Agronomic potential of four cassava (Manihot esculenta Crantz) varieties grown on soils fertilized with cocoa shell compost and chicken dropping compost in Côte d’Ivoire

doi:10.21203/rs.3.rs-4725290/v1

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Agronomic potential of four cassava (Manihot esculenta Crantz) varieties grown on soils fertilized with cocoa shell compost and chicken dropping compost in Côte d’Ivoire

https://doi.org/10.21203/rs.3.rs-4725290/v1

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This study was conducted in the Lamto area to evaluate the effect of cocoa shell compost and chicken dropping compost on cassava agronomic variables. The evaluation led to the monitoring of plant development until harvest by measuring some agronomic variables of growth and yield of four varieties of cassava, Alleda agba, Bonoua, Six mois and Yacé each grown on soil fertilized with cocoa shell compost or chicken dropping compost. The experimental design used for this study was a complete randomized block design with 3 replicates. The results revealed that both fertilizers used improved the agronomic variables of cassava. This was reflected in a high number of stems per cutting (3.62). However, the chicken dropping compost gave the best development in stem length for the Six mois variety (121.10 cm). The Bonoua variety gave the largest diameter stems (21.98 mm). This variety gave the highest number of leaves (59) and a wider span (109 cm) with wider (16.75 cm) and longer (17.96 cm) leaves. As for yields, the best was obtained with the Bonoua variety, respectively 27.13 t/ha and 35.26 t/ha with cocoa shell compost and chicken dropping compost. Thus, compost and chicken dropping compost can be recommended to improve cassava productivity in Côte d'Ivoire.

Compost

chicken dropping

cocoa shells

cassava

agronomic variables

In tropical countries, the physical degradation of crop soils is becoming a concern [1–2]. In Côte d'Ivoire, the agricultural sector is already strongly impacted by this phenomenon. Indeed, in rural areas, the combined effects of deforestation, mining, and bush fires expose crop soils to bad weather, making them infertile for agriculture. Also, extensive cultivation, especially of cash crops, as well as the recurrent and irrational use of chemical fertilizers and pesticides are all elements that impoverish the soil. Consequently, the interest in high-yield agriculture is not only advocated, but it must also take into account the preservation of biodiversity [3–4]. Thus, it is in this context of crop soil infertility that many difficulties in ensuring sustainable production of cassava (Manihot esculenta Crantz) in Côte d'Ivoire, whose mineral nutrition is very important, can be apprehended.

Despite these numerous economic and especially nutritional advantages, national cassava production is still low to cover the growing needs of the population. This interest in cassava has led to improvements in its cropping systems to increase yields [5]. Thanks to research, new cassava varieties have been created and made available to farmers. These high-yielding varieties are resistant to diseases, pests and can produce up to 40 t/h per year compared to less than 15 t/h for traditional varieties [6]. However, it must be noted that the yields of these new improved varieties are still low due to poor soils. Under these conditions, it seems necessary to solve this major problem of soil infertility, at the risk of further decreasing national cassava production.

Today, the interest in high-yield agriculture that is concerned with the preservation of biodiversity and the environment is recognized by many [3], [7]. Therefore, local cropping systems that allow for biodiversity and arable land management are to be promoted [8]. These cropping systems must be adapted to climate change and to the nutritional and economic requirements of local populations. Thus, agricultural systems have been developed to address this problem. Unfortunately, certain activities such as urbanization and the creation of parks and reserves are reducing the land available for agriculture [9].

This forces farmers to be increasingly sedentary. This sedentarization leads to a reduction in the duration of fallow periods and soil impoverishment, resulting in lower yields [10–11]. Faced with this decline in yields, producers are adopting cropping systems such as crop rotation or the burial of organic, plant or animal residues in the soil for better yields [12]. The application of poultry litter and cattle manure to sandy ferralitic soils increased yields by 63 t/ha and 61 t/ha, respectively, compared to 40 t/ha for the control [13]. Despite these relevant results, agricultural and animal wastes are little used to optimize agricultural production in general and cassava production in particular [14]. Indeed, our country, the world's leading cocoa producer, rejects about 4,000000 tons of cocoa shells that decompose in the plantations [15]. Similarly, large quantities of poultry droppings are produced every day in the breeding grounds but are the object of little interest. Yet, it would be more appropriate to value these agricultural by-products through processing to fertilize crop soils.

The objective of this study is to improve the production of cassava by an organic amendment based on cocoa shell compost and chicken droppings.

The present study took place in central Côte d'Ivoire, in the humid savannahs of the forest-savanna contact zone, more precisely, in the village of Ahérémou 2. This village is located between 5'10 − 5'15 N and 4'55 − 5'00 W and is 159 km from Abidjan and 15 km from the Lamto reserve. The soils of Ahérémou 2 are of two types: soils with vertic characteristics and moderately desaturated ferrallitic soils [16]. The rainfall regime in the village of Ahérémou 2 is similar to that of the Lamto reserve. The seasonal rhythm is sub-equatorial and includes four seasons: a long and short rainy season, a short and long dry season. The average annual rainfall is around 1200 mm and allows the climate of Ahérémou 2 to be classified in the rainy regime [17]. The vegetation landscape of Ahérémou 2 is a mosaic of dense semi-deciduous forests on fertile upland forest soils, gallery forests located along watercourses, fire-protected wooded savannah, and savannah with roasted palms [18].

The plant material used was composed of four varieties of cassava locally named Six mois, Alleda agba, Yacé and Bonoua. They all have a cropping cycle of about 12 months and come from the village plantations of Ahérémou 2. The Yacé and Alleda agba varieties are single-stemmed. The Six mois variety has a two-branched stem and the Bonoua variety a three-branched stem. The Bonoua variety has a short stem and a wider leaf span than the other three varieties. The Six mois variety has a longer stem than the others and a narrower leaf span than the Bonoua variety, but wider than the Alleda agba and Yacé varieties. For Alleda agba and Yacé, there was no difference between the width of the foliage spans and the size of the stem. Healthy stems of these four cassava varieties were selected from plants at least six months old. Cuttings of 20 to 25 cm were cut with pruning shears, avoiding the soft parts of the stem [19].

Fertilizer material was of two types. Compost made from cocoa shells with Acacia mangium leaves added and compost made from chicken droppings mixed with sawdust. These two types of fertilizer were used because of their availability in the area where our experiments took place.

For compost preparation, two pits (1m×1m×1m) were dug and the bottoms were cemented to prevent nutrient loss. Chicken droppings and cocoa shells were collected from the study area. The droppings were collected from a chicken farmer and the cocoa shells from a cocoa farmer. One pit was filled with 50 kilograms of chicken droppings and the other pit with 50 kilograms of dried cocoa shells. Five kilograms of sorted Acacia mangium leaves, weighed with a scale, were added to the cocoa shells in the composting pit. The cocoa shells are a very crumbly by-product of the harvest, so the addition of Acacia mangium leaves helped to consolidate the structure of the compost. The pits were covered with oil palm (Elaeis guineensis) leaves to maintain moisture. The contents of the pits were turned and watered every three days during the composting period according to the "Indian Indore method" to allow good activity of the microorganisms [20]. Three months after composting, the chemical composition of the different composts was determined.

5.1. Collection and preparation of soil and compost samples

Soil samples were collected at the site before the trials were set up and after the cassava was harvested. These samples were taken from the first 30 cm of soil depth using an auger. Five samples were taken using the diagonal sampling method described by Traoré [21]. A composite sample of 1.5 kg was made from these incremental samples for each treatment type. These composite soil samples were air-dried to a constant weight. They were then sieved to 2 mm for chemical analysis. Also, at the end of the production of the different composts, a sample of each was taken. The compost samples were air-dried and then ground in an agate mortar. They were sieved with a 2 mm sieve and a one-kilogram subsample of each fertilizer was taken for analysis. All these analyses were carried out at the soil laboratory of INP-HB in Yamoussoukro. The results were used to determine minerals such as carbon, nitrogen (N), phosphorus (P), potassium (K), calcium, magnesium and then to calculate the ratios of carbon and nitrogen (C/N).

5.2. Experimental design

The experimental design used for this study was a complete randomized block design with 3 replicates. Each block consisted of 12 subplots, each corresponding to a treatment. Each subplot was 4m × 3m, i.e. 12 m², and two consecutive subplots were separated by a 2 m wide, regularly weeded strip. A total of four cassava varieties × three different treatments were tested. The distance between the planting points of the cassava cuttings was 1 m × 1 m, i.e. 10 000 plants ha-1. A subplot replication corresponds to a seedling plot containing three lines of four plants. The trial was set up on a plot with a total area of 1200 m² (20 m × 60 m) with a 3 m wide border.

Regarding the maintenance of the plot, weeds were controlled by regular manual weeding to avoid competition with cassava. The rows and the planting points were made in line and spaced out from each other by 1 m. This gives a total of 12 points of planting of cassava cuttings per elementary plot. The planting was done on the same day for all treatments, with one cutting per hole and at a depth of 2 to 3 cm.

The treated unit plots received a single application of fertilizer two weeks after the cuttings were planted. All fertilizers were applied on the same day. The composts were applied at a rate of 1 kg/plant, i.e. 10 tons per hectare. The fertilizers were applied around the cassava plants on a 10 cm radius. Chicken dropping compost was applied at a rate of 10 t. ha^− 1 i.e. N:16.8 g. kg^− 1, P: 12.6 g. kg^− 1, K: 22.76 g.kg^− 1. Cocoa compost shells were applied at a rate of 10 t. ha^− 1 i.e. N:7.50 g∙kg^− 1, P: 2.30 g∙kg^− 1, P: 10.19 g∙kg^− 1.

The trials were carried out from March 2018 to January 2019 for the first season and from March 2019 to January 2020 for the second season.

5.3. Observations and measurement of cassava agronomic variables

Selected agronomic variables from the cassava descriptors [22] were measured. These variables that can be quantified in the field were divided into two distinct groups: vegetative variables and yield variables. Observations were made on ten plants in each elementary plot [23–24]. The vegetative variables measured were: number of stems per cutting (NSC), length of main stem (LS), number of leaves per plant (NLP), the neck diameter of the stem (NDS), length (LL)and width of leaf (LW), and scale of the plant (ScP). The measurements were made from the second to the sixth month after planting. As for the yield variables, they were measured after the harvest, ten months after sowing. The number of leaves per plant (NLP) was determined by multiplying the number of apexes per plant by the average number of leaves per apex [24]. Neck diameters of stems (NDS), stem lengths (SL) and leaf width were measured using the methodology described by Aniekwe et al. (2004) [23] and Ambang et al. (2007) [25]. Yield (Y) and its attributes as the average number of tuberous roots per plant (NTRP), the mean weight of a tuberous root (WTR), the weight of tuberous roots per plant (WTRP) were recorded.

5.4. Data analysis

A multivariate variance analysis (MVA) was performed with R software, version 3.1. The AMOVAs were supplemented by ANOVA tests when interactions were significant. When a significant difference was observed between the different factors, Least Significant Difference (LSD) multiple range-tests procedure was used to separate the means of the different treatments. Means were given as mean followed by standard deviation (M ± SD). Significant differences were determined at P ≤ 0.05, [26].

6.1. Chemical characteristics of the different broiler droppings and cocoa shells composts

Table 1 shows the data on the chemical characteristics of the two composts. The results showed that the cocoa shell compost is richer in carbon. On the other hand, nitrogen, phosphorus, potassium, calcium and magnesium contents were higher in broiler droppings than in cocoa shell compost. The C/N ratio was lower in the broiler compost.

Table 1

Chemical composition of broiler droppings and cocoa shell compost
Type of compost	pH	C(g.Kg^− 1)	N(g.Kg^− 1)	P(g.Kg^− 1)	K(g.Kg^− 1)	Ca(g.Kg^− 1)	Mg(g.Kg^− 1)	C/N
CCD	7.1^a	272.8^b	16.6^a	12.6^a	22.76^a	136.69^a	4.67^a	16.23^b
CCS	7.2^a	387.7^a	7.5^b	2.3^b	10.19^b	19.78^b	2.77^b	51.69^a

NB: Values followed by same letters in a column are not significantly different (P > 0.05).

CCS: cocoa shells compost; CCD: chicken dropping compost; C: carbon; N: nitrogen; P: phosphorus; K: potassium; Ca: calcium; Mg: magnesium; C/N: ratio carbon-nitrogen.

6.2. Physico-chemical parameters of the test soils

The results of laboratory analyses of the physical and chemical composition of the different cultivation soils, both before cultivation and after harvesting the tuberous cassava roots, are presented in table 2. Analysis of these results showed that the crop soils were less acidic (6.9–7.2) than the control soils. Soils where composts were applied were richer in mineral elements (14 to 19.70 g. Kg^− 1 of C and 1.20 to 1.80 g. Kg^− 1) than unfertilized subplots. Similarly, soils amended with broiler manure compost (78–82 ppm) and cocoa shell compost (66–70 ppm) were the richest in assimilable phosphorus. These same soils were also richer in organic matter. As for the absorbent complex, cation exchange capacity was shown to be higher on soils fertilized with composts (8 < CEC < 15). The results also showed that the same soils fertilized with composts were higher in calcium (Ca2⁺: 3.876 Cmol/Kg); magnesium (Mg2⁺:1.727 Cmol. Kg^− 1); potassium (K⁺:1.38 Cmol. Kg^− 1) and sodium (Na⁺:0.044 Cmol.Kg^− 1) than controls.

Table 2

Physical and chemical composition of the soils of the different subplots
								Absorbent complex (Cmol.kg^− 1)
Traitments	pH _eau	C (g. Kg^− 1)	Nt (g. Kg^− 1)	C/Nt	MO (g. Kg^− 1)	P.ass (ppm)		CEC	Ca2+	Mg2+	K+	Na+
Control	6,10	14,40	1,30	11	24,80		42	6,18	1,683	0,958	0,094	0,035
CYc	6,40	16,80	1,50	11	21,90		37	6,24	1,865	1,029	0,097	0,032
CAa	6,30	16,70	1,50	11	21,60		36	6,21	1,756	0,925	0,095	0,032
CSm	6,40	16,50	1,50	11	21,70		37	6,19	1,875	0,938	0,096	0,034
CBo	6,30	17,70	1,60	11	21,50		38	6,14	1,675	0,862	0,096	0,035
CCDYc	7,20	19,50	1,80	11	33,50		80	12,56	3,876	1,223	0,126	0,036
CCDAa	6,10	14,00	1,20	12	24,10		78	7,22	2,114	0,945	0,107	0,041
CCDSm	6,50	15,2	1,30	12	28,60		80	7,23	2,448	0,943	0,129	0,036
CCDBo	6,60	15,60	1,40	11	26,80		82	7,25	2,583	0,851	0,119	0,035
CCSYc	6,90	19,30	1,60	12	33,20		77	8,37	2,49	1,727	0,130	0,044
CCSAa	6,60	19,70	1,80	11	33,90		66	8,58	2,290	1,542	0,121	0,044
CCSSm	7,30	17,60	1,50	12	30,20		68	12,44	3,824	1,128	0,102	0,029
CCSBo	6,90	18,50	1,50	12	31,90		77	11,22	3,516	1,473	0,138	0,075

Nt: total nitrogen; P. ass: phosphore assimilable; MO: organic matter; Control: unfertilized soil; Ya: Yacé; Aa: Alleda agba; Bo: Bonoua ; Sm : Six mois ; CCD : compost of chicken droppings; CCS: compost of cocoa shells; ; C : Control.

6.3. Overall effect of different factors on cassava agronomic variables

AMOVA was performed to assess the overall effect of factors and their interaction on cassava agronomic variables. This test showed that fertilizers, cassava varieties and their interactions (fertilizers × varieties) had a significant effect on the agronomic variables of cassava (P < 0.001) Table 3.

Table 3

Multivariate analysis of the variance of the means of agronomic variables measured on four cassava varieties subjected to two types of fertilizers.
Factors	Growth variables			Performance variables
	DL	F	P	DL	F	P
Fertilizer	21	17,89	< 0,001	9	198,45	< 0,001
Variety	21	40,23	< 0,001	9	40,96	< 0,001
Fertilizer - Variety	63	1,95	< 0,001	27	5,11	< 0,001

DL: degree of freedom

6.4. Effect of fertilizer and variety interaction on agronomic variables of cassava growth

Table 4 summarizes the effect of fertilizers on cassava growth variables. From the analysis of the table, it appears that fertilizers positively influenced (P < 0.001) the growth variables of cassava. This analysis shows that the number of stems per cutting varied significantly (P < 0.01) depending on whether fertilizer was applied to the crop soil or not. Thus, the number was higher (3.62 ± 0.81) when chicken dropping compost was applied to the crop soil compared to the control (2.45 ± 1.21).

As for stem length, it varied from 61.27 ± 45.65 cm to 121.10 ± 75.07 cm while diameters varied from 11.35 ± 4.35 mm to 21.98 ± 8.08 mm. The six mois cassava variety produced the longest stems and the Bonoua variety produced the shortest and largest stems. However, the longest stems and the largest stems were recorded on soil fertilized with broiler dung compost.

Regarding the number of leaves produced per stem and the scale of the plant, the Bonoua variety developed more leaves and larger blades (length 17.96 ± 3.18 cm, width 16.75 ± 4.05 cm) regardless of the fertilizer used compared to the other cassava varieties. In addition, the highest number of leaves (59.71 ± 44.68) and the largest wingspan (109.95 ± 32.09 cm) were observed with the Bonoua variety grown on plots fertilized with chicken dropping compost.

Table 4

Classification of the means of growth variables measured on cassava varieties submitted to two types of fertilizers
Fertilisants	Variétés	NSC	LS (cm)	NDS (mm)	NLP	LL (cm)	LW (cm)	ScP (cm)
C	Yc	2.33 ± 1.19^b	68.23 ± 49.33^h	11.35 ± 4.35^h	31.59 ± 21.48^ij	13.14 ± 3.78^e	11.62 ± 2.42^f	62.78 ± 21.98^j
	Aa	2.33 ± 0.98^b	67.49 ± 45.81^h	11.35 ± 4.61^h	32.67 ± 22.94ⁱ	13.95 ± 4.81^e	12.15 ± 2.41^e	65.60 ± 25.18ⁱ
	Sm	2.48 ± 1.22^b	70.05 ± 52.64^g	11.53 ± 3.87^h	30.21 ± 18.02^j	13.62 ± 2.15^e	12.43 ± 1.27^e	66.17 ± 13.77ⁱ
	Bo	2.85 ± 0.91^b	61.27 ± 45.65ⁱ	12.35 ± 6.15^g	33.42 ± 25.59ⁱ	14.65 ± 4.71^d	14.13 ± 4.74^c	69.66 ± 32.26^h
CCD	Yc	3.37 ± 1.04^a	112.68 ± 66.17^c	17.37 ± 7.42^c	46.20 ± 26.04^e	15.29 ± 4.21^c	15.50 ± 3.87^b	100.65 ± 33.98^d
	Aa	3.23 ± 0.90^a	115.75 ± 63.80^b	17.50 ± 8.81^c	45.04 ± 44.80^ef	15.18 ± 4.18^c	15.95 ± 3.43^b	100.35 ± 34.87^d
	Sm	2.87 ± 1.12^b	121.10 ± 75.07^a	18.93 ± 73.82^b	51.51 ± 33.43^c	17.91 ± 3.78^a	16.66 ± 3.67^a	103.03 ± 29.70^c
	Bo	3.62 ± 0.81^a	108.05 ± 60.69^d	21.98 ± 8.08^a	59.71 ± 44.68^a	17.10 ± 4.21^a	16.75 ± 4.05^a	109.95 ± 32.09^a
CCS	Yc	2.31 ± 1.01^b	79.66 ± 59.90^e	13.81 ± 6.78^f	38.09 ± 26.21^h	15.07 ± 4.48^c	14.47 ± 3.70^c	82.99 ± 35.33^g
	Aa	2.43 ± 0.97^b	106.51 ± 64.60^d	15.61 ± 6.39^e	44.23 ± 30.80^fg	16.23 ± 4.51^b	15.14 ± 3.68^b	85.31 ± 27.55^f
	Sm	2.76 ± 0.96^b	111.67 ± 66.46^c	16.53 ± 5.54^d	47.82 ± 28.59^d	16.93 ± 3.16^b	15.32 ± 2.87^b	90.00 ± 15.30^e
	Bo	2.99 ± 0.79^b	74.36 ± 46.80^f	21.58 ± 8.68^a	57.30 ± 47.52^b	17.96 ± 3.18^a	16.30 ± .2.24^a	106.89 ± 88.19^b
F		1.445	3.56	3.62	6.05	2.49	3.13	4.71
P		< 0.001	< 0.001	< 0.001	< 0.001	< 0.001	< 0.001	< 0.001

For each variable, means followed by different letters in the same column are statistically different when P < 0.05.

NSC: number of stems per cutting; LS: length of main stem; LW: width of leaf; LL: length of leaves; NLP: number of leaves per plant; ScP: scale of the plant; NDS: neck diameter of stem diameter at the stem collar; CCD: Chicken droppings compost; CCS: cocoa shell compost; Yc: Yacé; Bo: Bonoua; Sm: Six mois; Aa: Alleda agba; C: control

6.5. Effect of fertilizer and variety interaction on cassava yield variables

The evolution of yield variables of different cassava varieties according to the type of fertilizers applied are represented in table 5 and Fig. 1. Statistically, the mean values of the yield variables differed significantly (P < 0.001) according to the type of fertilizer and cassava variety. The number of tuberous roots per plant ranged from 3 to 4. Compost allowed cassava plants to develop more (4.71) tuberous roots than controls (3.13). And for each treatment, there was no significant difference between the number of tuberous roots produced by the four cassava varieties. In contrast, the mass of a tuberized root varied significantly by variety for each type of fertilizer. The highest tuberized root mass was obtained in the Bonoua and Six mois varieties for all treatments. However, the largest roots were obtained with the broiler dung compost, respectively 3.53 ± 1.47 Kg/plant and 3.24 ± 0.56 Kg/plant for the Bonoua and Six mois varieties. The best yields were thus obtained with these two varieties. Thus, the yields with the Bonoua variety were 35.26 t/ha and 27.13 t/ha respectively with the compost of chicken droppings and cocoa shells; and the yields 32.48 t/ha and 2.51 t/ha when the crop soil is fertilized with the compost of broiler droppings and cocoa shells respectively.

Table 5

Classification of yield variables measured on four cassava varieties subjected to two types of fertilizers
Fertilizers	Varieties	Performance variables
Fertilizers	Varieties	NTRP	WTR (Kg)	WTRP (Kg/plant)
C	Yc	3.50 ± 0.69^b	0.35 ± 0.06^f	1.22 ± 0.39ⁱ
	Aa	3.33 ± 1.04^b	0.37 ± 0.06^f	1.23 ± 0.43ⁱ
	Sm	3.13 ± 0.68^b	0.38 ± 0.06^f	1.18 ± 0.38^j
	Bo	3.25 ± 0.50^b	0.42 ± 0.05^e	1.36 ± 0.71^h
CCD	Yc	4.12 ± 0.69^a	0.37 ± 0.12^c	1.52 ± 0.88^g
	Aa	4.12 ± 0.77^a	0.46 ± 0.12^d	1.89 ± 0.81^e
	Sm	4.45 ± 0.62^a	0.73 ± 0.05^a	3.24 ± 0.56^ab
	Bo	4.71 ± 0.66^a	0.75 ± 0.06^a	3.53 ± 1.47^a
CCS	Yc	4.03 ± 0.70^a	0.43 ± 0.10^e	1.73 ± 0.82^f
	Aa	4.03 ± 0.77^a	0.58 ± 0.18^c	2.33 ± 1.11^d
	Sm	4.06 ± 0.63^a	0.62 ± 0.05^b	2.51 ± 0,89^cd
	Bo	4.11 ± 0.67^a	0.66 ± 0.07^b	2.71 ± 1.00^c
F		2.68	6.92	3.428
P		< 0.001	< 0.001	< 0.001

For each variable, the means followed by different letters are statistically different when P < 0.05.

CCD: compost of chicken droppings; CCS: compost of cocoa shells; Yc: Yacé; Bo: Bonoua; Sm: Six mois; Aa: Alleda agba; C: control; NTRP: number of tuberous roots per plant; WTR: mass of a tuberized root; WTRP: mass of tuberized roots per plant.

The result of the laboratory analysis showed a difference in the composition of the different fertilizers used. The percentage of mineral elements (N, P, K, Ca and Mg) measured was higher in the chicken droppings compost than in the cocoa shells compost. This difference in the percentage of N, P, K, Ca and Mg in the fertilizers could be explained by the difference and specificity of the organic residues used in each treatment. Indeed, according to Blanchard et al. (2014) [27] the content of fertilizer elements varies according to the type of organic matter used. Chicken droppings are a by-product of livestock production, whereas cocoa shells are a by-product of harvesting and are very crumbly. The addition of Acacia mangium leaves helped to consolidate the structure of the compost.

The results of the laboratory analysis of the chicken droppings and cocoa shell compost showed that it has a neutral pH and is rich in mineral elements. The compost is rich in carbon and nitrogen and low in phosphorus and potassium. In addition, it has a high amount of calcium and magnesium. The value of the C/N ratio showed that the mineralization of chicken manure compost is slow. A neutral or basic pH at the end of the composting process would be an indicator of a successful composting process, while the acidic pH would be due to the presence of acetic and lactic acids in the pile during composting [28]. The richness of mineral elements in chicken droppings compost could be explained by the mineral elements contributed by the poultry feed. The results of these analyses are similar to those obtained by Biekré et al. (2018) [29]. Similarly, the work done on poultry manure composts by Weill and Duval (2009) [30] had also shown that poultry composts were significantly richer in mineral elements.

Chemical analysis of crop soils before and after cassava harvest showed that composts had different effects on soil physical and chemical parameters after application. These analyses showed the beneficial effect of broiler droppings compost and cocoa shell compost on pH, magnesium, phosphorus and potassium levels, soil calcium maintenance and cation exchange capacity. Soils fertilized with composts were richer than others. In fact, the degradation of composts in the soil enabled the gradual release of nutrients (N, P and K) and a good nitrogen/carbon balance. These results are similar to those of Gani (2014) [31], who found that poultry droppings improved organic matter, nitrogen, phosphorus, potassium, calcium and magnesium concentrations compared to NPK fertilizer. These observations confirm those of Adeleye et al. (2010) [32] and Imasuen et al. (2015) [33], who also found an improvement in the pH of soils fertilized with poultry manure compared with the control. The potassium levels obtained at harvest provide information on the considerable contribution of potassium by poultry manure. In fact, whatever the fertilizer, the quantities of potassium remaining in the soil are greater than those in the crop soil without fertilizer. The results of this study confirm those obtained by Enujeke (2013) [34], [31] Gani (2014) and [33] Imasuen et al. (2015), who found poultry droppings to be rich in potassium. Chemical analysis of the soils sampled from the various sub-plots showed them to be slightly acidic. Fertilized soils generally showed good cation exchange capacity (CEC), and exchangeable bases were generally higher than controls. This result would be typical of tropical soils and specific to soils with their vegetation cover degrading [34]. Indeed, the land in the study area is regularly used for agriculture. As a result, the area is currently undergoing large-scale deforestation. Less dense plant cover is exposed to high evapotranspiration linked to the heat of the sun. Similarly, soils are subject to leaching of unstable ions such as Na + after rainfall. This has a negative impact on their physico-chemical parameters. Thus, cocoa and broiler compost with high CEC will retain and exchange large quantities of nutrients readily available to the plant [36]. What's more, the structure of composts ensures a constant renewal of organic matter in the soil. This makes them a favorable habitat for the proliferation and nutrition of soil microorganisms, which in turn mineralize the organic matter, making the various nutrients available to cassava plants [36].

The different cassava growth variables assessed in this study included the number of stems per cutting, stem length, stem neck diameter, number of leaves, leaves length and width, and plant scale. Cassava variety and type of fertilizer applied to the soil influenced the agronomic variables assessed. The agronomic variables obtained with the chicken manure composts had better growth compared to those obtained with the control. This result could be explained by the availability of minerals in the crop soil. Indeed, the application of the composts brought minerals to the soil that could be used by the plant. The improvement of soil fertility by the supply of nutrients had a beneficial effect on plant growth. Macro-nutrients such as nitrogen (N), phosphorus (P) and potassium (K) contained in these fertilizers have played essential roles in plant life. Nitrogen, as a component of photosynthetic pigments, especially chlorophylls, is essential for the growth of the plant and the formation of its tubers through the synthesis of carbohydrates via photosynthesis. Moreover, it is involved in the synthesis of proteins, especially enzymatic proteins, without which no metabolic activity can occur in living organisms. As for phosphorus, it is involved in the synthesis of chlorophylls and proteins. It also plays a role in cell division and therefore is involved in plant growth. Potassium, which is an important component of plant cells, influences the absorption of water by the roots. It plays a role in plant respiration and photosynthesis. In total, these three minerals have a positive influence on the vital activity of plants, namely photosynthesis. Indeed, it is through photosynthesis that carbon is incorporated into the plant and contributes to the synthesis of organic compounds in the plant. The results of this study are similar to those obtained by Coulibaly et al. (2019) [14]. These authors also observed an increase in corn growth after compost application. They explained their results by higher nutrient content in the compost and thus the availability of these nutrients to the plants.

It also appeared in this study that, for each variety, the best averages of growth variables were observed with the chicken droppings compost applied on the Bonoua variety's crop soil. The efficiency of this compost would come from its richness in mineral elements compared to the cocoa shell compost. Thus, with the continuous decomposition of compost, this fertilizer made mineral elements available to the cassava plants over a long period of time, allowing for better development. Thus, the application of compost alone could not provide the crops with the quantity of nutrients required for good agricultural production. Several authors have confirmed the effectiveness of organic manure is a better approach to improve and maintain soil fertility and agricultural production [37]. Indeed, organic fertilizers that follows the slow but continuous release of minerals. Under these conditions, the plant does not lack nutrients during its growth.

The results also showed that the evolution of yield variables differed among cassava varieties. The highest yield variable values and the best yield were obtained with the Bonoua variety. These differences in yield and yield variable values can be attributed to the genetic characteristics of the varieties. Indeed, the Bonoua variety has a trichotomous branching. This type of bearing allows it to develop many leaves, which are the seat of photosynthesis. This strong photosynthetic activity allows the synthesis of carbohydrates accumulated in the tubers. These carbohydrates are involved in rhizogenesis as well as in the growth of assimilating roots. Moreover, there is a correlation between the leaf mass and the absorption of water and nutrients: the transpiration of water through the stomata leads to the entry of water into the roots and thus its absorption and that of minerals. The other varieties, Six mois, Yacé and Alleda agba could develop fewer roots and/or assimilate few nutrients, as a result of less efficient photosynthetic activity, which could negatively influence their yield. Some authors such as Olaiya and Salami (2017) [38] found a significant difference in yield variables and yield when growing four yellow cassava varieties (IITA TMS 01/1368, IITA TMS 01/1371, IITA TMS01/1412 and IITA TMS 01/1593). However, the yields obtained in this study were significantly higher than those recorded by Olaiya and Salami (2017) [38] i.e. 9.33 t/ha. The observed difference could be related to cassava variety and/or plot treatment.

Fertilization in agriculture is a contribution to yield improvement. The objective of this work was to evaluate the effect of cocoa shell compost and chicken droppings compost on cassava agronomic variables. This evaluation revealed a variability in the response of cassava varieties to these different fertilizers compared to the control block. The fertilizers improved the agronomic variables of cassava. However, the best improvements were observed when chicken dropping compost was incorporated into the soil of the Bonoua variety. Thus, in order to achieve higher yields, the Bonoua variety could be grown on a plot fertilized with chicken manure compost or cocoa shell compost.

Author Contribution

KKM carried out the field experiments and wrote the main textKKI supervised the experiments and wrote the main textKKH and BBS participated in processing and figuring. All authors revised the manuscript.

Data Availability

All data generated or analyzed during this study are included in this published article and its supplementary information files.

Plant ethics

The methods, study and protocol were carried out in accordance with current guidelines and regulations on cassava.

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Agronomic potential of four cassava (Manihot esculenta Crantz) varieties grown on soils fertilized with cocoa shell compost and chicken dropping compost in Côte d’Ivoire

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Version 1

Abstract

Figures

1. Introduction

2. Study site

3. Plant material and fertilizer

4. Preparation of cocoa shell compost and chicken dropping compost

5. Methods

5.1. Collection and preparation of soil and compost samples

5.2. Experimental design

5.3. Observations and measurement of cassava agronomic variables

5.4. Data analysis

6. Results

6.1. Chemical characteristics of the different broiler droppings and cocoa shells composts

6.2. Physico-chemical parameters of the test soils

6.3. Overall effect of different factors on cassava agronomic variables

6.4. Effect of fertilizer and variety interaction on agronomic variables of cassava growth

6.5. Effect of fertilizer and variety interaction on cassava yield variables

7. Discussion

8. Conclusion

Declarations

Author Contribution

Data Availability

Plant ethics

References

Additional Declarations

Status:

Version 1