Bat Guano Application Rate in Horticulture in Cambodia: An Experiment With Tomato

Bat guano is rich in carbon, nitrogen, essential minerals and beneficial microbes. It is considered as a potential organic fertilizer for plant growth and productivity. The aim of the study was to test the effect of varying amounts of bat guano on plant growth and productivity of tomato. The results showed that the growth and productivity increased significantly with the amounts of bat guano applied. With the amount of 0.5 or 1 t/ha was found to have the greatest impact compared to other treatment and control groups. The amount of 0.5 t/ha (or 35 g/plant) is an appreciate amount and recommended for tomato production


Introduction
For healthy and safe food, long-term sustainability and concerns regarding the environmental pollution related to the unregulated utilization of chemical fertilizers, organic farming has become an essential priority worldwide (Al-Erwy et al., 2016).Organic fertilizer has been promoted to avoid or reduce the negative effects attributed to the use of chemical (or synthetic) fertilizer.Vegetables and fruits grown on overfertilized soils are more susceptible to attacks by insects and disease (Karungi et al., 2006).Underfertilization can lead to the deterioration of soil characteristics and fertility, and as well it can lead to a reduction in fruit nutrition values and edible qualities (Shimbo et al., 2001).Organic fertilizers havelongterm benefits including enhanced soil quality, improve biodiversity, as well as the reduction of production cost and environmental pollution.
In Cambodia, although chemical fertilizers are most commonly applied to deal with nutrient deficiencies, livestock manure, compost and bat guano are also extensively used throughout the country as organic forms of fertilizer (Sothearen et al., 2014).Bat guano is collected from bat caves and commonly traded and used as fertilizer in the country (Furey et al., 2016).Bat guano serves as a source of organic manure for improvement of growth and photosynthetic response in crop plants (Palita et al., 2021).It is rich in carbon, nitrogen, essential minerals and beneficial microbes, and mineralises very quickly (Dimande et al., 2023a).Previous studies have documented with high amount of bat guano applied to tomato plants in Nigeria (Karimou et al., 2020), and a combination of bat guato and fermented seaweedd application for cherry tomato production in Cambodia (Anuada et al., 2021) and other studies on other crops (e.g., Sothearen et al., 2014;Dimande et al., 2023a;Dimande et al., 2023b).Providing an appropriate amount and option for a specific crop is an entry point of promoting organic farming.
Consequently, the aim of the study was to test varying rates of bat guano application to determine appropriate application rates for tomato (Solanum lycopersicum) production in Cambodia.The findings of this study will provide better understanding of the appropriate amount of bat guano needed for tomato production and to avoid over or under fertilization.This could lead to a more efficient use of natural sources of organic fertilizer.In a context of the rise in input costs, natural sources of fertilization are in demand (Arndt et al., 2023).Tomato is a good source of nutritive value, containing high vitamins specifically vitamin C and other minerals like phosphorus, iron, and calcium (Bhowmik et al., 2012) and is an increasingly important vegetable crop in rural Northwest Cambodia (Hav et al., 2021) In this region, the limestone mountains are habitat for thousands of bats and there is a continuous supply of bat guano from the caves there.Applications rates, based on experiments, will help to effectively manage this valuable natural resource.
A completely randomized design was used with four different treatments, with 10 replications (single pant per pot) for each treatment and the control.Four amounts of bat guano were included in the experiment, i.e., 0 t/ha for control, 0.25 t/ha (17 g/plant), 0.50 t/ha (35 g/plant), and 1.0 t/ha (70 g/plant) were applied into each treatment when preparing soil for each plastic pot.The plastic pots with a size of 20 L of volume, with 30 cm of diameter and 36 cm of height, were used as containers for the substrate.
Makis F1 hybrid tomato variety was used for this experiment; the seeds were were sown on trays containing mixed soil and composted cow manure (2:1) then kept under the net house and watered twice a day.Similar size seedlings with 2-3 leaves per plant with height of 18 to 20 cm, were transplanted in the container substrates when they were at 3 weeks old, one plant per each container of substrate.The plants were watered twice a day (at 8 AM and 4 PM).

Data Collection and Statistical Analysis
To compare plant growth and productivity among the treatments and control group, plant height, branch number per plant, fruit number per plant, and total fruit yield per plant parameters were measured at the end of the experiment (110 days after transplanting).
To test the significance of difference in means of each variable for multiple groups, one-way analysis of variance or the Kruskal-Wallis test (Kruskal & Wallis, 1952) was used due to the fact that the data have an unnormal distribution.Tukey's test (Tukey, 1949) was applied to compare all possible pairs of mean for each variable.All pairwise comparisons using least significant difference at α = 0.05.All statistical analyses were performed with the R statistical software, version 3.6.3(R Core Team, 2020); and the plots were performed using 'ggplot2' R package (Wickham, 2011).To visualize correlations between all pairwise combinations of the variables included plant height, branch number per plant, fruit number per plant, and total fruit yield per plant, and amount of guano applied, bivariate relationships were analysed using Pearson's correlation coefficient for numerical variables by performing correlation matrix using scatter plots in the 'Performance Analytics' R package (Carl & Peterson, 2010).

Results
The growth and productivities of the tomato plants were found to be significantly affected by different amounts of bat guano application (Figure 1; P < 0.001).The greatest plant height, branch number, fruit number and total fruit yield per plant were found in the treatment with the amount of 0.5 or 1.0 t/ha guano fertilizer, whereas the least plant growth and productivity in the control group.Between the amounts of 0.5 and 1.0 t/ha guano fertilizers were not significantly different for the plant growth and productivity, indicated that 0.5 t/ha (35 g/plant) was an optimal rate for tomato plant production in clay loam soil condition.Applying 35 g/plant of bat guano fertilizer could increase the fruit yield by double than those without guano fertilizer application.
Figure 1.Effect of different rates (0; 0.25; 0.5 and 1 tonne/ha) of bat guano application on cherry tomato plant growth and productivity; plant height (top left:), branch number (top right), fruit number (bottom left), and fruit weight (bottom right) The Pearson's correlation matrix plot (Figure 2) showed that the amounts of bat guano application (from 0 to 1 t/ha) were significantly positively correlated to the plant height, branch number, fruit number, and total fruit weight per plant.Figure 2. The Pearson's correlation matrix of the plant growth (plant height and branch number) and productivity (fruit number and total fruit weight per plant) variables and different amounts of bat guano application.Note: Bat guano: 0; 0.25; 0.5 and 1 tonne/ha, Plant.height:maximum plant height (cm), Branches.No: branch number per plant, Fruit No: fruit number per plant, and Total.fruit.weight:total fruit weight per plant (g/plant); ***P < 0.001

Discussion
The results of this investigation demonstrated that bat guano could be used as an organic fertilizer for tomato production as the plant growth and production increased with the amount of bat guano applied.However, the results show the amount of 0.5 t/ha (35 g/plant) would be an optimal rate for tomato production, applying more that this optimal amount would not increase plant growth and productivity, unless for other reasons such as soil quality improvement.The results are similar to previous studies on other tomato variety (Karimou et al., 2020), however, the present findings provided additional proofs to indicate less than 0.25 t/ha of guano is not enough amount for tomato growth and production, as well as more than 0.5 t/ha does not achieve better growth and yields for the soil conditions of the present study.Previous study (Anuada et al., 2021) recommended a combination between 0.5 t/ha of bat guano and 500 L/ha of fermented seaweed for cherry tomato production in Cambodia.Bat guano is rich in carbon, nitrogen, essential minerals and beneficial microbes; excess amount of Total.fruit.weight the guano does not cause negative plant growth and productivity, but may increase production cost.Bat guano mineralises very quickly (Dimande et al., 2023a), the application of bat guano to soils could also improve physical properties of soils and microbial population and the environment (Ghasem et al., 2014;Bharambe et al. 2017;Dimande et al., 2023b;Onunwa et al., 2023).Bat guano has been considered as important biowastes of the cave ecosystems containing high amounts of minerals (Giurgiu et al., 2013).The minerals of bat guano include phosphates and sulphates of potassium, ammonium, sodium, magnesium, and calcium (Shahack-Gross et al., 2004).
The use of organic fertilizer can avoid or reduce the negative effects attributed to the use of chemical (or synthetic) fertilizer.Applying chemical fertilizer leads to the deterioration of soil characteristics and fertility, and as well it leads to a reduction in fruit nutrition values and edible qualities (Shimbo et al., 2001), including the protein content of crops, and the carbohydrate quality (Marzouk & Kassem, 2011).Other issues caused by chemical fertilizer, excess potassium content on chemically overfertilized soil decreases Vitamin C, carotene content and antioxidant compounds in vegetables (Toor et al., 2006).

Conclusions
Bat guano application on tomato enhances plant growth and productivity of the tomato plant.Application rates of 500 kg/ha or 35 g/plant is an appropriate amount for tomato production, with less not providing sufficient nutrient requirements, and more not being efficient with this limited natural resource.Bat guano is recommended for tomato production as an alternative organic source of nutrients for sustainable soil fertility management.