Advances in the Use of Organic and Organomineral Fertilizers in Sustainable Agricultural Production

Abstract

To achieve high production in the current agricultural environment and increase soil quality for the plants, new technologies must be developed. It is becoming more and more important to adopt systems that can deliver higher production along with efficiency in the provision of nutrients in order to achieve sustainable agriculture. Despite improvements and novel techniques in modern agricultural practices, most of the global agriculture sectors still use conventional methods; as a result, it has sustainability and fertility issues. Since many yield-limiting problems are seriously hampering global agriculture, urgent action is needed to rehabilitate these soils; hence, the use of both organic and synthetic fertilizers was decreased by the usage of organomineral fertilizers (OMFs), which worked in concert with one another. When compared to inorganic fertilizers, the OMF improved soil physical qualities, as evidenced by a decrease in bulk density, high temperature, and preservation of soil moisture. The OMF increased soil organic matter, nutrient content, and cation availability compared to inorganic fertilizer. To increase the soil’s nutrient content, pH, and crop nutrient uptake, organic wastes like poultry manure, oil palm bunch ash, cocoa pod ash, kola pod husk, and sawdust ash were successfully blended with inorganic fertilizers for efficient productivity.

1. Introduction

In Africa, where population growth is growing at a pace of 3% annually, this problem of the adequate food supply is especially critical. Additionally, more than 50% of Africans live in rural areas and are totally reliant on locally cultivated food crops that are taken from their immediate surroundings [1]. The traditional bush fallow period for preserving soil productivity under shifting cultivation is no longer practical due to the growing strain of population on the land, causing a shift toward marginal lands and an intensification of cultivation on productive fields [2]. The quest for agricultural production has increased as a result of the growing world population. This has caused a shift into marginal lands and an intensification of cultivation on fertile lands [2] and resulting in an increase in the reliance on added nutrients. In the years 2016–2021, it is predicted that the global demand for N, P, and K will rise by 1.4%, 2.2%, and 2.6% annually, respectively [3].

Utilizing organic waste to create organomineral fertilizers (OMFs) is one promising alternative. OMF is the result of physically combining organic and mineral sources of nutrients. The proportion of the primary macronutrients (N, P, and K) or their combination with other nutrients such (NP, NK, PK, or NPK) should be at least 10% in these fertilizers. OMFs may be supplemented with supplies of P, N, or K in order to comply with the law [4]. The Food Agricultural Organization recently promoted integrated plant nutrition (IPN), often known as integrated nutrient delivery or integrated nutrient management system. In order to supply crops with nutrients, a system of soil conservation farming and both organic and inorganic fertilizers is used. The idea is mostly supported in the tropics, especially in the wet tropics, where chemical or inorganic fertilizers have not revolutionized agricultural productivity as expected [1]. Chemical fertilizer (CF) has continually increased crop productivity over the world, notably in temperate agriculture, with an average yield gain of 50% being attributed to it (CF). In addition to driving up production costs, excessive use of CFs jeopardizes food safety and exacerbates problems like energy depletion, resource scarcity, and environmental damage. These issues, which have become more pressing in recent years, pose significant challenges. The significance of organic matter (OM) returning to the field and the development of organic fertilizers (OFs) on this basis in agricultural output have attracted new attention in the modern context of ecological agriculture's rapid development and environmental protection [5].

In comparison to inorganic fertilizer, OMFs, a new fertilizer that combines the benefits of organic and synthetic fertilizers, have an effect on nutrient release that coincides with the crop's growth phase [6]. When compared to CFs, OMFs can lessen the loss of some nutrients like potassium leaching, nitrogen volatilization, and phosphorus fixation. When compared to typical OFs, OMFs are abundant in the minerals needed for agricultural growth [7]. A successful soil fertility management method has been demonstrated to involve complementary fertilizers usage [8]. To replenish the soil and enhance plant fertilization, OF may be produced with inorganic minerals added. It disperses nutrients into the soil in a way that makes them simple for plants to absorb. It may also encourage soil microorganisms and boost their population, which will speed up the breakdown of organic compounds. Increased plant growth, healthier crops, and improved fruit production will result from this. It lowers the demand for CF, resulting in cheaper production costs and indirect income growth [9].

An important fertilizer technology is an ability to combine organic and mineral sources into a single formulation because it increases the effectiveness of the nutrient sources, offers better protection from the elements, and encourages the monitoring of the physical, chemical, and microbiological properties of the soil [10]. Applications of OMF are essential steps in the growth of organic agriculture in karst mountain areas. Yet it is still unclear how OMF impacts soil microbial diversity's organization and functioning, as well as how these elements connect to crop output and quality [2]. It is known that CFs have not had an essential influence on tropical agriculture, particularly in Nigeria, where it is impossible to produce crops sustainably using only CFs [11, 12, 13].

CF use efficiency and effectiveness issues are widely known. They include soil acidity caused by the repeated use of acid-forming substances, applications that are frequently made without considering the results of soil tests, an imbalance in the supply of nutrients, physical degradation of the soil, scarcity, high cost, and insufficient use as well as losses from volatilization, erosion, and leaching [13, 14, 15]. There are benefits and cons to both conventional and organic farming. Combining organic and mineral inputs is one interesting strategy that could be used [16]. This may be the ideal alternative to increase agronomic effectiveness and crop output while maintaining the long-term fertility and health of the soil, according to several research studies [17, 18, 19, 20]. Theoretically, both resources are compatible. While interest in this concept has grown recently, a brand-new category of fertilizer product known as OMF has been developed.

Although modern biofertilizers like azolla and mycorrhiza as well as organic manures including sewage water, green manure, animal wastes, fallow fields, human excreta, and crop residues (e.g., in Ghana and China) has been essential to crop production for centuries, total dependence on OFs is hindered by issues like insufficient availability, heavy metal pollution, unsuitable or low quality, high C:N ratio, bulkiness, and gradual nutrients release [21, 22].

However, the only source utilized in small-scale cropping is organic wastes, which led to the accumulation of OM and nutrients, biological buildup, and significant advancements in the soil's physical characteristics, as shown by a fall in bulk density and a rise in porosity, a decrease in runoff and erosion due to an increase in infiltration, the stabilization of the soil structure, and an increase in soil pH, etc. High levels of macro- and micronutrients can be found in crop and animal waste. OMFs are frequently noted for their many advantageous effects on agrosystems, including their capacity to increase plant physiological features and soil physico-chemical and biological functions [23, 24, 25, 26, 27, 28, 29].

Combining organic and inorganic fertilizers is essential for maintaining soil fertility. A long-term increase in soil productivity and quality will result from efforts in this direction. It is believed that these elements will increase crop growth, yield, and quality while reducing the price of production and fertilizing and making sure that plants receive adequate nutrients [30, 31]. Utilizing agricultural, human, and municipal wastes, among other things, IPN will also help with environmental cleanliness. It is a program to turn waste into wealth. As compared to CFs, the physical, chemical, and biological properties of the soil will be improved overall using IPN [23]. The IPN improves crop performance by integrating the benefits of both organic and inorganic fertilizers.

Studies on soil fertility have recently concentrated on IPN in developing and tropical nations. Since the 1960s, India has been setting the bar higher in this area. IPN research is still very new in Nigeria. State governments in Nigeria started producing organic and OMFs after realizing the value of OM in sustaining soil production and the need to enhance its quality and nutrient release. Utilizing agricultural and municipal trash at their facilities is another goal to promote environmental sanitation. Nutrient cycling and conservation in farm systems are ensured by using agricultural wastes to create organic and OMFs. Additionally, nutrients that have already been taken away by towns can at least partially be recovered. The organic and OMF companies already functioning in Nigeria include those of Oyo and Ondo States, which, respectively, are named Pacesetter and Sunshine fertilizer companies.

2. Current fertilizer trends

In order to address these nutrient deficits, it has been recommended for crop production in the tropics to utilize CFs intensively at the recommended rate (NPK 15:15:15) [18]. Currently, employing CFs as soil amendment has grown expensive and is frequently associated with adverse environmental repercussions (causing residual effects on the soil). Given these issues, several alternatives to CFs include crop rotation, organic manure, agricultural waste, legumes, and green manure [21]. The bulk of the world's agriculture industry continues to use conventional ways despite advancements and contemporary approaches in current agricultural practices; as a result, it suffers sustainability and fertility problems. Additionally, the usage of CFs improperly to improve agricultural yields and the expansion of various cropping methods are both contributing to the continued reduction in soil fertility [32]. The application of abundant refuse in our community is an outcome of the capability of biological substances to boost output, enhance soil richness, and stimulate crop proliferation [33]. According to [34], the use of cow dung in combination with NPK manure was more potent in enriching soil chemical properties, nutrient uptake, growth, and yield of crops than using either biological (cow dung) or artificial (NPK) manure alone

Since many yield-limiting problems are seriously hampering global agriculture, urgent action is needed to rehabilitate these soils (a rise in disease outbreaks, an invasion of pests and insects, and unpredictable weather). Therefore, it is debatably believed that agricultural operations constitute a significant source of CO₂ that damages the climate and contributes to global warming. The amount of residues thrown away rose due to the huge agricultural expansion in the twenty-first century. Farmers started recycling or reusing materials in greater quantities as a result, discovering the synergistic benefits of organic and mineral fertilizers [16]. However, it is currently not economically feasible to spread significant amounts of OFs across a wide area. Mineral components are added to the biofertilizer to enrich it, which results in higher yields and lower costs. Farmers and businesses in the sector must deal with genuine challenges such as logistics, infrastructure for manufacturing, and the availability of raw materials suitable for enriching mineral sources. The method is hampered by constraints related to composition knowledge and residue treatment [16].

Natural organic elements are used to create OFs without being significantly altered. Depending on the source of the OM, they have varying levels of nitrogen, phosphorous, potassium, and other nutrients. In addition to providing the plants with nutrients, these fertilizers improve the physical, chemical, and biological properties of the soil, assisting in the growth of the plants. Organic fertilizers come in a wide range of varieties. The primary sources of OFs are farmyard manure, which includes animal excrement and litter, domestic organic wastes, wastes from the food and agriculture industries, wastes from wood processing and harvesting, compost, mosses, vermicomposts, treatment sludge, and waste from the production of biogas [35, 36].

CFs can quickly and considerably boost agricultural yield and soil fertility. CFs impair soil microbial populations and biological activities when they are applied in excess over an extended period of time, which lowers soil quality, increases crop growth's reliance on fertilizer nutrients, and exacerbates agricultural surface source pollution [37, 38]. More than 200 million tons of fertilizer (N, P, and K) will be used annually around the world by the year 2020 [39]. This is concerning since fertilizers have detrimental effects on nearby ecosystems and soils. Additionally, the use of insecticides to stop and manage plant diseases is expanding at a riskier rate. A new breakthrough is the creation of smart fertilizers based on nanotechnology, with a focus on controlled-release and/or carrier/delivery systems to synchronize nutrient availability with plant demands and minimize environmental losses (Figure 1) [41].

Figure 1.

Effects of smart fertilizers on the soil-plant system are shown schematically [40].

When CFs are irresponsibly used to boost production, it seriously jeopardizes the long-term soil fertility, the soil environment, and each of its constituent parts. However, the soil microbial community performs a significant and crucial function in promoting soil health and plant growth [4]. While CFs, especially N and P fertilizers, have a significant negative impact on the microbial community, they also have a profound negative impact on plant growth. Sustainable agricultural methods can preserve soil fertility and productivity while reducing the depletion of natural resources. Moreover, they safeguard against soil degradation, facilitate the development of beneficial soil particles, and can loosen the ground when applied as a natural fertilizer [42, 43].

Given that it is predicted that there will be 9.3 billion people on the planet by the year 2050, there will likely be a 60% rise in the need for food during that time [44]. The production of agriculture and food is one of the primary factors in the depletion of natural resources. The era of affordable feedstock has ended. Because demand grows more quickly than available production capacity, resource scarcity drives up input and production costs and tightens the market. Food security may be achieved through the efficient and sustainable utilization of natural resources [45].

In the current situation, the decline in fertility brought on by intensive agricultural methods is of enormous significance. Increased productivity might be achieved by raising fertility in intensive farms or on non-arable land, which would increase food output without further taxing the environment. The secret to balancing crop production on a commercial basis is fertile soil. Only a small percentage of agricultural soils contain enough nutrients to meet crop productivity requirements. Most of them start to rely increasingly heavily on fertilizer applications that are made often. By the end of 2018, it is anticipated that the overall fertilizer use (N + P₂O₅ + K₂O), which was expected to be 183,200,000 t in 2013, will reach 200,500,000 t [3]. Figure 2 shows the projected global demand for all nutrients in fertilizers from 2016 to 2021.

Figure 2.

Global nutrients consumption (N + P₂O₅ + K₂O).

China produced 33% of the world's fertilizer in 2021, according to FAOSTAT [40], making it the world's top producer. The Russian Federation (9%), India (9%), and the United States (which contributed 10% each to global fertilizer production) were other nations with large contributions. Prices for fertilizer are anticipated to be high [45]. Commercial fertilizer manufacturing uses a lot of energy. Around 74% of the energy used to produce fertilizer is provided by natural gas [46]. The key element in the manufacture of nitrogen fertilizer is natural gas. The cost of ammonia will rise when natural gas prices rise [47]. On the other hand, fertilizer prices are substantially impacted by transportation expenses. In contrast to the year 2010, the fertilizer price index will rise by 15% in 2014 (Figure 3) [3].

Figure 3.

Annual food price index.

3. Case studies with processed organic and organomineral fertilizers

Natural infertility, a lack of soil OM, and the rapid rate at which fertility diminishes during intensive farming make Sub-Saharan African soils unsuitable for cultivation [48]. These issues have been solved by using different fertilizers [49, 50]. It has been discovered that using inorganic fertilizer to boost yield is efficient in the near term but requires regular application over time.

Sugarcane output is increased when organic and mineral fertilizer are applied together [51] and larger residual advantages are encouraged, which have an impact on how each fertilizer is used differently. In this respect, OMF displays a comparatively lower reactive chemical potential than mineral fertilizer. Its solubilization happens gradually throughout the course of the culture's development although its agronomic effectiveness might be higher than that of sources of soluble minerals [16].

Subsistence farmers, who dominate Nigeria’s agricultural sector, cannot afford inorganic fertilizers because they are not only unsightly but also expensive [52]. Using minerals that naturally contain fertilizer ingredients is a very effective way to reduce emissions from processing chemical companies. During mineral weathering, organic materials from natural sources such as animal manure, agricultural biomass, and a source of microbial culture and a catalyst for the release of nutrients into the soil can be other organic materials [5]. OFs frequently completely or partially replace CFs to safeguard soil biodiversity and maintain the ecological balance of the soil [53, 54]. Intensifying the use of OFs has the potential to increase soil biological activity, plant nutrients, and soil carbon storage, all of which are essential for decreasing global warming and promoting sustainable agricultural output [55, 56].

Due to scarcity and high prices, peasant farmers have recently drastically decreased their use of mineral fertilizers [57, 58]. Also, their use has been discouraged due to the negative side effects on the soil, such as acidity and aluminum toxicity [59, 60]. Numerous research employing the OMFs Pacesetter and Sunshine have been conducted on various crops [11, 13, 59, 61, 62, 63].

Moreover, excessive use of CFs interferes with the rhizosphere's regular microbial population functioning (nutrient cycling, OM creation, and soil nutrient improvement). Large tracts of fertile soils, however, were either degraded or converted into non-agricultural activities as a result of the rapid development of industry, agriculture, and population growth [64], and numerous areas of recently reclaimed soil—the majority of which are poor soils—have been modified for plant cultivation. Many regenerated soils, like soil properties, have adequate nutrient quantities (K, Ca, and Mg), yet as these nutrients are distinct chemical phases and are not utilized by plants, they often exist as plant nutrients. Furthermore, the problem of heavy metal pollution in agricultural soil is made worse by continuing to utilize CFs [5].

The Department of Agronomy University of Ibadan also developed a poultry-based urea-fortified OMF [63, 65]. The yield, nutrient content, and nutritional quality of maize and vegetables were all observed to increase with the use of OMFs [66]. As part of a field study at the University of Ibadan, the agronomic and financial evaluation of five OMFs that combined poultry manure (PM), sorted trash, phosphate rock, and urea was evaluated. When using the formulations, maize yield improved to roughly 3.17 t/ha as opposed to 3.46 t/ha when using 300 kg/ha of NPK fertilizer.

In contrast to synthetic fertilizers, the chemical properties of OMFs are not predetermined or fixed; they vary based on the method of production [67]. For example, urea contains 46% nitrogen, while fertilizers such as monoammonium phosphate (MAP) and diammonium phosphate (DAP) have unique chemical compositions of 11% nitrogen and 52% P₂O₅ and 18% nitrogen and 46% P₂O₅, respectively. Each OMF product may differ since different nutrient ratios are utilized during production [35, 68].

Using organic manures in addition to mineral fertilizers has been shown to be a successful method for controlling soil fertility in many countries across the world [69]. When organic manures and inorganic fertilizer were applied combined, improvements to the soil's organic content, structure, water-holding capacity, nutrient availability, maintenance of soil nutritional status, cation exchange capacity (CEC), and soil organisms were seen [70]. This procedure enhances nutrient density, enabling the utilization of reduced dosages and yielding exceptional, immensely durable, and upgraded merchandise [71, 72]. The soil’s contents of organic carbon, nitrogen, phosphorous, and potassium increased when both organic and inorganic manure were applied together. Examining the benefits of all the various integrated nutrition management techniques is crucial rather than concentrating simply on the short-term benefits. As a result, the combined use of organic and inorganic fertilizer is a sustainable strategy for nutrient management that increases the effectiveness of CF while minimizing nutrient losses (Table 1) [73].

Treatment	Soil moisture (%)	Soil temperature (°C)	Soil bulk density (mg/m^3)
Control	7.1	33.0	1.05
SOF	8.3	31.6	0.92
SOMF	7.4	31.8	0.98
NPK	7.1	32.0	0.04
LSD (0.05)	0.1	0.25	0.004

Table 1.

Soil physical properties as influenced by sunshine organic and OMFs.

SOF = sunshine organic fertilizer; SOMF = sunshine organomineral fertilizer; and NPK = nitrogen, phosphorus, and potassium.

OMF is a low-input method that can help tropical soils’ poor nutritional conditions for sustained crop production. It combines both sources' positive qualities to increase yield. The emphasis is increasingly moving away from the straightforward use of either organic or inorganic fertilizers toward combinations used in many places of the world. As a result of the recent flooding that wreaked havoc in some areas of the nation and the rapidly diminishing productivity of our soils, Nigeria is currently confronting its worst challenges with regard to food insecurity. In order for our many farmers to meet their yield expectations and get the greatest benefits from their introduction, it is crucial to encourage and introduce the combined use of organic and inorganic fertilizers (OMFs). Recent studies on OMFs have revealed improved yield results compared to their single-use (Table 2) [26, 62, 74].

Treatment	pH	N	Avail. P	K	Ca (cmol/kg)	Mg (cmol/kg)
Control	6.7	0.04	2.9	0.22	3.22	2.87
SOF	7.1	0.07	4.5	0.32	3.68	4.53
SOMF	7.0	0.09	6.4	0.39	3.70	6.37
NPK	6.8	0.05	4.2	0.23	2.93	4.16
LSD (0.05)	0.004	NS	NS	NS	NS	NS

Table 2.

Soil chemical characteristics as affected by sunshine organic and OMFs [15].

SOF = sunshine organic fertilizer; SOMF = sunshine organomineral fertilizer; and NPK = nitrogen, phosphorus, and potassium.

In conclusion, BOMFs are fertilizers made from little processed materials (chemical agents such as urea, phosphates, etc.). When compared to traditional OFs or bio-fertilizers, BOMFs are mostly made up of bio-organic components like animal excreta (cow dung, chicken feces, etc.) and mineral sources. Table 3 lists the elements and key distinctions between organic and conventional CFs.

Different distinguishing components	Organomineral fertilizer	Conventional fertilizer
Mineral source (P, K, Ca, B, Mg, etc.)	Natural	Chemical
Mineral (dust or powder)	Available	Not available
Microbial agents	Available	Not available
Growth-promoting microorganisms for plants	Available	Not available
Plant-defense microorganisms	Available	Not available
Organic carbon	Natural (agri. waste)	Not available
Nitrogen source	Natural (animal waste)	Chemical (urea)
synthetic additives	Not available	Chemical additives (P, K, etc.)
Environmentally harmful conditions	Not available	available
Potential to sequester carbon dioxide	Available	Not available
Positively impacts soil properties	Available	Not available

Table 3.

Variations between standard synthetic fertilizers and OMFs in terms of composition and functionality [5].

Recent and current research suggest that OM, OF, dust, mineral powder (MP), and pasture legume cultivation as green manure can all improve soil quality [75, 76, 77]. This is in response to the numerous obstacles.

Two soil types that were gathered from Ikorodu and Ojoo in Lagos State were used in a greenhouse experiment by [78] along with amaranthus. The treatments included ground kola pod husk (GPH), pacesetter organic fertilizer (POF), and NPK fertilizer (NPK) mixed at 50:50 or 75:25. OF and inorganic fertilizers are applied together for the greatest yield and longest-lasting results; organic and OMFs greatly boosted amaranthus growth as compared to control. Additionally, combined applications significantly increased the nutrient content and nutritional quality (proximate study) [55, 68]. According to research by [65], when applied at 3t/ha to slightly acidic soil that is poor in OM, N, and P, sunlight organic (SOF) and organomineral fertilizers (SOM) significantly enhanced soil moisture, decreased temperature and bulk density, and elevated pH compared to NPK fertilizer and control. The percentages of N and Mg in garden eggplant leaves also dramatically rose. The application of OF and OMF increased the yield and nutritional value of garden eggplants while also enhancing the soil's fertility and physical qualities [79].

The effects of pacesetter OMF on soil and maize were examined in two locations in Ilesa. The soil was treated with 200 kg/ha of NPK fertilizer (NPK) and 0, 2.5, 5.0, 7.5, and 10.0 t/ha of OMF, respectively. OMF and NPK increased plant height, leaf area, grain production, cob and ear weight, soil, and plant N, P, and K, with 10.0 t/ha OMF producing the highest output. The soil's pH was at its ideal level, and the 7.5 and 10 t/ha rates provided adequate amounts of N, P, and K in the soil and on the leaves. The 2.5, 5.0, 7.5, and 10.0 t/ha OMF and NPK, respectively, increased the grain yield by 20%, 29%, 35%, 94%, and 46% [58, 60].

4. Studies with raw organic fertilizers

4.1 Sawdust ash

In order to produce an adequate and high-quality output, plants in organic agriculture need to absorb plant nutrients at their optimal level or be provided to the soil. However, in organic farming, the soil must be amended with organic forms of both macro and micronutrients. Important macro elements like potassium, nitrogen, and phosphorus must be available in their micro and macro forms. For optimum plant development and high production, plant nutrients alone are insufficient.

In addition to research using synthetic or produced OMF, studies using raw organic waste and CFs were also carried out. [11, 59] studied the integrated application of sawdust ash (SDA) with urea and compared different combinations of their reduced levels with urea or SDA alone. Tomato was the test crop. The co-application of urea, SDA (4.5 t/ha), and SDA increased the soil's OM levels of N, P, K, Ca, and Mg. The SDA offered the highest soil pH, OM, accessible P, exchangeable K, Ca, and Mg. Using urea, soil pH was decreased. The simultaneous application of urea and SDA, as well as the reduced amounts of each, improved leaf N, P, K, Ca, and Mg. The highest leaf N was delivered by urea, while SDA produced the highest amounts of leaf P, Ca, and Mg. When compared to controls, SDA, urea, and their mixtures all significantly raised growth metrics and the number of fruits, while combinations of 3.0 t/ha SDA + 120 kg/ha U and 1.5 t/ha SDA + 80 kg/ha U significantly increased fruit weight. It is ascertained that SDA is an effective source base element and can be integrated with urea at reduced levels to maximize yield, soil, and plant N, P, K, Ca, and Mg content (Table 4) [18].

Treatment	Soil pH	OM (%)	N (%)	P (%)	Ca (cmol/kg)	Mg (cmol/kg)
Control	5.7a	0.46b	0.11c	11.0d	0.42c	0.47b
240 kg/ha-1U	5.7a	0.64ab	0.15b	10.6d	2.10b	1.03b
1.5 t/ha SDA + 180 kg/ha U	6.1a	1.23a	0.24a	18.9a	3.47ab	1.27ab
3.0 t/ha SDA + 120 k/ha U	5.9a	0.79ab	0.17b	15.6b	4.93ab	1.20ab
4.5 t/ha SDA + 60 kg/ha U	5.8a	0.89ab	0.12c	20.5a	4.80ab	2.00ab
6.0 t/ha SDA	5.9a	0.67b	0.11c	13.5c	5.47a	3.63a

Table 4.

Effects of urea (U) and SDA on soil nutrients contents at 12 weeks after application [59].

SDA = sawdust ash; U = urea.

According to the findings of the Duncan's Multiple Range Test, the means within each column that are separated by the same letter are not significantly different (P = 0.05).

Results show that adding urea and SDA alone enhanced soil pH although the increases were not statistically significant. In 2013, its growing OM and impact were tremendous. In 2012 and 2013, urea alone, along with 1.5 t/ha SDA + 180 kg/ha U, 3.0 t/ha SDA + 150, 1.5 t/ha SDA + 180 kg/ha U, 3.0 t/ha SDA + 120 kg/ha U, 4.5 t/ha SDA + 60 kg/ha U, and 6.0 t/ha SDA, significantly increased N. Urea significantly increased P in 2013 as well [59].

4.2 Poultry manure

Because animal dung, regardless of form, has a favorable effect on soil and crops, its usage cannot be overstated. A major goal of modern agriculture is to increase soil fertility and improve environmental quality. There is a global trend toward creating agricultural production systems that use inputs more effectively and produce less waste in an effort to create a more environmentally friendly, ecologically sound, and economically viable agricultural system. An innovative idea for managing animal waste includes mixing animal feces with fertilizers that are mineral-based to produce fertilizers that are organomineral [80]. In Akure, Nigeria, researchers compared the effects of 300 kg/ha of NPK 15-15-15 fertilizer, 7 t/ha of PM, six combinations of lower amounts of N-P-K 15-15-15 and PM, and control (no fertilizer) over the course of two years [30, 72]. The soil's chemical characteristics, the yield of dry matter from maize, the yield of grain, plant height, leaf area, and nutrient uptake were all considerably improved by the PM, lower levels of PM and NPK, and NPK alone. The highest values were given by 3 t/ha PM + 260 kg/ha NPK fertilizer with regard to dry matter yield and nutrient uptake, resulting in the highest grain yields.

Cow dung applications of 5 and 10 t/acre considerably improved soil OM compared to other approaches (Table 5). The increase in soil OM brought on by the application of cow dung may be attributable to organic waste's capacity to enrich soil OM [18].

Experiment	pH	OM (%)	N (%)	P (mg/kg)	K (cmol/kg)	Ca (cmol/kg)	Mg (cmol/kg)
Control	5.85	2.91	0.09	9.12	0.21	2.55	2.53
5 t/ha CDM	6.13	6.72	0.24	12.61	0.39	4.40	3.09
10.0 t/ha CDM	6.11	6.48	0.20	12.66	0.33	4.50	3.17
200 kg/ha NPK	5.94	4.74	0.23	11.69	0.31	3.27	2.63

Table 5.

Effects of NPK Fertilizer and Cow Dung on Soil Nutrient Contents [18].

CDM = cow dung manure; NPK = nitrogen phosphorus and potassium.

4.3 Oil palm bunch ash

Synthetic fertilizers frequently release nutrients inequitably and insufficiently into the soil, which tends to exacerbate soil acidity. These deficiencies can be compensated for by the synergistic effect of using organic ingredients such as oil palm bunch ash along with synthetic fertilizer. The application of both organic and inorganic nutrient sources together is anticipated to have positive effects, as opposed to complete reliance on any one source, which will result in lower costs for CFs, better-balanced plant nutrition, and soil acidity control [23]. Integrated application of NPK and oil palm bunch ash (OPBA) together. The study looked into the effects of applying OBA and NPK fertilizer together (NPK). Six treatments: NPK, OBA 4 t/ha, and control (15-15-15) At NIFOR and Ekiadolor, 300 kg/ha of maize received applications of 25% NPK + 75% OBA, 50% NPK + 50% OBA, and 75% NPK + 25% OBA. Other treatments boosted SOM, N, P, K, Ca, Mg, and pH plant nutrients, growth, and yield in comparison to controls (Table 6) [65, 81].

Experiment	pH	OM (%)	N (%)	P (mg/kg)	K (cmol/kg)	Ca (cmol/kg)	Mg (cmol/kg)
Control	5.66b	1.43f	0.14f	9.70j	0.14h	1.06g	0.88e
100% U	5.60b	1.60f	0.68a	20.00i	0.17gh	3.37e	1.20cd
75% U + 25% OPBA	5.85b	2.20d	0.64ab	21.60h	0.23fgh	4.80d	1.30c
50% U + 50%OPBA	5.93b	2.73ab	0.58abc	22.00h	0.26f	5.25cd	2.08b
25% U + 75% OPBA	5.98ab	2.25d	0.50c	24.90g	0.30f	4.90d	2.05b
100% OPBA	6.06a	2.41bcd	0.47cd	36.70d	0.64d	3.90e	2.63a
100% NPK	5.68b	1.90f	0.59abc	47.40a	0.75c	2.60fe	1.00cd
75% NPK + 25% OPBA	5.83b	2.40cd	0.53bc	44.20b	0.85b	6.20a	1.25c
50% NPK + 50%OPBA	5.96b	2.79a	0.50c	41.60c	0.96a	6.00ab	2.07b
25% NPK + 75% OPBA	5.99ab	2.78a	0.48cd	35.80cd	0.92ab	5.50bc	2.03b
100% OPBA	6.07a	2.40bcd	0.48cd	36.70d	0.64d	3.90e	2.62a
75% OPBA	6.03ab	2.37bcd	0.37e	30.10e	0.62d	3.45e	2.50a
50% OPBA	6.00ab	2.30cd	0.30e	26.30f	0.60d	3.20f	2.59a
25% OPBA	5.93b	2.10e	0.28e	23.70g	0.41e	3.11f	2.23ab

Table 6.

Effect of OPBA and its combined use with urea and NPK fertilizer on soil nutrient composition [22, 47, 65].

According to Duncan's Multiple Range Test, means in the same columns that are not separated by the same letters are substantially different at the 5% level of significance.

OPBA = oil palm bunch ash; U = urea; NPK = nitrogen phosphorus and potassium.

The use of OPBA alone or in combination with urea or NPK generally led to higher soil K, Ca, and Mg concentrations, which in turn raised pH. Using OPBA had a liming impact and decreased soil acidity in this manner. Usman et al. [82] states that OPBA is alkaline and has relatively high quantities of K, Ca, and Mg but low levels of OM, N, and P.

4.4 Kola pod husk

Eight fertilization methods were applied to amaranthus, including control, pacesetter grade B organic fertilizer (PGB) applied at a rate of 3 t/ha (100%), 300 kg/ha NPK fertilizer (NPK), PGB + NPK applied at a rate of 75:25, PGB + NPK applied at a rate of 50:50, kola pod husk (KPH) applied at a rate of 3 t/ha (100%), and KPH + N (50:50). Study was done on the residual impact on the second and third crops. A close analysis was conducted. Crude protein (CP) and EE (ether extract) were considerably increased both immediately and subsequently by the PGB, KPH alone, or in combination with lowered NPK. Reduced crude fiber from organic materials alone or in combination with NPK (CF). NPK produced the least CP, ash, CF, and EE in comparison to organic materials. In contrast to NPK, which failed to sustain appropriate CP and EE in the second crop, OFs and OMF did so in both the first and second crops [58, 60]. All amounts of OG, OMF, and NPK fertilizers significantly increased (P0.05) the height, number of leaves, leaf area, stover, dry matter, and grain yields of maize when compared to the control (Table 3).

The highest plant height was achieved with the application of 300 kg/ha NPK fertilizer, followed by 5 t/ha OMF for the highest number of leaves, stover yield, and grain production; 2.5 t/ha OMF for the highest leaf area; and the lowest results with the control experiment (Table 7) [56, 83]. [56] To produce African eggplant, cocoa pod husk that has been treated with urea is used (Solanum macrocarpon). Aleshinloye grade A and Sunshine grade A fertilizers were employed by [81] to improve the fluted pumpkin’s growth, yield, and nutritional makeup. In Ilorin, North-central Nigeria, little to no research has been done on how these fertilizers affect the soil and amaranth plants.

Plant height (cm)	No. of leaves (cm^2)	Leaf area (t/ha)	Stover yield (t/ha)	Grain yield (t/ha)	Root dry (%)	Matter	Increase in grain
Control	72.60e	8.00c	14d	3.23c	2.84c	0.67b	—
2.5 t/ha OG	89.70e	9.33bc	20c	3.59c	3.00b	0.93a	5.63
5 t/ha OG	107.90d	9.23c	19c	3.97bc	3.11b	0.97a	9.51
10 t/ha OG	149.40c	12.0b	32b	4.99b	4.25a	0.99a	49.65
2.5 t/ha OMF	129.40c	12.20b	44a	5.34a	4.55a	1.10a	60.21
5 t/ha OMF	169.20b	14.59a	31b	5.36a	4.78a	1.00a	68.31
10 t/ha OMF	164.10b	12.4b	30b	4.63b	3.94a	0.97a	38.72
300 kg/ha NPK	194.00a	12.3b	24c	4.23b	3.44ab	0.93a	12.13

Table 7.

Effect of OG, OMF, and NPK fertilizers on growth and yield of maize [83].

Means with the same letter in the same column are not significantly different at 5% using Duncan Multiple Range Test.

The yield data at the Ikorodu and Ojo sites in Lagos State showed that other treatments significantly increased plant height, number of leaves, and girth in comparison to the control. In comparison to KPHT, PGB, and NPK alone, soil treated with KPH + NPK (50:50) primarily boosted growth parameters, while PGB + NPK (50:50) also had a better residual effect on yield parameters in Ikorodu. The combined treatments had the highest yields and were recommended [84].

5. Conclusions

From an economic and environmental perspective, using organic waste as fertilizer is a tempting option. Recycling the nutrients found in the farmer-accessible organic materials can replace the application of expensive conventional fertilizers while reducing the likelihood of environmental damage due to improper waste disposal from agricultural activities. Furthermore, it is debatably believed that agricultural operations constitute a significant source of CO₂ that damages the climate and contributes to global warming. As a result, this chapter reviews recent modifications to Nigeria's usage of organic and OMFs. So it may be concluded that a variety of organic wastes could be utilized either independently of or in combination with mineral fertilizers. More lasting effects, balanced nutrition, and an increase in the physicochemical qualities of the soil are all guaranteed by the inclusion of organic manures in OMFs. Utilizing the two resources together has a synergistic impact and lowers spending on rare and pricey mineral fertilizers. It is a sustainable strategy for assuring high agricultural output and soil productivity.

Acknowledgments

Special appreciation to the Henan Agricultural University, Zhengzhou, China. The authors are also thankful to the National Natural Science Foundation of China (No. 32071890) and supported by Henan Center for Outstanding Overseas Scientists (No. GZS2021007).

Conflict of interest

The authors declare no conflict of interest.