Sugar Beet Response to Nitrogen and Potassium Fertilization Treatments in Sandy Soil

Introduction

The population of the world will exceed 9 billion by the year 2050. It is, therefore, of vital importance to improve crop yield to match the requirements for food. However, as the environment was becoming worse, the quantity and quality of crop production were significantly decreased by a variety of biotic and abiotic stresses. The practice of intensive fertilization to support massive food production for an increasing global population is a must. However, consumption of excess N fertilization and K deficiency cause a reduction in crop yields and quality in many regions. Therefore, to enable closing yield gaps and allow for a much higher productivity in many regions, a significant increase in fertilization application is required. K is an essential plant nutrient that impacts a number of physiological and biochemical processes that are involved in plant resistance to biotic and abiotic stresses. Maintaining an optimum K nutritional status is essential for plant resistance to biotic and abiotic stresses. Balanced fertilization and efficient K usage in combination with other nutrients not only contribute to sustainable crop’s growth, yield and quality, but also influence plant health and reduce the environmental risks (Wang et al., 2013).

In addition, Potassium (K) is one of the essential macronutrients for higher plants, not only important for plant growth and development, but also crucial for crop yield and quality (Wang and Wu, 2015). Nitrogen (N), one of the most important mineral nutrients in higher plants, is involved in plant metabolism as a constituent of amino acids, proteins, nucleic acids, lipids, chlorophyll, co-enzymes, phytohormones, and secondary metabolites (Wang et al.,. 2016).  The application of too little nitrogen will result in reduced root tonnage, however, the application of too much nitrogen will result in reduced sugar concentrations and increased impurities (Hergert, 2010).

Now, Egypt faces many problems that affect the productivity of crops in general and sugar crops in particular, including sugar beet, which evolves significantly at the moment.  So that, it became the first source for the production of sugar in Egypt, where the production of sugar from beets has 57% (1,347 Million tons) of sugar production in Egypt. While the sugar cane production was 43% (1,025Million tons), (Sugar Crops Council , 2016). One of the main problems is the water after building El- Nahda Dam and the high prices of fertilizer, particularly nitrogen and potassium.

Now, there is no accurate and wide-ranging information which considers to consequence of nitrogen and potassium fertilizer rates on yield and quality of sugar beet in sandy soil under drip irrigation system at West Noubaryia region conditions.

Material and Methods

Two field experiments were conducted at km 71 West Noubaryia, Alex. Cairo desert Road, El Behiera governorate, Egypt during two successive seasons, 2014/ 15 and 2015/ 16, to study the effect of nitrogen and potassium fertilizer rates and their interactions on yield characters, quality and impurity parameters of multigerm sugar beet (Beta vulgaris L.) cv. Magribl. The nitrogen and potassium fertilizers were in the forms of urea (46 %N) and potassium sulphate (48 % K₂O), respectively, were applied as a side- dressing in two equal doses. The first was applied after thinning and the other was applied four weeks later.

- The nitrogen rates used

Without nitrogen fertilizer (N₀), 33.5 kg N/ fed. (N₁), 67 kg N/ fed.(N₂) and 100.5 kg N/ fed.(N₃)

- Potassium rates used

Without potassium fertilizer (K₀), 16 kg K₂O/ fed.(K₁), 32 kg K₂O/ fed.(K₂) and 48 kg K₂O/ fed.(K₃)

Before soil preparation, soil samples were taken at a depth of 0: 30 cm depth from different experimental sites, to determine physical and chemical properties of soil according to Piper (1950) as shown in Table (1).

Table (1). Some physical and chemical properties of the experimental soil in   2014/2015 and 2015/2016 seasons

Each field experiment was including two factors in split- plot design with three replications. The main plots were assigned to rates of nitrogen fertilizer and potassium rates Z6 meters in length, thus, the area of the plot was 21 m² (6 x 3.5 m) 1/200 fed.

The experimental field well prepared through two ploughing, leveling, compaction, ridging, and then divided into the experimental units. Calcium super phosphate (15.5 % P₂O₅) was applied during soil preparation at the rate of 100 kg/ fed. Sugar beet balls were hand sown 3- 5 balls/ hill using dry sowing method on one side of the ridge in hills 20 cm apart on 13^tsoctober during two seasons. The plots were irrigated immediately after sowing directly. Plants were thinned at the age of 4 leaf stage to obtain one plant/ hill. The common agricultural practices for growing sugar beet according to the recommendations of Ministry of Agriculture were followed, except the factors under study.

Data Recorded:

The outer two ridges (1^st and 6^th) were considered as a belt, while plants of the 2^nd, 3^rd, 4^th and 5^th were kept for determination of yield characters and technological qualities.

I- Yield characters

At harvest, plants that produced from the four ridges (from 2 to 5) of each sub sub-plot were collected. Roots and tops were separated and weighted in kilograms, then converted to estimate:

1. Roots yield  (tons/fed)
2. Top yield.    (tons/fed)
3. Sugar yield  (tons/fed)

It was calculated by multiplying roots yield × sucrose percentage

II- Juice Quality

Total soluble solids percentage (TSS %) in roots.

 It was measured in juice of fresh roots by using Hand Refractmeter (Me Ginnis 1982).

1. Sucrose percentage.
2. Purity percentage.

III- Impurities parameters:

1. Sodium (Na ; meq/100 g )
2. Potassium (K;  meq/100 g )
3. α- amino nitrogen (α- AN;  meq/100 g)
4. Extractable white sugar % (ZB%).

Correct sugar content (white sugar) of beet was calculated by linking the beet non K, Na and α-amino Nitrogen expressed a (meq/100 g) according to Reinfeld et al. (1974) as described by Harvey and Dutton (1993) as follows

     ZB = (Pol- 0.29) - 0.343 (K + Na) -  0.094  α-amino-N

1. Quality% (QZ%) 

    QZ = (ZB × 100)/ (α-amino-N)

1. Alkalinity Coefficient (AK)

    was determined as described by Harvey and Dutton (1993) as follows:

    AK= (K + Na) / (α-amino-N)

1. Loss Sugar %

Loss Sugar % = Gross sugar % - White sugar%

Gross sugar % = Sucrose%

White sugar% = Extractable white sugar% (ZB%)

Sucrose, quality, purity and impurity parameters were determined in Sugar Nile Company.

Statistical analysis:

All data were statistically analyzed according to combine of two seasons by “MSTAT” Computer software package and least significant difference (LSD) method was used to test the differences between treatment means at 5% levels of probability.

Results and Discussion

The effects of different nitrogen, potassium fertilizer rates and their interactions on sugarbeet yield characters, quality and impurity parameters in sandy soil field under drip irrigation system are illustrated in Tables (2 to 5).

I- Yield characters:

Data of the effects of different nitrogen, potassium fertilization rates and their interactions on sugarbeet yield characters i.e. roots yield, top yield and sugar yield were recorded in Table (2).

I-1- Roots yield (tons / fed.)

The result in Table (2) cleared that the roots yield (tons/fed.) was significantly increasing with increasing nitrogen rate from N₀ [without] to N₁ (33.5), N₂ (67.0), and N₃ (100.5) kg N/ fed. Application nitrogen at the higher rate (100.5kg N/ fed.) produced the highest roots yield (34.98 tons/ fed.), while, the lowest one (19.70 tons/ fed.), resulted from control treatment (without nitrogen fertilizer). The increasing than control treatment (N₀) for N₁, N₂, N₃ rates were 24.18, 41.15 and 77.55 %, respectively. Such effect might have due to improved beet growth in term of more dry matter accumulation.

Also, the results in Table (2) showed that increasing potassium fertilizer rate from K₀ [without] to K₁ (16 kg K₂O/ fed.), K₂ (32 kg K₂O/ fed.), and K₃ (48 kg K₂O/ fed.) rates significantly increased roots yield by 15.65, 20.41 and 27.31 %, respectively as compared with the control treatment (K₀). The highest yield (29.39 tons/ fed.) resulting from potassium fertilizer at K₃ rate. Roots yield /fed. Significantly effected by the interaction between nitrogen and potassium fertilizers revealed that the combination of N₃ + K₃ (100.5 kg N/ fed. + 48 kg K₂O / fed.) had the highest roots yield (40.75 tons/fed.)

I-2- Top yield (tons/ fed.)

The data in Table (2) indicated that top yield (tons/ fed.) significantly increased as a results of increasing nitrogen fertilizer rates. Roots yields resulting from nitrogen fertilizer were 12.35, 17.24, 21.83 and 28.73 tons/ fed. at the rates of 33.5, 67 and 100.5 kg N/ fed., respectively . Relative percentages of increase in top yield to control treatment were 39.55, 76.73 and 132.62 % for N₁, N₂ and N₃ rates, respectively.

According to potassium fertilizer rates, increasing potassium fertilizer rate from K₀ (without fertilizer) to K₁, K₂ and K₃ significantly increased top yield. No significant difference was found between applied K₂ and K₃ rates in this respect. Fertilizing sugarbeet plants with K_0, K₁, K₂ and K₃ rates produced 17.04, 19.18, 21.41, and 22.53 tons/ fed. of top yield, respectively. The increase percentage in top yield as compared with control treatment were 12.60, 25.61, and 32.27 for K₁, K₂ and K₃ rates, respectively. There were significant effects for the interaction between nitrogen and potassium fertilization rates on top yield/ fed. The highest top yield values (30.50 and 31.48 tons/ fed.) was obtained by planting beets with combination of N₃ + K₂ (100.5 Kg N/ fed. + 36 kg K₂O/ fed.) or N₃ + K₃ (100.5 kg N/ fed. + 48 kg K₂O/ fed.) Table (2).

Table (2). Effect of different nitrogen, potassium fertilizer rates and their interactions on yield characters of sugarbeet crop in combine analysis of 2014/15 and 2015/16 seasons.

        In% = increase% than control treatment                ns=not significant

I-3- Sugar yield:

Significant difference was noticed in sugar yield among nitrogen fertilizer rates. The highest sugar yield (4.76 tons/ fed.) value was produce from the highest rate of nitrogen fertilizer of 100.5 kg N/fed. followed by 67 N/fed (3.62 tons/ fed.), 33.5 N/fed (3.13 tons/ fed.) and control treatment (2.38 tons/ fed.) rates.

Therefore, the nitrogen had the greatest direct effect on sugar yield value .The relative increases than control treatment were 31.71, 52.12 and 100% for 33.5, 67.0 and 100.5 kg N/ fed. rates, respectively as shown in Table (2). Comparing among potassium fertilizer rates, increasing rate of potassium fertilization enhanced sugar yield/ fed. The rates of K₂ (3.73 tons/ fed.) and K₃ (3.82 tons/ fed.) significantly increased sugar yield /fed. than both K₀ (2.14 tons/ fed.) and K₁ (3.44 tons/ fed.) rates, without significant differences between them. Relative increases than control treatment for K₁, K₂ and K₃ potassium rates were 17.08, 26.18 and 30.8 %, respectively. There was not significant effected for interaction between nitrogen and potassium rates on sugar yield.

The data in Table (2) showed that increasing nitrogen significantly increased roots yield, top yield, and sugar yield. The same results had been observed throughout different experiments which were obtained by Agami (2005); Maareg et al. (2005 a & b); Leilah et al.(2005); Ouda (2007); Osman (2011); Sarhan (2012); Shaban et al. (2014); Abdelaal and Tawfik (2015) and El–Deeb (2016). Also, Table (2) cleared that increasing nitrogen rate significantly increased yield characters i.e. roots, top and sugar yields. These results are in agree with those of Abido et al. (2015).

The data observed that roots and top yield significantly affected in the interaction between nitrogen and potassium fertilization rates. On the contrary, sugar yield/ fed. insignificantly affected by the interaction between nitrogen and potassium rates. These results are in agreement those of Osman (2005) andEl-Shafai (2000).

II- Juice Quality:

The effects of nitrogen and potassium fertilizer treatments on sugarbeet juice quality i.e. total soluble solids (T.S.S%), sucrose and purity percentages were tabulated in Table (3)

II-1-Total soluble solids percentage (T.S.S%):

Significant difference was noticed for T.S.S % value among nitrogen rates. The highest T.S.S % value was resulted by adding higher nitrogen rate (100.5 kg N/ fed.) followed by 67 and 33.5kg N/ fed. rates, with an average of 21.37, 20.17, 19.84 and 18.5%, respectively. The relative increase than control treatment (without nitrogen fertilizer) were 7.25, 9.06, and 15.52% for N₁ (33.5), N₂ (67.0), and N₃ (100.5) kg N/ fed. respectively (Table, 3). Comparing among potassium rates, increasing potassium rate enhanced T.S.S %. The rate of K₂ (20.43) and K₃ (20.40) significantly increasing T.S.S % than both K₀ (19.36 %) and K₁ (19.67 %) rate, without significant difference between them. Relative increase than K₀ rate for K_1, K₂ and K₃ rates were 1.59, 5.53, and 5.38 %, respectively (Table 3).

II-2-Sucrose percentage:

The data in Table (3) showed that increasing nitrogen rates from N₀ (14.94%) to N₁ (15.87%), N₂ (16.16%) and N₃ (17.04%) increased sucrose% by 6.22, 8.21 and 14.08%, respectively. These differences were significant values. Also, the data showed that the highest sucrose % values were recorded by applying K₂ (16.36%) and K₃ (16.25%) potassium fertilizer rates, without significant differences between them. These two potassium rates significantly increased sucrose% than K₀ and K₁ rates (Table 3)

II-3- Purity percentage:

The tested different rates of nitrogen, potassium fertilizer and their interactions on purity% were no significant differences.

III- Impurity Parameters:

      Data of the effects of nitrogen, potassium fertilizer rates and their interactions on sugarbeet impurity parameters (Na, K, α- amino nitrogen percentages, Extractable white sugar% (ZB%), Quality% (QZ %), Alkalinity Coefficient (AK) and loss sugar%) were recorded in (Tables 4 and 5).

Table (3).Effect of different nitrogen, potassium fertilizer rates and their interactions on TSS%, Sucrose% and purity% of sugarbeet crop in combine analysis of 2014/15 and 2015/16 seasons.

    Inc% ( increase%) or dec% (decrease) than control treatment          ns=not significant

III-1- Sodium ( Na meq/100g)

The data in Table (4) observed that increase nitrogen rates from N₀ to N₁, N₂ and N₃ rates significantly increased Na% by 21.05, 41.65 and 79.06%, respectively. Also, there were positive correlation between potassium rates and Na%. The ascending sequences of tested potassium rates were as follows: K₀ (1.43 meq/100 g) < K₁ (1.60 meq/100 g) < K₂ (1.66 meq/100 g) < K₃ (1.83 meq/100 g). The last rate (the higher rate) of potassium increased Na % by 79.06% in compared with K₀ rate (without potassium fertilizer) or control treatment, as show in Table (4).

III-2- Potassium (Ka meq/100g)

The data in Table (4) also showed that increasing nitrogen fertilizer rates from N₀ to N₃ kg N/ fed. significantly increased potassium percentage from 6.66 to 11.67 (meq/100 g) in roots juice.

Table (4). Effect of different nitrogen, potassium fertilizer rates and their interaction on impurity parameters of sugarbeet crop in combine analysis of 2014/15 and 2015/16 seasons.

        Increase% = increase% than control treatment             

The relative increases in K% than control treatment (N₀) were 18.54, 37.47 and 75.20% for N₁, N₂ and N₃ rates, respectively. Potassium concentration in roots juice significantly increased with increasing potassium fertilizer rates. K% values could be arranged in the following descending order according to potassium rates: K₃ (9.72 meq/100 g), K₂ (9.15 meq/100 g), K₁ (8.83 meq/100 g) and K₀ (7.68 meq/100 g), without significant differences between applied K₁ and K₂ potassium rates. The increases in potassium% were 14.97, 19.08 and 26.57% than control treatment for K₁, K₂ and K₃, respectively.

III-3- Alpha – amino nitrogen (α- AN meq/100g )

Raising nitrogen fertilizer rate from N₀ (without nitrogen fertilizer) to N₁, N₂ and N₃ rates significantly increased α- AN in root juice from 3.45 to 3.80, 4.46 and 5.60 meq/100 g respectively. These increases than control treatment were 10.01, 29.31 and 62.17 % for N₁ , N₂ and N₃  rates , respectively (Table 4).

Regarding to the effects of potassium fertilizer rates, K₂ (4.65 meq/100 g) and K₃ (4.60 meq/100 g) rates significantly increased α- AN than K₁ (4.37 meq/100 g) and K₀ (3.70 meq/100 g). However, there was no significant difference between the first mentioned potassium rates and vice versa between the last ones as shown in (Table 4).

The results in (Table 5) illustrated that all tested impurity parameters not significantly affected by interaction between nitrogen and potassium rates. The results inducted that increasing nitrogen fertilizer rate significantly increased the impurity characters, these results are similar to those achieved by Osman et al (2010); Abd El- Kader (2011); Ferweez et al (2011) and Mekdad (2015). In contrast, Tawfik, Sahar (2000) found that the effect of nitrogen fertilizer rates from 30 to 120 kg N/fed. had insignificants effects on these juice impurities. Also the results observed that increasing potassium fertilization rate significantly increased Na, K, α- amino nitrogen in juice roots .The results are in agreement those obtained by  Abo El-Ghait (2013) and Abdou (2014).

It could be concluded that 100.5 Kg N/ fed. accompanied with 48 Kg K₂O/ fed. gave the optimum and improving the yield and quality of sugarbeet grown in sandy soil.

III-4- Extractable white sugar% (ZB%)

Table (5) revealed effect of different nitrogen, potassium fertilizer rates and their interactions on Extractable white sugar% (ZB%), Quality% (QZ%), Alkalinity Coefficient (AK) and Loss Sugar % of sugarbeet crop.

The effect of N levels on ZB% was neglect, where the relative increases than N₀ was not more than 1.73%, therefore there were no significant differences among N levels. In regards to K levels, the highest effective level was K₁ (12.17%) followed by K₀ (11.86%) without significant differences.

Also, K₃ (11.61%) gave the higher ZB% than K₂ (11.55%) without significant differences. The relative increase than K₁was 2.61 % for K₂ and its relative decrease was 2.66 % and 2.17% at K₁ and K₃, respectively.   The lowest effective K level was K₂.  Thus, the effect of K levels gave varied responses without exact direction. In conclusion, only K levels had effects on ZB%.

III-5- Quality% (QZ %)

Both N and K levels harbored significantly effects on QZ% (Table 5). Increasing both N and K levels decreased QZ%. Consequently, the highest effective N and K levels were N₀ (80.55%) and K₀ (76.45%). On contrary, the lowest ones were N₃ (69.96%) and K₃ (71.51%). The relative decrease for previous levels than N₀ and K₀ were 13.14% and 6.46%, respectively. In regards to the interaction between N and K levels, the highest and the lowest values of QZ% were N₀K₀ (83.01%) and N₃K₃ (64.15%). The effect of N levels had more effects than K ones.

III-6- Alkalinity Coefficient (AK)

The efficacy of N and K levels on AK was presented in Table (5). The effects of N and K levels gave variant responses. The highest effective N and K levels were N₂ (2.43) and K₀ (2.39), respectively.

Table (5). Effect of different nitrogen, potassium fertilizer rates and their interactions on Extractable white sugar% (ZB%), Quality% (QZ%), Alkalinity Coefficient (AK) and Loss Sugar % of sugarbeet crop in combine analysis of 2014/15 and 2015/16 seasons.

    Inc% ( increase%) or dec% (decrease) than control treatment           ns=not significant

In addition, the lowest values for both previous factors were N₀ (2.29) and K₂ (2.30), respectively. Although these variations, there were no significant differences among both tested factors.

III-7- Loss Sugar %

Table (5) illustrated that the tested factors significantly effected on loss sugar%. N levels could be arranged in the following descending order according to Loss sugar%:   N₃ (5.18%) > N2 (4.68%) > N1 (4.02%) > N0 (2.85%). The relative increase than N₀ for N₃, N₂ and N₁ levels were 81.69, 64.21 and 40.88%, respectively.

K levels indicated that the highest loss sugar% was recorded at K₃ (4.70%) followed by K₂ (4.47%), K₁ (3.88%) and the least one was K₀ (3.69%). However, the respective relative increases than K0 were 27.39, 21.27 and 5.08%.

The interaction between N and K levels was significant. The highest and lowest loss sugar% were observed at N₃K₃ (6.41%) and N₀ K₀ (2.44%).

Generally, increasing both N and K levels enhanced loss sugar%. Moreover, the N levels had superior effects on loss sugar% than K levels.

In generall, the quality parameters, T.S.S%, sucrose%, purity%, ZB% and AK insignificantly affected by the interaction between nitrogen and potassium rates. The present results showed that increasing nitrogen or potassium fertilizer rates significantly increased T.S.S%, sucrose% and loss sugar%, as well as decreased QZ%. Similar results were reported by Ramadan and Nassar (2004); Ismail and Abo El-Ghait (2005); Maareg et al. (2005 a& b); Ouda, (2007), Osman et al. (2010); Sarhan (2012); Abdou (2013), and Mekdad (2015). There was not effect for nitrogen or potassium fertilizer on purity% and AK, these results are in line with the findings of Abo El-Ghait and Mohamed, (2005) and Abdelaal and Tawfik (2015).