The experiment was conducted at the Magbosi Land, Water and Environment Research Center (MLWERC) experimental site of the Sierra Leone Agricultural Research Institute (SLARI). MLWERC is located at Yoni Mabanta Chiefdom, Tonkolili District in the North-Eastern Province of Sierra Leone on latitude 80˚ 28' 17.88'' N and longitude 120˚ 14' 33.02'' W. The climatic condition experienced in the study area is not too different from the rest of the country with two distinct seasons, the rainy season (May-October) and the dry season (November-April). The ecology in this area is mainly grassland savanna mostly covered with grasses like Andropogon species, Pennisetum species, etc., and shrubs like Lophira. The soils are mostly sandy loam in texture, porous and black. The bulk density and cation exchange capacity are also low in this region. As the soil is porous, the water holding capacity is very low in this region. Soils of the savanna grassland area are mostly Alfisols and Ultisols. These soils are very old and low in fertility and very porous with rapid drainage of water.

A split-plot arrangement in a randomized complete block design with three replicates was used. Planting dates were assigned to the main plots and genotypes to the sub-plots. The total area for the trial was 36 m × 21 m and each sub-plot was 4.5 m². Each sub-plot was separated by 0.5 m and 1 m spacing between replicates. A total of 8 sub-plots per replication were planted and the whole trial had 24 plots.

The experimental area was cleared and plowed using a hand hoe. Two local groundnut genotypes (Senegal and Bandugu) were cultivated. The two genotypes were planted at four (4) dates with fourteen days intervals from 8^th May to 19^th June 2021 for the first planting season and from 14^th August to 20^th September 2021 for the second planting season.

The genotypes were sown at 20 cm between plants in a row and 30 cm between rows. No fertilizer was applied. Weeding was done 1 month after planting and as and when necessary. Harvesting was done when pods were physiologically matured that is when 80% of the inside of the pods shell have dark markings and kernels are plump with colour characteristics of that variety.

Sketch of the experimental design

P-Planting date (4), V-Variety (2).

Assessment of the rainfall and temperature regimes over the experimental site: Both the watchdog and the rain gauge were used to collect data on rainfall, relative humidity and temperatures. Data from the watchdog were collected every month and the rainfall data was collected daily at the end of any rainfall till the end of the experiment.

Plant height was measured with a meter rule on 4 plants of each plot. Height was measured from ground level to the topmost leaf axil of the main stem and the mean height was expressed in centimetres. Number of leaflets per plant-was determined by counting the number of leaflets on 4 plants at five stages and mean recorded. Fresh groundnut biomass (FGB) and Dry groundnut biomass were measured from 4 plants randomly harvested for each treatment by destructive sampling at 1, 2 and 3 months after planting. For Dry groundnut biomass, plants were dried in an oven for 2 days and the dry weight were measured using an electronic weighing balance. Mean dry weight per plant was recorded in grams. Fresh and Dry pod weight (FPW) were measured from 4 plants randomly harvested for each treatment by destructive sampling at 1, 2 and 3 months after planting. The pods were plucked from the groundnut plants immediately after harvest. Weights were measured using an electronic weighing balance. Pod yield (kg /ha) was calculated by using the formula.

$\text{Pod yield}\left(\text{kg}/\text{ha}\right)=\frac{\text{Pod weight}\left(\text{kg}\right)}{\text{Harvested area}\left({\text{m}}^{\text{2}}\right)}\times {\text{10000 m}}^{\text{2}}$

The total rainfall distribution for the growing period of 2021 during the experimental periods is shown in Table 1 . The total amount of rainfall recorded in the first cropping season 1356 mm was 46% higher than in the second cropping season (732 mm). August recorded the highest amount of rainfall (450 mm) followed by July (409 mm) in the first cropping season. Conversely, August and July months recorded the lowest evapotranspiration (61 mm and 62.3 mm respectively). The total evapotranspiration rate for the first cropping season was 280 mm and the second cropping season was 273.1 mm.

Air temperatures ranged between 22.3˚C to 34.3˚C in the first cropping season and from 22.4˚C to 33.5˚C in the second cropping season. Relative humidity was between 90% to 92% in the first cropping season and 67 and 75% in the second cropping season.

The results of the soil analysis of the experimental site are presented in Table 2 . The results showed that the 0 - 20 cm depth had a sandy - loam soil type whilst the 20 - 40 cm depth had a sandy - clay loam soil type. Organic carbon, total Nitrogen, total Phosphorus, exchangeable Ca, Mg, electrical conductivity, and exchangeable acidity were higher in the 0 - 20 cm soil depth than the 20 - 40 cm soil depth. Organic carbon percent is low (1.4%) in the topsoil of the experimental site. Generally, the soil can be described as acidic with pH ranging from 4.9 to 5.3.

Table 2. The initial physical and chemical properties of the experimental soil in 2021.

The results of the present study showed that highly significant differences (p < 0.001) were observed in fresh and dry groundnut biomass during the first cropping season due to planting date. The 22^nd May planting date had significantly higher fresh and dry groundnut biomass than the other planting dates ( Table 3 ). Variety did not influence the fresh and dry groundnut biomass as no significant difference (p > 0.05) was obtained from the analysis. The interaction between planting date and variety was also statistically not significant (p > 0.05).

The results from the analysis revealed that highly significant (p < 0.001) were observed in fresh and dry groundnut biomass. The August 28^th planting date significantly had higher fresh and dry groundnut biomasses after harvest (1.07 and 0.76 kg) respectively. The lowest fresh and dry groundnut biomass were recorded from the 28^th of September planting time. ( Table 4 ). The Senegal groundnut variety had higher fresh and dry groundnut biomass than the Bandugu variety.

Results obtained from the combined analysis of first and second cropping seasons indicate that the mean number of pods was higher in the first cropping season (125.6) than the second cropping season. Planting in the second season decreased number of pods by 26%. Yield components such as the number of pods per plants, pod yield per hectare were significantly affected by the planting dates in the two seasons indicating that environmental conditions are essential for yield of groundnut. Where such environmental conditions such as temperature and rainfalls are favorable yield is increased, as such planting dates must target such favorable periods for optimum yield.

Combined analysis of the two seasons showed that the yield produced was significantly affected by the season (p < 0.001), planting date (p = 0.013) and planting date interaction with season (p = 0.003). The first season cropping significantly had higher yield (48.5%) than the second planting. These results are consistent with those of [12] who reported seasonal differences significantly affected crop phenology, growth, and productivity of groundnut cultivars. This was attributed to early and normal planting dates allowed a long growth period and plants been exposed to suitable temperature regimes during the vegetative and reproductive growth stages for the entire growing period. The results obtained from this study also confirmed earlier results from [13] who observed that May 20 and genotype ICGV-8623 produced the highest pod and seed yield in Ghana. Similar results were reported by [14] also found first season planting of groundnut in Bimodal rainy season in Kumasi, Ghana had significantly higher yield than second season planting. This can be attributed to the uniform and higher rainfall experienced during the first cropping season (1356 mm) ( Table 5 ).

Mean Yield (t/ha) of groundnut genotypes as affected by different planting dates

From the results of the analysis of variance, planting date significantly (p < 0.05) influenced yield. The 8^th May planting date recorded the highest yield (0.89 t/ha) followed by the 22^nd May planting date (0.77 t/ha). The lowest yield obtained was from the late planting on 19^th June ( Table 6 ). These results are in agreement with earlier results obtained by [15] . Senegal variety had a higher yield than Bandugu though the difference was not statistically significant. Previous results of [16] confirmed that early sowing of groundnut resulted in maximum yield and delay in sowing resulted in significant decline in pod yield due to decrease in vegetative cycle. The difference observed among the groundnut varieties regarding the number of pods/plants could largely be attributed to the genetic traits of the varieties ( Figure 1 ).

The results of the regression analysis showed that number of pods per plant in the groundnut varieties is strongly positive correlated with yield (R² = 0.92) at different planting dates during the first cropping season. This implies that 92% of the variation of yield is explained by number of pods in groundnut. The number of pods per plant strongly correlated with total yield ( Figure 2 ).