Field experiments on Kenaf were carried out in 2020 and repeated during the 2021 cropping season at the Manga Station (11˚01'N, 0˚16'W)) of the Savannah Agricultural Research Institute of the Council for Scientific and Industrial Research (CSIR-SARI), Bawku of the Upper East Region (UER) of Ghana. The region lies in the Sudan savanna agro-ecological zone, which forms the semiarid part of Ghana. The area is part of what is sometimes referred to as the interior savanna and is characterized by level to gently undulating topography. Important crops cultivated here include millet, sorghum, maize, rice, sweet potato, groundnut, cowpea, soybean, cotton onion and tomato. The shea nut tree grows wild and it is an important cash crop. It has alternating wet and dry seasons with the wet season occurring between May and October during which about 95% of rainfall occurs. Maximum rainfall occurs in August, and severe dry conditions exist between November and April each year. Annual rainfall ranges from 800 - 1200 mm. There is wide fluctuation in relative humidity with values as low as 30% in dry season and above 75% in the wet season.

In each year, the experimental area was first ploughed, harrowed and ridged using bullock-drawn implements. Lining and pegging were done to establish the plots for the treatments. The treatments consisted of 3 × 5 factorial combinations of three planting dates (1^st July, 7^th July and 14^th July) and five levels of N (0, 20, 40, 60 and 80 kg/ha) replicated three times. Plot size of 22.5 m² (5 m × 4.5 m) was used for each treatment. The design of the experiment was a split-plot with the N fertilizer as the main plot and the planting date assigned to sub plot. The ridges were separated by a distance of 1 m. Planting in the experimental field was done manually based on the proposed treatments on the same day. The seeds were planted manually at a depth of 3 - 5 cm. Three seeds per hill were sown at an intra-row spacing of 50 cm inter-row spacing of 75 cm. The three seeds per hill were later thinned to one plant per stand at the first weeding two weeks after sowing. Forty-five (45) kg P₂O₅/ha as single super-phosphate was applied as basal dose at the time of plot layout. Weeding was done manually at 2 & 6 weeks after sowing (WAS) using hand hoe. The plot with zero level of nitrogen was used as a control treatment.

The soil characteristics were determined in order to know nutrients status of the experimental site before application of the fertilizers. At the beginning of the experiment (in 2020), 15 samples were randomly collected by using an auger and composited. Then, soil samples were also taken from each treatment at harvesting (in 2021). The samples were air dried, crushed with mortar and sieved to pass through 2 mm mesh. The characteristics analyzed for included; Soil pH, Organic matter, Total Nitrogen, Exchangeable Calcium, Magnesium, Potassium, Sodium and Effective Cation Exchange Capacity, and Bray NO.2 Extractable Phosphorus and Potassium. The air-dried soil samples were ground at the laboratory and sieved through a 2 mm sieve. Soil pH was determined using a glass electrode (pH meter) in a soil ratio of 1:2.5 as reported by [20] IITA (1979) and [21] Mclean (1982). Soil organic matter was determined by the wet combustion method [22] (Walkey and Black, 1934). Percentage total nitrogen was determined by the micro Kjeldahl-technique [20] (IITA, 1979). The available phosphorus was extracted by the Bray method and determined colorimetrically [23] (Bray and Kurtz 1945). Potassium was determined by flame emission photometry [20] (IITA, 1979). The exchangeable cations calcium, magnesium, potassium and sodium were determined as recommended by [20] IITA (1979) using EDTA Titration after extraction with 0.1 N Ammonium Acetate at pH 7. Effective Cation Exchange Capacity (ECEC) was calculated as the sum of the exchangeable bases and exchangeable acidity [20] (IITA, 1979).

The mineral fertilizer was applied two weeks after planting and by side placement using Urea (46% N) and Triple Super Phosphate (45% P₂O₅) as mineral sources. Half of the N and the whole P fertilizer rate was applied 2 weeks after planting; and the remaining half of the N dose was applied during the first earthing up as side dressing. Lime (CaO: 0.5 t/ha), Muriate of Potash (60% K₂O) and 20 kg/ha MgSO₄ were broadcast and worked into the soil two weeks before planting. This was necessary for timely mineralization for adequate uptake of the nutrients by the plants. Weeds were managed by hoeing and hand picking.

At harvest, two 3-meter rows were harvested by hand in each plot. The number of plants (stand density) and the wet weight were determined on those two rows for each harvest. Ten random individual stems from each plot were selected and subjected to morphological, and physical analyses. Plant density, Stem height at maturity and diameter at half height were measured. The mean over these 10 plants per plot was then recorded. The 10 stems were then combined into one sample to represent the plot, stripped by hand, and separated into bast and core yields. To obtain dry bast and dry core yields, the wet bast and core yields were weighed, oven-dried at 60˚C until constant weights were attained.

Data collected were analyzed statistically using GenStat 12^th Edition. Mean separation for significant effects was performed using least significant difference at 5% probability level.

In both years, the effects of planting date (D) and nitrogen application (N) were significant (P < 0.01) while D × N interaction effects were not significant (P > 0.05) for plant density, stem height, stem diameter, dry bast yield and dry core yield.

Planting date and Nitrogen application significantly (P < 0.05) affected plant density in both cropping seasons (Table 2). In 2020, plant density ranged from

@SRI: Soil Research Institute of Ghana.

** = significant at 1%, Ns = Not significant. Means in a column followed by the same letter(s) do not differ significantly at 5% level of significance using LSD.

15 (at 14^th July) to 30 (at 1^st July) and also ranged from 12 (at 0 Nkg/ha) to 26 (at 60 Nkg/ha) beyond which there was no further increase. In 2021, it ranged from 16 (at 14^th July) to 28 (at 1^st July). Thus, plant density was greater when kenaf was planted in early July. As plant density represents the number of plants that were recorded at harvest, the plant density can be linked to the plants that have fully emerged and survived. Therefore, according to these results, most of the seeds germinated and survived better when kenaf was planted in early July. The dependence of stand density on planting date in this study did not confirm what was observed previously by [24] (Webber and Bledsoe, 2002) who reported that kenaf plants fully emerged and survived at the middle of the season rather than the early stages of the season.

The N application effects showed that the plant density generally increased with increased application rates. Increased application rates of Nitrogen from zero to 60 kg/ha increased plant density by 57% in (2020) and 63% (in 2021) over the control. The reason for this trend could be the availability of nutrients to the crop resulting in increased photosynthetic and metabolic activities. In addition, the trend could be due to stimulation of root growth and development resulting from adequate N supply as well as the uptake of other nutrients [25] (Ansa (2015). This could be due to the function of N in promoting plant growth and survival which appears to be more enhanced with the N fertilizer application. This observation is consistent with reports by [26] (Sharma et al., 2014) who reported that plant growth increased with increasing fertilizer levels of nitrogen. In their study, [27] Banerjee et al. (2016) found that adequate nitrogen had significant effect on plant growth and yield.

Planting date and Nitrogen application significantly (P < 0.05) affected stem height in both cropping seasons (Table 3). In 2020, stem height ranged from 2.23 m (at 14^th July) to 3.23 m (at 1^st July) and also ranged from 2.22 m (at 20 Nkg/ha) to 3.67 m (at 60 Nkg/ha) beyond which there was no further increase. In 2021 it ranged from 2.20 m (at 14^th July) to 3.15 m (at 1^st July) and also ranged from 2.32 m (at 20 Nkg/ha) to 3.57 m (at 60 Nkg/ha) beyond which there was decline in stem height. Thus, stem height which is an indicator for fibre yield declined as planting date advanced from 1^st to 14^th July. The results show that in both cropping seasons, kenaf planted in early July were taller than those sown later in the month. Thus, planting kenaf in early July or N fertilization at the rate of 60 kg/ha increased stem height. This could be due to the fact that the growing season became shorter as the planting date advanced which would give less time to the plants to reach high heights. This result is at variance with the views of [28] Berger (1969) who reported that stalk height was not significantly affected by planting date.

As with plant density, the N application effects showed that the plant height generally increased with increased application rates in both seasons. Increased application rates of Nitrogen from zero to 60 kg/ha increased plant height by

** = significant at 1%, ns = Not significant. Means in a column followed by the same letter(s) do not differ significantly at 5% level of significance using LSD.

40% in (2020) and 35% (in 2021) over the control. The reason for this trend could be the availability of nutrients to the crop resulting in increased photosynthetic and metabolic activities. In addition, the trend could be due to stimulation of root growth and development resulting from adequate N supply as well as the uptake of other nutrients [25] (Ansa (2015). This could be due to the function of N in promoting vegetative growth which appears to be more enhanced with the N fertilizer application. This observation is in line with that of [29] Ullah et al. (2017) who reported that plant height increased with increasing levels of nitrogen.

Planting date and Nitrogen application significantly (P < 0.05) affected stem diameter in both cropping seasons (Table 4). In 2020, stem diameter ranged from 21.22 mm (at 14^th July) to 25.20 mm (at 1^st July) and also ranged from 21.20 mm (at 20 Nkg/ha) to 26.10 mm (at 60 Nkg/ha) beyond which it declined. In 2021 it ranged from 21.2 mm (at 7^th July) to 24.20 mm (at 1^st July) and also ranged from 21.30 mm (at 20 Nkg/ha) to 25.20 mm (at 60 Nkg/ha) beyond which it declined. Thus, planting kenaf in early July or N fertilization at 60 kg/ha increased stem diameter. These results confirm the positive effect of management

** = significant at 1%, ns = Not significant. Means in a column followed by the same letter(s) do not differ significantly at 5% level of significance using LSD.

practices such as timely planting and adequate N application on yield of kenaf productivity [8] (Hossain et al., 2011). In addition, all fiber morphological properties were also significantly improved when fertilizers were added, which was strongly supported by previous study by [30] (Salih et al., 2014).

From the above observations, timely planting of kenaf (in early July) or N fertilization at the rate of 60 kg/ha increased plant density, stem height and stem diameter. These traits increased with increased N rates in both cropping seasons, indicating that either the crop was efficient in its capture and use of fertilizer N or the soils were low in plant available nutrients or both. In the environments where these studies were carried out, the soils were low in plant available nutrients with average pH of 5.50. [31] Adamtey et al. (2016) reported low maize yields for soils that received no fertilizer and attributed it to reduced plant growth as a consequence of low levels of nutrients, particularly N supply and uptake. This could be applicable to kenaf as well.

The results of growth parameters were not consistent with reports by other researchers, who reported significant (P ≤ 0.01) interaction between the planting date and N rate in kenaf plant diameter and plant height (Al-Mamun et al., 2022).

Planting date and Nitrogen application significantly (P < 0.05) affected dry bast yield in both cropping seasons (Table 5). In 2020, dry bast yield ranged from 12.80 t/ha (at 14^th July) to 15.10 t/ha (at 1^st July) and also ranged from 11.10 t/ha (at 0 Nkg/ha) to 16.10 t/ha (at 60 Nkg/ha) beyond which it declined. In 2021 it ranged from 13.10 t/ha (at 14^th July) to 15.80 t/ha (at 1^st July) and also ranged from 12.10 t/ha (at 20 Nkg/ha) to 15.90 t/ha (at 60 Nkg/ha) beyond which it declined. Thus, planting kenaf in early July or N fertilization at the rate of 60 kg/ha increased dry bast yield. The increased dry bast from early planting could be as a result of the fact that, as the season advanced, kenaf had shorter period to grow and develop thick stems than when kenaf was planted earlier. On the other hand, the increased dry bast from 60 Nkg/ha application rate suggests that this rate was adequate for improved kenaf bast and fibre yield. [27] Banerjee et al. (2016) reported that optimal level of nitrogen had significant effect on plant growth, yield, and fiber quality. [29] Abd Eldaiem & El-Borhamy (2015) reported that yield and quality properties were improved by applying the adequate level of N, which was one of the favorable factors for increasing kenaf productivity.

** = significant at 1%, ns = Not significant. Means in a column followed by the same letter(s) do not differ significantly at 5% level of significance using LSD.

Similar to the dry bast yield, planting date and Nitrogen application significantly (P < 0.05) affected dry core yield in both cropping seasons (Table 6). In 2020, dry core yield ranged from 34.40 t/ha (at 14^th July) to 40.10 t/ha (at 1^st July) and also ranged from 33.20 t/ha (at 0 Nkg/ha) to 39.90 t/ha (at 60 Nkg/ha) beyond which it declined. Similarly, in 2021 it ranged from 35.20 t/ha (at 14^th July) to 39.70 t/ha (at 1^st July) and also ranged from 32.20 t/ha (at 0 Nkg/ha) to 41.10 t/ha (at 60 Nkg/ha) beyond which it declined. Thus, timely planting of kenaf (1^st July) or N fertilization at the rate of 60 kg/ha increased dry core yield. The increased dry core from early planting could be due to the fact that, kenaf had shorter period to grow and develop thick xylem than when kenaf was planted earlier

Planting could not be done earlier than 1^st July as a result of delay in the onset of rain and the results indicated that kenaf sown in mid-July has lower dry bast and core yields. This may be connected to unfavourable climatic condition [32] (Fernado et al., 2004) which could suppress kenaf development and yield. This study revealed that early July is most appropriate for kenaf planting for dry bast and core yields in the study area. This agrees with the report of [33] Alexopoulou et al. (2015), who reported that early sowing favoured growth and fibre yield

** = significant at 1%, ns = Not significant. Means in a column followed by the same letter(s) do not differ significantly at 5% level of significance using LSD.

of kenaf than late planting except with irrigation. Thus, sowing date has a direct effect on the growth and yields of kenaf. The observation that dry core yield started declining after 60 Nkg/ha suggests that the 60 Nkg/ha was the adequate application rate for kenaf dry core yield. This is in line with reports by [30] Salih et al., 2014 that all fiber morphological properties were significantly improved when adequate rates of fertilizers were added.