Influence of Bed Size and Irrigation Methods on Potato (Solanum tuberosum)

Water is the key input in potato production and the problem of water management vary from region to region. Water is the vital factor for the germination. To initiate the germination process optimum moisture is required. India occupies a unique position where potato can be grown throughout the year in different parts of the country. About 81 per cent of the potato is grown in plains during winter under short day conditions whereas 13 per cent in hills during summer under long day and about 6 per cent in plateau during rainy season under equinox conditions. High frequency water management by drip irrigation minimizes soil as a storage reservoir for water and provides at least daily water to the root zone of each plant and maintains a high soil matric potential the rhizosphere to reduce plant water stress (Phene and Sanders 1976). Optimizing irrigation efficiency through properly designed, maintained and managed irrigation system to derive the maximum crop yield from every increment of water available will generally lead to more economic return than any other change in management (King et al., 2003).
       
The earlier studies have highlighted the importance of economizing irrigation water by micro irrigation is 30 per cent and improvement in crop yield by 15-20 per cent over furrow method of irrigation (Singh and Sood, 2012). Based on experimentation, (Singandhupe and Verma 2002), also gives a significant increase in yield and water saving under micro irrigation compared to furrow irrigation. Potatoes have shallow root zone and a lower tolerance for water stress then most other crops. Low moisture levels can contribute to common scab, early dying, hollow heart, knobby tubers, low dry matter, low tuber set and low tuber yield. Excessive water soil moisture resulting in poor aeration and water logging of the soil reduces the yield and in extreme cases causes the rot and enlarged lenticels. As water application in furrows causes more soil cracking and it also produces more green heads and infested tubers. The effect of tuber worm is more in furrow irrigation (Shelton and Wyman 1997). Therefore, an efficient irrigation systems and water saving techniques such as drip irrigation have been found useful to improve water productivity. Drip irrigation minimizes leaching losses due to which utilization of water and nutrients increases and water losses due to surface runoff and deep percolation is decreases. It also enhances the potato production and keeps productivity at high level. All these factors may play a crucial role in yield and improvement of processable grade tuber.
       
So, the present investigation is proposed to study the effect of bed size on the yield and size of the tuber and to study the effect of wide raised bed planting pattern under different irrigation methods.

The present experiment was carried out at Student’s Research Farm, Khalsa College Amritsar during rabi season of 2016-17 and 2017-18. The field was laid out in Factorial Randomized Complete Block Design with three replications including two factors i.e. method of sowing in factor A and method of irrigation in factor B. Treatments for factor A were B₁: 60cm bed, B₂: 75cm bed, B₃: 90cm bed with single row, B₄: 90cm bed with double row, B₅: 105cm bed with double row, B₆: 105cm bed with triple row and treatments for factor B were I₁: drip irrigation and I₂: furrow irrigation. The soil of the experimental field had sandy loam texture with neutral pH and electrical conductivity, low in organic carbon and available N, medium in available P and high in available. The crop was sown manually on 20^th October and 14^th October during crop season of 2016-17 and 2017-18, respectively. The recommended fertilizers (187 kg N, 62 kg P₂O₅ and 62 kg K₂O per hectare) were applied. First irrigation was given immediately after planting. Further irrigations were applied according to the treatments. In furrow irrigation total 7-9 irrigations were applied throughout the growing period. On the other hand drip irrigation was applied according to the following schedule:-
 

       
Water measurement was done for the calculation of Water Use Efficiency.
 
Volumetric method was used for measuring the flow in drip system. In this method flow rate was determined by dividing the volume of the container (liters) by the time (seconds) taken to fill it.
       
V-Notch a triangular thin plate weir was used to measure the flow in furrow irrigation system.             
 
Formula,
   
Where,
Q = discharge in m³/sec
H= difference between the crest and water surface at point upstream from the weir at a distance of four times the maximum head on the crest (m).
 
Reducing sugars (mg/100g fresh weight)
 
Reducing sugars were estimated by Nelson-Somogi method (Pearson 1976).
 
Nelson’s arsenomolybdate reagent
 
a)   25 g ammonium molybdate [(NH₄)₆Mo7O₂₄.4H₂O] was dissolved in 450 ml distilled water and then add 21 ml of concentrated sulphuric acid (H₂SO₄) in to it.
b)   Dissolved separately 3g sodium arsenate (Na₂HAsO₄.7H₂O) in 25 ml distilled water. Then this solution (b) was added with continuous stirring to the previously prepared ammonium molybdate solution (a) and stored in an amber coloured corked bottle.
 
Procedure
 
i.    One ml each of extract (sample) and distilled water (as blank) were taken in test tubes.
ii.   Add 1 ml of freshly prepared reagent C on each test tube.
iii.  Started heating of test tubes in boiling water bath for 20 minutes and then cooled.
iv.  After cooling 1 ml of Nelson’s arsenomolybdate reagent was added to each tube.
v.   Test tube contents were then diluted to 13 ml with distilled water.
vi.  Then the absorbance of extract was recorded at 520 nm with spectromic 20-D spectrophotometer (Milton Roy).
 
Calculations
 
  
                                                               
Sucrose
Sucrose content in tubers was estimated by a method suggested by Van Handle (1968) as explained below:
i.     0.2 each of sample extract and distilled water (as blank sample) were taken in test tube.
ii.    Then add 0.1 ml KOH (30%) to each test tube.
iii.   Test tube was heated in water bath for 40 minutes and then immediately chilled in ice cold water.
iv.   3.0 ml of 0.15% anthrone solution in 76% H₂SO₄ was added to each test tube.
v.   Then tubes were brought to room temperature and incubated at 400C for 40 minutes.
vi.   After this, absorbance was recorded at 620 nm.
vii.  The concentration of sucrose was estimated by employing the standard curve based on 25-100 µg sucrose range.
 
Calculations
 

 
Range of chip color score.
 

 
Chip recovery (%)
 
A total of 30 chips were weighed immediately before and after frying in cotton seed oil. Per cent recovery was
calculated as follows:
   
Where,
   
The benefit:cost (B:C) ratio is computed on the basis of formula given below:-
     
Statistical analysis
 
Statistical analysis of the data recorded was done as per split plot design using EDA 1.1 software developed by PAU, Ludhiana. The comparisons were made at five per cent level of significance. The analysis of variance (ANOVA) is as in the Table.
 
Analysis of variance.
 

Yield attributes
 
Number of tubers per plant
 
The number of tubers per plant is an important yield bearing parameter. The data presented in Table 2 showed that bed size had a significant effect on number of tuber per plant. The data revealed that maximum number of tubers per plant was recorded in treatment B1 followed by treatments B₂, B₅ and B₃. The treatments B₁ were B₂ were statistically at par with each other during both crop years. The trend in treatments was B₁> B₂> B₅> B₃> B₄ and B₆. This might be due to variation in spacing and bed size. It could be attributed to increase in plant density area leading to more competition and consequent reduction in tuber weight and number of tubers per plant. Above results were in accordance with the findings of Singh and Sood (2016).
 

 

       
Among irrigation treatments, data demonstrated in Table 2 showed that number of tubers per plant were significantly higher under drip irrigation in comparison to furrow irrigation. It might be due to optimum availability of soil moisture and fertilizer nutrients in the plant root zone during entire period of crop growth in drip method of irrigation. Above results were in accordance with the findings of Singh and Sood (2016).
 
Tuber weight (g)
 
Persual of data in Table 2 showed that average tuber weight significantly influenced by bed size. Maximum tuber weight was achieved in 105cm triple row (B₆) bed followed by 90cm double row (B₄) and 105cm double row (B₅) bed. All these treatments were statistically at par with each other. Whereas minimum average tuber weight was noticed in 75 cm (B₂) bed. This might be due to intra row competition.
       
Persual of data in Table 2 showed that drip irrigated achieved significantly higher tuber weight as compare to furrow irrigated. This could be due to the availability of optimum moisture and nutrients throughout the entire growth period. Singh and Sood (2016) also published the same results.
 
Tuber yield            
 
Yield of a crop is the final output of successful completion of growth and development of its individual plant which in turn depends upon rate of carbon assimilation and converts into harvestable products. Tubers collected from each of the experimental treatment plots were hand graded into processing (40-75mm) and non-processing (<40mm/>75mm) tuber grades. Bed size and irrigation both factors showed their effect on plant yield. Yield of each grade and total yield are presented in Table 3.
 
Processable yield (40-75mm)
 
Regarding bed size, the data presented in Table 3 showed that maximum processable tuber yield 178.6 qha^-1 and 172.7qha^-1was obtained in treatment B1( 60cm bed) during 2016-17 and 2017-18, respectively which were significantly higher than other treatments. The treatments B₆> B₄ > B₃> B₅>B₂ in the same trend were statistically at par with each other. Similar result was observed by Kumar et al., (2011).
 

       
Regarding irrigation treatments, the recoded in Table 3 showed that during both crop year drip irrigation produced significantly higher processable yield than furrow irrigation. Above results were in accordance with Singh and Sood (2016).
       
The data presented in the Table 3.1 showed that interaction between irrigation and bed size was significant during both crop years. Maximum yield was obtained in drip irrigated 105cm triple row (I₁B₆) bed followed by 60 cm (I₂B₁) which were statistically at par with each other. Minimum yield was obtained in 105 cm triple row (I₂B₆) bed with furrow irrigation. It was due to less moisture availability in the central part of the bed. The results are in accordance with the results of Boujelben and M’barek (1997).



Non-processable yield (<45/>75mm)
 
The data presented in Table 3 showed that bed size has its own effect on non-processable tuber yield. Maximumnon-processable tuber yield during both crop years was recorded in B₅ (105 cm double row) followed by treatments B₄ (90 cm double row), B₁ (60 cm single row)which were significantly at par with each other. Whereas, minimum processable yield was obtained in B₂ (75 cm bed) which was significantly differ from the treatment B₅, B₄ and B₁. Similar result was observed by Kumar et al., (2011).
       
Data regarding irrigation treatments presented in Table 3 in which maximum non processable yield drip irrigation and minimum was observed furrow irrigation during both crop years. Above results were in accordance with Singh and Sood (2016).
 
Total tuber yield
 
Regarding bed size, the data presented in Table 3 showed that bed size had a significant effect on total tuber yield. The data revealed that during both cropping years maximum total tuber yield of 236.2 qha^-1and 246.3 qha^-1,  respectively was obtained in treatment B1 (60 cm) which was significantly higher than bed size 90 cm (B₃ and B₄) and 105 cm (B₅ and B₆) where treatments B3, B4, B₅ and B₆ were statistically at par with each other. Ridge planting with drip irrigation attributed highest tuber yield. Singh and Sood (2016) reported the same results.
       
Among irrigation treatments, the given data in Table 3 further examined that in both cropping years maximum total tuber yield was recorded drip irrigation and minimum was observed in furrow irrigation. The drip irrigation was significantly differed from furrow irrigation. Above results were in accordance with Singh and Sood (2016).              
       
The data presented in the Table 3.2 showed that during both crop years interaction among irrigation and bed size was significant. Maximum yield was obtained in drip irrigated 105cm triple row (I₁B₆) bed. It was due to the availability of proper moisture in the center of bed. Minimum yield was obtained in same bed with furrow irrigation (I₂B₆) it was due to the less moisture availability in the central part of the bed. This might be due to the availability of proper moisture and nutrients during the active period of growth in drip irrigation system Singh and Sood (2016).
 

       
The above results might be due to low availability of soil moisture and fertilizer nutrients during active period of crop growth under conventional furrow irrigation as compared to drip irrigation method. It also be due to increase in tuber weight and numbers per m^-2 under double and triple row raised beds with drip irrigation as compared to other patterns.
 
Quality parameters
 
Tuber dry matter (per cent)
 
Tuber dry matter is an important quality parameter. Tuber dry matter content more than 20 per cent is acceptable for processing (Sandhu et al., 2010). The data presented in the Table 4 showed that tuber dry matter accumulation was not influenced significantly due to bed size. All the treatments of bed size were non-significant.
 

       
Among irrigation treatments, perusal of data in Table 4 further revealed that irrigation had a significant effect on the tuber dry matter. Maximum tuber dry matter was obtained in drip irrigation I1 and minimum was obtained in furrow irrigation I₂. Where I₁ was significantly higher than I₂ in both cropping years. This might be due to the presence of moisture for longer duration in the plant root zone.
 
Chip recovery (per cent)
 
Chip recovery is good index of final products. Data presented in Table 4 revealed in cropping years 2016-17 and 2017-18 that maximum chip recovery was obtained from followed by B₄, B₅, B₆, B₃ and B₂. It was observed that there was no significant effect on chip recovery per cent due to bed size.
       
In irrigation treatments, data presented in table 4 suggested that during both years slightly higher chip recovery was obtained in drip irrigated treatment I₁ then furrow irrigated treatment I₂. However treatment I₁ and I₂ were statistically at par with each other.
 
Reducing sugars (mg/100g FW)
 
Reducing sugars affects the chipping quality of tuber. Low reducing sugars are preferable for good chipping quality. The data presented in the Table 5 revealed that bed size had a non-significant effect on the reducing sugars in potato. It was observed that B₁ had slightly higher reducing sugars content as compared to other treatment. Similarly data presented in Table 5 showed that irrigation treatments also had non-significant effect on the reducing sugars in tubers.
 

 
Sucrose content (mg/100g FW)
 
Sucrose content in potato tuber is an important quality parameter because it may participate as substrate for reducing sugars after undergoing heat induced hydrolysis during frying and can affect chip colour negatively. Data regarding sucrose content in tubers is presented in table 5 revealed that maximum sucrose content was observed in B₆ followed by treatments B₁, B₃, B₂, B₅  and B₄. It was observed that sucrose content was not influenced due to the bed size.
       
Among irrigation treatments data presented in Table 5 Data showed that maximum sucrose content was observed in drip irrigation which was slightly higher than furrow irrigation. Therefore, drip and furrow irrigation had a non-significant effect on sucrose content in potato tubers.
 
Chip colour score
 
The colour of fried chips is most important visual character for determining the suitability of potatoes for processing. Chips having dark colour are unacceptable to consumers due to poor aesthetic appeal and bitter taste. Chip colour score up to 3 is considered highly acceptable. The data in Table 5 revealed that there was no significant variation in the chip colour score due to variation in the bed size.
       
In irrigation treatments data in the table 5 revealed that chip colour score in drip irrigation and furrow irrigation was found in acceptable range (<3). However both the treatments had no significant effect on chip colour score.
 
Water use efficiency (WUE kg ha-1 mm)
 
Maximum water use efficiency was recorded in drip irrigated 105 cm double row bed followed by triple row in same bed size. Whereas in furrow irrigation maximum water use efficiency was recorded in 60cm bed followed by 90 cm double row and 105 cm double row. From given data it was noticed that drip irrigation saved 48% water as compared to furrow irrigation.
 
Benefit Cost ratio
 
Data in Table 6 depicts that in drip irrigation B₆ gave maximum return followed by B₅> B₁> B₄> B₃ and B₂. Whereas among furrow irrigation B1 gave maximum returns followed by B₄> B₂> B₃> B₅ and B₆.
 

Drip irrigation (236.1qha^-1) and 60cm bed size (246.3qha^table) yielded maximum potato as compared to other treatments. Maximum WUE was obtained in drip irrigated broad beds and saves 45-50 per cent water as compared to furrow irrigation during both crop seasons. Furrow irrigated with narrow bed size beneficial than other treatments.