Direct and Residual Effects of Different Levels of Chicken Manure Fertilization on the Growth and Biomass Production of Brachiaria ruziziensis (Poaceae) at the Bolting in West Cameroon

The direct and residual effects of different levels of chicken manure fertilization on the growth and biomass production of B. ruziziensis at the bolting were studied in West Cameroon. The objective of this study was to evaluate the effects of different levels of chicken manure fertilization on the growth and biomass production of Brachiaria ruziziensis at the bolting. A factorial device comparing five doses of nitrogen into chicken manure (0, 25, 50, 75 and 100 kg N/ha) on plot of 6 m 2 (3 × 2 m) in four replicates, (i.e. a total of 20 experimental plots) was used. Chicken manure was spread one month after planting pieces of stump during the first year. In the second year, no fertilization was brought up. 40 plants were harvested by treatment for heights and diameters measurements. The evaluation of stems biomass, leaves and whole plants was done on each plot based on the level of fertilization. The results obtained showed that chicken manure fertilization had a positive effect on the growth and biomass production of the B. ruziziensis on the direct and residual effect of fertilization. Thus, the height, diameters and biomass of whole plants in the fertilized plots were significantly larger than in the control plots. suitable for an optimal B. ruziziensis growth in order to avoid providing the soil with mineral fertilizer.

device comparing five doses of nitrogen into chicken manure (0, 25, 50, 75 and 100 kg N/ha) on plot of 6 m 2 (3 × 2 m) in four replicates, (i.e. a total of 20 experimental plots) was used. Chicken manure was spread one month after planting pieces of stump during the first year. In the second year, no fertilization was brought up. 40 plants were harvested by treatment for heights and diameters measurements. The evaluation of stems biomass, leaves and whole plants was done on each plot based on the level of fertilization. The results obtained showed that chicken manure fertilization had a positive effect on the growth and biomass production of the B. ruziziensis on the direct and residual effect of fertilization. Thus, the height, diameters and biomass of whole plants in the fertilized plots were significantly larger than in the control plots. The mineralization of the organic matter contained in the chicken manure with doses of 100 kg N/ha was done on the direct and residual effect in order to assure a maximal plant growth. The level of T 4 fertilization (corresponding to the dose of 100 kg N/ha) gave the best results. Referring to the result obtained, the level of T 4 fertilization corresponding to 100 kg N/ha would be

Introduction
The necessity to feed an ever-increasing population in developing countries is pushing farmers to exploit marginal land considered unsuitable for agriculture [1], to expand arable land at the detriment of pastoral land, resulting in conflicts over the use of rural space between farmers and herders [2] [3]. This situation leads to the narrowing of natural rangelands [3] [4], and to their displacement towards marginal areas [5] which are already overexploited. Natural grasslands, which have been used extensively to date, are becoming depleted and losing their capacity to raise livestock [6]. It is, therefore, necessary to develop a sedentary type of livestock farming which, being based on active land work, ensures its conservation and increases its productivity [6]. This type of livestock farming allows for intensive and sustainable use of land resources and facilitates livestock management. If the aim is to move from nomadic to sedentary livestock farming, then there is a need to increase the supply of fodder within the sedentary area [6]. Fodder cultivation can be an alternative in tropical countries. It would thus ensure availability both in favorable periods (rainy season) and in unfavorable periods (dry season) [7] [8]. In this case, production systems will no longer have the only aim of producing milk and meat, but will also make it possible to produce good quality fodder using cultivation techniques accessible to farmers [9]. Among the many forage species introduced into Cameroon, there is the Brachiaria ruziziensis. This perennial gramineae has the advantages of better adaptation in different regions, good nutritional value and produces a good appetite to the animals [3] [4]. It is proposed for profitable use not only in improving natural pastures, but also as green or conserved forage [3] [10]. The cultivation of B. ruziziensis and especially the intensification of its use can thus constitute a palliative to the shrinking of natural rangelands [11]. It would improve animal rations throughout the year. Plants of genus Brachiaria are able to extract the few nutrients left in poor soils. As a result, their intensive use as fodder, without the use of fertilizer (fertilizer or manure) as compensation, may lead to the depletion of soils that will become uncultivated [12]. Considering the high cost of mineral fertilizers and their harmful role in soil ecology, the use of chicken manure has enormous potential for managing soil fertility and improving crop growth and yields [13]. It is with this in mind that this study aims to evaluate the effect of chicken manure on the growth and biomass production of B. ruziziensis. The aim is to determine the optimal level of certain nutrients such

Experimental Device
A factorial device (5 × 3) comparing five doses of nitrogen in the form of chicken manure (0, 25, 50, 75 and 100 kg N/ha) on 6 m 2 (3 × 2 m) plots in four replicates, for a total of 20 experimental plots was used.

Origin and Chemical Composition of the Fertilizer
The organic fertilizer used in this study is chicken manure. It was obtained from a breeding at a producer in the division of Menoua (Dschang). Its chemical composition was analyzed at the Laboratory of Soil Analysis and Environmental Chemistry of the University of Dschang in order to determine the quantities to be applied. The results of the analysis of the chemical composition of chicken manure were presented in Table 1.

Soil Preparation, Plant Placement and Fertilization
Soil samples were collected at the test site in a depth range of 0 -20 cm before soil preparation and stump splinters were placed. The soil chemical analysis was carried out at the Laboratory for Soil Analysis and Environmental Chemistry of the University of Dschang using the method described by Pauwels et al. [18].
The results obtained showed that the average textural class of this soil is silty. This soil is slightly acidic with an average pH of 5.5, which excludes the risk of toxicity due to excess aluminum and manganese. Total nitrogen levels are low (0.6 g/kg soil). For most Cameroonian soils, levels of 1 g/kg already allow a crop cycle in traditional agriculture, but for intensive cultivation, these levels must be increased to 2 g/kg. It is, therefore, necessary to provide a nitrogen supplement. The organic matter rate (with a C/N ratio = 11.66) is within the ideal range (8% -12%) reflecting good organic matter mineralization [19]. This gives this soil a greater retention capacity that can allow it to withstand massive fertilization. As for exchangeable bases, the soil is poorly supplied with magnesium, potassium, calcium and phosphorus. The absorbent complex of this soil has a high cation exchange capacity (7.84 cmol /kg soil) due to the high organic matter.
These characteristics make it possible to consider without fear fertilization with high doses of fertilizer. Indeed, the fertility level of soil is optimal when the physico-chemical and climatic conditions specific to a given cultivar are provided. In the case of B. ruziziensis, which requires highly fertile soil [10], these conditions are acceptable in the West Cameroon highlands and subsequent inputs may positively modify this environment in order to improve its cultivation.
The preparation of the 6 m 2 (3 × 2 m) seedling blocks was done manually us- Fertilization levels at chicken manure have been defined in terms of the amount of nitrogen contained in chicken manure not only because nitrogen is the most deficient nutrient in agricultural production systems through its role in the synthesis of living matter [20], but also because it is a yield and sometimes quality factor that increases the protein content in plants [21].
Thus, five nitrogen doses were defined (0, 25, 50, 75 and 100 kg nitrogen per hectare) for the cultivation of B. ruziziensis. Each dose was assigned a specific quantity of chicken manure as summarized in Table 2. In the second year (January 2016), regularization mowing was carried out at 5 cm above the ground, and no fertilization was carried out after the regularization mowing.
The maintenance of the plots consisted each month of manual weeding of the weeds.

Growth Assessment
To assess growth, ten (10) plants were randomly collected from each replicate, for a total of 40 plants per treatment to assess measurements (height and diameter). Plant heights (from the mowing point to the end of the longest leaf) were measured using a tape measure per centimeter and diameters were measured (before the first internode) using an electronic caliper graduated to the millimeter.

Statistical Analysis
The data on height, diameter and biomass produced were subjected to a multifactorial analysis of variance according to the General Linear Model (GLM) using the SPSS software version 20.0. When there were differences between the different treatments, the means were separated by the Duncan test at the 5% significance level [22].

Direct and Residual Effects of Different Levels of Chicken Manure Fertilization on the Height of Brachiaria ruziziensis during the Bolting
The variations in the height of B. ruziziensis under the direct and residual effect of increasing levels of fertilization at the bolting are presented in Table 3.

Direct and Residual Effects of Different Levels of Chicken Manure Fertilization on the Diameter of Brachiaria ruziziensis during the Bolting
The variation in the diameter of B. ruziziensis as a function of the different levels of fertilization under the direct and residual effect of the fertilizer is presented in Table 4.

Direct and Residual Effects of Different Levels of Chicken Manure Fertilization on Biomass Production of B. ruziziensis during the Bolting
The evolution of the biomass of leaves, stems and the whole plant of B. ruziziensis under the direct and residual effect of the different levels of fertilization at the bolting is presented in Table 5.     were higher than those in the unfertilized plots. The differences observed between the heights of the plants in the fertilized plots and those in the unfertilized plots can be explained by the fact that the low nitrogen contents (0.6 g/kg soil) contained in the soil of the unfertilized plots did not correspond to the quantity necessary for optimal growth of this plant. Thus, nitrogen inputs in the form of chicken manure made it possible to obtain significant differences in the plant diameters of the fertilized plots compared to those of the control plots. In addition, the results of studies conducted by Yerima et al. [13] showed that chicken Under the residual effect, despite the absence of fertilization, the organic matter from the remaining chicken manure in the soil for these two levels of fertilization continued to mineralize to provide sufficient nitrogen for optimal plant growth. The results obtained from the direct and residual effect of chicken manure fertilization levels on the evolution of the height and diameter of B. ruziziensis are in line with those obtained by Tendonkeng [11]. These Tendonkeng's results showed that the heights and diameters of B. ruziziensis plants increased with increasing levels of nitrogen fertilization. On the other hand, Zamil et al. [23] and Yerima et al. [13] have shown that chicken manure improves the availability of nitrogen, phosphorus and potassium, which promotes plant growth.

Conclusion
This study was initiated to assess the direct and residual effects of increasing doses of chicken manure on the growth and biomass production of Brachiaria kg N/ha) was carried out in such a way as to ensure maximum plant growth, while fertilization at doses of (25 and 50 kg N/ha) could only provide the nutrients that could contribute to plant growth under the direct effect before it was exhausted. The level of T 4 fertilization (corresponding to the dose of 100 kg N/ha) gave the best results. Referring to the result obtained, the level of T4 fertilization corresponding to 100 kg N/ha would be suitable for an optimal B. ruziziensis growth in order to avoid providing the soil with mineral fertilizer.