EFFECT OF DIFFERENT NITROGEN SOURCES AND DOSES ON LETTUCE PRODUCTION

EFFECT OF DIFFERENT NITROGEN SOURCES AND DOSES ON LETTUCE PRODUCTION

El-Bassyouni, M.S.S

Horticulture Dept., Fac. of Agric., Al-Azhar Univ., Assiut, Egypt.

Key Words: Lettuce, ammonium nitrate, ammonium sulphate, organic manure, growth, productivity, quality.

ABSTRACT

Two field experiments were conducted in clay soil during the two winter seasons of 2014/2015 and 2015/2016 to study the response of lettuce plants (Lactuca sativa L.) to different sources and doses of nitrogen fertilizer. Two mineral N fertilizer sources, i.e., Ammonium Nitrate (33.5% N) and Ammonium Sulphate (20.5% N) were compared to organic manure (2.07-2.21% N) as a natural organic N source at different application doses, i.e., 60, 80 and 100 kg N/feddan (4200 m2). The experiments were carried out in a split plot design with three replicates, where three different N sources were occupied the main plots and three different N doses were randomized in sub experimental plots. Plant fresh weight, dry matter, total chlorophyll and heads yield as well as chemical composition of lettuce heads, i.e., vitamin C, nitrate, N, P and K were evaluated.

The data showed that applying of mineral-N sources increased plant fresh weight, chlorophyll content and heads yield as well as N, P and K in lettuce heads compared to organic-N source. Ammonium Sulphate ranked the first in increasing lettuce yield followed by Ammonium Nitrate and lastly coming organic manure. Organic manure resulted in the highest values of dry matter and vitamin C in lettuce heads and the lowest value of nitrate in lettuce heads. The productivity of lettuce and most of chemical contents in lettuce heads were increasing with increasing application doses from 60 to 100 kg N/feddan. The moderate application dose (80 kg N/feddan) resulted in the highest values of dry matter and vitamin C in lettuce heads, and the samestatistically productivity with less nitrate content compared to the highest application dose (100 kg N/feddan).

INTRODUCTION

Lettuce (Lactuca sativa L.) is one of the most popular among leafy vegetables and salad crops in all world countries grown in cool season (Rubatzky and Tamaguchi, 1997). In Egypt, lettuce is an important vegetable crop for both formers and consumers. For farmers, it is consider a fast cash crop in the winter season. For consumers, lettuce is eaten fresh and salad, where it is rich in vitamins and minerals.

Most of vegetables growers are often over fertilized their crops by mineral fertilizers due to high relatively return of extra yields (Stewart et al., 2005; Schenk, 2006). Vegetable crops require nitrogen in large amounts because it’s essential for plant productivity (Marschner, 1995). The extra availability of nitrogen which is not tailored to the plant requirement may reduce product quality through nitrate accumulation in the edible parts (Parenteet al., 2006). Moreover, overuse of mineral fertilizers is causing environmental pollution due to the excessive accumulation and leaching of harmful elements to the ground water (Juet al., 2007). Leafy vegetables particularly lettuce may accumulate nitrate when the supply of nitrogen is high (Reinink, 1991; Premuzicet al., 2004; Prasad and Chetty, 2008), although it’s short cultivation cycle. Therefore, nitrogen fertilization process in lettuce fields has to take into accounts not only farming economics but also the consumer preference and human health as well as environmental issues (Schenk, 2006).

Nowadays, consumers are interested in their health and high product quality which rich in vitamins and minerals and free from chemical residue specially nitrate and heavy metals (FAO, 2002). Natural nutrients resources are increasing around the world. Therefore, it is advisable to pay a special attention to use safe agriculture system for lettuce production. Organic manure as a natural nitrogen source contains relatively good nutrient elements, which are essentially required for plant growth and its productivity (Saleh et al., 2010; Ezzoet al., 2012; Shams, 2012; Zakiet al., 2012 and Saleh et al., 2013). Moreover, organic manure has an important role for improving soil physical properties. The supplied vegetable crops with natural nitrogen source such as chicken manure was proved to be very essential for the production of higher yield and for improving their quality (Fawzyet al., 2006; Uddin et al., 2009 Saleh et al., 2010; Shams, 2012; Zakiet al., 2012 and Saleh et al., 2013).

The presented study is aiming to evaluate head lettuce production under different sources of nitrogen comparing mineral sources, i.e., Ammonium Nitrate and Ammonium Sulphate with using the natural organic nitrogen source at different application doses.

MATERIALS AND METHODS

Two field experiments were conducted in Monoufya Governorate (Delta region, Egypt) to study the effect of different sources and doses of nitrogen fertilizer on lettuce productivity during winter cultivation season of 2014/2015 and 2015/2016. Good quality seedlings (one month old) of head lettuce seedlings (Oviation cultivar) were transplanted on 29th and 30th October, respectively in 2014 and 2015. The soil texture is clay soil (74.1% clay, 20.3% silt and 5.6% sand). The chemical analysis of soil contained 2.3% organic matter and 1.1% nitrogen. The pH was 7.1 and EC was 1.5dS/m. Nine treatments in two-factorial experiment as combined among three different nitrogen fertilizer sources (factor A) and three different application doses (factor B) were conducted. The experiment was carried out in a split plot design with three replicates as follows:

Factor A: Sources of N fertilizer (main plots):

1. Ammonium Nitrate (33.5% N).

2. Ammonium Sulphate (20.5% N).

3. Organic Manure (2.07-2.21% N).

Factor B: Doses of N fertilizer (sub plots):

1. 60 kg N/Feddan (4200 m2).

2. 80 kg N/Feddan (4200 m2).

3. 100 kg N/Feddan (4200 m2).

The mixture of farmyard manure, chicken manure and compost in ratio of 1:1:1 was used as a natural organic manure source for N. The chemical analysis of organic manure which used for lettuce plants in this experiment is shown in table (1).

Table (1): The chemical analysis of organic manure used for lettuce plants during the growing seasons of 2014/2015 and 2015/2016.

The area of sub experimental plot was 12.5 m2, including two ridges and containing 80 lettuce plants. Lettuce seedlings were transplanted on two sides of ridge (10 meters long and 50 cm wide) at 50 cm apart between each two plants on the ridge.

The total amounts of both of Ammonium Nitrate and Ammonium Sulphate were divided into three equal amounts and applied top-dressing each 15 days intervals after 20 days from transplanting. The organic manure (mixture of farmyard manure, chicken manure and compost in ratio of 1:1:1) was applied through the ditches and covered by soil before transplanting. The three previous sources of N (Ammonium Nitrate and Ammonium Sulphate and Organic Manure) were added at three different doses, i.e., 60, 80 and 100 kg N/Feddan.

During soil preparation, Calcium super phosphate (15.5% P2O5) was added to all sub experimental plots as a source of phosphorus at a rate of 45 kg P2O5/feddan. Also, all sub experimental plots were fertilized with equal amounts of Potassium Sulphate (48% K2O) as a source of potassium at a rate of 50 kg K2O/feddan, which divided into two equal splits doses and added as top-dressing at 35 and 50 days after transplanting. Surface irrigation was used and the other agriculture practices were applied wherever they were necessary needed and as commonly recommended in the commercial production of head lettuce at the local experimental site.

Measurements:

Randomly selected ten plants were harvested from each sub experimental plot at edible maturity after 60 days from transplanting as a

represented sample for data collection. The following measurements were recorded:

1. Fresh weight (g/plant).

2. Dry matter percentage, representative samples from lettuce heads were dried for three days in an oven at 70°C until constant weight.

3. Total yield was calculated as ton lettuce heads per feddan (4200 m2).

4. Leaf chlorophyll content (SPAD) was measured using a Minolta Chlorophyll Meter (SPAD-501).

5. Ascorbic acid (Vitamin C) was determined as mg/kg fresh weight of lettuce heads using dye 2, 4, 6-di-chlorophenolindophenol method as described in A.O.A.C. (1990).

6. Nitrate (mg/100g), NO3 was determined in distilled water extracts of lettuce heads tissues by the procedure of Cataldoet al. (1975).

7. Total nitrogen (N %), was determined in dried lettuce heads tissues according to a modified method of Kjeldahl(Horneck and Miller, 1998).

8. Total phosphorus (P %), was determined in dried lettuce heads tissues according to Watanabe and Olsen (1965).

9. Total potassium (K %), was determined in dried lettuce heads tissues according to a modified method of Jackson(1965).

Statistical analysis

All data values were subjected to the analysis of variance and significant differences between treatment means were compared according to LSD test at P<5% as described by Gomez and Gomez (1984).

RESULTS

Fresh weight, dry matter and yield:

1. Effect of different nitrogen sources:

The effect of different sources of N-fertilizer on fresh weight, dry matter content and heads yield of lettuce plants during the growing seasons of 2014/2015 and 2015/2016 is presented in Table (2). The obtained data showed that, the addition of Ammonium Sulphate ranked the first in increasing lettuce growth represented by plant fresh weight and total heads yield, followed by Ammonium Nitrate without any significant variation between the two mineral N fertilizers, and lastly coming organic manure. Organically fertilized plants produced the highest value of dry matter percent. These findings were completely similar in both growing seasons.

2. Effect of different nitrogen doses:

The effect of different doses of N-fertilizer on fresh weight, dry matter content and heads yield of lettuce plants during the growing seasons of 2014/2015 and 2015/2016 is presented in Table (2). Results indicated that increasing the application doses of N-fertilizer from 60 to 100 kg N/feddan increased plant fresh weight and heads yield of lettuce plants during the growing seasons of 2014/2015 and 2015/2016 (Table 2). The moderate application dose (80 kg N/fed.) produced the highest value of dry matter content in heads lettuce. Whereas, the obtained variations within dry matter content during the two growing seasons (2014/2015 and 2015/2016) and in both fresh weight and heads yield of lettuce plants during second season (2015/2016) between application doses of 80 and 100 kg N/fed. were not enough to reach the 5% level of significance. The lowest values of fresh weight, dry matter content and heads yield of lettuce plants were related to application of lowest dose (60 kg N/fed.) during the two growing seasons.

Table 2.Effect of different nitrogen sources and doses on fresh weight, dry matter and yield of Lettuce plants during the growing seasons 2014/2015 and 2015/2016.

3. Effect of interaction:

Table (2) exhibited the interaction effect of three different N sources and their three different application doses on fresh weight, dry matter content and heads yield of lettuce plants during the two growing seasons. Application of Ammonium Sulphate at highest dose (100 kg N/fed.) resulted in highestvalues of plant fresh weight and total heads yield of lettuce plants during the two growing seasons. On the opposite, organic manure at lowest dose (60 kg N/fed.) resulted in lowest values of plant fresh weight and total heads yield of lettuce plants during the two growing seasons. On the other hand, organic manure at highest dose (100 kg N/fed.) produced the highest value of dry matter content in heads lettuce, while the lowest value was related to those plants were fertilized by Ammonium Nitrate at highest dose (100 kg N/fed.) during first season (2014/2015). Whereas, there was not any significant effect for all interaction treatments on dry matter content of lettuce plants during second season (2015/2016).

Chlorophyll, vitamin C and nitrate contents:

1. Effect of different nitrogen sources:

`The results presented in Table (3) exhibit the effect of different nitrogen sources on chlorophyll, vitamin C and nitrate contents of lettuce plants during the growing seasons of 2014/2015 and 2015/2016. Total chlorophyll and nitrate contents in lettuce plants were significantly increased by addition of the two mineral N fertilizer sources (Ammonium Nitrate and Ammonium Sulphate) compared to organic manure during the two growing seasons. Ammonium Nitrate ranked the first in increasing total chlorophyll and nitrate contents in lettuce plants. Fully N-organically fertilized plants resulted in the highest content of vitamin C in lettuce heads, while the lowest content of vitamin C was found in those plants were fertilized by Ammonium Nitrate. These findings were completely similar during the two growing seasons.

2. Effect of different nitrogen doses:

Increasing of application doses of N-fertilizer from 60 to 100 kg N/feddan increased total chlorophyll and nitrate contents in lettuce plants during both growing seasons (Table 2), in spite of these increases were not enough to reach the 5% level of significance during the first growing season. The highest value of vitamin C was recorded in lettuce plants which fertilized by moderate application dose (80 kg N/fed.), while the lowest vitamin C was found in those plants which fertilized by lowest application dose (60 kg N/fed.) during the first growing season. Whereas, there was not any significant variation obtained among all three application doses concerning their effect on head content of vitamin C during the second growing season.

3. Effect of interaction:

The presented data in Table (3) showed that the highest nitrate content in lettuce heads was related to application of Ammonium Nitrate at the highest dose (100 kg N/fed.) to lettuce plants during the two growing seasons. On the opposite, organic manure at the lowest dose (60 kg N/fed.) resulted in the lowest values of nitrate content in lettuce heads during the two growing seasons. On the other hand, total chlorophyll and vitamin C did not record any statistical variations at 5% level of significance among all interaction treatments during the two growing seasons.

Table 3. Effect of different nitrogen sources and doses on chlorophyll, vitamin C and nitrate contents in Lettuce plants during the growing seasons 2014/2015 and 2015/2016.

N, P and K contents:

1. Effect of different nitrogen sources:

Table (4) show the response of chemical constituents, i.e., total nitrogen, phosphorus and potassium in heads tissues of lettuce plants as affected by different sources of N-fertilizer during the two growing seasons. The obtained data showed that, applying of mineral-N sources increased all chemical constituents, i.e., total nitrogen, phosphorus and potassium in heads tissues of lettuce plants compared to organic-N source. The highest values of K content in lettuce heads during the two growing seasons and P content during first season were associated with the application of Ammonium Sulphate. On the other hand, the highest values of N content in lettuce heads during the two growing seasons and P content during second season were associated with the application of Ammonium Nitrate.

2. Effect of different nitrogen doses:

With increasing the application doses of N-fertilizer within the range of 60 up to 100 kg N/fed., all chemical constituents, i.e., total nitrogen, phosphorus and potassium in heads tissues of lettuce plants were increased during the two growing seasons of 2014/2015 and 2015/2016 (Table 4).

However, the increment in phosphorus was not great enough to be significant at 5% level during the second growing season.

3. Effect of interaction:

The application of Ammonium Nitrate at the highest dose (100 kg N/fed.) to lettuce plants increased N content in lettuce heads during the two growing seasons (Table 4). The application of moderate dose (80 kg N/fed.) of Ammonium Sulphate resulted in the highest P content in lettuce heads during the first growing season. On the opposite, the lowest N content during the two growing seasons and the lowest P content during the first growing season were found in lettuce plants which fertilized by organic manure at the lowest dose (60 kg N/fed.). However, no statistical differences among all interaction treatments concerning their effects on K content during the two growing seasons and P content during the second growing season were recorded at 5% level of significance.

Table 4. Effect of different nitrogen sources and doses on N, P and K contents in Lettuce plants during the growing seasons 2014/2015 and 2015/2016.

DESCUSION

The presented study reported that the maximum growth of lettuce and its productivity as well as highest of most chemical contents of lettuce heads are associated to the application of mineral sources of N fertilizer at highest dose. This is due to high essentiality of N as a component of amino acids, proteins, nucleic acids, pigments and many enzymes (Marschner, 1995).So, N is critical for growth and development of plants, especially during cell division and cell enlargement phase of growth. Haque and Jakhro (1996) reported that N promotes vigorous growth and its deficiency leads to stunted growth and low production. The observed enhancement in lettuce productivity under higher dose of nitrogen under the presented study condition is inagreement with those findings of Shams, 2012; Zakiet al., 2012 and Saleh et al., 2016, who reported that plant productivity increased as N dose increased. The maximum yield under higher supply of mineral nitrogen due to increasing the photosynthetic rates and the assimilation rates, which leading to increase the vegetative growth and heads yield of lettuce (Saleh et al., 2010). With increasing of nitrogen dose, growth and productivity increased due to reciprocal relationship between nitrogen and carbohydrates exist within the plant (Patilet al., 2003) leading to more accumulation of carbohydrates and proteins which are the final products of photosynthesis and metabolic activities.

Although, lettuce growers are seeking to increase the productivity, the consumers are extremely preferred high product quality (FAO, 2002).McCall and Willumsen (1998) mentioned that higher doses of N are unlikely to achieve more gain in yield but risk increasing the nitrate content of the crop to non-acceptable rate. Increasing the used of mineral-N causes environmental problems due to the excessive nitrate accumulation in the edible parts (Parenteet al., 2006). The application of nitrogen fertilizer in appropriate mode (source and dose) is important to get optimum lettuce productivity and to improve its quality. Organic manure is a part of the solution to decrease nitrate accumulation, therefore it can be used to reduce the amount of nitrate produced by mineral fertilizers in vegetables, hence improving the quality of salad vegetables produced as well as human health (Fawzyet al., 2006; Uddin et al., 2009 Saleh et al., 2010; Shams, 2012; Zakiet al., 2012 and Saleh et al., 2013). The presented study reported that, lettuce organically fertilized resulted in the highest product quality (the highest vitamin C and dry matter as well as less nitrate content) compared to the mineral-N source. Also, the superiority in vitamin C and dry matter in heads tissues plus less nitrate content wereassociated to medium application dose of N-fertilizer. The slight decrease in lettuce yield by using organic manure is acceptable and may partly be compensated by saving of the mineral fertilizers cost and the positive environmental effect as well as the possible higher price for higher nutritional quality of the yield (Uddin et al., 2009). So, it is possible to reach remarkable yield even by application of moderate mineral-N dose (Parenteet al., 2006) and using organic manure (Saleh et al., 2010; Saleh et al., 2013). As a consequence there is the double advantage by increasing product quality (vitamin C and dry matter) and reducing nitrate accumulation (Premuzicet al., 2004). In conclusion, it is possible to achieve acceptable yield and more quality by providing moderate dose of N and using organic manure.

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تأثیرمصدروکمیةالتسمیدالنیتروجینی علی إنتاج الخس .

محمد سلیمانسلیمان البسیونى

قسمالبساتین - کلیةالزراعة - جامعةالأزهر - أسیوط - مصر.

أجریت تجربتین حقلیتین خلال موسمى الزراعة الشتوى لعامى 2015 / 2014و2015   2016/لدراسةإستجابةنباتات خس الرؤس لمصادر وکمیات مختلفة من التسمید النتروجینى.حیث تم مقارنة الأسمدة المعدنیة الشائعة مثل نترات الآمونیوم وسلفات الآمونیوم مع إضافة السماد العضوى کمصدر طبیعى للسماد النتروجینى فى ثلاثة مستویات إضافة مختلفة (60 ، 80 و 100 کجم نتروجین للفدان(  صممت التجارب بنظام القطع المنشقة فى ثلاث مکررات ،حیث تضمنت القطع الرئیسیة مصادر التسمید النتروجینى الثلاثة ، فى حین وزعت معدلات الإضافة الثلاثة عشوائیا بالقطع الفرعیة. سجلت بیانات الوزن الغض للنبات، والمادة الجافة، وبیانات المحصولوالمحتوى الکیمیائ مثل الکلوروفیل الکلى ، وفیتامین ج، والنترات، والنتروجین، والفسفور، والبوتاسیوم .

ولقدأظهرت البیانات أن مصدرى التسمید المعدنى )نتراتالآمونیوم وسلفات الآمونیوم( تفوقاعلى المصدر العضوى من حیث التأثیر على الوزن الغض للنبات والمحصول وکذلک المحتوى من الکلوروفیل الکلى، والنتروجین، والفسفور، والبوتاسیوم ،وکان لنترات الآمونیوم أکبر زیادة فى ذلک.

وعلى العکس وجد أن السماد العضوى أدى الى زیادة المحتوى من فیتامین ج مع تقلیل محتوى النترات .

من ناحیة أخرى وجد أن إنتاجیة الخس ومعظم المحتوى الکیمیائى له زادت تدریجیا مع زیادة معدل الإضافة للسماد من 60 وحتى 100 کجم نیتروجین/فدان،فى حین أن معدل الإضافة المتوسط ) 80 کجم نیتروجین/ فدان(   أدى إلى زیادة نسبة المادة الجافة والمحتوى من فیتامین ج مع تقلیل المحتوى النتراتى .

الکلماتالمفتاحیة: الخس،نترات الآمونیوم،سلفات الآمونیوم،السمادالعضوى،النمو،الإنتاجیة،الجودة .