ARTICLE INFORMATION

ABSTRACT

Corresponding author: Ihab I. Sadek E-mail: dr.ihabsadek@yahoo.com Keywords: Okra Chitosan Supplement fertilizer Apply method of chitosan Concentration of chitosan Yield Received: 26.06.2023 Received in revised form: 29.07.2023 Accepted: 01.08.2023

This experiment was conducted under modified greenhouse (net house) conditions at the Central Laboratory for Agricultural Climate (CLAC), Agricultural Research Center (ARC), to investigate the effect of using chitosan as a supplement fertilizer. Seeds of okra (Abelmoschus esculentus cv Balady) were sown on 15th February from each season in 2020 and 2021. Two factors were tested (i) applied method of chitosan (spry and adding to soil), and (ii) concentration of chitosan such as (100, 150, 200, 250 and 300 ppm) with fourth replicates designed in a randomized complete block. Results reflected the positive role of using a high concentration of chitosan on the growth, yield and quality of okra plants. The greatest values of all tested parameters i.e., vegetative growth (plant height, number of leaves and fresh and dry weights of leaves), chemical contents of leaves (N, P and K plus chlorophyll reading) and yield and its components (number of fruits/plant, average fruit weight, early and total yield, total protein, phosphorus and potassium) were obtained with 80% recommended doses from “N” chemical fertilizer + chitosan adding to soil 250 ppm “T10” and 80% recommended doses from “N” chemical fertilizer + chitosan spray 300 ppm “T6” treatments rather than grower treatment and reduced content of dietary fiber in okra fruit. While stem diameter was not affected by applied two tested factors.

INTRODUCTION  

Okra (Abelmoschus esculentus) is an important  vegetable crop with high demand and high economic  value. Okra is an important and high-yielding  vegetable of the mallow family grown in many  countries. Okra, also known as ‘Lady’s cinquefoil’ or  ‘Bendi’ in Malaysia, is popular for its health benefits  such as high fiber content, antioxidants, vitamin C,  minerals, potassium and calcium. It is also important  as a medicinal plant for plasma replacement in  tropical and subtropical countries (Kumar et al., 2013;  Sorapong, 2012). Popular for its short production time  and ease of cultivation, okra is a versatile crop as fresh  leaves, flowers, buds, pods, stems and seeds provide  multiple uses. Additionally, the medicinal properties of volume-increasing agent or plasma substitute for  medical purposes. Okra mucilage binds cholesterol,  toxins in bile acids are excreted by the liver, and most  parts of okra are edible and used as food (Gemede et  al. 2015; Maramag, 2013). 

Chitosan is a biopolymer, a chitin derivative, and a  compound that is completely harmless to the  environment. That is mean it’s very safe and  environmentally friend. Moreover, this compound is  characterized by unique properties such as bioactivity  and biocompatibility (Dias et al., 2013). Its derivative,  chitosan, is therefore described as a linear, semi crystalline polysaccharide composed of glucosamine   (C6H13NO5) and N-acetylglucosamine linked by  glycosidic β-linkages (1-4), with free amino groups. It  differs from chitin polymers by the presence of in the  polymer; we distinguish the second carbon atom of  the D-glucose unit, not the acetamide group  (Agbodjato et al. 2021). Also, literature results show  that the use of chitosan in plants increases yield  (Mondal et al., 2012), decreases transpiration (Dzung  et al. 2011), and induces many metabolic changes to  reduce plant viral load. It has been shown to increase  tolerance to bacterial and fungal infections (Al-Hetar  et al. 2011). In addition, chitosan-treated plants may  be less susceptible to stress caused by adverse  conditions such as drought, salinity, cold or hot  temperatures (Lizarraga-Pauli et al. 2011; Jabeen and  Ahmad, 2013; Pongprayoon et al. 2013). Chitosan  stimulates important plant processes at all levels of  biological organization, from single cells and tissues,  through physiological and biochemical processes, to  molecular changes associated with gene expression  (Limpanavech et al. 2008; Hadwiger, 2013; Nguyen  Van et al. 2013). Chitosan refers to a group of  commercially available copolymers rather than a  unique compound. In addition, treatment with  chitosan makes plants more resistant to various soil  and foliar pathogens and induces root-knot formation  (Hamel and Beaudoin, 2010), making chitosan a useful  tool for agricultural sustainability (Iriti and Varoni,  2015; Pichyangkuraa and Chadchawanb, 2015).  Moreover, Kah et al. (2013) found that chitosan  increases the absorption of bioactive compounds,  allowing plants to absorb nutrients more effectively. 

On other hand, the main goal of modern agriculture is  to produce sufficient quantities of good quality food  to meet the growing world population with low  environmental impact (FAO, 2013). Agricultural  production is severely affected by many pests and  diseases, which can lead to huge losses. Chemical  fertilizers and pesticides have been used over the past  100 years to combat these problems and increase  yields. Large-scale development of these products has  greatly increased productivity, but has also led to  biodiversity loss and degradation of natural and  agricultural systems. Furthermore, residue  accumulation has caused environmental pollution and  public health problems with the emergence of  resistant pests (Sun et al. 2012). Therefore, alternative  methods are needed to address these issues and  reduce the environmental impact of activities without  compromising agricultural productivity and achieving  economic returns. Recently, chitosan-based materials  have been used to create nanoparticles that can efficiently supply chemicals and nutrients to plants  (Kah et al., 2013). Indeed, chitosan is readily absorbed  by the epidermis of leaves and stems, prolonging the  contact time and facilitating the absorption of  bioactive molecules. 

Furthermore, fertilizer requirements are important in  early growth to improve okra productivity and quality.  Currently, chemical fertilizers such as NPK (nitrogen,  phosphorus, and potassium) are widely used in  agricultural fields, including vegetable cultivation,  because they can achieve high productivity in a short  period of time. However, it is very expensive and  causes nutrient imbalance and soil acidification  (Akande et al. 2010). Furthermore, overuse of  chemicals used to fertilize plants can lead to the  accumulation of minerals and nutrients that are not  readily available for plant consumption, ultimately  leading to soil contamination and toxicity (Savci,  2012). Therefore, increasing crop production depends  on improving soil fertility to ensure food for all in the  current global food security scenario (Godfray et al. 2010). Therefore, it is imperative to develop various  eco-friendly methods to improve soil fertility and  increase agricultural production. 

This investigation aims to evaluate the effect of using  two ways for adding chitosan as a supplement  fertilizer on the growth, yield, and quality of okra  plants. 

MATERIAL AND METHODS 

This investigation was conducted at Central  Laboratory for Agricultural Climate (CLAC),  Agricultural Research Center (ARC), Giza, Egypt, under  a modified greenhouse (net house). Through two  summer seasons 2020 and 2021 to evaluate using  chitosan as a supplement fertilizer on growth, yield  and quality of okra plants. 

Experimental layout 

A modified greenhouse coved by a white net was 40m  long, 8m wide and 5.25m height. This house was  divided into 5 beds (1m wide and 40m long). Seeds of  okra (Abelmoschus esculentus cv Balady) were sown  on 15th February from each season by the spacing of  0.5m between plants inside the raw and separated  0.50m between beds. A drip irrigation system was  placed in this experiment. Recommended doses from chemical fertilizer which should be added “200 Kg ammonium nitrate (33.5% NH4NO3), 100 Kg  potassium sulphate (48% K2O) and 150 Kg calcium  super phosphate (15.5 % P2O5)/fad.” was applied (as  100%) only with grower treatment (control), while,  application chitosan treatments as supplement  fertilizer were applied by 80% from nitrogen chemical  fertilizer recommended doses. Fertilizer treatments  were divided into three equal doses; the first was  added after 30 days from the sowing date, the second  at the flowering stage and the third after 30 days from  the second does.  

Treatments 

Two factors were tested as follows compared to the  grower treatment (as control): 

(A) The applied method of chitosan (spry and adding  to soil), and  

(B)The concentration of chitosan such as (100, 150,  200, 250 and 300 ppm).  

Treatments were arranged as follows: 

1.100% recommended doses from chemical fertilizer  (control treatment) “T1”, 

2. 80% recommended doses from “N” chemical  fertilizer + chitosan spray 100 ppm “T2”, 

3.80% recommended doses from “N” chemical  fertilizer + chitosan spray 150 ppm “T3”, 

4. 80% recommended doses from “N” chemical  fertilizer + chitosan spray 200 ppm “T4”, 

5. 80% recommended doses from “N” chemical  fertilizer + chitosan spray 250 ppm “T5”, 

6. 80% recommended doses from “N” chemical  fertilizer + chitosan spray 300 ppm “T6”, 

7.80% recommended doses from “N” chemical  fertilizer + chitosan adding to soil 100 ppm “T7”, 8.80% recommended doses from “N” chemical  fertilizer + chitosan adding to soil 150 ppm “T8”,  9.80% recommended doses from “N” chemical  fertilizer + chitosan adding to soil 200 ppm “T9”,  10. 80% recommended doses from “N” chemical  fertilizer + chitosan adding to soil 250 ppm “T10”, and 11. 80% recommended doses from “N” chemical  fertilizer + chitosan adding to soil 300 ppm “T11”. 

Data recorded 

(1) Vegetative growth parameters 

Plant height, number of leaves, fresh and dry weights  of leaves and stem diameter were measured at med  of the season from fifth okra plants as random  samples. 

(2) Chemical contents of leaves 

Content percentages from N, P and K in leaves were  recorded plus chlorophyll reading at med of season.  Nitrogen was determined in leaves by the distillation  in a Macro-Kjeldahle according to (FAO, 2008).  Phosphorus was colorimetrically determined in leaves  in the acid digest using ascorbic acid and ammonium  molybdate as described by FAO (2008). Potassium was  estimated in leaves photometrically as described by  FAO, 2008. When, chlorophyll reading was measured  in leaves by using a digital chlorophyll meter (model  Minolta chlorophyll meter SPAD-501). 

(3) Yield and its components 

A number of fruits/plant, average fruit weight (from  10 fruits), and early and total yield (per plant) were  measured at the harvest stage. Additionally, total  protein and dietary fiber were determined according  to A.O.A.C. (2005). Phosphorus and potassium  concentration was determined according to FAO  (2008). 

Experimental design and data analysis 

This experiment was designed in randomized  complete block with fourth replications and obtained  data were statistically analyzed using the analysis of  variance method. Duncan’s multiple range tests at a  5% level of probability were used to compare the  means of the treatments (SAS, 2005). 

RESULTS 

Vegetative growth parameters 

Data in Table (1) reflected the effect of applied  chitosan as a supplement fertilizer on the vegetative  growth of okra plants at tested two grown seasons  2020 and 2021. 

Generally, indicated that, the application of okra  plants with a high concentration of chitosan (spray or  adding to soil) enhanced all tested vegetative growth  parameters such as (plant height, number of leaves,  fresh and dry weights of leaves) through two grown  seasons compared to grower treatment. Contrary, the  stem diameter parameter was not affected by the  applied two tested factors at all two growing seasons.  The greatest values of those parameters were obtained with applied treatments T10 (80%  recommended doses from “N” chemical fertilizer + chitosan adding to soil 250 ppm) and T6 (80%  recommended doses from “N” chemical fertilizer +  chitosan spray 300 ppm) more than other treatments  without any significant difference. When application of okra plants by 80% of recommended doses from  “N” chemical fertilizer + chitosan spray 100 ppm “T2”  reduced all those parameters followed by 80% of  recommended doses from “N” chemical fertilizer +  chitosan spray 150 ppm “T3”, respectively. 

Table (1): Effect of using chitosan as supplement fertilizer by spraying or adding to soil on vegetative growth  parameters i.e., plant height (cm), number of leaves, fresh and dry weights of leaves (g) and stem diameter  (cm) of okra plants through 2020 and 2021 seasons. 

Treatments	plant height	number of  leaves	Fresh weight of  leaves	Dry weights of  leave	stem diameter
	Frist Season
T1	60.24D	16.25E	78.68D	16.20G	1.40A
T2	52.63G	12.92J	64.94H	13.88K	1.34A
T3	56.76EF	13.77I	68.65G	14.35J	1.36A
T4	61.54D	15.55F	79.35D	16.66F	1.41A
T5	64.33C	17.66D	80.55C	18.83E	1.44A
T6	72.80A	24.96A	93.85A	23.54B	1.51A
T7	54.35FG	14.25H	72.77F	14.99I	1.37A
T8	58.85DE	14.86G	75.83E	15.53H	1.39A
T9	65.42C	19.68C	82.66C	19.68D	1.46A
T10	73.95A	25.22A	95.45A	24.15A	1.54A
T11	68.53B	22.12B	88.67B	21.75C	1.49A
	Second Season
T1	58.43D	15.93E	75.53D	15.55G	1.39A
T2	51.05G	12.66J	62.34H	13.32K	1.33A
T3	55.06EF	13.49I	65.90G	13.78J	1.35A
T4	59.69D	15.24F	76.18D	15.99F	1.40A
T5	62.44C	17.31D	78.29C	18.08E	1.43A
T6	70.62A	24.46A	90.10A	22.60B	1.49A
T7	52.72FG	13.97H	69.86F	14.39I	1.36A
T8	57.08DE	14.56G	72.80E	14.91H	1.38A
T9	63.46C	19.29C	79.35C	18.89D	1.45A
T10	71.73A	24.72A	91.61A	23.18A	1.52A
T11	66.47B	21.68B	85.12B	20.88C	1.48A

Chemical Contents of Leaves 

Illustrated data in Table (2) showed the effect of  applied chitosan (spray or adding to soil) on the  chemical contents of leaves (N, P, K and chlorophyll  reading). The greatest contents in leaves from those  parameters were observed with application  treatments 80% recommended doses from “N”  chemical fertilizer + chitosan adding to soil 250 ppm  “T10” and 80% recommended doses from “N”  chemical fertilizer + chitosan spray 300 ppm “T6”,  respectively, without any significant differences  compared to other treatments. Although, the  application of 80% recommended doses from “N”  chemical fertilizer + chitosan spray 100 ppm “T2” led  to reduced it. 

Yield and its components 

Presented data in Tables (3 and 4) indicated the effect  of using chitosan as supplement fertilizer yield and its  components such as (number of fruits/plant, average  fruit weight fruits), early yield, total yield and fruit  quality i.e., (total protein, dietary fiber, phosphorus  and potassium). 

Both tables observed that applying a high concentration of chitosan increased yield and enhanced fruit quality more than the grower  treatment (control). The highest yield and quality  were obtained with okra plants applied by 80%  recommended doses from “N” chemical fertilizer +  chitosan adding to soil 250 ppm “T10” and 80%  recommended doses from “N” chemical fertilizer +  chitosan spray 300 ppm “T6” treatments, without any  significant differences. When, applied 80%  recommended doses from “N” chemical fertilizer +  chitosan spray 100 ppm “T2” treatment reduced  values of all tested yield and its components  parameters. Furthermore, control treatment (100%  recommended doses from chemical fertilizer (control  treatment) “T1”) replaced sixth rank after 80%  recommended doses from “N” chemical fertilizer +  chitosan spray 200 ppm “T4”, without any significant  differences. 

Table (2): Effect of using chitosan as supplement fertilizer by spraying or adding to soil on chemical contents  of leaves chlorophyll reading (SPAD), N, P and K (%) of okra plants through 2020 and 2021 seasons. 

Treatments	Chlorophyll reading	N	P	K
	Frist Season
T1	40.75E	1.65D	0.39D	1.68D
T2	31.20I	1.43G	0.31G	1.52G
T3	33.34H	1.49F	0.33F	1.57F
T4	41.95E	1.67D	0.40D	1.70D
T5	45.87D	1.73C	0.42C	1.74C
T6	56.53A	1.88A	0.47A	1.85A
T7	35.42G	1.53F	0.34F	1.59F
T8	39.65F	1.59E	0.37E	1.64E
T9	49.84C	1.79B	0.44B	1.78B
T10	57.76A	1.92A	0.48A	1.87A
T11	53.27B	1.82B	0.45B	1.81B
	Second Season
T1	39.12E	1.58D	0.37D	1.61D
T2	29.95I	1.37G	0.30G	1.46G
T3	32.01H	1.43F	0.32F	1.51F
T4	40.27E	1.60D	0.38D	1.63D
T5	44.04D	1.66C	0.40C	1.67C
T6	54.27A	1.80A	0.45A	1.78A
T7	34.00G	1.47F	0.33F	1.53F
T8	38.06F	1.53E	0.36E	1.57E
T9	47.85C	1.72B	0.42B	1.71B
T10	55.45A	1.84A	0.46A	1.80A
T11	51.14B	1.75B	0.43B	1.74B

DISCUSSION 

In this study obtained that using chitosan as a  supplement fertilizer in high concentration had the  best impact on improving and increasing all evaluated  parameters of okra crop i.e., (plant height, number of  leaves, fresh and dry weights of leaves, chlorophyll  reading in leaves, content percentage from N, P and K  in leaves, number of fruits/plant, average fruit weight  fruits, early yield/plant, total yield/plant, total protein,  dietary fiber, phosphorus and potassium). 

This increase may be due to the use of chitosan which  increases the activity of key enzymes of nitrogen  metabolism (nitrate synthesis, glutamine synthetase,  proteases), improves nitrogen transport in functional  leaves, and promotes plant growth (Chibu and  Shibayama, 2003; Shehata et al., 2012). Also, Hafez et  al., 2019 found that chitosan application played a  positive role in promoting functional leaf nitrogen  transport, which promoted plant growth.  Furthermore, Mondal and Malek et al., 2012 stated  that vegetative growth parameters of okra increased  with increasing chitosan application concentration.  On the other hand, chitosan facilitated plant growth by treating the plants with necessary mineral  elements, which the plants could not supply in  sufficient supply, probably due to soil problems or the  supply of certain necessary amino compounds to the  plants (Chibu and Shibayama, 2003). In addition,  plants grew better due to improved root growth and  greater root spread in the soil (Zubaidi and Zainab,  2016). 

Table (3): Effect of using chitosan as supplement fertilizer by spraying or adding to soil on number of  fruits/plant, average fruit weight (g), early yield/plant (g) and total yield/plant (Kg) of okra plants through  2020 and 2021 seasons. 

Treatments	Number of fruits	Average fruit weight	Early yield/plant	Total yield/plant
	First season
T1	60.78E	3.05E	188.65E	2.850E
T2	50.00I	2.32H	110.38I	2.150I
T3	52.64H	2.54G	122.24H	2.335H
T4	61.28E	3.08E	192.50E	2.995E
T5	64.58D	3.32D	215.12D	3.162D
T6	74.92A	3.86A	298.85A	3.724A
T7	55.15G	2.58G	131.28G	2.510G
T8	57.23F	2.83F	162.47F	2.680F
T9	68.42C	3.55C	235.34C	3.388C
T10	75.76A	3.98A	300.79A	3.853A
T11	72.55B	3.62B	275.29B	3.558B
	Second season
T1	57.74E	2.93E	182.991E	2.793E
T2	47.50I	2.23H	107.069I	2.107I
T3	50.01H	2.44G	118.573H	2.288H
T4	58.22E	2.96E	186.725E	2.935E
T5	61.35D	3.19D	208.666D	3.099D
T6	71.17A	3.71A	289.885A	3.650A
T7	52.39G	2.48G	127.342G	2.460G
T8	54.37F	2.72F	157.596F	2.626F
T9	65.00C	3.41C	228.280C	3.320C
T10	71.97A	3.82A	291.766A	3.776A
T11	68.92B	3.48B	267.031B	3.487B

Chitosan has various functional groups such as  hydroxyl groups and amine groups, and because it  binds to metal ions by chemisorption or physical  adsorption, it has a high adsorption capacity for  various metal ions. Chitosan works with metallic  elements because it fits the basic natural properties of  multiple cations. Chitosan stimulates the activity of  key enzymes in nitrogen metabolism and improves  nitrogen transfer to leaves. This stimulates leaf  function in growth and development. In addition,  chitosan is a polysaccharide that is very important for  plant defense and yield increase in plant nutrition,  especially in horticulture. It causes a doubling of  photosynthesis. The action of chitosan molecules varies from cell to cell and depends on their  physiochemistry. It leads to increased root mass,  flowering and final production (Abdel-Mawgoud et al.,  2010; Monirul et al., 2018; Al-Hassani and Majid,  2019). Furthermore, chitosan had a positive effect on  root effectiveness and nutrient uptake, leading to  increased photosynthetic efficiency and carbohydrate  and sugar production, resulting in increased internode  growth and length and food accumulation led to an  increase in stem diameter (Monirul et al., 2018). 

Also, this result is harmony with Mondal et al., 2013, who, indicated that photosynthesis and chlorophyll in  cowpea plants are increased by chitosan treatment, 

which also influences the increase in biomass to water  content by reducing transpiration (Bittelli et al., 2001).  In addition, chitosan played an important role in plant  nutrition and also had positive effects on growth rate,  plant properties, and increasing metallic elements  (Mondal and Malek, 2012; Mondal et al., 2013).  Similarly, Guan et al., 2009 have shown that, this  increases the availability and uptake of water and  essential nutrients by modulating cellular osmotic  pressure, and the release of harmful free radicals by  increasing antioxidants and enzymatic activity. We  believe this is due to a decrease in accumulation.  Malerba and Cerana, 2016 reported that chitosan  application enhances leaf chemistry, promotes water  and nutrient uptake by vigorous roots, combats  oxidative damage by reactive oxygen species (ROS),  and enhances antioxidant enzymes. Furthermore,  found that it can activate both defense systems and  photosynthetic enzymes. Photosynthesis and  biosynthesis of essential organic molecules are  improved, increasing the accumulation of assimilates. 

Table (4): Effect of using chitosan as supplement fertilizer by spraying or adding to soil on total protein (%),  dietary fiber (%), phosphorus (%) and potassium (%) of okra fruits through 2020 and 2021 seasons. 

Treatments	Total protein	Dietary fiber	Phosphorus	Potassium
	First season
T1	3.58E	2.18A	0.68E	2.42E
T2	3.24I	1.55B	0.52I	2.04I
T3	3.33H	1.52C	0.57H	2.13H
T4	3.62E	1.37F	0.70E	2.44E
T5	3.83D	1.34G	0.74D	2.53D
T6	4.54A	1.24I	0.84A	2.82A
T7	3.44G	1.46D	0.60G	2.22G
T8	3.52F	1.41E	0.64F	2.33F
T9	4.22C	1.30H	0.78C	2.64C
T10	4.57A	1.25I	0.86A	2.88A
T11	4.35B	1.29H	0.82B	2.73B
	Second season
T1	3.47E	2.09A	0.65E	2.40E
T2	3.14I	1.49B	0.50I	2.02I
T3	3.23H	1.46C	0.55H	2.11H
T4	3.51E	1.32F	0.67E	2.42E
T5	3.72D	1.29G	0.71D	2.50D
T6	4.40A	1.19I	0.81A	2.79A
T7	3.34G	1.40D	0.58G	2.20G
T8	3.41F	1.35E	0.61F	2.31F
T9	4.09C	1.25H	0.75C	2.61C
T10	4.43A	1.20I	0.83A	2.85A
T11	4.22B	1.24H	0.79B	2.70B

Furthermore, the enhancement at yield and its  components parameters attribute to chitosan containing plants were the best in most traits of  vegetative growth and had a high proportion of  mineral matter, which allowed the plants to build  carbohydrate matter and high carbonation, reflected  in an increase in average fruit weight (Al-Hassani and  Majid, 2019). Application of chitosan increased all  vegetative growth traits and yields and their  constituents (Hafez et al., 2019). The important effects of chitosan on yield and its composition are likely due to the fact that chitosan has mimetic effects  on physiological processes, improving nitrogen  transport in functioning leaves and improving  vegetative growth and development (Gornik et al.,  2008). 

The vast impact of chitosan is probably because of  that chitosan is a brand new plant boom promoter  which include GA3 that can be have impact at the  plant boom and yield (El-Bassiony et al., 2014). On the other hand, for the impact of chitosan on macro and micro elements (N, P, K, Fe, Zn, Cu and B), chitosan  may be used as a remedy for mineral factors infected  soil (Sheikha and Al-Malki, 2011). Also, the main  position of chitosan in ameliorating plant roots  potential to uptake water and vital elements and use  them correctly inside plant in promoting of  antioxidant enzyme sports, prevention of reactive  oxygen species (ROS), activation of photosynthesis  and biosynthesis of carbohydrates, proteins and  different natural compounds that wanted for distinct  plant metabolic sports and manufacturing of greater  assimilates which translocated to end result in result  of K and P mode of action, and there for the  marketable end result yield and first-rate increased  (El-saady, 2016). Moreover, the effective effect of  chitosan on chemical additives leaves in phrases of  photosynthetic pigments and NPK elements can be  ascribed to the chitosan-mediated enhance root  device performance to soak up greater to be had  water and nutrients that wanted for critical  physiological sports which include photosynthesis and  biosynthesis of critical assimilates which ameliorate  leaves chemical first-rate (Malekpoor et al., 2016). 

In addition, chitosan increases the uptake and  availability of water and essential nutrients by  regulating intracellular osmotic pressure, promoting  plant growth. Over the past decade, the signaling  mechanisms of chitosan and its derivatives that  regulate plant growth and developmental processes  have been studied. Initial results show that chitosan  helps activate the hydrolytic enzymes required to  degrade and mobilize stored food materials such as  starch and protein. Chitosan promotes root cell  division by activating plant hormones such as auxin  and cytokinin, further increasing nutrient intake.  Furthermore, the increased yield can be attributed to  chitosan’s plant growth-promoting activity may be  directly related to its effects on plant physiological  mechanisms such as nutrient uptake, cell division, cell  elongation, enzyme activation, and protein synthesis  (Amin et al., 2007). In addition, Chissan improved the  photosynthetic index by improving stomatal function  and chlorophyll content, and also significantly  increased crop yield. Polycationic chitosan increases  the osmotic pressure of stomatal cells, resulting in  increased stomatal opening and CO2 uptake  (Chakraborty et al., 2020). 

On other hand, soil-applied chitosan also significantly  enhanced seedling growth and induced early  flowering in many ornamental plants (Pichyangkura  and Chadchawan, 2015). Similarly, Xu and Mou (2018)   found that applying chitosan to soil increased lettuce  leaf number, area, fresh weight, dry weight, and  chlorophyll index. Suppression of plant diseases,  insects and nematodes, increased biomass and  beneficial microbial activity, high nitrogen and  calcium content, improved soil physical structure and  nutrient availability, direct stimulation of plant growth  the synergistic effect of many factors, may play a role  derived from chitosan as a soil conditioner. 

Furthermore, addition of chitosan alters rhizosphere  conditions, shifting the microbial balance in favor of  beneficial organisms and against plant pathogens  (Sharp, 2013). Chitosan provides a carbon source for  soil microorganisms, promotes the conversion of  organic matter to inorganic matter, and helps roots to  absorb more nutrients from the soil (Xu and Mou,  2018). 

Chitosan and all other chitin derivatives have a high  nitrogen content of 6% to 9%. Plants can access  nitrogen in chitin through microbial degradation and  release of inorganic nitrogen, or by direct uptake of  monomers as organic nitrogen (Roberts and Jones,  2012). Chitosan can be used to add organic matter to  soil without increasing the carbon-to-nitrogen ratio. In  addition to nitrogen, chitosan also contains large  amounts of calcium minerals that provide structural  strength to crustacean exoskeletons (Boßelmann et  al., 2007). Although chitosan contains nitrogen and  calcium, its beneficial effects on plant growth and  yield are not due to that nutrient alone, and some  studies have shown that the control plots treated with  mineral fertilizers have been shown to contain  chitosan nutrients was balanced. 

Chitosan significantly enhanced the seedling growth  of several plants compared to conventional mineral  fertilizers. Due to its cationic properties, chitosan is  also suitable as a vehicle to provide additional  essential nutrients (Sharp, 2013). Hydroxyl and amino  functional groups on deacetylated chitosan allow the  formation of coordination compounds with ions such  as copper, zinc, iron, but not alkali metals (e.g.  potassium) or alkaline earth metals (e.g. calcium or  magnesium) is not possible (Ramírez et al., 2010). For  this reason, chitosan is a sustainable alternative to  synthetic chelators such as ethylenediaminetetra acetic acid, which are routinely used to supply iron  and other nutrients to overcome their low solubility in  calcareous/neutral soils. It has become a viable  alternative (Strawn et al., 2019). Due to its high  molecular weight and porous structure, chitosan forms a gel that absorbs large amounts of water and  enhances the water-holding capacity of soil  (Jamnongkan and Kaewpirom, 2010). 

Application of chitosan to soil increased levels of  nitrogen, phosphorus, potassium, total sugars, soluble  protein and total amino acids (Farouk et al., 2011).  Chitosan application to soil has been reported to  increase chlorophyll content in leaves of many crops  (Farouk et al., 2011; Sheikha and Al-Malki, 2011). As a  bio-stimulant, chitosan may also enhance the  fluorescence of chlorophyll and enhance the  photosynthetic rate. 

Furthermore, the use of chitosan as a bio-stimulator  in plant development can increase leaf and shoot size.  Chitosan has been found to exert molecular effects on  flowers, directly affecting growth and physiological  parameters (Salachna and Zawadzińska, 2014). 

CONCLUSION 

From this investigation indicated that application  chitosan by high concentration started by 200 ppm  have a positive role for increasing and enhancing all  tested parameters of okra plants such as (vegetative  growth, chemical contents in leaves, yield and fruits  quality. On other hand, the suitable concentration  depending on method applies of chitosan. The greatest values of almost i.e., vegetative growth,  chemical contents in leaves, yield and best fruits  quality parameters were obtained with applied 80%  recommended doses from chemical fertilizer +  chitosan adding to soil 250 ppm “T10” and 80%  recommended doses from chemical fertilizer +  chitosan spray 300 ppm “T6” treatments, without any  significant differences followed by 80% recommended  doses from chemical fertilizer + chitosan adding to soil  300 ppm “T11”, 80% recommended doses from  chemical fertilizer + chitosan adding to soil 200 ppm  “T9”, 80% recommended doses from chemical  fertilizer + chitosan spray 250 ppm “T5” and 80%  recommended doses from chemical fertilizer +  chitosan spray 200 ppm “T4” treatments, respectively.  More that, control treatment (100% Recommended  doses from chemical fertilizer (control treatment)  “T1”) placed the six place.  

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