EFFECT OF PLANTING DATE , IRRIGATION LEVEL AND FOLIAR SPRAYING WITH CALCIUM AND BORON TREATMENTS ON POTATO 1. PLANT GROWTH , PLANT WATER RELATIONSHIP AND PLANT CHEMICAL CONSTITUENTS

 INTRODUCTION

Potato (Solanum tuberosum L.) belongs to Solanaceae family is one of the most important vegetable crops in the world and in terms of human consumption, it comes in the fourth grade after wheat, rice, and corn, it is rich in carbohydrates, nutrients and amino acids (Hassan 2003).

Planting date plays an important role in potato production as manipulation of light and temperature can be done to a certain extent by altering planting date. For best yields, potato crop needs long day conditions during growth and short day conditions during tuberization (Chadha, 2009). Optimum temperatures for foliage growth and net photosynthesis are 15-25°C and 20°C for tuberization. At temperature above 29°C tuberization is inhibited, foliage growth is promoted and net photosynthesis and assimilate partitioning to the tubers are reduced (Levy, 1992).  There were a significant differences  between planting date  regarding  plant growth  of potato (Sandhu et al. 2014 , Thongam et al. 2017 and Dash et al. 2018). 

Potato plant is sensitive to the changes in the soil moisture content .The decrease of water (water stress), leading to a significant reduction in tubers quantity and quality. The requirement for water irrigation of  potato plants vary in different plant growth stages; tubers initiation and tubers bulking are the more sensitive stages in the plant growth life (Abdallah 1996).

Most studies found that irrigated potato plants with the highest  levels  caused significant  increasing  in  plant growth ( El Saidi et al. 2010, Al-Janaby 2012, Abu Baker et al., 2014 and Dash et al., 2018) of potato. As for total chlorophyll (Abdel-Al 2001 and Bao-Zhong et al., 2003). Concerning plant water relationship in leaves (Abdel-Rheem, 2003,El-Ghamriny et al. 2005, Mahmoud 2006 and Khalel 2015) of potato. Regarding   plant chemical constituents' (Anwar 2005, Abou El-Khair et al. 2011 of potato  and  Kamal, and El-Shazly  2013) on tomato.

Calcium is one of the essential plant nutrients and performs a significant role in plant membrane structure and function where it contributes to maintenance of cell membrane stability and wall structure (Marschner 1995). Also promotes root development and growth of the plant as it is involved in root elongation and cell division, Calcium therefore increases plant tissue resistance against biotic and abiotic stress (Ilyama et al. 1994).

Boron is second most widespread and economically important micronutrient which is essential for several growth related parameters. Its requirement is high after 45 days of crop emergence and remain high till crop maturity. It improves calcium absorption and stabilizes calcium in cell wall. Boron reduces the oxidation of phenols and prevent discolouration of tubers (Brown et al., 2002). Under drought condition the deficiency of boron is observed due to lower availability of (B) in sub-soils (Prasad, 2014). Its deficiency causes the formation of a bushy plant with droopy leaves.

Sprayed  potato plants with  Ca and/or B had affected  on  plant growth ( El-Mahdy, 2007, El- Dissoky and Abdel-Kadar  2013,  Chowdhury 2017, Simango and Walls 2017 and Tantawy et al. 2017) ,  total chlorophyll  (Awad et al. 2010 and Singh et al. 2018 on potato) and (Kazemi 2013 of tomato) and  plant chemical  constituents ( El -Dissoky  Abdel –Kadar 2013,  Tantawy et al. 2017  and  Seifu,  and  Deneke 2017) of potato.

Therefore, the present study was planned to evaluate the more appropriate planting date and suitable amount of irrigation water as  well  as  calcium  or/ and  boron as foliar  application on growth,  plant water relationship and chemical composition of  potato plants  using  flood  irrigation system  under clay soil  conditions.

MATERIALS AND METHODS

A filed experiment was carried out in the successive winter seasons of 2016/2017 and 2017/2018 at the experimental Farm El- Gemmeiza, Agric Res. Station, ARC, Gharbiya Governorate (Middle Nile Delta, Egypt) to study the effect of planting date, irrigation water level and foliar sprays of Ca and/or B and their interactions on potato on growth, plant water relationship and plant chemical composition of potato (Mondial cv.) under furrow irrigation. The soil in the experimental site is clayey in texture with bulk density, field water capacity and available water values, in the 60 cm depth of the soil profile, comprised 1.25(gcm^-3), 43.01 and 17.92% by mass, respectively.

The mechanical and chemical analysis of the used soil are presented in Table (A). Particle size distribution was carried out using the method of Piper (1950). Calcium carbonate was determined using Collins calcimeter according to Wright (1939). Organic matter was assayed according to method of  Walkley (1947). Total available nitrogen was determined using the microkjeldohl and Phosphorus was determined according to methods as described by  Chapman and Pratt (1961). Potassium was determined using Flam photometeric method described Piper (1938). Available B was determined by Bingham (1982). pH value was measured  in the soil  past using  Bechman pH  meter.

Table (A): The  mechanical and chemical analysis  of the  experimental   soil 

Parameters	Values
1. Mechanical analysis	First season	Second season
Corse sand  (%)	1.60	1.50
Fine sand (%)	12.91	14.4
Silt (%)	37.23	35.9
Clay  (%)	42.79	43.20
CaCO3 (%)	3.90	3.20
Organic matter (%)	1.57	1.80
Texture class	Silty clay loam
2. Chemical  analysis
Available nitrogen  (ppm)	33.0	35.0
Available phosphorus  (ppm)	8.0	8.8
Available potassium (ppm)	420	440
Available boron (ppm)	0.10	0.12
Soluble calcium ( Ca++)	6 meq/l
Soil reaction (pH) in 2.5 soil  suspension	8.0	8.0

The present experiment included 24 treatments, which were the combination of two planting date e.g. planting on 20^th Sept and 10^th Oct, three irrigation water  level vis 50, 75 and 100 %FC and three foliar spray treatments i.e. Ca(1%, wt/vol) as calcium chloride and/or boron (60 ppm as boric acid), besides the control  (unsprayed treatment). The assessed treatments were arranged in a split - split plot design with three replicates. The planting dates were represented in the main plots, sub plots were assigned for irrigation levels and Ca and/or B foliar sprays and control treatments were randomly distributed in the sub - sub plots.

The experimental unit area was 14.7 m² containing three ridges with 7m length and 70 cm apart, and the potato seeds (Solanum tuberosum L. Mondial cv) were sown at 20 cm in between. One ridge was used to measure the morphological and physiological traits and the other two ridges were left for yield determinations. In addition, one ridge was left as buffer zone between each two experimental units to avoid lateral seepage of irrigation water. All the agronomic practices recommended for potato production in the area e.g. seed – bed preparation, N, P &K fertilization, weed and pest control etc., were executed. Calcium chloride and boric acid were sprayed three times in two 2- week interval, and started 45 days after planting using a manual atomizer.

         The irrigation water was added each three weeks intervals beginning at 10^th and 30^th October (20 days after planting) and ended 5^th and 25^th Jun. (15 days before harvesting) in the 1^st and 2^nd seasons, respectively. Under the adopted irrigation treatments, four irrigation events plus the planting one were applied throughout the entire growing season. To determine water quantity required under each adopted irrigation level, a soil sample (up to 60 cm depth) was taken before each irrigation from 100% FC treatment, and soil moisture content (%,wt/wt basis) was calculated. The water quantity required to refill the 60 cm of soil profile to field capacity could be determined as follows:

Water required, mm = FC – MC x Bd x soil layer depth (600 mm) /100

Where: FC = Soil field capacity% by weight (g), MC = Soil moisture content(%) by weight before irrigation(g), Bd = Bulk density of 60 cm depth, gcm^-3     ….  And  600 = depth of root zone, mm.

Then, multiplying water quantity required for 100% FC level by       0.75and0.50 to attain water quantities required for 75and 50%FC, respectively. 

  On applying the pre-determined water quantity, a plastic tube (spile) with internal diameter of 3 inches was used to apply and calculate the water quantity according to Michael (1987) as follows:

Water quantity, cm³sec^-1 = 0.61 x A √ 2 x 981x h

Where: A= sectional tube area, cm² and h =Effective water head over the tube, cm.

Data recorded

Growth traits and shoot chemical analysis were determined at 90 days after planting, while yield determinations were recorded at harvesting on 20^th Jun and 10^th Feb. in the 1^st and  the 2^nd seasons, respectively. Five plants from each experimental plot were used to measure the growth traits and plant chemical analyses. The recorded data were:

1. 1.      Plant growth: It was recorded as plant height, number of leaves/ plant,    both fresh and dry weight of shoot / plant (g).
2. 2.      Plant water relations: It was recorded in the fourth upper leaf of potato plant as: total, free and bound water as well as cell sap and osmotic pressure according to the method described by Gosev (1960).

3. Proline amino acid content: It was determined in dry leaves according to the method described by Bates (1973).

4. Total chlorophyll in leaf tissues (chlorophyll a + chlorophyll b) was extracted  and determined according to Moran (1982).

5. Percentages of N, P and K in shoots: Total Nitrogen, phosphorus and potassium percentages were determined in dried and wet digested shoots according to the methods described by A.O.A.C. (1990),  also  boron  was determined in shoots calorimetrically  using azomethine –H method according to Bingham (1982) and soluble  calcium was determined by the method of   Cottenie et al. (1982), total Hydrolysable carbohydrates (T.H.C.) were determined in shoots using  picric acid method according to Thomes and Dutcher (1924).

 

  Statistical Analysis:

Collected data were subjected to statistical analysis of variance according to Snedecor and Cochran (1980), and means separation was done using L.S.D. at5 % level of probability.

RESULTS AND DISCUSSION

1. Soil chemical constituents  after planting

Data  in Table 1 show the effect of   the interactions  among  planting date, irrigation levels and  foliar  spray  treatments with calcium and boron on soil  chemical  constituents   after  potato plants ( average the two seasons).

Both planting dates, irrigation at 100 %  from FC  and spraying  plants with Ca and B gave the highest values of available N in soil ( 52.30 ppm) average  both seasons),  available  P was the  highest ( 12.40 ppm)  with the interaction between  planting on 10^th October, irrigation with 100 % from FC and spraying plants with  B at 60 ppm,  while  the highest available K in the soil  (587.33 ppm ) was recorded with the interaction among  planting on 10^th Oct., irrigation at 75 % from FC and spraying  plants with Ca and B. on the other  hand , the lowest values of  pH (7.90) and EC (0.24) were recorded with  the interactions among  planting on 20^th Sep. and irrigation plants with  50 %  from FC  and unsprayed  plants.

 

2. Plant Growth

2.1. Effect of planting date   

Data in Table 2 show that, there were significant differences between the two planting  date  regarding  plant growth of potato in both seasons, except number of leaves / plant in the 2^nd season.  Planting potato on 10^th Oct.   gave the tallest plants, highest  values  of  both fresh and dry weight of shoots/ plant than planting  on 20^th Sep. in both seasons. The increases  in dry weight of shoots/ plant were about 14.51 and 12.41% for  Planting potato on 10^th Oct.  over than planting  on 20^th Sep.  in the 1^st and  the 2^nd  seasons, respectively.

The higher plant growth in planting date on 10^th Oct. as compared to the planting date on 20^th Sep. could be attributed to favorable climatic conditions in general and temperature in particular (Thongam et al. 2017). These results are harmony with those reported by Sandhu et al. (2014) and Thongam et al. (2017).

 

2.2. Effect of  water irrigation levels  

 The obtained results in Table 2 show  also that irrigation levelhad a significant effect on plant height, number of leaves/ plant, both fresh and dry weight of shoots/ plant in both seasons. Potato plants which irrigated with 100 % from FC gave the highest values of different plant growth characters in both

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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seasons. While the lowest values were recorded with 50 %  from FC.  On the other side, irrigation   at 75 %  from  FC recorded the   moderate values in  both seasons.

The increases in shoot dry weight were about 23.48 and 20.04 % for irrigation treatment  at 100 %  from  FC than plants which  irrigated with  50 % from  FC in  the 1^st and the 2^nd seasons, respectively.

The improvement of vegetative growth with increasing irrigation level may be due to the proper balance of moisture in plant, which creates  favorable conditions for nutrients uptake, photosynthesis and metabolites translocation, which ultimately accelerated the rate of vegetative growth (Ezzo  et al., 2010). Moreover the reduction effect of the lowest level of  irrigation water (50 % of FC )  may be related to the negative effects of water stress on the activities of many enzymes leading to decrease in plant growth and dry matter accumulation (Hamlyn, 1986). On the other hand, Marschner (1995) reported that, under sufficient water conditions, there were decrease in Abscisic acid (ABA) and increase in Cytokinins (CYT), Gibberllic acid (GA) and Indole butyric acid (IAA)  which reflected in  good growth and dry matter content.

The obtained results are in good line with those reported by Shiri-e- et al. (2009),   El Saidi et al. (2010),  Al-Janaby (2012) , ABuBAker, et al. (2014) and Dash et al. (2018)on potato. They reported that increasing irrigation water quantity or soil moisture content up to the maximum level significantly increased vegetative growth such as plant height, number of leaves/ plant  both fresh and dry weight of shoots/ plant.

 

2.3. Effect of foliar spray treatment 

Spraying potato plants with Ca and /or B had significant effect on all plant growth  parameters than  unsprayed plants in both seasons (Table 2). Furthermore combined application of Ca and boron improved the growth trails of potato plants more than which recorded by single application of  Ca  or boron.  

 In this regard,  the plants  which sprayed  with   both  Ca and B  gave the   higher values of plant height , number of leaves / plant , both  fresh and dry weight of potato plant  than  that  of plants which sprayed with calcium or  boron singly in both seasons.

The increases in shoot dry weight were about 18.57 and 16.84 % for  sprayed plants with  calcium and  boron  than unsprayed plants   in the 1^st and  the 2^nd seasons, respectively.

Calcium sensing proteins are involved in many cellular processes like cytoplasmic streaming, organelles and vesicles transport, microtubules dynamics, cell division, chromosome segregation, cell elongation, tip growth and morphogenesis (Reddy, 2001).  Also, Jafari et al. (2013) showed that spraying of boron significantly improved growth parameters of potato plants (plant height, leaves per plant and shoot weight) as compared with control,

These results confirmed by the findings of  El-Mahdy, (2007), El- Dissoky and Abdel-Kadar (2013),  Chowdhury (2017), Simango and Walls (2017) and Tantawy et al. (2017) all on potato, they reported that  spraying plants  with  calcium or  boron  singly or in combination  gave the best  plant growth then unsprayed plants.

 

2.4. Effect of the  interaction between planting date  and irrigation level

It can be seen from the data presented in Table 3 that the interaction between planting date and  irrigation water level  had significant effect on  all potato growth than the other interaction treatments in both seasons. The interaction between planting potato on 10^th Oct.  and irrigation  water  at 100 % from FC   gave the  highest  values  of  plant height , number of  leaves/ plant and  both  fresh and dry weight of shoots/ plant   in both seasons.

These increases in shoot dry weight were about 38.37 and 32.11% for the interaction between planting potato on 10^th Oct. and irrigation  water  at 100 % from  FC   than   the interaction between planting potato on  20^th Sep.  and irrigation  water  at 50 %  from FC   in the 1^st and the  2^nd seasons, respectively.

2.5. Effect of the interaction between planting date and foliar spraying treatments

The interaction between planting date and foliar spraying treatments reflected in a significant effect on all plant growth characters of potato in both seasons (Table 3).  Planting  potato on 10^th Oct. and  spraying plants with  calcium and boron recorded the highest values of  plant height  , number of   leaves/ plant and  both  fresh and  dry weight of shoots/ plant.

These increases in shoots dry weight were about 36.32 and 32.80% for the interaction between planting potato on 10^th Oct. and spraying plants with both 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

calcium and boron  than that plants which planted  on   20^th Sep. only   in the 1^st and the 2^nd seasons, respectively.

 

2.6. Effect of interaction between irrigation levels and foliar spray treatments 

The interaction between irrigation level and foliar spray treatments had a significant effect on all plant growth characters of potato plants   than the other interaction treatments in both seasons (Table 4).  Irrigation  the   plants with   100 %   from  FC  and spraying plants with   both calcium and  boron recorded the highest values of  plant height,  number of  leaves/ plant ,  both  fresh  and dry weight of shoots/ plant in both seasons, while the lowest values in this respect was recorded with the interaction between the plants which irrigated with 50 %  from  FC in both seasons.  The increases in shoots  dry weight  of sweet potato plant were about 45.33 and 40.74% for the interaction between irrigation plants with 100 %   from  FC  and spraying plants  of  calcium and  boron  over that plants which irrigated with 50 %  from FC  in the 1^st and  the 2^nd seasons, respectively.

 

2.7. Effect of tertiary interaction of planting date,  irrigation level and some foliar spray treatments 

The interaction of planting date, irrigation level and foliar spray treatments had a significant effect on some  plant growth characters parameters of potato in both seasons  (Table 5). The tertiary interaction of  planting on 10^th Oct. , irrigation with  100 %  from  FC and spraying plants  with calcium  and  boron recorded the highest values of   plant height, number of  leaves/ plant and   both fresh  and dry weight of shoots/ plant in both seasons. The lowest values in this respect was recorded with the interaction between planting on 20^th Sep., irrigation with  50 %  from FC and unsprayed plants  in both seasons. The increases in shoot  dry weight of potato plant were about 71.60 and 63.93 % for the  tertiary interaction of planting on  10^th  Oct., irrigation with  100 %  from FC and sprayed with  calcium  plus boron  over the interaction among planting on 20^th Sep., irrigation with 50 %  from  FC in the 1^st and the 2^nd seasons, respectively.

 

3. Plant water relations, proline  amino acid  and leaf pigments 

3.1. Effect of planting date  

 Data in Table 6 show that planting date had a significant effect on plant water relation, proline amino acid in leaves and total chlorophyll in both seasons.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Planting  potato on 10^th Oct.  gave the highest values of  total  and free water %, as well as total chlorophyll in  the leaf tissues, while planting on 20^th Sep.  gave the   highest values  of   bound  water % and proline amino acid in  leaf tissues in both seasons.

 

3.2. Effect of  irrigation  water level   

 Irrigation water levels had a significant effect on  total , free and bound water % in leaf tissues as well as  proline amino acid and  total chlorophyll in leaf tissues in both seasons ( Table 6).        

Total and free water  as well as total chlorophyll  in leaf tissues  were the highest significantly increased by increasing  irrigation water levels up to 100 %   from FC  in both seasons. While,   bound water (%) and proline amino acid in leaf tissues were the  superior  with the lowest level of irrigation water in both seasons.

From the previously mentioned results, it could be suggested that, the increment in water supply would increase the soil moisture content, which in turn would probably led to increase the available water in the soil. Which  resulted to  increase water absorption and then increased both total and free water in leaf tissues. As free water content increase, bound water content should be decrease. Moreover, the increase in the bound water and decrease in free water under water stress was mainly due to the increases in cell sap concentration and its osmotic pressure resulted from the conversion of starch into soluble carbohydrates (Lancher, 1993).

These results are in accordance with those reported by Abdel-Al  (2001) ,    Bao-Zhong et. al. (2003) and Youssef  (2007) as for  total chlorophyll  and  Abdel-Rheem (2003), El-Ghamriny et al. (2005),  Mahmoud (2006)  and Khalel (2015) for  plant water relationship and proline amino acid in potato leaves tissues .

3.3. Effect of foliar spray treatments 

Spraying potato  plants with calcium and boron had significant effect on total, free water % and total chlorophyll  in leaf tissues than unsprayed plants , while  unsprayed plants significantly increased bound water % and proline  amino acid in  leaf tissues  in both seasons ( Table 6).

Similar observations also recorded by Awad et al. (2010) and Singh et al. (2018) on potato) and Kazemi (2013) on tomato.

3.4. Effect of interaction between planting date and irrigation level

Data presented in Table 7 show that, the interaction between planting date  and irrigation level had a significant effect on studied  plant water  relationships , proline amino acid  and total chlorophyll in leaves  of potato  in both seasons. The interaction between  planting  on 10^th Oct.  and  irrigation with 100  %  from FC   gave the higher  values of total ,  free water % and total chlorophyll in leaves  tissues , while the interaction between  planting  on 20^th Sep.  and irrigation with  50 % from FC  recorded the higher values of  bound water % and proline amino acid in both seasons.

3.5. Effect of interaction between planting date and foliar spray  treatments

The interaction between planting on 10^th Oct.  and  foliar spray with calcium and boron in the combination  significantly increased total , free water % and  total chlorophyll in leaf tissues in both seasons, while the interaction between planting on 20^th Sep.  and unsprayed  plants  significantly increased bound water  %  and proline amino acid  in leaf tissues in both seasons               (Table 7).

3.6. Effect of interaction between irrigation level  and foliar spray treatments 

The interaction between irrigation levels and some foliar spray treatments   had significant effect on all plant water relationship, proline amino acid and total chlorophyll in leaf tissues in both seasons (Table 8). The highest values of total , free water % and  total  chlorophyll were obtained  with the interaction between irrigation  potato plants with  100 %  from FC and sprayed plants  with  the combination of  calcium  and  boron, while the  bound water % and proline amino acid  were highest  in plants which irrigated with 50 %  from FC and unsprayed with  calcium  or  boron in both seasons.

3.7. Effect of tertiary interaction among planting date, irrigation level and foliar spray treatments

 Total, free water % and total chlorophyll in leaf tissues significantly increased with the tertiary interaction among planting on 10^th Oct., irrigation with 100% from FC and sprayed potato plants with calcium and boron in combination in both seasons. While  the  tertiary  interaction  among  planting on  20^thSep., irrigation with50% from FC and unsprayed plants with calcium or boron significantly increased  bound  water % and proline amino acid in  tissues  in both seasons (Table 9).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4. Nitrogen , P,K , Ca,  B  and total carbohydrates in  shoots

4.1. Effect of planting date   

Planting date  had a significant effect on Ca, B  and total  carbohydrates in both seasons  and  P in the 1^st and K content in shoots  in the 2^nd season , but  it had no significant effect in N content in shoot in both seasons ( Table 10).

 Planting potato on 10^th Oct. gave the highest values of Ca,  B and  total carbohydrates contents in  their shoots in both seasons, P content  in the 1^st and K content in shoots  in the 2^nd season.

These results are agree with those reported with  Sandhu et al. (2014)  and Dash et al. (2018).

 

4.2. Effect of irrigation  water level 

Calcium , Boron  and total  carbohydrates contents in  potato shoots  in both seasons  , N contents in the 2^nd season and P content in the 1^st season significantly increased by increasing  irrigation  water  levels  up  to the highest levels  100 %  form FC, while  irrigation level  had no effect on K content  in shoots in both seasons. (Table 10).

Increasing the quantity of water applied to the soil increased the moisture content that make minerals more available to the plant. The increase in vegetative growth of potato plant by increasing irrigation water quantity might be due to that irrigation at 100 % from FC resulted in lower stomata resistance, and hence higher conductance and photosynthetic activity. On the other hand, unfavorable effect of drought on dry matter production might be due to the reduction in uptake of nutritional elements that cause a disturbance in the physiological processes needed for plant growth (Slatyer, 1969) and or to the reduction in leaf area and photosynthetic rate (Fisher and Hagan, 1965) and/or to that low water level also caused reduction in CO₂ assimilation due to stomata close (Hsiao and Acevedo, 1974), and/or to that the photosynthetic efficiency began to decrease  with a slight deficit in the soil moisture content  due to the decrease in the mesophyll photosynthetic activity at high xylem water potential  (Gawish, 1992).

These results are in lines with those reported by Nahar and Gretzmacher (2002) on tomato,  Anwar (2005), Abou El-Khair et al. (2011)  on potato  and  Kamal, and El-Shazly (2013) on tomato.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4.3. Effect of foliar spray treatments

Spraying potato plants with Ca and B singly or in combination had significant effect  on all minerals contents and total carbohydrates in shoot than unsprayed plants in both seasons ( Table 10).

N,P, K, Ca and B  were highest in plants which sprayed with Ca and B in combination  in both seasons, and  total carbohydrates  were highest  in plants  which sprayed with  B in both seasons.

The enhancement in  mineral uptake  by foliar application of boron may be a result of its roles in stimulating plant biological activities such as photosynthesis, enzyme activities, nutrient uptake and rate of translocation of photoasssimilates. Moreover, the stimulating effect of B on plant growth may be due to its role in cell development and the production of IAA which is essential for the elongation of plants (Follett et al., 1981).

Canda (2002) explained  the higher P content due to the influence of boron on membrane-bound ATPase activity in addition, heavy K-demanded crops in the bulking stage of production will require 60-80 ppm boron levels in the tissue in order to take up their demand of potassium. The increment in boron content is expected due to the application of this nutrient.. The higher K content was explained by Mengel and Kirkby (1978) based on the synergism relationship between K and B at sugar and carbohydrate transport.

These results are in harmony with those reported with El –Dissoky and Abdel –Kadar (2013), Tantawy et al. (2017) and  Seifu, and  Deneke (2017) on potato.

 

4.4. Effect of interaction between planting date and irrigation level

Data presented in Table 11 showed that, the interaction between planting dates  and irrigation levels had significant effect in all mineral  and total carbohydrates  contents in shoots  both seasons, except N and K  in the  2^nd and P  in  1^st season.

The interaction between  planting on 10^th Oct. and  irrigation levels with 75 %  from FC recorded the highest values of N and K contents in the 2^nd season , P in the 1^st season   and total carbohydrates in both seasons, Ca and  B content  were  highest with the interaction between planting on 10^th Oct. and  irrigation levels  with 100 % from  FC in both seasons.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4.5. Effect of interaction between planting date and foliar spray  treatments

The interaction between planting on 10^th Oct. and  foliar  spray with  Ca and B in combination reflected a significant effect on of N,P , K, Ca and  B  contents in shoots in the two seasons, total carbohydrates was highest with  the same date and sprayed plants with boron  in both seasons (Table 11).

 

4.6. Effect of interaction between irrigation level  and foliar spray treatments 

Irrigation potato plants with 100 % from FC and sprayed their plants with Ca and B in combination had a significant increase in N,P ,K, Ca and B  contents in shoots in both seasons. Total carbohydrates were highest with the same levels of irrigation and spraying plants with B in both seasons. On the other hand, the lowest values of above mentioned traits were recorded with  the plants which  irrigated with  50 % FC and  unsprayed plants with Ca or boron in both seasons (Table 12).

 

4.7. Effect of tertiary interaction of planting date, irrigation level and foliar spray treatments

The tertiary interaction of planting date, irrigation level and foliar spray treatments had a significant effect in all mineral contents and total carbohydrates  in shoots in both seasons ( Table 13). The interaction between planting on 10^th Oct., irrigation levels  at 75 %FC and spraying plants with Ca and B  gave the highest values of N  and K contents,  P content was highest  with  the interaction among planting in  the same  date,    irrigation level  at  50 %  from FC and spraying  plants with Ca and B in combination. Calcium,  B and total  carbohydrates  were highest with  the interaction of  planting on 10^th Oct. ,  irrigation  plants with 100 %  from FC and spraying  plants with Ca and B in combination. The interaction among planting on 10^th Oct., irrigation plants with 100 %  from FC and spraying  plants with  B  gave the highest  total  carbohydrates  in both seasons.

Conclusively, it could be concluded that, the interaction between planting on 10^th Oct. irrigation level at 100 % form  FC and spraying plants with Ca and B in combination  were the best interaction treatments for enhancing plant growth  and chemical constituents  of  potato under clay soil.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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