab and Kyber Pakhtunkhwa, the sugarcane lies in areas where its successful growth needs artificial irrigation. Water is not always available in desired quantities during the long growth period of the crop and drought conditions result in considerable loss of yield. To overcome drought stress against the sugarcane crop, a factorial arrangement was laid out in randomized complete block design (RCBD) with four replications. The net plot size was 6×4 m². Each year the crop was planted during the first week of September and harvested in the first week of December the following year. The seed was used at the rate of 70,000 double-budded setts ha⁻¹. A cane cultivar, “HSF 240,” was used as test variety. Chemical fertilizer was applied at the rate of 200, 200, and 100 kg NPK ha⁻¹ on the farm of urea, P₂O₅, and K₂O, respectively. All the phosphorus, potassium, and one-quarter of total nitrogen were applied at the time of sowing while the remaining nitrogen was applied in two equal splits each at completion of germination at the end of February and at the start of cane formation at the end of March. The crop was kept free of weeds. All agronomic practices were kept normal and uniform for all the treatments. The experiment comprised the treatments shown in Table 21.1. Water was applied to the respective plots as soon as the desired available soil moisture depletion level was reached in the soil within the crop root zone.

21.2.2 Moisture percentage on volume basis

The moisture content percentage on volume basis was computed with the following details:

${\mathrm{O}}_{\mathrm{w}}=\frac{({\mathrm{WS}}_1-{\mathrm{WS}}_2)\times 100}{{\mathrm{WS}}_2}$ (21.1)

(21.1)

where:

O_W=soil moisture percentage on dry weight basis

WS₁=soil sample weight before oven drying

WS₂=soil sample weight after oven drying

The bulk density of soil was calculated as below:

${\mathrm{P}}_{\mathrm{b}}=\frac{{\mathrm{W}}_{\mathrm{d}}}{{\mathrm{V}}_{\mathrm{i}}}$ (21.2)

(21.2)

where:

P_b=bulk density of soil in g/cm³

W_d=weight of oven dry soil core in g

V_i=total volume of soil and voids in cm³

${\mathrm{O}}_{\mathrm{v}}\%=\frac{{\mathrm{P}}_{\mathrm{b}}\times {\mathrm{O}}_{\mathrm{W}}}{{\mathrm{P}}_{\mathrm{W}}}$ (21.3)

(21.3)

where:

O_v=soil moisture content on a volume basis in percent

P_b=bulk density of soil in g/cm³

P_W=density of water in g/cm³

$\mathrm{ASMDL}=\frac{\mathrm{RAW}\times 100}{\mathrm{AW}}$ (21.4)

(21.4)

where:

ASMDL=available soil moisture depletion level in percent

RAW=readily available water in cm

AW=available water in cm; and

AW and RAW are defined as under:

$\mathrm{AW}=\frac{{\mathrm{D}}_{\mathrm{r}·\mathrm{z}}({\mathrm{F}}_{\mathrm{c}}-{\mathrm{P}}_{\mathrm{w}·\mathrm{p}})}{100}$ (21.5)

(21.5)

where:

D_r.z=depth of root zone in cm

F_c=field capacity in percent by volume

P_w.p=permanent wilting point in percent by volume

$\mathrm{RAW}=\frac{{\mathrm{D}}_{\mathrm{r}·\mathrm{z}}({\mathrm{F}}_{\mathrm{c}}-{\mathrm{O}}_{\mathrm{c}})}{100}$ (21.6)

(21.6)

where O_c=critical soil water content in percent by volume.

By combining Eqs. 21.4, 21.5, and 21.6 we get critical soil water contents in percent by volume for different ASMD levels. Critical soil water contents in percent by volume basis (O_c) were calculated by the above-mentioned formulae and are given in Table 21.2.

Table 21.2

Critical Soil Water Contents in Percent by Volume for Different ASMD levels

Available Soil Moisture Depletion Levels (ASMDL)	Critical Soil Water Contents Percent by Volume Basis (Oc) Calculated by Above Formulae
	Location-I		Location-II
	2003–2004	2004–2005	2003–2004	2004–2005
ASMDL1=20%	21.4	21.8	14.0	16.0
ASMDL2=40%	18.9	19.3	12.3	14.1
ASMDL3=60%	16.5	16.8	10.6	12.2
ASMDL4=80%	14.0	14.3	8.9	10.3

Irrigation was applied to respective plots as soon as the desired available soil moisture depletion level reached in the soil in the crop root zone.

21.2.3 Measurement of depth of irrigation water applied

The irrigation requirements of each plot were predetermined on the basis of soil sampling, and irrigation was applied at four different ASMD levels, being 20, 40, 60, and 80% depletion of available moisture in the root zone to bring back the soil moisture to field capacity (F_c); a measured quantity of water was applied to each treatment. A cut throat flume (3′×8″) was installed in the water course at the field entrance to measure irrigation water applied to each plot. Water was allowed to flow up to 10 minutes in the non-experimental area to maintain constant flow of water. The depth of irrigation water applied to each plot (Table 21.3) was calculated from the pre-irrigation soil moisture content in the root zone by using the following relationships:

${\mathrm{d}}_{\mathrm{w}}=\frac{{\mathrm{D}}_{\mathrm{r}\cdot \mathrm{z}}({\mathrm{F}}_{\mathrm{c}}-{\mathrm{O}}_{\mathrm{i}})}{100}$

where:

d_w=depth of water to be applied in mm

D_r.z=depth of root zone in mm

F_c=field capacity in percent by volume

O_i=soil moisture content before irrigation in percent by volume

Table 21.3

Water Applied to Different Treatments During Both Years at Both Locations

Available Soil Moisture Depletion Levels (ASMDL)	Location-I (Silty Clay Soil) 2003–2004			Location-II (Sandy Loam Soil) 2003–2004
	Total Number of Irrigations Applied	Depth of Irrigation (mm)	Irrigation + Rainfall (mm)	Total Number of Irrigations Applied	Depth of Irrigation (mm)	Irrigation + Rainfall (mm)
ASMDL1=20%	55	36.93	2359.15	93	25.71	2820.76
ASMDL2=40%	16	73.86	1509.76	28	51.42	1869.49
ASMDL3=60%	15	110.80	1990	22	77.13	2126.59
ASMDL4=80%	12	147.72	2100.64	16	102.84	2075.17
Total rainfall received=328.00 mm				Total rainfall received=373.23mm

	Location-I 2004–2005			Location-II 2004–2005
ASMDL1=20%	50	37.17	2442.5	87	28.92	2896.28
ASMDL2=40%	14	74.33	1624.62	25	57.84	1826.24
ASMDL3=60%	13	111.50	2033.5	20	86.76	2115.44
ASMDL4=80%	11	148.65	2219.15	14	115.68	1999.76
Total rainfall received=584.00 mm				Total rainfall received=380.24 mm

The time required to supply the required depth of irrigation water to each plot was calculated with the help of following equation:

$\mathrm{t}=\frac{d(a)}{\mathrm{q}}$

where:

t=time in minutes

d=depth of water in cm

a=area in m²

q=discharge of irrigation water in liter/sec

In a well-leveled field, a border strip irrigation system was adopted to check conveyance losses and conserve application and distribution efficiencies.

21.2.5 Observations

The following observations were recorded through standard procedures:

• Germination percentage

• Number of shoots (m⁻²)

• Crop growth rate (g m⁻² day⁻¹)

• Leaf area index

• Total leaf area duration (days)

• Net assimilation rate (g m⁻² day⁻¹)

• Plant height (m)

• Weight per stripped cane (kg)

• Mean stripped cane length (m)

• Mean cane diameter (cm)

• Unstrapped cane yield (t ha⁻¹)

• Stripped cane yield (t ha⁻¹)

• Harvest index percentage

• Sugar recovery percentage

• Sugar yield (t ha⁻¹)

• Net field benefit (Rs ha⁻¹)

The weather data of two locations are shown in Figures 21.1–21.3.

21.3 Results and discussion

21.3.5 Total leaf area duration (days)

As shown in Table 21.9, the greatest total leaf area duration (TLAD) of 847.41 and 980.92 days at Location-II and Location-I, respectively was recorded with a 40% ASMDL×30/90 cm spaced paired row strip planting pattern followed by a 40% ASMDL×75 cm, 40%×60 cm, 40%×30/120 cm planting pattern spaced_. Minimum TLAD of 621.34 and 681.87days was recorded at Location-II and Location-I, respectively, in an 80% ASMDL×30/120 cm spaced paired row strip planting pattern. It was seen that a 36.38 and 43.86% increase in TLAD at Location-II and Location-I, respectively, was recorded with a 40% ASMDL×30/90 cm spaced paired row strip planting pattern compared to an 80% ASMDL×30/120 cm spaced paired row strip planting pattern. The increase in TLAD with a 40% ASMDL×30/90 cm spaced paired row strip planting pattern might be due to the complementary effect of increased nutrient availability and improved air circulation and light interception, which enhanced photosynthetic efficiency and ultimately TLAD.

21.3.6 Net assimilation rate (g m⁻² day⁻¹)

Both excessive and deficient irrigations for sugarcane crop are equally harmful. Due to frequent irrigation, soil remains continuously wet, while due to the arid climate at Location-I and Location-II, frequent wind storms in summer season caused lodging of crop during the growth period. The highest net assimilation rate (NAR) of 1.93 and 2.02 g m⁻² day⁻¹ at Location-II and Location-I, respectively, was recorded with a 40% ASMDL×30/90 cm planting pattern followed by a 40% ASMDL×75 cm, 40% ASMDL×60 cm, 40% ASMDL×30/120 cm spaced paired row strip planting pattern. NAR was minimum at 1.25 and 1.48 g⁻² day⁻¹ at Location-II and Location-I, respectively, with an 80% ASMDL×30/120 cm planting pattern. It was found that a 35.23 and 36.49% increase with a 40% ASMDL×30/90 cm planting pattern at Location-II and Location-I, respectively, was recorded compared to an 80% ASMDL×30/120 cm spaced paired row strip planting pattern. It was also observed that optimum NAR with a 40% ASMDL×G-30/90 was due to enhanced LAI, TLAD, and CGR attributes. These results are in agreement with those of Bashir (1997) and Ali (1999) who reported that planting patterns had a significant effect on NAR. The maximum NAR was recorded in pit planting system compared to the minimum from the crop sown with a 60 cm spaced single rows of sugarcane crop. It was also noted that too much of an increase in inter-strip spacing, as in a 30/120 cm spaced paired row strip planting pattern, decreased the number of strips per plot and the number of plants per unit area was increased to maintain equal plant population, due to increased inter-plant competition causing adverse effects on LAI, TLAD, and CGR (see Table 21.10).

21.3.7 Plant height (m)

A larger plant height of 4.07 and 4.46 m at Location-II and Location-I, respectively, was documented (Table 21.11) with a 40% AMSDL×30/90 cm planting pattern, and a minimum of 1.79 and 1.71 m at Location-II and Location-I, respectively, with interaction of 80% AMSDL×30/120 cm planting patterns. It was observed that a 127.37 and 160.82% higher plant height at Location-II and Location-I, respectively, was recorded in the interaction of a 40% AMSDL×30/90 cm planting pattern followed by 56.02 and 58.39% at Location-II and Location-I, respectively, in a 40% AMSDL×75 cm spaced planting pattern compared to the interaction of 80% AMSDL×30/120 cm planting patterns. The maximum plant height at 40%×30/90 cm planting pattern might be ascribed to better CGR. Pandian et al. (1992) concluded that cane height was taller at 1.1 IW/CPE than at 0.9 IW/CPE. Naik et al. (1993) observed the effect of moderate and severe water stress and evaluated that plant height was 117.3 and 105.7 cm at moderate and sever water stress, respectively, against control where a 148 cm plant height was found. Lal (1988) in India compared conventional planting at 90 cm row spacing with 60 cm clumps (also at 90 cm row spacing) and pit plantation (4167 pits ha⁻¹) with up to 20 setts per pit and a row spacing of 2 m. He found that plant height increased with increase in space around the cane clumps. Domini and Plana (1989) reported that planting patterns had a significant effect on plant height. Nisachon et al. (2012) found that drought significantly reduced stalk diameter, but it did not significantly affect relative rate of height growth.

21.3.8 Weight per stripped cane (kg)

The reciprocal effects of ASMD levels and planting patterns on weight per stripped cane were found significant at P=0.05 (Table 21.12). Maximum individual stripped cane weight of 0.95 and 1.22 kg at Location-II and Location-I, respectively, was recorded in the interaction of a 40% AMSDL×30/90 cm planting pattern. Minimum weight per stripped cane of 0.42 and 0.47 kg at Location-II and Location-I, respectively, was recorded with the interaction of an 80% AMSDL×30/120 cm planting pattern. It was further observed that a 126.19 and 159.57% increase in individual stripped cane weight at Location-II and Location-I, respectively, was traced by the interaction of a 40% AMSDL×30/90 cm planting pattern compared to the interaction of an 80% AMSDL×30/120 cm planting pattern.

21.3.9 Stripped cane length (m)

Significant improvement was seen by mutual effects of ASMD levels and planting patterns on individual cane length (Table 21.13) at both locations and maximum individual cane length 2.38 and 2.59 m at Location-II and Location-I was recorded with a 40% AMSDL×30/90 cm planting pattern. Individual cane length was a minimum of 1.0 m at both locations with an 80% AMSDL×30/120 cm planting pattern. It was observed that a 138 and 159 % higher individual cane length at Location-II and Location-I, respectively, was achieved by a 40% AMSDL×30/90 cm planting pattern compared to an 80% AMSDL×30/120 cm planting pattern. Ingram (1986) also stated a 40 to 50% greater stalk length in 75 cm spaced rows than in 150 cm spaced rows.

21.3.10 Cane diameter (cm)

A combination of ASMDL and planting pattern on individual cane diameter was identified by a 40% ASMDL×30/90 cm planting pattern, which resulted in individual cane diameter of 7.83 and 8.11 cm at Location-II and Location-I, respectively (Table 21.14). Lesser values of 3.46 and 3.13 cm at Location-II and Location-I, respectively, were noticed with an 80% ASMDL×30/120 cm planting pattern. An increase of up to 126.30 and 159.11% higher individual cane diameter was recorded in the interaction of a 40% ASMDL×30/90 cm planting pattern compared to an 80% ASMDL×30/120 cm planting pattern at Location-II and Location-I, respectively. Naidu and Venkataramana (1989) reported that cane girth was decreased as compared to 80% ASMD level, when the crop was subjected to water stress. Sharma and Gupta (1990) investigated the effect of different moisture regimes (0.75, 1.0, and 1.5 IW/CPE) and stated that a greater cane girth of 9.29 and 9.95 cm was obtained at 1.0 and 1.51 IW/CPE, respectively, as compared to 8.38 cm obtained from 0.75 IW/CPE.

21.3.11 Unstripped cane yield (t ha⁻¹)

Different ASMD levels exhibited different unstripped cane yield at both the locations (Table 21.15). The highest unstripped cane yield of 180.88 and 215.75 t ha⁻¹ at Location-II and Location-I, respectively, was recorded in a 40% ASMDL followed by 60 and 20% ASMD levels. The lowest unstripped cane yield was 126 and 159.13 t ha⁻¹ at Location-II and Location-I, respectively, in an 80% ASMD level. About 43.56, 34.92, 23.02% and 35.58, 28.83 and 12.25% higher unstripped cane yield was obtained at Location-II and Location-I in 40, 60, and 20% ASMDL over an 80% ASMD level, respectively. The increased unstripped cane yield at 40% ASMD level might be ascribed to increased nutrient availability, which resulted in greater number of stalks per square meter.

The highest unstripped cane yield of 176.62 and 212.13 t ha⁻¹ at Location−II and Location-I, respectively, was recorded in 30/90 cm (G-30/90) followed by a 75 cm (G-75), 60 cm spaced single row planting pattern (G-60), and the lowest stripped cane yield of 126.50 and 153.13 t ha⁻¹ at Location-II and Location-I, respectively, in 30/120 cm spaced paired row planting pattern (G-30/120). The increase was to the tune of 39.62, 32.32, 27.57% and 38.53, 30.37, and 26.45% at Location-II and Location-I, respectively, with G-30/90, G-75, and G-60 over G-30/120. It was observed that improvement in unstripped cane in the 30/90 cm spaced paired row planting pattern was due to accelerated CGR, more NAR, longer TLAD, and greater LAI attributes.

The ceiling of the unstripped cane yield of 197.50 and 238 t ha⁻¹ at Location-II and Location-I, respectively, was obtained with 40% ASMDL×G-30/90 followed by 40% ASMDL×G-75 and 40% ASMDL×G-60, respectively. The minimum unstripped cane yield of 100 and 128.5 t ha⁻¹ at Location-II and Location-I, respectively, was calculated in ASMDL₄×G-30/120 treatment. It was noteworthy that 97.50 and 85.21% higher unstripped cane yield was recorded in the interaction of a 40% ASMDL×30/90 cm planting pattern compared to an 80% ASMDL×30/120 cm planting pattern at Location-II and Location-I, respectively. The optimum unstripped cane yield in 40% ASMDL×G-30/90 might be due to accelerated CGR, more NAR, longer TLAD, and greater LAI.

21.3.12 Stripped cane yield (t ha⁻¹)

The challenges faced by the agricultural sector under the climate change scenarios are to provide food security for an increasing world population while protecting the environment and the functioning of its ecosystems (Rosenzweig et al., 2012). Sugarcane crop is one of those challenges. The highest stripped cane yield of 135.50 and 171.38 t ha⁻¹at Location-II and Location-I, respectively, was taken with a 40% ASMD level followed by 60 and 20% ASMDL (Table 21.16), while the lowest cane yield of 87.06 and 100.25 t ha⁻¹ was observed at Location-II and Location-I, respectively, with an 80% ASMD level. It was further observed that 55.64, 41.72, 26.35% at Location-II and 70.95, 54.36, and 31.42% higher stripped cane yield at Location-I, were recorded in 40, 60, and 20% ASMD levels, respectively, over an 80% ASMD level. The increased stripped cane yield at the 40% ASMD level was ascribed to greater weight per cane, cane length, and cane diameter. It was found that excess or deficient irrigation water was equally harmful for sugarcane crops in the case of irrigation at the 20% ASMD level (excess irrigation). Due to the longer intervals between successive irrigations the soil remained deficient in available soil moisture content and both of these conditions adversely affected the yield components and ultimately stripped cane yield of sugarcane crop at both locations. Similar results were also reported by Sharma and Gupta (1990), Pandian et al. (1992), Malik et al. (1992), and Ghugare et al.(1995), whereas Ali (1996) studied the effect of two moisture levels, i.e., 45% ASM (available soil moisture) and 15% ASM, and found no significant effect on cane yield at both the levels. Siddique et al. (2008) obtained the highest yield of sugarcane as well as cabbage as an inter-crop at a pan ratio of 1 with 450 mm irrigation water in addition to 176.43 mm of rainfall. Siddique et al. (2008) also reported in another study that varieties intolerant to water stress gave better response to optimum soil moisture than varieties tolerant to water stress.

The maximum stripped cane yield of 130.87 and 162.12 t ha⁻¹ at Location-II and Location-I, respectively, was recorded in a 30/90 cm spaced paired row strip planting pattern, while the lowest stripped cane yield of 88.19 and 106.25 t ha⁻¹ at Location-II and Location-I, respectively, was obtained in a 30/120 cm spaced paired row strip planting pattern. It was found that 48.40, 37.20, 20.06% as well as 52.58, 40.24, and 32.47 % higher stripped cane yield at Location-II and Location-I, respectively, was recorded in 30/90, 75, and 60 cm planting patterns over a 30/120 cm planting pattern. It was also noted that too much increase in inter-strip spacing, as in the 30/120 cm spaced paired row strip planting, decreased the number of strips per plot and the number of plants per unit area were increased (by decreasing plant-to-plant distance to maintain equal plant population in all the treatments) due to inter-plant increased competition causing adverse effects on yield components and ultimately on yield of sugarcane crop. Higher stripped cane yield in a 30/90 cm spaced paired row planting pattern was attributed to improved weight cane⁻¹, and increased cane length, and accelerated CGR. The maximum stripped cane yield of 152.50 and 198.50 t ha⁻¹ at Location-II and Location-I, respectively, could be seen with 40%×30/90 cm followed by 40%×75 cm, 40%×60 cm, and 40%×30/120 cm planting patterns. Minimum stripped cane yield of 67.25 and 76.50 t ha⁻¹ at Location-II and Location-I, respectively, was entered with an 80% ASMDL×30/120 cm planting pattern. It was also observed that 126.77 and 159.48% higher stripped cane yield at Location-II and Location-I, respectively, was recorded in the interaction of a 40%×30/90 cm planting pattern compared to an 80%×30/120 cm planting pattern. Similar results were reported by El-Geddawy et al. (2002). Khan et al. (2004) reported that crop planted at an inter-row spacing of 0.72 m produced maximum stripped cane yield compared to wider inter-row spaces of 0.90 and 1.20 m. Whereas, Singh et al. (2006) reported significantly higher cane yield at 45 cm spacing followed by 60 and 75 cm in ratoon crop.

21.3.13 Harvest index percentage

The analysis of 2 years of pooled average data of Location-I and Location-II regarding harvest index (HI), shown in Table 21.17, revealed that HI was not significantly different under different ASMD levels at Location-II. Whereas at Location-I, a maximum HI of 79.08 was recorded at the 40% ASMD level, which was statistically similar to 60% ASMDL and 20% ASMDL. HI was a minimum of 62.56 at the 80% ASMD level. HI was not significantly affected by different planting patterns at Location-II. Whereas at Location-I the maximum (HI) of 75.76 was recorded in a 30/90 cm spaced paired row strip planting pattern followed by 75 and 60 cm spaced single row planting patterns. A minimum HI of 68.66 was calculated in a 30/120 cm spaced paired row strip planting pattern. The variation in HI values between the two sites might be due to the difference in local soil and climatic conditions. Interactive effects of ASMD levels and planting patterns regarding HI were not significantly different at Location-II, whereas a maximum HI of 83.38 was recorded in a 40% ASMDL×30/90 cm planting pattern followed by 40% ASMDL×75 cm, 40% ASMDL×60 cm, and 40% ASMDL×30/120 cm spaced paired row strip planting patterns, while a minimum of 59.36 at Location-I was recorded in an 80% ASMDL×30/120 cm planting pattern. The variation between HI values of the two sites might be due to the difference in soils and microclimate of both locations. A literature survey indicated straw yields of sugarcane in the range of 7.4–24.3 mg ha⁻¹ (dry basis), and a straw-to-stalk ratio ranging from 9.7 to 29.5%. The averages were, respectively, 14.1 mg ha⁻¹ and 18.2% (Hassuani et al., 2005).

21.3.14 Sugar recovery percentage

Although the quality components of sugarcane are mainly genetic characters, they are also influenced by various agronomic practices. The analysis of 2 years of pooled average data of Location-II and Location-I regarding sugar recovery percentage shown in Table 21.18 revealed that sugar recovery percentage was significantly affected by different ASMD levels at Location-I rather than at Location-II. Sugar recovery percentage was 9.60% higher at the 80% ASMD level as compared to 20% ASMDL. However, it was statistically similar in 40 and 60% ASMD levels with a minimum of 8.40% in the 20% ASMD level at Location-I. It was noted that higher sugar percentage recovery of 7.7, 4.88, and 2.71% and 14.29, 10.12, and 6.07% was recorded at Location-II and Location-I, respectively, in 80, 60, and 40% ASMD levels, respectively, over the 20% ASMD level. In India, Sharma and Gupta (1990) concluded that juice extraction was increased but juice purity, commercial cane sugar (CSS%), and sucrose content decreased drastically as moisture level increased from 0.75 to 1.5 IW/CPE. Ghugare et al. (1995) studied the effect of 50, 75, 100, and 125 CPE against canal rotation as control and found non-significant effects in sucrose content in juice as well as in purity percentage. Ali (1996) reported that irrigation applied at 15 and 45% ASM did not affect the CCS percentage.

With respect to different planting patterns, the maximum sugar recovery of 10.39 and 10.17% at Location-II and Location-I, respectively, was recorded in a 30/120 cm spaced paired row strip planting pattern followed by a 30/90 and 75 cm spaced planting pattern. Minimum sugar recovery percentage of 8.79 and 7.96% at Location-II and Location-I, respectively, was observed in a 60 cm spaced planting pattern. It was noted that 18.20, 10.81, 6.60% and 27.76, 16.21, and 10.30% higher sugar recovery was recorded in 30/120, 30/90, and 75 cm spaced planting patterns over a 60 cm planting pattern. These results are in line with those of Kathirisan and Narayanasamy (1991), who reported that sugarcane grown in widely spaced rows had higher sucrose content than that grown in narrow spaced rows. On the contrary, Vains et al. (2000) reported that sucrose content in cane juice was not significantly affected by different spatial arrangements and plantation methods. Such differential impact of row spacing on sucrose content might be due to the difference in soil and climatic conditions under which the various experiments were conducted.Regarding interactive effects, the maximum sugar recovery of 10.78 and 10.87% at Location-II and Location-I, respectively, was recorded in an 80% ASMDL×30/120 cm planting pattern followed by 80% ASMDL×30/90 cm, 80% ASMDL×75 cm, and 80% ASMDL×60 cm spaced planting patterns, respectively, while a minimum of 8.44 and 7.28% at Location-II and Location-I, respectively, was recorded in a 20% ASMDL×60 cm planting pattern. It was logical that 27.73 and 49.31% higher sugar recovery percentage at Location-II and Location-I, respectively, was recorded in the interaction of an 80%×30/120 cm planting pattern compared to a 20%×60 cm planting pattern.

21.3.15 Sugar yield (t ha⁻¹)

Sugarcane is a highly productive crop plant with the capacity of storing large amounts of sucrose (Monica et al., 2011). Sugar yield (t ha⁻¹) is the product of stripped cane yield (t ha⁻¹) and sugar recovery percentage. As is evident from the data given in Table 21.19, the highest sugar yield of 12.75 and 15.16 t ha⁻¹ at Location-II and Location-I, respectively, was recorded in 40% ASMD level followed by 60 and 20% ASMD levels, while the lowest sugar yield of 8.56 and 9.53 t ha⁻¹ at Location-II and Location-I, respectively, was recorded in 80% ASMD level. It was also observed that 48.95, 38.43, 16.82 and 59.08, 49, and 15.11% higher sugar yield at Location-II and Location-I, respectively, was recorded in 40, 60, and 20% ASMD levels, respectively, over the 80% ASMD level. The higher sugar yield at the 40% ASMD level is ascribed to higher stripped cane yield. Saini and Chakor (1992) stated that irrigated plots produced significantly higher commercial cane sugar and extraction percentage over unirrigated plots with no effects on quality parameters. Pandian et al. (1992) obtained 12.93 and 12.75 t ha⁻¹ sugar yields at 0.9 and 1.1 IW/CPE, respectively. Ali (1996) reported that irrigation applied at 15% ASM and 45% ASM did not affect the CCS%; however, total sugar was significantly reduced at 45% ASM due to decrease in cane yield at this moisture level.

Maximum sugar yield of 12.68 and 14.93 t ha⁻¹ at Location-II and Location-I, respectively, was recorded in a 30/90 cm spaced paired row strip planting pattern. The lowest sugar yield of 9.13 and 10.76 t ha⁻¹ at Location-II and Location-I, respectively, was obtained in a 30/120 cm spaced paired row strip planting pattern. It was found that 38.88, 23.33, 10.51 and 38.75, 21.19, and 3.53% higher sugar yield at Location-II and Location-I, respectively, was recorded in 30/90, 75, and 60 cm planting patterns over the 30/120 cm planting pattern. Higher stripped cane yield in a 30/90 cm spaced paired row planting pattern was attributed to higher stripped cane yield. Similar results were reported by El-Geddawy et al. (2002).

The maximum stripped cane yield of 14.74 and 18.36 t ha⁻¹ at Location-II and Location-I, respectively, was recorded in the interaction of 40%×30/90 cm followed by 40%×75 cm, 40%×60 cm, and 40%×30/120 cm planting patterns. Whereas the minimum sugar yield of 7.25 and 8.31 t ha⁻¹ at Location-II and Location-I, respectively, was recorded in an 80%×30/120 cm planting pattern. It was also observed that 102.76 and 121.20% higher sugar yield at Location-II and Location-I, respectively, was recorded in the treatments interaction of a 40% ASMDL×30/90 cm planting pattern compared to an 80% ASMDL×30/120 cm planting pattern. The increase in sugar yield in the interaction of the 40%×30/90 cm planting pattern was ascribed to complementary effects of increased nutrient availability at the 40% ASMD level and improved air circulation and light interception in the 30/90 cm paired row strip planting pattern, which resulted in higher stripped cane yield.

21.3.16 Net field benefit (Rs ha⁻¹)

Water for irrigation is a limited resource and its effective management is critical, not only in reducing wasteful usage, but also in reducing production costs and sustaining productivity (Qureshi and Afghan, 2005). Total water requirement (cm) for sugarcane ranges from 140 to 240 cm through irrigation (Narendra, 2008). To have this amount, farmers have to resort to artificial irrigation through tubewells, therefore the demand for available water resource is fast exceeding the economic supply (Namara et al., 2007). Net field benefit (NFB) was calculated on the basis of 2-year pooled data of Location-I and Location-II (Table 21.20). Regarding ASMD levels, the crop receiving irrigation at the 40% ASMD level gave more NFB of Rs 70,917 ha⁻¹, followed by 60 and 20% ASMD levels and the lowest NBF of Rs 25022 ha⁻¹ in an 80% ASMDL. Sugarcane grown in different planting patterns generated different NFB. The crop grown in the 30/90 cm spaced paired row strips gave the maximum NFB of Rs 65,266 ha⁻¹, followed by 75 and 60 cm spaced planting patterns with Rs 55,871 and Rs 45,561 ha⁻¹, respectively, while a minimum NFB of Rs 26,241 ha⁻¹ was obtained from the crop grown in a 30/120 cm spaced paired row strip planting pattern. Higher NFB in the 30/90 cm spaced paired row strip planting pattern was ascribed to added stripped cane yield than the other three planting patterns.

Different treatment combinations resulted in different NFB. The combination of 40%×30/90 cm planting pattern gave the maximum NFB of Rs 88,577, followed by 40%×G-75, 60%×G-30/90, 40%×G-60, with NFB of Rs 79,277, 74,127, and 73,327 ha⁻¹, respectively, against the minimum of Rs 8392 ha⁻¹ with 80%×G-30/120 combination.