1.  Introduction

Livestock manure supplies all major nutrients (N, P, K, Ca, Mg, S) necessary for plant growth, as well as micronutrients [1]. The effects are long lasting as the application of manure improves the performance of the crops grown in a given year while the residual effects will continue to influence crops in the succeeding years [2]. This arises because the decomposition of the organic material is continuous and not completed within one year [3]. Thus, in the many experiments conducted to compare manure with an equivalent amount of NPK (chemical fertilizer) and most often, the results favoured manure [4-6]. The reasons for the superiority of manure include: low decomposition rate of organic matter resulting in a slow release of nutrients; increase in infiltration rate with more rain water and irrigation water entering the soil; and decrease soil bulk density resulting in a greater capacity for more air and water within the soil.

Compost is an organic fertilizer made from the regulated and monitored biological breakdown of organic materials that have been sterilized, stabilized, and cured to the point where they are useful to plant growth [7-8].  Its use alleviates the nutritional, physical and biological aspects of soils by increasing soil organic matter quality and quantity, as well as the number, diversity, and activity of soil organisms [9]. Therefore, compost has become a valuable ingredient in organic farming on account of several beneficial aspects: saves money that could have been used for buying fertilizers; improves the soil physical, chemical and biological properties; feeds the soil which feeds the plants that feed the animals and the whole world; increases the nutrition of growing plants which leads to good nutritional quality and increased human health [10].

The word amaranthus comes from the Greek word “amarantos” meaning the one that does not wither or never fading (flower). Amaranthus species are ancient cultivated crops that have long been neglected by Western agriculturists and gardeners. Amaranthus species were ranked major potential crops with the most promising economic values among the 36 underexploited tropical plants indicating that there are untapped prospects and potentials in their utilization [11].  Amaranthus (vegetable and grains) is one of the food plants to improve nutrition and the quality of life in developing countries. Amaranthus hybridus is an important vegetable crop in Nigeria and other parts of the world. In Nigeria, vegetable amaranth is planted all year round and harvested for food [12]. The local synonyms in Nigeria are alayyafu or aleho (Hausa), ẹfọtẹtẹ or tẹtẹ (Yoruba), and inine (Igbo). In the 70s, there was renewed interest in the cultivation of amaranth due to the discovery that the crop is a cheap and rich source of protein, vitamins and minerals [13]. Amaranthus hybridus is useful for livestock feed [14] and human consumption being a source of leaf protein concentrates, essential amino acids (Lysine and Methionine), minerals (especially calcium and iron), vitamins (carotene, riboflavin, niacin) and other essential nutrients needed for feeding young children and other persons with nutritional deficiencies or malnutrition [15-16].

Amaranthus plants thrive well on poultry and other farmyard manure-amended soils. It grows in full length and is most productive on soils with high organic matter and adequate nutrient reserves [5, 17]. This is on account of nitrogen (N) needed for luxuriant growth of crops, especially leaf vegetables, but only a small quantity, between 0.5 to 2.5 % (dry weight basis) exists in finished composts [18]. Thus, there is the need to identify the materials which will give higher N quantity when composted, or used to enrich the composted materials with N. Inorganic fertilizers had been used to fortify/amend organic fertilizers, to raise their N content; but these have recently been reported as scarce and expensive, and therefore unavoidable to most farmers apart from the fears that the use of synthetic products, including inorganic fertilizers is unhealthy for the contact environment. Therefore, the need has become urgent to evaluate the potential of organic materials as N-enriching substances in composts. The positive effects of composts enriched with organic N-rich substances on soil N, P and K have been reported [19-20]. In this study, the organic N-rich materials (common agricultural wastes and weeds) were added to the common compost materials in order to improve the N status. The materials were Mexican sunflower, neem, blood and bone meals, hoof and horn meals.

1.1 The organic wastes used in the study

1.1.1    Poultry manure

Poultry manure is a valuable, concentrated and quick releasing organic fertilizer [21]. It contains all the basic nutrients necessary for crops but in much greater amounts; 3-5% N, 1.5-3.5 % P and 1.5-3.0% K [22], 3% N, 2.5% P and 1.8% K [23]. All nutrient contained in poultry manure takes the form of available compounds. Most of the nitrogen (N) in it is in the form of uric acid which turns in storage, first to urea and then to ammonium carbonate under unfavourable storage conditions [24]. Poultry manure is applied both before sowing and for dressing. Poultry manure enhances soil fertility by combating soil improvement, promoting soil structure, supplying and retaining water until decomposition is completed, this aids the breakdown of organic matter and also makes a living soil moister than soil with no organic matter. Poultry manure activates soil life: giving food to soil inhabitants that change them into organic matter, which decays and is in turn changed into humus releasing mineral nutrients.

1.1.2    Cow dung

Cow dung is the waste of bovine animal species. Cow dung is the undigested residue of herbivorous matter which has passed through the animals guts. The resultant faecal matter is rich in minerals [25]. Cow manure contains 3% nitrogen, 2% phosphorus, and 1% potassium—3-2-1 NPK [26]. Colour ranges from greenish to blackish, often darkening in colour soon after exposure to air. Cow dung (usually combined with soil bedding and urine) is often used as manure (agricultural fertilizer). If not recycled into the soil by species such as earthworms and dung beetles, it dries out and remains on the pasture, creating an area of grazing land which is unpalatable to livestock [27].

1.1.3    Sawdust

This is composed of fine particles of wood. This is produced with the use of cutting wood with a saw. It has a variety of practical uses including serving as mulch, as a fuel or for the manufacture of particle board. Sawdust is high in carbonaceous compounds (lignin, cellulose and pectin) and low in useful plant nutrients such that for bacterial decay to occur, carbohydrates for energy and N to build new bodies as they grow and multiply are needed [28]. The N deficiency limits building of bacterial tissues and can deplete available nitrogen in soils and thereby hinder plant growth. The N consumed by microorganisms becomes available and utilizable to crops after the sawdust is degraded.

1.1.4    Bone meal

From every cattle slaughtered, about 70-90 kg bones are obtained, which could thereafter be washed, dehydrated and burned-out so as to convert to bone meal which has a huge market in livestock feed and fertiliser industries [29]. Animal bones are cooked, ground, packed and then sold as a slow release fertiliser that adds a good amount of P to the soil [30]. It also contains Ca [30]; of about 12–13% [31] and NPK ratio of approximately 3:15:0, indicating that they are low in nitrogen (N) and potassium (K) but high in phosphorus (P) [32-33]. Bone meal is emphasized as an effective soil amendment especially on degraded soils where the physical properties of soil are unaffected by inorganic fertilisers [34].

1.1.5    Blood meal

Slaughtered cattle give out 25 litres of blood which is rich in N as it contains 12% N [35] and so can be used as an enrichment material for a finished compost in order to increase its N content [29]. Blood meal is a high-nitrogen fertiliser created from a dry, inert powder made from blood. The release of N is rapid and it is suited to fast growing vegetables. Blood meal is water soluble and it can be used as a liquid fertiliser [30], which could balance the C: N ratios of composts.

 1.1.6    Hoof and horn meal

The cooked, ground and dehydrated hooves and horns obtained from cattle slaughter houses are good N sources (12%) and contain about 2% P which makes the meal a 12-2-0 NPK fertiliser. It is alkaline in nature and so a good choice for improving acidic soils [36]. The N is locked inside the horn and hoof meal is released slowly so that it does not burn the plants [37]. The N release starts at 4-6 weeks after application and can last for 12 months [38].

1.1.7    Tithonia diversifolia

Mexican sunflower (Tithonia diversifolia) is a juicy soft shrub belonging to the Asteraceae family, which had its source in Mexico and Central America but has a practically pan-tropical distribution [39]. It is currently found in most parts of America, Asia, and Africa [40]. The leaves and succulent stems decompose readily when applied to the surface of the soil or integrated into it to release and make available nearly all the N in about 2 weeks [41]. As a result, it provides a vital source of biomass and nutrients for short term crops, supplying N, P and K in quantities comparable to or better than poultry, cattle and swine manure [42]. It has nutrients averaging 3.5% N, 0.37% P and 4.1% K on dry matter basis [43]. The best fertilizer is made when the plant is dark green and about 1 m tall. Once the plant has flowered it is no longer high in N as most of it has been used in producing the flowers and seeds [44].

 1.1.8     Neem

The tree called neem (Azadirachta indica) is a member of the family Meliaceae. It reportedly originated from India, Pakistan, and Bangladesh, but it can also be found in tropical regions [45]. Its leaf litter brings the surface pH of acid soils to neutral [46] and the leaves are valuable as mulch, amendments to neutralize soil acidity, as fertilisers, resulting in increased crop growth and output [47]. Neem by-products (the seedcake and leaves) can be used to enhance local soils and encourage long-term productivity. Neem fruits contain 3.3% N, 4.1% P and 3.8% K while neem leaves contain 2-3% N, 1% P and 1.4% K. [48-49] Neem leaf mould applied to the soil along with sawdust was used in suppressing the populations of plant parasitic nematodes on tomato [50]. The azadirachtin repels and disrupts the growth and reproduction of insects; melantrior causes insects to cease feeding and sallanin inhibits feeding while nimbin and nimbidin have antiviral activities [51].

2. Materials and methods

2.1 Study site

The experiment was conducted at the Teaching and Research Farm of the Ekiti State University, Ado-Ekiti, Ekiti State, Nigeria. The soil was a slightly acidic (pH (H2O = 6.4) loamy sand, with moderate organic matter content (22.2 g/kg), total N (2.3 g/kg) and exchangeable K (0.3 cmol/kg) while the available P was low (4.47 mg/kg) [19-20].

2.2 The treatments

The two composts were alkaline with pH at 8.0 and 8.3 for PDS and CDS respectively. The CDS contained higher total N and K (6.4 and 6.1 g/kg) while PDS contained higher total P (23.0 g/kg) [19-20].

The Sixteen (16) treatments applied in three replicates are:

PDS=Poultry dung/ Sawdust

PDSBN= Poultry dung/Sawdust enriched with Bone meal at 60 g/kg N

PDSBM=Poultry dung/Sawdust enriched with Blood meal at 60 g/kg N

PDSTM=Poultry dung/Sawdust enriched with Tithonia at 60 g/kg N

PDSHN= Poultry dung/Sawdust enriched with Horn meal at 60 g/kg N

PDSHM=Poultry dung/Sawdust enriched with Hoof meal at 60 g/kg N

PDSNM=Poultry dung/Sawdust enriched with Neem at 60 g/kg N

CDS=Cow dung/Sawdust

CDSBN=Cow dung/Sawdust enriched with Bone meal at 60 g/kg N

CDSBM=Cow dung/Sawdust enriched with Blood meal at 60 g/kg N

CDSTM=Cow dung/Sawdust enriched with Tithonia at 60 g/kg N

CDSHN=Cow dung/Sawdust enriched with Horn meal at 60 g/kg N

CDSHM= Cow dung/Sawdust enriched with Hoof meal at 60 g/kg N

CDSNM=Cow dung/Sawdust enriched with Neem at 60 g/kg N

NPK, Soil Alone, there were a total of 48 plots.

2.3 Parameters measured

The parameters measured on the field are plants height, number of leaves, stem girth, leaf width, leaf area and total yield. The parameters were measured at 5^th, 6th, and 7^th week after sowing.

2.4 Planting, Weeding and Harvesting

Compost treatments were randomly assigned to various plots, of 2 m × 4 m each using completely randomized design (CRD). The different treatments were weighed and mixed with soils of the assigned plots at the rate of 30 t/ha. Sowing of amaranth seeds, at 2.5 kg/ha was done by broadcasting, two weeks after composts’ application. Application of NPK, to the designated plots, at 400 kg/ha was also done by broadcasting, two weeks after sowing. Weeding was done twice during the period of study, by uprooting at 3 and 6 weeks after sowing. Sample seedlings were taken for measurements of growth parameters: plant height, leaf area, stem girth, number of leaves and marketable yield (obtained by uprooting and rinsing of vegetables to remove the attached sands). Harvesting was done at 5, 6 and 7 weeks after sowing, by uprooting the vegetables.

2.5 Data analysis

Data collected were analyzed using the analysis of variance (ANOVA) and the means were separated using Duncan multiple range test at p=0.05.

 3. Results and discussion

3.1     Performances of Amaranth treated with the organic N-enriched composts

Growth and yield performances of amaranth treated with composts enriched with organic N sources at 5 weeks (WAS) are as indicated in Table 1. CDSNM and PDSNM produced the tallest plants (29.7 cm), and highest number of leaves (PDSNM= 13.7 and CDSNM= 13.3 cm) which did not differ from more leaves (PDSNM= 13.7 and CDSNM= 13.3 cm) though not significantly different from NPK treatment. The thickest stems were obtained from the NPK treatment but which were not significantly different from all N-enriched CDS based composts but significantly differed from all PDS based composts except the PDSNM. The NPK treatment gave the highest leaf width (43.3 cm) which was not different significantly from only CDSNM while the leaf area (53.83 cm²) was significantly different from the control, PDSBM, PDSHN, CDSBM and CDSHN. The highest marketable yield of leaf amaranth (17.6 t/ha) was produced from the NPK treatment which was not significantly different from 15.2 t/ha obtained from (CDSNM) while the composts gave higher yields than the control. The CDSNM compared well with NPK as an indication of fast N-releasing ability of CDSNM. [19] reported a steady release of N, and probable reduction in fixation of available N in CDSNM.

Table 1: Responses of Amaranth to composts enriched with organic N sources at 5 WAS 

Treatments	Plant Height (cm)	Number of leaves	Stem Girth (cm)	Leaf Width (cm)	Leaf Area (cm2)	Marketable Yield (t/ha)
Control	22.00def	8.00d	2.50abc	20.00e	29.26f	8.00d
NPK	27.30abc	11.30abc	2.80a	43.33a	53.83abc	17.60a
PDS	19.70f	9.70cd	2.10bc	28.00cde	46.15abcde	11.20bcd
PDSBN	24.70bcde	11.30abc	2.07cd	25.00de	44.20abcdef	10.00cd
PDSBM	26.00abc	11.70abc	2.03dc	30.67bcd	36.42def	12.27bc
PDSTM	21.00ef	10.70abcd	2.17bc	35.00bc	43.97abcde	13.00bc
PDSHN	22.00def	10.00cd	1.57d	27.00cde	32.80def	10.80cd
PDSHM	28.70ab	12.70abc	2.10c	28.67cd	37.87cdef	11.37bcd
PDSNM	29.70a	13.70a	2.67ab	31.00bcd	54.33ab	12.40bc
CDS	25.7abcde	11.30abc	2.03cd	26.00de	47.13abcd	10.40cd
CDSBN	22.70cdef	10.30bcd	2.30abc	23.67de	40.67bcdef	9.47cd
CDSBM	25.3abcde	11.30abc	2.37abc	26.33de	30.33ef	10.53cd
CDSTM	27.00abc	11.70abc	2.53abc	29.67cd	44.13abcdef	11.87bcd
CDSHN	24.3bcdef	10.70abcd	2.43abc	27.33cde	33.33def	10.93cd
CDSHM	25.0abcde	10.00cd	2.30abc	27.33cde	38.22bcdef	10.93cd
CDSNM	29.70a	13.30ab	2.57abc	38.00ab	57.83a	15.20ab
Means with the same letters in the same columns are not significantly different at α0.05

At 6 WAS (Table 2), the NPK treatment produced the tallest plants (54.67 cm), which differed significantly from all treatments except CDS (51.00 cm) while PDS gave the shortest vegetables (29.00 cm). The values of the growth parameters for CDSNM were lower than those obtained at 5 WAS probably as it released the N faster than PDSNM and some of the other composts. [19] reported a lower C: N ratio of the CDS than PDS which is an indication that N would be released earlier and faster in CDS. The NPK treatment outperformed most of the enriched composts, including CDSDNM in most of the growth parameters measured and marketable yield (18.53 t/ha) which was not significantly different from PDSHM (16.40 t/ha), PDSNM (17.47 t/ha), CDS (17.47 t/ha) and CDSBM (16.00 t/ha). The thinnest vegetables (28.33 cm) with the smallest leaves (20.67 cm in width) and lowest yield (8.27 t/ha) were obtained from plots treated with CDSHN.

Table 3 shows that the NPK-treated plots at 7 WAS produced the highest marketable yield (22.67 t/ha) but was not significantly different from the control, PDSHM, CDSHM and CDSNM. The CDSBM gave the lowest vegetable yield of 8.93 t/ha at 7 WAS. The CDSBM gave the lowest vegetable yield of 8.93 t/ha at 7 WAS. Some of the composts decreased in yield and most of the growth parameters between the weeks PMSD, PDSTM, CDSTM, CDSHN and CDSNM gave lower yields at 6 WAS but increased at 7 WAS while PDSHN, PDSNM, CDS, CDSBN and CDSBM had yield increase at 6 WAS but reduced at 7 WAS. The yields of PDSBN, PDSHM and CDSHM treatments increased throughout the study period.

The enriched composts were comparable to NPK 15-15-15 and PMSD, PDSTM, CDSTM, CDSHN and CDSNM, which gave reduced yield values at 6 WAS could be recommended for short-season vegetables. [19] had noted the suitability of PDSTM for short-season vegetables and CDSNM for both short and long-season crops, including vegetables.

Table 2: Responses of Amaranth to composts enriched with organic N sources at 6 WAS 

Treatments	Plant Height (cm)	Number of leaves	Stem Girth (cm)	Leaf Width (cm)	Leaf Area (cm2)	Marketable Yield (t/ha)
Control	31.00efg	11.00a	2.90ab	29.00fg	32.00e	11.60fg
NPK	54.67a	13.67a	3.00a	46.33a	53.83bc	18.53a
PMSD	29.00fg	11.00a	2.90ab	25.00gh	48.15bcd	10.00gh
PDSBN	30.00efg	13.67a	2.60abcd	26.00gh	45.95cde	10.40gh
PDSBM	30.00efg	12.67a	2.43bcd	23.00gh	38.13de	9.20gh
PDSTM	34.00edf	14.00a	2.60abcd	28.33fg	47.17bcd	11.33fg
PDSHN	31.67ef	13.00a	2.63abcd	33.33def	35.02de	13.33def
PDSHM	36.00cde	12.67a	2.87ab	41.00abc	37.73de	16.40abc
PDSNM	41.33bc	12.33a	2.73abcd	43.67ab	110.30a	17.47ab
CDS	51.00a	14.00a	2.93ab	43.67ab	41.65de	17.67ab
CDSBN	33.33def	12.67a	2.83ab	37.33bcde	38.73de	14.93bcde
CDSBM	42.33b	12.33a	2.80abc	40.00abcd	31.73e	16.00abcd
CDSTM	24.67g	10.67a	2.63abcd	24.33gh	42.15de	9.73gh
CDSHN	28.33fg	11.67a	2.33cd	20.67h	37.07de	8.27h
CDSHM	31.67ef	12.33a	2.87ab	30.33efg	39.75de	12.13efg
CDSNM	38.33bcd	14.00a	2.90ab	34.33cdef	60.50b	13.73cdef
Means with the same letters in the same columns are not significantly different at α0.05

 

Table 3: Responses of Amaranth to composts enriched with organic N sources at 7 WAS 

Treatments	Plant Height (cm)	Number of leaves	Stem Girth (cm)	Leaf Width (cm)	Leaf Area (cm2)	Marketable Yield (t/ha)
Control	38.00bcd	15.00a	2.700cd	44.00ab	39.25fg	17.20ab
NPK	52.00a	13.00abc	3.200a	56.67a	63.08b	22.67a
PDS	31.00cde	11.33bc	2.700cd	31.00bc	42.25fg	12.27bc
PDSBN	26.67de	10.67c	2.700cd	30.33bc	52.72cde	12.00bc
PDSBM	29.33cde	13.00abc	2.77abcd	36.00bc	43.33efg	14.40bc
PDSTM	37.33cde	11.33bc	2.73bcd	31.33bc	55.33bcd	12.40bc
PDSHN	30.67cde	11.33bc	2.50cd	25.67bc	37.82fg	10.27bc
PDSHM	40.00bc	13.33abc	2.97abc	44.33ab	39.40fg	17.33ab
PDSNM	32.00cde	12.33abc	2.83abc	37.00bc	112.00a	14.67bc
CDS	29.67cde	10.67c	2.63cd	29.33bc	47.83def	11.73bc
CDSBN	25.00e	11.33bc	2.73bcd	36.33bc	38.07fg	14.40bc
CDSBM	25.67e	13.33abc	2.30d	22.33c	33.33g	8.93c
CDSTM	29.67cde	15.33a	2.63cd	29.33bc	38.82fg	11.60bc
CDSHN	25.33e	12.67abc	2.60cd	24.33bc	37.33fg	9.73bc
CDSHM	44.00ab	14.00ab	2.17ab	43.00ab	40.67fg	16.80abc
CDSNM	37.00bcde	14.00a	2.83abc	42.00abc	62.32bc	16.40abc
Means with the same letters in the same columns are not significantly different at α0.05

 

4. Conclusions

The composts: CDS and PDS did not differ from the control treatment in leaf amaranth growth and marketable yields. This makes additional N input inevitable to ensure that the N level in composts would support crop performance. This was achieved with organic N materials as the ensuing enriched composts gave higher growth and yield parameters than the control and compared favourably with the quick nutrient-releasing NPK 15-15-15 fertilizer in the growth and yield measurements. The implication is that the enriched composts would effectively replace inorganic fertilizers for soil management and improvement, especially while putting the life cycle of crops into consideration. PMSD, PDSTM, CDSTM, CDSHN CDSNM PDSHN, PDSNM, CDS, CDSBN and CDSBM, are recommended for short-season crops and PMSD, PDSTM, CDSTM, CDSHN and CDSNM, whose yield values increased at 7 WAS could also be useful for long-season crops, while PDSBN, PDSHM and CDSHM with continuous yield increase should be adopted for both short and long-season crops.

Authors’ contributions

Conceptualization, A.F.O; Methodology, A. F. O.; Software, A.F.O. and O.S.O.; Validation, A.F.O. and O.S.O.; Formal Analysis, A.F.O.; Investigation, A.F.O.; Resources, A.F.O.; Data Curation, A.F.O.; Original Draft Preparation, A.F.O.; Review & Editing, O.S.O.; Supervision, A.F.O.; Project Administration, A.F.O; Funding Acquisition, A.F.O. and O. S. O.

Availability of data and materials

All data generated or analyzed during this study are included in this published article.

Funding

This research received no specific grant from any funding agency “(the public, commercial, or not-for-profit sectors).

Conflicts of interest

The author declares that there is no conflict of interest regarding the publication of this paper

Acknowledgement

We wish to acknowledge the student who worked with us, in person of Adetoro, Bukola Eniola. Immense thanks to her.        

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