1. Introduction

In recent years, the use of urine as an organic fertilizer has gained increasing attention due to its high content of essential plant nutrients, particularly nitrogen, phosphorus, and potassium, as well as its capacity to support plant growth when properly managed [1]. Its effectiveness in promoting crop growth makes it a viable option [2] as an organic fertilizer for crop production. Rabbit urine is a rich source of nutrients, such as nitrogen and phosphorus, which are essential for plant growth [3]. Fertilization using rabbit urine has been reported to improve soil fertility and increases crop yield [4]. In addition to an organic fertilizer, it is cost-effective and environmentally friendly. Therefore, rabbit urine possesses qualities that promote improved yield and environmental safety.

Brachiaria ruziziensis (Congo grass) is an excellent source of fodder for animals with decent palatability [5]. It exhibits outstanding productive features such as excellent acceptance, effective quick response to fertilization, great fodder quality and feeding value [6], quick establishment, swift growth at the inception of the rainy season, ability to work well in a consortium with legumes, dense flowering, and enormous seed yield [7]. However, despite these noteworthy traits, factors such as poor soil fertility and defective fertilization practices affect the herbage yield and nutritive value of the grass. Meanwhile, the majority of studies on pasture organic fertilization have concentrated primarily on manure from poultry and livestock and limited attention has been paid to microlivestock (rabbit urine) as a potential fertilizer source for pasture crops. Therefore, this study evaluated the efficacy of rabbit urine concentrations as a fertilizer on the herbage yield and nutritive value of Congo grass (Brachiaria ruziziensis). 

2. Materials and methods

2.1. Experimental location

The research was conducted at the pasture plot of the Department of Animal Science Teaching and Research Farm, College of Agriculture, Ejigbo, Osun State University, Osun State. Nigeria. The experimental site lies within the Derived Guinea Savanna ecological zone of Nigeria with an average annual rainfall of 1330 mm, which covers 6 months of the year and spans April to October. The temperature ranges from 18.88 °C to 33.88 °C and it rarely falls below 15 °C or above 37.22 °C. It has an average elevation of 426 m and latitude of 7.9045 0N and 4.3025 0E [8].

2.2. Experimental layout, design and treatment

Existing pasture fields of Congo grass (Brachiaria ruziziensis) were used for the experiment. The plots were cut back to a uniform height of 10 cm with the aid of a hand mower. The experiment was laid out in a randomized complete block design with four treatments, replicated four times, resulting in a total of sixteen (16) plots. Each plot measured 8 m × 5 m, with an inter-plot spacing of 1.0 m. Rabbit urine was collected from the rabbit unit of the College of Agricultural Production Teaching and Research Farm, Osun State University and diluted with pipe-borne water in ratios of 1:2.5, 1:5 and 1:7.5. These fertilizer concentrations were applied immediately by foliar application on Brachiaria ruziziensis plots; 0, 714,  834 and 867 mL/l.

The concentration of urine in each water-urine mixture was estimated by the following formula as of Harris [9]:

                                  

2.3. Determination of nutrient contents of urine concentrations

The samples of the different urine concentrations used in this study were analysed for nitrogen, phosphorus, potassium, calcium, magnesium, sodium, pH and electrical conductivity according to the standard procedure [10].

2.4. Measurement of agronomic parameters

At ten weeks of age the morphological parameters estimated included plant height, root length, leaf length, leaf width, number of leaves, number of tillers and leaf-stem ratio [11]. Three Congo grass plants were randomly selected from each plot, and the height was measured from the lowest point of the stem up to the apex of the tallest leaf of the grass using a tape rule. Subsequently, the average height was estimated and recorded. Root length was measured using a tape rule from the base of the stem to the tip of the longest root. This was determined by counting the number of tillers of three randomly selected Congo grass plants from each plot. Then, the mean number of tillers was determined and recorded as the number of tillers. Leaf number was determined by counting the number of leaves on three randomly selected plants from each plot. The mean number of leaves per plant was then determined. Three leaves were randomly selected from each plant was carried out. Each leaf was measured from the base of the collar region to the apex of the leaf using a tape rule, by the reported procedure [12]. The leaves and stems of the three sampled plants were separated differently and each part was measured separately using a weighing balance. The ratio of the mass of the leaf to stem was then determined and recorded.

2.5. Determination of herbage yield

The biomass yield was estimated by random tossing of a wooden quadrat measuring 0.5 m2 [13]. The grass that fell within the quadrat was harvested completely using a sharp matchet, and it was repeated three times on each plot. The herbage was collected, packed into a sack, and measured using a weighing scale. The weight of each cut was recorded and the average weight was estimated. The results were then interpolated in tons per hectare. The estimated parameters included fresh matter or biomass yield and dry matter yield.

2.6. Determination of dry matter yield

This was achieved by oven-drying 100 g samples from each plot at 65°C for 72 h. The percentage weight loss after drying was then calculated. The product of the percentage weight loss and the fresh sample resulted in the dry matter yield. The results of the dry yield were expressed in tonnes/ha.

2.7. Chemical analysis

The chemical composition of the Congo grass samples from each treatment was analysed using the reported technique [14] technique. The dry matter, crude protein, crude fibre, ether extract, organic matter, and nitrogen-free extract of the stored samples were estimated. The fibre fractions determined were neutral detergent fibre, acid detergent fibre, and acid detergent lignin and were determined in accordance with previous method [15]. Other constituents of fibre, cellulose and hemicellulose were determined using the earlier procedure [16]. Cellulose was estimated by deducting the values of acid detergent lignin from those of acid detergent fibre, and hemicellulose was calculated as the difference between neutral detergent fibre and acid detergent fibres.

2.8. Statistical analysis

Data collected were subjected to two-way analysis of variance (ANOVA) using [17] package and significant means were separated using Duncan’s Multiple Range Test at 5% significance level.

3. Results and discussion

3.1. The chemical composition of urine concentrations

There were significant differences in the chemical composition of the urine concentrations used in this study (Table 1). The 834 and 867 mL/l urine concentrations had significantly higher (p < 0.05) nitrogen, phosphorus, potassium,calcium and magnesium than the 714 mL/l urine, indicating that a higher dilution rate enhanced nutrient availability, likely driven by improved solubility and reduced precipitation rather than direct mineralization. Furthermore, the sodium content was significantly highest (p < 0.05) in 867 mL/l (1.72), followed by 834 mL/l (1.63) and then 714 mL/l (1.42). However, the 714 mL/l 7.57) and 834 mL/l (7.67) groups  had significantly lower (p < 0.05) than the 867 mL/l (8.03) group. The electrical conductivity had a similar trend to that of the sodium content. 

Table 1. The chemical composition of urine concentrations.

 

Parameters	714 mL/l	834 mL/l	867 mL/l	SEM	P Value
Nitrogen	5.88b	7.07a	7.43a	0.0212	0.28
Phosphorus	0.61b	0.72a	0,77a	0.0017	0.02
Potassium	2.77b	3.29a	3.42a	0.0231	0.12
Calcium	0.71b	0.80a	0.85a	0.0008	0.02
Magnessium	0.34b	0.41a	0.41a	0.0206	0.01
Sodium	1.42c	1.63b	1.72a	<0.0001	0.04
pH	7.57b	7.67b	8.03a	0.0328	0.09
Electrical conductivity	12.43c	14.47b	15.33a	0.0002	0.45

The significant differences observed in the chemical composition of urine indicate that the dilution level strongly influences nutrient availability and ionic behavior within the system. This trend is unlikely to be solely due to increased mineralization; rather, it can be attributed to changes in physicochemical equilibria, particularly improved solubility and reduced precipitation of nutrient-bearing compounds in the soil.

Nutrient elements, such as phosphorus and calcium, are known to undergo precipitation reactions, forming compounds, such as struvite (MgNH₄PO₄·6H₂O) and calcium phosphates, which reduce their measurable concentrations in solution. Wei et al. [18] demonstrated that high concentrations of nitrogen, phosphorus, and potassium in solution can induce coprecipitation processes that significantly influence nutrient partitioning and their availability. Similarly, it was reported [19] that phosphorus recovery systems are strongly governed by precipitation and dissolution mechanisms, which determine the fraction of nutrients remaining in soluble form. Therefore, the lower nutrient concentrations observed at 714 mL/l may reflect increased precipitation or reduced solubility, whereas the higher concentrations (834 and 867 mL/l) likely favored conditions that maintained nutrients in dissolved and measurable forms. The observed increase in sodium concentration with increasing urine concentration, with the highest value recorded at 867 mL/l, further supports the influence of ionic accumulation. This trend was mirrored by the electrical conductivity, which exhibited a similar pattern. Electrical conductivity is directly related to the total concentration of dissolved ions in a solution, and its increase with sodium content is therefore expected. Santos et al. [20] reported that ionic strength and the presence of coexisting ions significantly influence solution chemistry and nutrient recovery processes, particularly in systems with a high dissolved salt content. The elevated sodium and electrical conductivity levels observed at higher concentrations may indicate increased ionic strength, which can influence nutrient interactions and stability. The significantly higher pH observed in the 867 mL/l treatment suggests enhanced alkalinity at higher concentrations. This increase in pH can be associated with biochemical transformations, such as urea hydrolysis, which leads to the formation of ammonium and ammonia, thereby raising the pH of the solution. Gonçalves, et al.  [21] reported that such transformations significantly alter the physicochemical properties of the solution, including the pH and nutrient speciation. However, the relatively moderate pH range observed in this study indicates that these processes may not have been completed, suggesting the presence of buffering mechanisms or incomplete transformation.

3.2. Morphological parameters of Congo grass fertilized with varying concentrations of rabbit urine

Table 2 shows the effects of varying concentrations of rabbit urine on the morphological parameters of Brachiaria ruziziensis. Most of the morphological parameters presented a similar trend, as urine concentrations increased, morphological parameters also showed a corresponding increase. All the Congo grasses treated with different concentrations of rabbit urine had significantly higher values (p < 0.05) in plant height, root length, leaf length, number of tillers, and leaf/stem ratio than those in the no fertilizer treatment. However, the 867 mL/l concentration was significantly highest (p < 0.05) in these parameters. Furthermore, the number of leaves was significantly highest (p < 0.05) in 867 mL/l (615.00), followed by 0 mL/l (491.50), 714 mL/l (472.00) and 834 mL/l (376.00). However, there were no significant differences (p > 0.05) in leaf weight among of all the different concentrations.

The application of fertilizers has been shown to have significant effects on the morphological parameters of various species.  According to Yakubu et al. [22], rabbit urine fertilization results in a notable increase in morphological traits such as plant height and number of leaves, due to the release of nitrogen into the soil. The difference observed in this study could be linked to the disparity in the concentration of rabbit urine. The highly concentrated treatment released more nutrients to the plants than the other treatments with a high dilution ratio. This observation in the current study is in accordance with Yakubu et al.  [22], in which an increase in rabbit urine concentration resulted in a corresponding increase in the height and number of leaves. Similar results were also reported [23, 24], in which the application of organic and inorganic fertilizers caused significant variations (p < 0.05) in the morphological traits of Brachiaria ruziziensis. However, a contrasting observation was experienced in the study was reported [13], who found that the application of fertilizers had no significant impact on the morphological traits of Congo grass. Since the application at 867 mL/l concentration showed improved morphological traits over other treatments, it should be considered for improved morphological traits to ensure an abundant supply of feed to livestock.  

Table 2. Herbage and agronomic yields of Congo grass fertilized with rabbit urine.

Parameters	0 mL/l	714 mL/l	834 mL/l	867 mL/l	SEM	P Value
Plant height (cm)	115.95d	150.88b	125.76c	170.05a	4.03	<0.0001
Root length (cm)	29.95d	40.13b	34.60c	55.10a	21.96	<0.0001
Leaf length (cm)	25.00c	31.88b	25.13c	38.05a	1.61	0.0006
Number of leaves	491.50b	472.00c	376.00d	615.00a	2.45	<0.0001
Number of tillers	33.50d	36.75c	43.50b	73.00a	5.48	<0.0001
Leaf/stem ratio	0.87d	1.15c	1.63b	2.35a	0.44	<0.0001
Leaf weight (kg)	2.28	2.23	1.85	2.03	3.69	0.1804
abcd Means with different superscripts are significantly different (p<0.05).

3.3. Fresh and dry matter yield of Brachiaria ruziziensis fertilized with varying concentrations of rabbit urine.

As the concentration of rabbit urine increased, both fresh and dry matter yields increased (Table 3). The values recorded revealed that 867 mL/l had significantly higher (p < 0.05) fresh (54.75) and dry matter (9.59) yields than other urine concentrations. Plots fertilized with rabbit urine showed significantly higher values (p < 0.05) than the plots with no urine (0 mL/l). The disparity observed in the yields could be attributed to the varying nutrient concentrations in the rabbit urine used for fertilization. According to the report [25], rabbit urine contains nutrients such as nitrogen, phosphorus and potassium, which are essential for plant growth and improved yield. Several studies have verified that the addition of nitrogen increases soil nutrients, thereby resulting in plant growth and consequently, increasing the yield of grass. It is possible that the treatment with the highest concentration enriched the soil with nutrients at a higher rate than the others. The results obtained in this study are similar to those reported data [26], in which varying levels of swine liquid manure were applied to Congo grass. An increase in yield was observed with increasing levels of swine liquid manure. In another similar study [27] was observed that a varying levels of goat manure were used for the fertilization of Congo grass. An increase in yield was also observed with increasing dosage of goat manure. To substantiate this further [28], adopted the foliar application of rabbit urine in crops such as desmodium, oat and spinach. A tremendous increase in the yield of those crops was reported with the use of rabbit urine. However, the best performance was observed in a rabbit-urine mixture at 50:50 [28]. The difference in performance at different mixing ratios may stem from plant species, soil and ecological conditions. Since Brachiaria ruziziensis fertilized with 867 mL/l concentration produced more dry matter (9.59 t) than others with lower concentrations. Therefore, application at that rate might provide improved yield for animal feeding, and this could contribute considerably to the availability of forage in dry and wet seasons.