The soil used in the experiment belongs to the “Pirojpur series”. Soil samples were collected from the agricultural field behind the Khulna University in Khulna district, Bangladesh. The soil sample was collected from surface (0 - 15 cm) on the basis of composite sampling method as suggested by the soil survey staff of the USDA (1951). The location of sampling area was 22˚48.302N and 89˚31.962E. According to Reconnaissance soil survey report [14] , the Pirojpur series comprises seasonally shallowly to deeply flooded, poor drained soils, developed in tidal clay deposits. They have dark non-calcareous silty clay to clay subsoil with strong prismatic and blocky structure with dark grey cutans along ped faces overlying buried peat or muck within a depth of 4 feet [15] . This soil could therefore be successfully used to study the changes in the growth and yield of Ipomoea aquatica as influenced by different levels of coconut peat treatments. General information of the experimental soil was shown in Table A1.

The collected soil samples were air dried ground and screened to pass through a 2.0 mm sieve and then mixed thoroughly to make it a composite sample. Dry roots, grasses and other vegetative residual parts were discarded from the soil. One kg of composite sample was kept in a plastic container for physical and chemical analysis. Three (3) kg of air-dried composite soil samples were taken in each of the earthen pots and used in this experiment, had no pore in the bottom to protect leaching of coconut peat from the soil. In addition, soil moisture was maintained at field capacity as required and room temperature was maintained in the pots.

Coconut peat was collected from coconut peat production site, Rampal Upazila under Khulna district in Bangladesh. Coconut peat was applied at the different rates such as 1000 kg coconut peat ha⁻¹, 1500 kg coconut peat ha⁻¹, 2000 kg coconut peat ha⁻¹, 2500 kg coconut peat ha⁻¹ and 0 kg coconut peat ha⁻¹ (Control). Coconut peat was applied by broadcasting worked into the experimental pots. In order to provide enough time to decompose the coconut peat, they were applied to the soil before the seed was sowed.

The effect of coconut peat in the environment and its impact on the growth and yield of a selected leafy vegetable Water spinach (Ipomoea aquatica) was used as the test crop for the experiment. This particular variety has gained popularity among the farmers of the study area for their high yielding potential and can be grown throughout the year and harvested in a short time within one month [16] .

The experiment was laid to fit a completely randomized design (CRD) [17] with five treatments, each having three replications. Three (3) kg supplied soil sample was used in each earthen pot (15.5 cm × 9.5 cm) for this experiment.

Four different rates of decomposed coconut peat were used as treatments in the experiment and a control experiment was also conducted. Three replications were conducted for each treatment to avoid experimental error. The treatments are as follows:

T₀ = 0 kg coconut peat ha⁻¹ (Control),

T₁ = 1000 kg coconut peat ha⁻¹,

T₂ = 1500 kg coconut peat ha⁻¹,

T₃ = 2000 kg coconut peat ha⁻¹,

T₄ = 2500 kg coconut peat ha⁻¹.

The seeds were sown on 24^th May, 2017. The seeds were sown thoroughly as it was possible to keep uniformity and then the seeds were covered by soils. 0.01 g seeds (5 Kg ha⁻¹ as recommended by BARI, 2005) were sown in each pot and maximum seeds germinated within 7 days. After germination only five plants were kept in each pot.

The pots under experiment were frequently observed to note any change in the crop growth and other characteristics. The crop growth was very luxuriant in some pots and lower in some pots.

After 31 days plant was harvested manually by uprooting the plant carefully from the pot. Then the sampling plants were kept separately. Collected plant samples were carefully washed thoroughly with distilled water to remove soil particles and soaked by tissue paper to remove water. After taking fresh weight the plant samples were dried in the oven at 65˚C temperature for 48 hours until moisture content reached to a minimum level. The dried material of plants per pot from each treatment was recorded.

Different growth and yield parameters were recorded and their mean values were calculated from the sample plants during experiment. The number of leaves of five plants of each pot was counted and average value was considered. Shoot length was measured using a measuring scale from root level to the tip of the plant. From each pot five plants were measured and averaged. Root length was measured using a measuring scale from root level to the tip of the longest root at harvest and their average was taken as the root length in cm. Harvest of five plants from each pot, fresh weight of whole plant was taken by an electrical balance and their mean value was calculated as fresh weight expressed in gm plant⁻¹.

Five plants of each pot were collected and oven dried at 65˚C for 48 hours, weighed in gm plant⁻¹ by an electrical balance and average value was recorded.

Percent moisture was calculated by using the formula:

Moisture   content   ( % ) = W f − W o W f × 100

where,

W f = Fresh weight of the plant sample,

W o = Oven dry weight of the plant sample.

The collected data were compiled and tabulated in proper form and were subjected to statistical analysis. Standard deviation, Standard error, Analysis of variance (ANOVA) and Duncan Multiple Range Test (DMRT) were done for completely randomized design by using the SAS 6.12 software package [18] .

The effect of decomposed coconut peat on the growth and yield of water spinach (Ipomoea aquatic) was studied following the pots experiment. The number of leaves per plant, fresh weight per plant, dry weight per plant and percent moisture contents were measured for the plants treated with 1000 kg ha⁻¹, 1500 kg ha⁻¹, 2000 kg ha⁻¹ and 2500 kg ha⁻¹ of coconut peat were compared with plants growth and yield with 0 kg ha⁻¹ coconut peat which was control for this experiment. The results are presented in Table A2.

The result show that the number of leaves per plant ranged between 8.2 to 10.3 and the maximum number of leaves was counted in T₄ (10.3) and the lowest number of leaves was counted in T₀ (8.2) presented in the Figure 1. The control treatment gives minimum number of leaves per plant (8.2) showing statistically significant (P < 0.05) variation fromT₃ and T₄ and exception was found in T₁ and T₂ for the use of less coconut peat.

The increase in leaf number as well as size due to enough nutrition can be explained in terms of possible increase in nutrition absorption capacity of plant as a result of better root development and increase translocation of carbohydrates from source to continuous mineralization of organic manures such as coconut peat. The use of organic manure when properly applied, benefits fruiting in plants like maize and generally enhance size, height and number of leaf’s [19] . The maximum number of leaves per plant was obtained in T₄ (2500 kg coconut peat ha⁻¹) was probably due to high amount of coconut peat provided good soil condition for the growth and supplied sufficient plant nutrients.

Coconut peat had an insignificant influence in root length presented in the Figure 2. The longest root (6.9 cm) was produced by applying 2500 kg coconut peat ha⁻¹ (T₄) and the control treatments (T₀) produced shortest root length (5.56 cm). The result show that the different rates of coconut peat has statically insignificant level of effects on the root length of water spinach and magnitude of difference is at the order of T₄ > T₃ > T₂ > T₁ > T₀ (Figure 2).

According to the results, all treatments of coconut peat showed positives effect on root length of plants from eye observation and data from Table A2. Organic manure improved soil properties, finally, better root growth, better plant growth and biological yield. Development of mineral nutrients in the manure increased root growth, absorption and nutrients, ultimately leading to increase yield [20] . Its soft structure promotes easy root penetration and healthy growth.

The result shows that shoot length per plant ranged between 13.26 cm to 18 cm in applying different treatments and the maximum shoot length was obtained T₄ (18 cm) and minimum shoot length was in T₀ (13.26 cm) shown in the Figure 3. Results show that shoot length varied statistically insignificantly against control for test crop (Figure 3). According to the results, all treatments of coconut peat showed positive effect on stem height of plants on the basis of data from Table A2.

The positive effect of organic manure like shoot length could be due to the contribution made by manure to fertility status of the soils. Organic manure such as coconut peat play direct role in plant growth as a source of all necessary macro and micro nutrients in available forms during mineralization and improving physical and chemical properties of soils [21] . Babu et al. [22] observed that the plant height was significantly influenced by the incorporation of organic manures. The growth of shoots with increasing manure fertilizer could be due to microorganism activity in soil [23] .

The results show that the fresh weight per plant ranged between 1.48 gm to 2.32 gm and maximum fresh weight 2.32 gm per plant was measured in 2500 kg coco peat ha⁻¹ treated plants (T₄) and the lowest was measured 1.48 gm in control plants (T₀) on the basis of data from Table A2. Result shows that fresh weight per plant was found statistically (P < 0.05) significant variation against control for test crop (Figure 4). The result shows that the different treatments also have significant level on the effect on the receiving plants and magnitude of the difference is at the order of T₄ > T₃ > T₂ > T₁ > T₀ (Figure 4). Four different rates of coconut peat gave positive effect on fresh weight of plant in the present study. Role of organic manure in increasing yield of water spinach was attributed to supply of all essential nutrients due to continuous mineralization of organic manure. Manure acts as nutrient reservoir and upon decomposition produces organic acids, thereby absorbed ions are released slowly during entire growth period leading to higher yield components. Bardar et al. [24] reported the beneficial effects of organic manure on growth of cowpea plants. The increase in fresh weight has also been reported by Sarwar et al. [25] and Manivannan et al. [26] .

The results show that the dry weight per plant ranged between 0.2 gm to 0.31 gm

and the maximum dry weight 0.31 gm was obtained for applying 2500 kg coconut peat plant⁻¹ (T₄) and the minimum was measured 0.31 gm from control plats (T₀) on the basis of data from Table A2. Result shows that dry weight per plant varied statistically (P < 0.05) significantly against control for test crops (Figure 5). The results reveal that the application rate has a significant impact on the fresh weight of the plants. According to the results, all treatments of coconut peat showed positive effect on dry weight of plants. It is possible that increased application rate could be increased the fresh weight per plan. Adding manure in soil improve soil physical and biological conditions and create a more favorable environment for root growth and nutrients availability, increased plant growth and dry matter [20] [27] .

The results show that the moisture content (%) ranged between 85% to 86.57% and the maximum moisture content was 86.57% obtained for applying 0 Kg coconut peat ha⁻¹ (T₀) and the lowest was measured 85% for applying 1000 kg coconut peat ha⁻¹ in treatment (T₁) on the basis of data from Table A2. The results show that the different application rate has insignificant level of effect on receiving plants and magnitude of the difference is at the order of T₄ > T₃ > T₂ > T₀ > T₁ (Figure 6) on moisture content (%). However, the difference of moisture content (%) among treatments was statistically insignificant in most of the cases (Figure 6). The causes of variation may due to the nutrient availability of the plants.