Effects of Soil and Foliar Applied Fertilizers on Growth, Yield and Sugar Quality of Two Sugarcane Cultivars under Rainfed Conditions

Sugarcane (Saccharum officinarum L.) is grown in over 1.91 million hectares in Thailand with an average productivity of 44.31 t ha^-1. Out of total area, 43.7% is cultivated in the northeast Thailand (Office of the Cane and Sugar Board, 2020) of which approximately 90% is under rainfed conditions. Most agricultural land in the region are toposequence; a sequence of sloped land separated into a series of upland fields and lowland fields. At different position lowland fields along the toposequence and the upper fields are commonly planted to early maturing rice (Oryza sativa L.) varieties while the lower fields are grown with late maturing rice varieties. In general, the upper paddy fields produced low yield since most underground water level occur below the soil surface during growing season (Hayashi et al., 2007; Boling et al., 2008). Recently, farmers began managing these paddies by growing sugarcane instead of rice crop. However, sugarcane planted in late rainy season may expose to drought during the period of dry season (January-March) and subsequently to temporary flooding (August-September) during the peak of rainy season in the region. As mentioned earlier, sugarcane faces drought in the formative phase and flood in the grand growth phase which may reduce yield. Nutrient uptake by plants generally decreases under drought conditions owing to a substantial decrease in transpiration rates and impaired active transport and membrane permeability. A decline in soil moisture content is associated with a decrease in the diffusion rate of nutrients from the soil matrix to the absorbing root surface (Steffens et al., 2005). The application of potassium (K) has been found to increase sugarcane growth during drought consequently increasing cane yield (Manickam et al., 2009). Under limited water supply, more K is required for the balance of photosynthetic CO₂ assimilation rates, defense of chloroplasts from oxidative damage, important of related disruption in carbohydrate metabolism, regulation of stomatal and relations of water status (Cakmak, 2005). Foliar application is the method to support plant nutrient uptake through leaves. Foliar application of potassium salt of active phosphorus increased the photosynthetic activities by protecting the photosynthetic machinery during unfavorable conditions (Verma et al., 2021). In flooded soil, nutrient uptake decreased due to reduce root activity cause by oxygen deficiency (Drew, 1992). Sugarcane flooded (three months) reduced by 10 to 78% of N, P and K concentration in leaf which indicated that the decrease in sugarcane growth during flooding might be due to reduced uptake of both macro and micro-nutrients (Gillbert et al., 2007). The application of urea (0.3%), potassium nitrate (KNO₃, 0.5%) and calcium nitrate (CaNO₃, 0.4%) increased leaf area and shoot weight of sugarcane grown under flooding conditions (Jain et al., 2016). In previous work, its focus normally on fertilizer application through the soil. There is little information on soil combined foliar fertilizer application and dual effect of drought and flood stress in different sugarcane cultivars. Hence, the present study was conducted to determine the effects of soil NPK and soil NPK combined foliar N and K fertilizer applied during drought and flood period on growth, yield and sugar quality of two sugarcane cultivars grown under rainfed conditions.

Experimental site
 
The field experiment was conducted on farmer’s field at Na-Fai-Nue village, Nampong district with latitude of 16°43'N and longitude of 102°59'E, Khon Kaen province of Thailand from November 2016 to December 2017. The field was converted from a paddy field where rice was cultivated for one year. The soil is loamy sand in texture; sand 73.6%, silt 15.6% and clay 10.7%. The soil is slightly acidic with a pH of 5.23, electric conductivity (EC) 0.025 dS/m and low organic matter content (0.5%). The total N, available P and exchangeable K measured from the soil were 138.51, 7.42 kg and 254.4 mg/kg, respectively. The total amount of rainfall during the growth period was 890 mm with rainfall peak in July. However, rainfall exhibited distribution for the entire growth period with an additional summer rain in March and April at tillering stage and late rain in October at ripening phase.
 
Experimental design and treatments
 
The experiment was laid out in a split-plot design with three replications. The two sugarcane cultivars (KK3 and K93-219) were assigned as main-plot. The four methods of fertilizer application were assigned as sub-plots (Table 1). Soil was tilled two times and the furrows were built from topsoil by tractor with 1.5 m spacing between rows. Sugarcane stalks at 11 months of age were used for planting material with the middle section of the stalks mostly used as material. Single node stalk segments of each cultivar were planted on December 19, 2016, in 5 rows × 4 meters long plots with 0.50-meter plant spacing. The crop used residual soil moisture at early growth stage with initial soil moisture at 17% (by weight). Soil-applied fertilizers using fertilizer grade 16-16-8 (N, P₂O₅, K₂O) at rate of (100-100-50) kg ha^-1 in all treatments were applied in split, first at planting (50%) and then 120 DAP (50%) in all treatments. For foliar application, urea 5% (12.4 kg ha^-1) (Sangplung, 1978) and K₂O 0.5% (1.24 kg ha^-1) (Jain et al., 2016) were diluted in one liter water and sprayed to the crop about 30-40 cm from the leaf canopy using backpack sprayer. The foliar fertilizer application was done at 90 DAP during rainless period (30 March) and at 210 DAP during flooding period (28 July). The plots were kept weed-free by manual weeding twice at 60 and 90 DAP. No insects and disease were detected thus no control was implemented in the present experiment.
 

 
Water level below and above ground surface
 
Observation wells of perforated polyvinyl chloride (PVC) tubes were installed at 150 cm depth in the middle of experimental field. Ground water level below soil surface and standing water above soil surface were recorded at two-weeks interval for entire the growth period according to Polthanee (1989). In the present experiment mean ground water level initiated about 100 cm below soil surface at time of planting (December) (Fig 1). Then, ground water level came up above soil surface at the peak (June to mid-August) of rainy season for 85 d (Fig 1).
 

 
Plant growth
 
The plant height was measured at harvest by measured from base (soil surface) to the leaf tip of main stalk using a meter rod. For leaf area, the leaves were selected randomly from 10 main stems at 90 and 210 DAP of each plots. Thereafter, the leaf samples were measured with a leaf area meter (ACC-400, Hayashi Denken, Japan).
 
Yield components and cane yield
 
The number of millable cane was counted from four plants randomly selected from each plot at harvest. Thereafter, the samples were determined as fresh weight plant. The single millable cane fresh weight was calculated with fresh weight plant^-1 divided by the number plant. For cane yield, the millable cane fresh weight was recorded from the areas of 3.50 m ´ 6.50 m located in the middle rows of the plots and expressed as cane yield (t ha^-1).
 
Nutrient concentration and sugar qualitative parameters
 
The top visible dewlap (TVD) of three plants were randomly selected from each plot at 300 DAP. The plant samples were dried at 80°C for 48 h until constant dry weight and analyzed for total N (%) and total K (%). The qualitative parameters such as brix (%), purity (%), polarity (%), fiber (%) and commercial cane sugar (CCS-%) were evaluated at harvest from the stalk samples.
 
Statistical analysis
 
The data was analyzed using the computer software Statistix 10 (Statistix 10, Analytical Software, USA). Analysis of variance (ANOVA) with the main factor fertilization treatment and cultivar (factor fertilization treatment nested in factor cultivar) was performed for the parameters yield and other variables. For parameters with significant fertilizer treatment effect (p≤0.05), comparison of treatment means was performed using the least significant difference test (LSD) at p£0.05 level of confidence.

Nutrient concentration in top visible dewlap leaf (TVD)
 
Fertilizer application methods and cultivars had no significant effect on N and K concentration in TVD leaf but there was significantly effect on K (Table 2). Foliar N and K application gave higher N and K concentration than that of no-foliar application in all treatments (Table 2). As mentioned above, the plants experienced prolong flooding stress. For this reason, sugarcane plants formed adventitious roots on their submerged stems during the flooding events. The adventitious roots formation is considered an important adaptation of sugarcane to flooding stress (Gomathi et al., 2010a; Jaiphong et al., 2016). Under flooding condition, soil rapidly become anoxic, causing nutrient availability in the soil to decrease (Kozlowski and Pallardy, 1984). Flooding induced severe deficiencies of N, P and K in sugarcane; the N and K concentration were below critical deficiency level (Singh et al., 2019). Furthermore, the lack of oxygen may cause decay of the primary root systems (Visser et al., 2015). By lower nutrient availability together with impeded functioning of the primary roots may lead to nutrient deficiency in the plant (Trought and Drew, 1980). Previous studies reported that the adventitious roots can take up nutrients and water from flood water (Trought and Drew, 1980; Khan et al., 1982; Zhang et al., 2017). However, flooding in sugarcane (three months) resulted in reduction by 10 to 78% in N, P and K concentration in leaf (Gilbert et al., 2007). The application of farm yard manure and foliar spray of KCl and urea proved effective in increasing K ions concentration which regulates the opening and closing of stomata hence transpiration rate (Chand et al., 2010). Under drought conditions, the application of nitrogen (N) in solid and foliar forms on two broad leave and narrow leave cane varieties proved to be advantageous (Ali et al., 1997). Foliar N and K under waterlogged conditions can improved nutrients uptake through leaves. Foliar absorption occurs through a process that initially requires penetration into the cuticle (passive percolation or surface adsorption) and then passes (active absorption) through the cells (Fernandez and Brown, 2013). For cultivars, KK3 was significantly (p≤0.05) higher K⁺ concentration in TVD leaf than K93-219 (Table 2). Waterlogging induced 28% and 30% reduction in leaf and stem N content, respectively and the reduction was comparatively lesser in resistant clones (Gomathi et al., 2010a; Gomathi and Chandran, 2012).
 

 
Growth character performances
 
Plant height at harvest and leaf area at 90 and 210 DAP had no significant affected by fertilizer application methods but there is significantly different between two cultivars in plant height and leaf area (Table 3). The highest plant height was observed in KK3. While, K93-219 gave the highest leaf area at 90 and 210 DAP. Foliar N application under waterlogged condition increased leaf area and shoot weight was reported by Jain et al., (2016).
 

 
Yield components and cane yield
 
Fertilizer application methods was significantly different (p≤0.05) in millable cane number (Table 3). The maximum millable cane numbers were attained in the soil NPK + foliar N and K application at 90 and 210 DAP. Similar result was observed in single millable cane weight (Table 3). This was associated with higher K concentration in TVD of such treatment than those of the other treatments in the present study (Table 2). This means that high K content in plants play an important role in contribution the single millable cane weight. A sustained supply of K⁺ throughout the growing season will facilitate greater shifting of dry matter from leaf to stem, enhancing the translocation of more assimilates from source to sink (Mengel and Haeder, 1977). It is an enzyme activator in photosynthesis, protein synthesis, starch formation and translocation of proteins and sugars (Filho, 1985; Kwong, 2002; Wood and Schroeder, 2004).  Furthermore, additional foliar N and K at 90 and 210 DAP providing N and K for sugarcane at tillering and grand growth phase supports better plant growth and development reach to ripening phase (millable cane) than the other treatments. Foliar K application at tillering phase (90 DAP) resulted in increased millable cane count was reported by Mathew et al., (2004). The increase in blackgram and cowpea grain weight due to the application of foliar spray were also reported by Geetha and Velayutham (2016); Anitha et al., (2005).       
       
For cultivars, millable cane number and single millable cane weight were significant different in single millable cane weight (Table 3). The cultivars K93-219 produced higher single millable cane weight than KK3 cultivar. This was associated with K93-219 cultivar gave higher leaf area than KK3 cultivar (Table 3). The cultivar K93-219 identified as waterlogging tolerance cultivar (Office of the Cane and Sugar Board Thailand, 2016; Palachai et al., 2019). Therefore, the K93-219 could provide more of food from photosynthesis and translocate to stalk than that of KK3 cultivar.
       
Regarding cane yield, fertilizer application methods and cultivars were significantly different in cane yield (Table 3). The maximum cane yield was obtained in soil NPK combined foliar N and K application at 90 and 210 DAP. This was probably due to higher single millable cane weight and millable cane number than those of other treatments. The cultivar K93-219 produced significantly higher cane yield than KK3. This was due to the K93-219 gave higher single millable cane weight and millable cane number than KK3 cultivar.
 
Sugar quality
 
Fertilizer application methods and cultivars had no significant effect on sugar quality components including brix (%), polarity (%), purity (%), fiber (%) and CCS (%) (Table 4). In general, sugarcane responded to K fertilizer by an increase in cane yield without any change in sucrose concentration in the cane (Kwong, 2002; Shukla et al., 2009). In contrast, nitrogen applied split into solid and foliar forms on two broad leaves and narrow leaves cane varieties increased polarity (%) juice and CCS (%) of sugarcane (Ali et al., 1997).
 

The soil NPK + foliar N and K application in dry season at 90 DAP and rainy season at 210 DAP during flooding stress had compounding positive effect on yield components and subsequently improving cane yield, but it had no significant effect on sugar quality components. The sugarcane cultivar K93-219 produced significantly higher cane yield than KK3.

We would like to express our gratitude to the Thai Royal Golden Jubilee Program (Grant no. PHD/0071/2556) and Research Scholarships Organized by Graduate School, Khon Kaen University, Thailand.

None.