EFFECTS OF GUANO MANURE ON HEIGHT GROWTH AND FOLIAR NUTRIENT CONCENTRATIONS OF SELASIH ( OCIMUM TENUIFLORUM L.)

ABSTRACT


INTRODUCTION
Herbal medicine is the oldest form of healthcare known to mankind. It is sometimes referred to as Herbalism or Botanical Medicine. It is the use of herbs for their therapeutic or medicinal value. Herb is a plant or plant part valued for its medicinal, aromatic or savoury qualities. Herbal plants produce and contain a variety of chemical substances that act upon human body. The World Health Organization (WHO) estimates that 80% of the world population used herbs for their primary health needs (WHO, 2019). Therefore, major pharmaceutical companies are currently conducting extensive research on plant materials gathered from the rain forests and other places for their potential medicinal value. This may lead to over exploitation of this natural resources of medicinal plants in forest leading to extinction. Hence, to avoid the valuable herbs from extinction, it necessary to cultivate them.
One example of the medicinal plant is Selasih (Ocimum tenuiflorum L.). This plant is native to India and grown in the tropical and subtropical regions of the world. O. tenuiflorum prefers partial to full sunlight and thrives on well-drained soil rich in organic matter. It can be found growing along roadsides and in wastelands, as it can adapt well to its environment (Samy et al., 2005). O. tenuiflorum is an erect, hairy, branched, fragrant and an annual herb. It may attain a height of about 75 to 90 cm when mature. Its leaves are nearly round and up to 5 cm long with the margin being entire or toothed. They are aromatic because of the presence of a kind of scented oil in them. In Ayurveda (Indian traditional remedy), the leaves, flowers and occasionally the whole plant of O. tenuiflorum are used medicinally in the treatment of heart and blood diseases, asthma, bronchitis, and purulent discharges of the ear (John, 2001). The infusion of the leaves is given in malaria and as a stomachic in gastric diseases of children. Juice of the leaves could be taken internally and is very effective as a cure of skin diseases such as itches, ringworm, and in impurities of the blood.
On another aspect, plants need water, air, light, suitable temperature, and nutrients to grow. Plants get carbon, hydrogen and oxygen from the air and water while other nutrients are from the soil. Although some soils are naturally fertile, most need the addition of some form of fertilizer. A fertilizer is any material, organic or inorganic, natural or synthetic, that supplies plants with the necessary nutrients for plant growth for optimum yield . There are two major kinds of fertilizers mainly the organic and inorganic or chemical fertilizers. Organic fertilizers are natural materials of either plant or animal origin, including livestock manure, green manures, crop residues, household waste, compost, and woodland litter. On the other hand, inorganic or mineral fertilizers are fertilizers mined from mineral deposits with little processing such as lime, potash, or phosphate rock, or industrially manufactured through chemical processes such as urea. A study on the nutrient uptake of plants could be done by conducting soil testing and leaf diagnosis. Soil testing has the advantage of being able to measure the level of nutrients available in the soil, and the extent to which these will be available to the crop during the growing period. The leaf diagnosis on the other hand indicated nutrient status of the plant at particular time of sampling.
The international market for herbal medicines has an immense impact on the populations of medicinal plant species and their habitats. As demand for herbs, phytotherapies, and naturally derived pharmaceuticals products increases, it can often lead to over-harvesting of desired medicinal plant species. Therefore, preventive steps must be taken to ensure the availability and existence of particular herbs and other medicinal plants. Thereby, the present study was conducted as an attempt to get basic knowledge about the suitable rate of organic fertilizer which must be applied to enhance growth and foliar nutrient concentrations of the medicinal plant. Specifically, the present study aimed to determine the effects of different rates of guano manure organic fertilizer on height growth and selected foliar nutrients of Selasih (Ocimum tenuiflorum L.) and soil nutrient concentrations before planting and at harvest.

Experimental Design and Treatments
The pot-trial experiment was conducted under net house conditions using a Completely Randomize Design (CRD). The herb (Selasih) O. tenuiflorum was grown in the polybag using mixed soil. Plant cuttings of about 3 months old were used with 1 plant cutting grown per polybag. The polybags were arranged randomly. A total number of 50 experimental units consisted of 10 levels of treatments with 5 replications were involved. The organic fertilizer used was guano manure. Treatments applied were a mixture of guano manure with mixed soil by volume basis (Table 1). Treatments arrangements were as shown in Table 2. 10% of guano manure mixed with 90% of soil T2 20% of guano manure mixed with 80% of soil T3 30% of guano manure mixed with 70% of soil T4 40% of guano manure mixed with 60% of soil T5 50% of guano manure mixed with 50% of soil T6 60% of guano manure mixed with 40% of soil T7 70% of guano manure mixed with 30% of soil T8 80% of guano manure mixed with 20% of soil T9 90% of guano manure mixed with 10% of soil T10 (Control) Soil without guano manure

Data Collection and Statistical Analysis
Plant height of each treatment was recorded at the end of the experiment (four months after planting). Foliar nutrient concentrations after harvest and nutrient concentrations in the soil before planting and after harvest and soil pH were also analysed and recorded. Soil total N was determined using Kjeldahl method while total P was determined using Aqua regia method. The exchangeable K, Ca, Mg, Zn, Cu, and Na were extracted using double acid method and their concentrations determined using atomic absorption spectrophotometry (AAS). Dry ashing method was used for the determination of P, K, Ca, Mg, Zn, Cu, and Na concentrations in plant leaves. All data were analysed using the analysis of variance (ANOVA) at p≤ 0.05 followed by the mean comparison analysis of Duncan multiple range test (DMRT) using the Statistical Analysis System (SAS) software.

Effects of Guano Manure on Plant Height
Plant height is the actual measurement of plant from the soil surface to the tip of the tallest panicle or shoot. It could be one of the visual indicators of plant growth rate. As shown in Table 3, there were significant differences at p≤0.05 among treatments with T3 recorded the highest height at 76.50 cm while T9 recorded the lowest height at 50.60 cm. The T3 thus appeared to be the optimum guano level for plant growth. A group researchers stated that organic manure could result in significant effect on plant growth including plant height (Maheshbabu et al., 2007). According to some researcher's other factors such as nutrients availability and soil pH also influenced plant growth . In contrast, T9 showed the lowest plant height probably due to the toxic effect of over fertilization since T9 consist of a mixture of 90% guano manure with only 10% of soil. As stated by plants need all nutrients in sufficient amounts for optimum growth but too much of some nutrients can cause negative effects on plant growth (White and Brown, 2010).

The Soil Nutrient Concentrations Before Planting and at Harvest
Nutrient concentrations of total N, total P, exchangeable K, Ca, Mg, Zn and Ca were significantly different at p≤0.05 between treatments except for exchangeable Cu (Table 4). In the case of total N in the soil before planting, T8 showed the highest concentration (0.15%) while T3 recorded the lowest value at 0.08%. On the other hand, T9 showed the highest value of exchangeable Ca at 0.77% while the lowest was T10 at 0.17%. For exchangeable Mg, T6 recorded the highest value at 490.40 ppm while T8 recorded the lowest value at 160.80 ppm. The highest value of exchangeable Zn in the soil before planting was recorded in T2 (113.07 ppm) while the lowest was in T9 (5.60 ppm). There was no significant difference in the concentrations of exchangeable Cu in the soil before planting. The exchangeable Na showed significant difference among treatments with the highest value was T1 at 232.53 ppm while the lowest was T9 at 124.80 ppm.
In the case of total N in the soil after harvest (  Notes: Means within the same column with different letters are significantly different at p≤ 0.05 The total N concentrations in the soil before planting and after harvest were significantly different between treatments. T8 showed the highest value of total N in the soil before planting at 0.15% and also in the soil after harvest at 0.06%. Decreasing amounts of total N concentration in the soil before planting as compared to after harvest might be caused by factors such as nutrient uptake by plant, leached from soil or being used up by soil organisms. Dennis stated that the soil is the main source of nutrients for plants thus nutrient availability in the soil will decrease with time (Dennis, 2005). Other nutrients which showed the same trend before planting and after harvest are exchangeable K, Ca, Mg, Zn, Cu and Na. A group researchers stated that nutrient deficiency for plant uptake can occur as a consequence of inadequate supply of the nutrients and leaching losses (Roy et al., 2007). Other than that, the root is a plant organ that also responsible for nutrient uptake. The longer the root, the better the plant's ability to absorb nutrients due to wider range of coverage (Putra et al., 2020). However, total P concentration showed an opposite trend whereby P concentration in the soil after harvest was much higher compared to before planting. T9 showed the highest total P concentration in the soil after harvest at 3.70% while in the soil before planting, the concentration was only 0.63%. According to microbial activities could influence nutrient amount in the soil thus breakdown of organic residues with high amounts of phosphate will increase the amount of phosphorus in the soil (Dennis, 2005). However, microbial activity depends much on temperature and is the highest in the range of 30 to 45 0 C (Mengel et al., 2001).

Comparison of pH Values in Soil Before Planting and at Harvest
There were significant differences in soil pH before planting and at harvest. As shown in Table 5, soil pH increased with increasing levels of manure. Among treatments, T10 recorded the lowest pH value at 4.82 (KCl) and 6.47 (water) in the soil before planting, and 5.89 (KCl) and 6.77 (water) in the soil at harvest. This indicated that the control treatment (soil without manure) have higher acidic value. In contrast, T9 recorded the highest pH value at 7.55 (KCl) and 7.61 (water) in the soil before planting and 7.56 (KCl) and 7.61 (water) in the soil at harvest. In general, there was an increasing trend in soil pH as the level of guano manure increases. According to pH will increase with increasing rate of organic manure application (Salleh, 2015). Therefore, organic manure can be used to remediate problems of acidic soil as it will increase soil pH when being applied to the soil. However, soil pH from 6.50 to 7.00 provides the most suitable condition for optimum plant growth (Mengel et al., 2001). Hence, in the present study, T3 with soil pH at 7.00 recorded the highest plant height compared to the other treatments. Dennis stated that soil pH ranges near neutral pH is important to ensure proper plant growth because most essential elements reach near maximal availability and most plant toxic elements become unavailable in this pH range (Dennis, 2005).

Foliage Nutrient Concentrations at Harvest
As shown in Table 6, T4 recorded the highest N concentration at 0.70% while T9 recorded the lowest value (0.35%). The highest total P concentration was in T9 at 0.50% whereas the lowest was in T4 with only 0.28%. The concentration of exchangeable K however showed no significant difference among treatments. The highest value of exchangeable Ca was recorded in T9 at 3.89% while the lowest was in T4 with only 3.21%. For exchangeable Mg, T9 recorded the highest value at 0.43% while the lowest was in T5 at 0.13%. The highest value of exchangeable Zn was in T8 (96.25 ppm) while the lowest value was in T4 (50.00 ppm). Meanwhile, T3 recorded the highest value of exchangeable Cu (987.50 ppm) while T5 was the lowest with only 200.00 ppm. However, all of the treatments are not significantly different at p≤0.05. In the case of exchangeable Na, it was also found that there was no significant difference among all treatments. The highest value of exchangeable Na was in T9 at 0.81% while the lowest was in T8 at 0.34%. In general, the concentrations of total N, total P, exchangeable Ca, Mg and Zn showed significant differences among treatments while exchangeable K, Cu and Na showed opposite trend with no significant difference. For total N concentration, T9 recorded the lowest value of foliar nitrogen at harvest. This might cause by the change during growing stages since as plants mature, the concentration of nitrogen in the leaves, stem and roots will decrease as a result of conversion to protein stored in the plants ( Barker and Pilbeam, 2007). In contrast, concentration of total P in T9 showed the highest value as compared to the other treatments. This condition may be due to physiological changes as the plants mature and produced flowers and fruits. As stated by phosphate is of particular importance for fruit setting, fruit quality and resistance to diseases hence insufficient phosphate nutrition may delay fruit maturation (Mengel et al., 2001). Exchangeable K concentrations in the leaves of O. tenuiflorum do not show any significant difference among treatments. The lowest value was shown by T2 while the highest was showed by T9. It shows that potassium supplied by the mixture of guano manure with soil was sufficient for plant growth since potassium is the second most abundant mineral nutrient in the plants after N (Roy et al., 2007).
Concentrations of exchangeable Ca, Mg and Na showed the highest amount in T9 since it has the highest organic manure. A group researchers stated that Ca ranks with Mg in the group of least abundant nutrients in plants (Roy et al., 2007). Ca is immobile in the phloem and is involved in cell division, growth, root lengthening and activation or inhibition of enzymes. The exchangeable Ca in plant leaves was higher compared to exchangeable Mg. High calcium concentration in the soils sometimes limit magnesium accumulation and may cause magnesium deficiency symptoms (Barker and Pilbeam, 2007). However, exchangeable Na showed no significant difference among treatments. Barker and Pilbeam, stated that sodium and potassium have similar chemical properties but these two elements have very different roles and are treated very differently by mechanisms involved in short-and long-range transport (Barker and Pilbeam, 2007). For the exchangeable Zn, T8 showed the highest amount but with only little amount compared to other nutrients. According to plant requires only trace amount of zinc which functions to promote RNA synthesis which in turn is needed for protein synthesis (Roy et al., 2007).

CONCLUSION
Application of guano manure as organic fertilizer in this study showed significant effect on plant height. The optimum rate of fertilizer which produced the tallest plant was the T3 (30% of guano manure mixed with 70% of soil). In contrast, T9 (90% of guano manure mixed with 10% of soil) appeared to retard height growth may be due to over fertilization. In the case of nutrient concentrations in the leaves of O. tenuiflorum, total N, total P, exchangeable Ca, Mg and Zn showed significant differences among treatments while exchangeable K, Cu and Na showed no significant difference at p≤0.05. The soil nutrients before planting recorded higher concentrations compared to after harvest probably due to several factors such as nutrient uptake by plant, leaching from soil or being used up by soil organisms. Soil pH increased as the level of fertilizer increased for both soil before and after harvest. For the control treatment, the soil without fertilizer was found to be highly acidic while guano manure was found to be more alkaline. Organic manure seems to act as a soil conditioner and soil amendment to improve soil characteristics including soil acidity. Findings of the present study might be further confirmed by conducting multi-location field trial experiments.