Analysis of Asparagus Africanus Vigor from Split-Plot Experimental Design

ABSTRACT

This research performed analysis on a four-year experiment on Asparagus africanus. The experimental design layout is a 4² splitplot design where both the whole and split plots had a single factor each at four different levels. The experiment was to determine if there is any significant difference in the mean vigor (weight) of A. africanus at four different years and cutting dates. The result from the analysis shows that year, cutting dates, and the interaction effect have significant effect on the vigor of harvested A. africanus at 5%. A post hoc test was performed using the least significant difference statistic and it was found that A. africanus cultivated in 2021 has the largest mean vigor compared to other cultivated years and cutting dates of 1^st and 15^{th, June produced the largest mean vigor. Also, it was found that the experiment was well managed and controlled but the split-plot designed experiment was not efficient enough.}

KEYWORDS

Asparagus africanus; Relative design efficiency; Split-plot design; Plant vigor

INTRODUCTION

Asparagus africanus Lam (Liliaceae) is a plant with many medicinal properties from the leaf and root extracts for treating ailments like malaria, lishmaniansis, bilharziasis, syphilis, and gonorrhoea [1], headache, backache, stomach pain, and for aiding child delivery [2], externally for the relief of pain, rheumatism and chronic gout [3], used as a diuretic, for sore throat and otitis [4]. Its analgesic and anti-inflammatory activities have been studied extensively confirming the plants potential dose-dependent analgesic and anti-inflammatory activities [5]. Many studies have been carried out on A. africanus to ascertain its medicinal potentials [6-11]. Asparagus africanus can be described as a perennial climbing vertical armed herb that can grow up to five feet tall or between 700 and 3800 m above sea level and it is widely distributed in tropical Africa at 1450m and 2900m altitude range. In Nigeria, it is traditionally called “Shekan bera” in Hausa language and “aluki” in Yoruba language. The objective of this study is to compare the vigor (weight) of harvested Asparagus Africanus for a period of four years at four different cutting dates.

MATERIALS AND METHODS

Most field (agronomic) experiments are large and the selection of an appropriate experimental unit may have some scope of resourcefulness. Division of the experimental materials into blocks in such a way that the plots within blocks are as homogeneous as possible, that is, block should remove as many trends in the material as possible is necessary [12]. In this research a 4² splitplot experiment with four blocks was designed to measure the vigor of A. africanus. The two factors considered in the experiment is plant year and harvested dates. Four different years (2018, 2019, 2020, and 2021) were considered as whole plot (WP) factor and the different cutting dates (1^st June 15^th June 1^st July and 15^th July) as subplot (SP) factor.

SPLIT-PLOT DESIGN MODEL

The split-plot design model (SPDM) is a linear additive superimposition of two different experimental design models and it is given below mathematically as follows:

Y_ijk=μ+γ_i+A_j+w_ij+B_{k+(AB)jk+εijk} (1)

be the linear SPDM with two factors A and B where, Y_ijk is the response variable (measured vigor); i = 1, ..., s block; j = 1, ..., a levels of the WP factor A (Year); k = 1, ..., b levels of the SP factor B (Cutting dates); w_ij is the WP error, and ε_ijk is the SP error; and (AB) is the interaction between the WP and SP factors (Year × Cutting dates). The parameters block, A and B are assumed fixed. Also, the WP error and SP error are independent identically distributed normal random effects, that is, and . A detailed theory of the SPDM with intrinsically linearity and nonlinearity in parameters can be found in [12-18].

EFFICIENCY AND CONTROL OF THE SPDM FOR A. AFRICANUS

Experimenters utilize the SPDM for certain specific reasons like applying one factor to the large area due to lack of optimal control of the experimental factor in smaller area or the inability to randomize one of the factors appropriately in smaller units or plots. Therefore, it is imperative to evaluate the relative efficiency of the SPDM to sub models like the randomized complete block design (RCBD) to ascertain the design gain efficiency. This is done to determine how much information have been gained or lost for all treatment comparisons. The efficiency statistic in [19] is given below as

where, Ef is the weighted average of whole plot and subplot mean square errors, is the mean square WP error, is the mean square SP error, a and b are the levels of the WP and SP factors respectively. The information on WP treatments from the split-plot experiment relative to RCBD is then and it is expected to be less than one. For SP factor and interaction effect from the split-plot experiment relative to RCBD is and it is expected to be greater than one. To determine how well the experiment was controlled and managed, the coefficient of variation (CVS) statistic is used, and a value less than 30 is expected from the experiment. The CVS is given as follows.

where, MSE is the mean square error of the SPDM, and GM is the grand mean from the data.

MEAN A. AFRICANUS VIGOR COMPARISON TEST

In this research, the least significant difference (LSD) mean comparison test is applied. However, it is valid if and only if the experimental factors are significant. Suppose following the analysis of variance test and there is a significant effect, it is worth to determine how large the mean vigor of A. africanus is at different years, cutting dates and years by cutting dates interaction. Each pair of mean A. africanus vigor difference is compared to the corresponding LSD value. The test is given as follows.

where, t is the t-test table value at 5% α significance level, dfE is the degree of freedom for error, and SED is the standard error of difference. The SED for the SPDM is given for the WP factor, SP factor and interaction effect as follows.

RESULTS AND DISCUSSION

The SPDM analysis was performed using SAS 9.4 and MSTATC for the mean comparison analysis. (Table 1) shows the analysis of variance table (ANOVA) for the SPDM with the CVS values. The results indicate that the WP factor, year (A), SP factor, cutting dates (B), and the interaction effect (A × B) are all significant at 5%. Also, the CVS values obtained for the WP and SP experimental units indicates that the experiment was well managed and controlled because both values of 8.19% and 10.79% are less than 30%. However, the efficiency statistic (Ef) values of 1.591 and 0.915 for the WP and SP respectively shows that the experiment is not efficient since the Ef value for the WP is greater than one and less than one for the SP. In line with the results obtained it can be said that there is significant difference Among A. africancus vigor (weight) in the four different years and at four different cutting dates. Likewise, there is a significant effect of years by cutting dates on the vigor of A. africanus. This result surely supports a posthoc analysis to determine which year and cutting dates have the largest mean vigor of A. africanus. (Table 2,3) presents the mean comparison results and Figure 1 shows the A. africanus vigor mean interaction plot.

The mean interaction plot in Figure 1 clearly shows that there exists an interaction effect between cutting dates and the four different planting years of A. africanus vigor.

Table 2 shows that A. africanus mean vigor from year 2020 has a significant larger mean than the means from year 2018, 2019, and 2021, therefore year 2020 has the maximum yield vigor of A. africanus. However, for cutting dates, Table 2 shows that 1^st June has the largest mean vigor of A. africanus but its mean is not significantly larger than A. africanus mean vigor at 15^th June but the mean vigor at the cutting date of 15^th June is not significantly larger than the mean vigor of A. africanus at 1^st July while the mean vigor of A. africanus at the cutting date of 15^th July has the lowest mean compared to all other cutting dates.

Table 3 shows that at 1^st and 15^th June of year 2020 produced the largest means vigor of A. africanus of 499 and 484.75 respectively. These two means are not significantly larger than each other (both ranked a) but the two-mean vigor of A. africanus at 1^st and 15^th June cutting dates at year 2020 are significantly larger than all other mean vigor of A. africanus. 15^th July cutting date for year 2021 has the lowest mean vigor but not significantly different from the mean vigor at year 2018. Hence, it can be concluded that 1^st and 15^th June cutting dates at year 2020 produced the maximum mean vigor of A. africanus.

CONCLUSION

In this research four different year effect and four different cutting dates effect on Asparagus africanus from a split-plot experiment was studied. It was found that both the WP and SP factors were significant to A. africanus vigor and as well the interaction effect between the plant year and cutting dates. The experiment for measuring the A. africanus vigor was found to be well managed and controlled based on the results from the coefficient of variation but the SPDM for the experiment was found not to be efficient based on the efficiency statistic results. Also, the mean vigor analysis using LSD clearly shows that A. africanus planted in 2021 had the highest mean vigor while on 1^st June and 15^th June cutting dates produced A. africanus with the largest mean vigor compared to 1^st and 15^th July cutting dates.

AUTHORS CONTRIBUTION

Both authors contributed equally towards the drafting of the topic, analysis of the data, and the writing of the manuscript.

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