Effect of combined application of organic manure and nitrogen fertilizer rates on yield and yield components of potato: A review

Abstract

Potato (Solanum tuberosum L.) is one of the main tuber crops that contribute to global food security. Fertilizer is an important input for potato production. However, potato productivity is still constrained by soil depletion. Unfortunately, research done on the rate of organic manure and nitrogen fertilizer on potato production are very limited. This review scrutinizes the gaps of organic manure and nitrogen fertilizer rates on the yield and yield components of potato. For the cultivation of potatoes, smallholder farmers use various rates of nitrogen and organic manure fertilizers. Combined application of nitrogen and organic manure fertilizer improved potato growth parameters and yield components (tuber number, average tuber weight). Tuber quality components such as dry matter and starch contents are also influenced by the combined application of nitrogen and organic manure. With the addition of high amount of organic manure with a certain level of nitrogen, fertilizer also gave the highest volume of marketable and total tuber yield. Based on the report of research works done in different parts of the world at different periods, an average of 31 tons/ha of organic manure and 187.5 kg/ha of nitrogen fertilizer are the ideal combinations for the optimum yield of potato. Hence, in order to increase the quality and availability of organic manure, its production should be supported by technologies alike to inorganic fertilizer production. This will boost potato yield, tuber quality, and maintain the soil health. The government should also due attention to the environment and sustainable development.

Keywords:

• Combined effect
• farmyard manure
• inorganic fertilizer
• soil environment

1. Introduction

Potato (Solanum tuberosum L.) ranks third after rice and wheat in terms of consumption in the world, and first among root and tuber crops, followed by cassava, sweet potato and yams in production (Vollmer et al., 2017). Potato can be compared only with rice, wheat, and maize for its contribution towards securing food and nutrition and avoiding poverty and hunger, especially in developing countries, where food is eternally on demand to feed a higher population living with inherent social and political conflict (Shetty, 2009). High nutrition (carbohydrates, protein, dietary fibre, vitamins, minerals, amino acids, etc.), easy digestibility, bulk quantity production, etc. have made potato the most popular vegetable of the world (Fernández-López et al., 2020). A total of 376 million tons of potatoes were produced worldwide, with China (94 million tonnes) and India (54 million tons) the largest potato producing countries in 2021 (Munnaf et al., 2021). Africa produced 17,625,680 tons (1,765,617 ha), and the tuber yield in Ethiopia was projected to be 921,403.9 tons (66,423.33 ha), with an average yield of 13.76 tons ha, and the country’s productivity on farmer’s fields was lower than the average yield of experimental areas (38 tons ha) (Tolessa, 2018). In addition, globally millions of people depend on potatoes. It is also a popular tuber crop in the highland areas of Ethiopia. Because in the highland parts of Ethiopia, potato is well suited for double cropping since its growth cycle is short (3 to 4 months). To ensure effective potato production, organic manure and nitrogen fertilizer are said to be vital for fertilization (Xu et al., 2022). Although nitrogen is a mineral nutrient that is frequently added to agricultural soils, the rate and time of application can have a significant inference on the crop yield. As nitrogen accounts for 1% to 4% of plant dry matter and is absorbed from the soil as nitrate (No⁻³) or ammonium (NH⁺⁴) form, it is regarded as the primary force behind plant development, including potato (Kumari et al., 2022). Due to the fast and quick foliage growth, during the first two months, an additional quantity of nitrogen fertilizer is essential. In potatoes, nitrogen is combined with other substances made by metabolism process and which is used to make amino acids and proteins (S. Selim et al., 2022). It is obvious that amino acids are organic compounds made from amino and carboxylic groups and varying side chains, and which are also recognized as the building blocks of proteins (Trobe et al., 2022). While, proteins are nitrogenous macromolecules made up of chains of amino acids. As a result, it is a crucial component of macromolecules and is vital for potato growth and tuber formation (Karam et al., 2014). However, intensified nitrogen fertilization decreased the content of dry matter and starch in potato tubers (Margus et al., 2022). Moreover, it increased the nitrogen content in dry matter and in non-starch dry substance of the potato tubers.

Researchers described some of the varieties of natural fertilizers, such as animal manures (cow dung and goat manure), compost (plant residues, and food wastes), oil cakes and biological wastes, rock phosphate (sedimentary rock), chicken litter and bone meal (Khan et al., 2022; Le Pera et al., 2022; Madhu et al., 2022; Wakawa et al., 2022). Organic manure is made from plant or animal sources which contain elements that improve soil fertility. The manure is the feces sourced as a byproduct from raising animals, while compost is an organic matter that’s undergone a natural decomposition process. In many parts of the world, potato farmers prefer using chicken manure as a fertilizer. Potato flourish in calcium-rich soil, which contributes to high crop production. Moreover, potassium has a crucial role in the higher productivity of potato tubers because it plays an important role in photosynthesis, regulation of opening and closing of stomata, favoring high energy status which helps in timely and appropriate nutrients translocation and water uptake in plants (Pervez et al., 2013). Despite potatoes can grow in any soil, the crop will perform better if the soil is rich with organic matter (Edwards & Arancon, 2022).

Integrated nutrient management is also a crucial strategy for potato production, and studies conducted on the combined application of organic and inorganic fertilizers reported considerable potato yield augmentation. Being a heavy feeder of nutrients, potato requires high amount of nitrogen, phosphorus, and potassium, and chemical fertilizers are the main source of nutrients used for potato cropping (Koch et al., 2020). However, continuous dependence on chemical fertilizers causes nutritional imbalance and adverse effects on the physico-chemical and biological properties of the soil.

Due to the usage of ammonium fertilizers and the leaching of cations from the root zone, many soils now utilized for the production of potatoes have grown more acidity over time. Regular requirements for the growth of potato tubers during bulking stage are 4.5 kg ha⁻¹ N, 0.3 kg ha⁻¹ P and 6.0 kg ha⁻¹ K (Muthoni, 2016). Overuse of fertilizers, especially inorganic fertilizers, slows the growth of tubers, which have a watery texture and poor cooking quality (Sandhu & Sandhu, 2023). Moreover, plants with high nitrogen have dense foliage that is sensitive to blight and delays the initiation and maturation of tubers. Excessive nitrogen leads to poor root growth, rolled and deformed leaves. Improper nutrient administration strategy would lead to low potato yield and poor tuber quality (Munyaneza & Bizimungu, 2022). A scarcity of nutrients is brought about by the widespread use of extractive agricultural techniques, such as crop residue clearance, slow or no use of organic and inorganic fertilizers, and excessive and unrestrained grazing.

Integrated nutrient management is a better approach for supplying nutrition or food to the crop by including organic and inorganic sources of nutrients (M. M. Selim, 2020). Thus, the integrated use of all sources of plant nutrients (chemical fertilizer, organic manures, biofertilizers) to be important not only for increasing crop productivity but also for improving soil health essential for sustaining crop productivity in a long term (Chen, 2006). On the other side, a careful combination of organic and inorganic sources of nutrients might be helpful to obtain a good economic return with excellent soil health (Fahad et al., 2022).

For the majority of agricultural crops, including potatoes, the kind of fertilizers, the quantity required, application time, and the technique of application are not sufficiently investigated.

Thus, the purpose of this review is to assess the gaps of organic manure and nitrogen fertilizer rates on the yield and yield components of potato.

2. Methodology

During the process of conducting a literature search for this review, the author has used different strategies, and reputable journals from Scopus, Web of Science, and PubMed databases have been also used for the write-up of this review.

3. Description of potato plants

Potato plants can reach heights of up to 1 m, have hairy stems, leaves with four leaflet pairs, and flowers that can be white, pink, purple, or blue with yellow centers (Hawkes, 1992). These flowers are produced with stalks that are approximately 3 cm long and have a 2.5 cm diameter. The potato plant produces starch as it develops, which is then transported to the tips of its subterranean stems (stolons), where it thickens to form a few or as many as 20 tubers close to the soil’s surface (Rubatzky et al., 1997). The potato is a tuber, round or oval, with small white roots called eyes that are growth buds, and the size varies depending on the variety. The skin color can be white, yellow, or even purple. According to Struik, potato is a herbaceous plant with a typical plant structure of below-ground roots and above-ground shoots with leaves (Struik, 2007). The physical attributes of potatoes, including their size, shape, surface area, actual density, bulk density, and porosity, are mostly connected to heat and mass transport (M. Kumar et al., 2022).

Potato is both a determinate and indeterminate crop type (Thornton, 2020). Early and mid-season determinate potato types have shorter plants and grow quickly in about 70 to 90 days. While late-season indeterminate potato varieties may produce extremely long, spreading stems and frequently takes 110 to 135 days to mature (Wohleb et al., 2014).

4. Features of organic manure and inorganic nitrogen fertilizer

Organic manure is a nutrient that comes from natural sources such as animal waste, composted vegetables, agricultural waste, and human excreta (Koul et al., 2022). In essence, they are organic materials that decompose and combine with the soil, improving its fertility. The “feed the soil to feed the plant” idea informs organic soil fertility management, and this fundamental idea is put into practice through a variety of techniques meant to boost soil organic matter, microbial activity, and nutrient availability (D. Smith et al., 2019). The use of manure in crop cultivation is becoming more popular since it increases yield and enhances the physical and chemical characteristics of the soil (S. Kumar et al., 2022). Regular manure applications may produce the best results by maintaining soil fertility and adding organic matter (MacLaren et al., 2022). In addition to providing nutrients, organic manures help enhance the physical environment to promote better plant and tuber growth, and for the best potato production, manures alone are inadequate providers of nitrogen, although they do help the soil’s organic carbon status (Agbede & Oyewumi, 2022). The nutrients in the substrate can be activated by using organic fertilizer, which can also enhance the soil’s physical and chemical properties, encourage plant nutrient uptake, increase nutrient content, supply the nutrients required for dry matter accumulation, and encourage both vegetative and reproductive growth (Deena et al., 2022). As there are several elements that might influence the potato production response to Ethiopian farming conditions, most farmers prioritize fertilization and high-yielding crops such as potato (Zelalem et al., 2009). According to several studies, organic compounds or manures generally have four characteristics, which are as follows: all of them include carbon, most of them are combustible, all of them are soluble in nonpolar solvents, and most, if not all, of them are molecules that are covalently bound (Mota et al., 2022).

Ammonium (NH4⁺), nitrite (NO^2-), nitrate (NO^3-), nitrous oxide (N₂O), nitric oxide (NO), and elemental nitrogen (N₂) are all examples of inorganic nitrogen (Tan et al., 2022). These forms make about 2 to 5% of the total nitrogen in soil (N₂O), and they are not significant nitrogen forms that are lost to denitrification. Microorganisms in the soil and water turn nitrate and ammonia into one another, and plants absorb these inorganic forms and transform them into proteins (Shahi Khalaf Ansar et al., 2022). The most popular strategy for managing crop nitrogen fertility is inorganic nitrogen fertilization, especially in intensively managed agricultural and forest production systems (Allam et al., 2022). For the development of eutrophication and toxic algal blooms, inorganic nitrogen is a crucial component (Shi et al., 2022).

Organic farming has the ability to increase soil fertility by enhancing the physical and chemical characteristics of the soil. Although the sustainability of it is frequently asked, organic farming is suggested as a possible strategy for developing sustainable food systems (Van Grinsven et al., 2015). Furthermore, organic farming helps farmers to produce nutritious food with minimal harm to the environment. Therefore, organic farming may make significant contributions to a trajectory toward a more diverse food production (Sroufe & Watts, 2022). Likewise, there is significant potential for carbon retention in the soil and greenhouse gases (GHG) emission reduction through organic farming (L. G. Smith et al., 2019). In addition, it is a method of integrated production management that helps to enhance the biodiversity of agroecosystems. Applying high-efficiency organic fertilizers can help both long-term food security and environmental protection since they can boost crop output without compromising soil quality (X. Wang et al., 2023). Organic farming employs fewer chemicals than conventional agriculture, lessens soil erosion, minimizes nitrate leaching into groundwater and surface water, and recycles animal waste back into the farm (Pimentel & Burgess, 2014).

One strategy that should be used to achieve the objective of sustainable agriculture is organic farming, and it is the practice of growing plants without using dangerous synthetic chemicals like fertilizers, pesticides, antibiotics, etc (Soni et al., 2022). Regarding producing food, organic farming is typically seen as a far more sustainable option. A broader range of plants and a lack of pesticides improve soil quality, improve biodiversity, and minimize run-off pollution from fertilizer and pesticides (Rasool et al., 2022). In order to produce food free of toxins for customers while also preserving soil fertility and promoting ecological balance, this form of farming practices eco-friendly sustainable economic growth (Thakur et al., 2022).

5. Types of organic manure

Farmers utilize a variety of organic manures, which are natural ingredients, to increase crop yields in a sustainable manner (Muluneh et al., 2022). The following figure shows some of the most widely used and reported organic manures (Figure 1).

Figure 1. Common types of organic manure.

Source: Own data collection and simplification.

5.1. Green manure

Green manuring is the process of incorporating green plants into the soil, either by growing them in the same field or by incorporating plants that have been grown elsewhere at the green stage just before flowering (Rani et al., 2021). It also increases soil organic carbon for the maintenance of soil quality and future agricultural productivity. Scholars recommend intercropping green manure with potatoes as a component crop since it can boost crop productivity and improves soil fertility (Gitari et al., 2019). Potatoes can be intercropped or relay planted with other crops to increase ground cover, increase soil quality, reduce erosion, and increase food security in the event that one crop experiences unfavorable biotic or abiotic conditions (Nedunchezhiyan et al., 2022). Green manuring increases rotational diversity and lessens weed chances of adapting to a particular cropping pattern, such as potato (Altieri, 1999). Successful vegetable producers around the globe, using a variety of crops and soils, rely almost exclusively on animal manure. Applying a large amount of manure ensures that soils will improve more quickly and will reach a greater level of fertility than they would with green manure (Yao et al., 2019). It is advised to utilize animal-based manures to enhance soil quality and boost crop yield, and the average nutritional content of animal-based concentrated organic manure is shown in the following table (Table 1).

Table 1. The nutritional value of concentrated organic manure

Organic manure	Nutrient content (%)			Ref.
	N	P2O5	K2O
Blood meal	10–12	1–2	1.0	(Choudhary et al., 2022; Verma et al., 2022)
Meat meal	10.5	2.5	0.5
Fish meal	4–10	3–9	0.3–1.5
Horn and Hoof meal	13	-	-
Raw bone meal	3–4	20–25	-
Steamed bone meal	1–2	25–30	-

The type of livestock, stage of growth, feeding methods, amount of bedding or water added to the dung, method of manure storage, duration of time the manure stays in storage, and weather conditions are the main factors that determine how preferable animal-based manure over other manure is (Rubio et al., 2022). This factor has a substantial impact on the quality of animal-based manure compared to plant-based manure.

In general, the nutrients provided by animal manure are very vital for the production of vegetables, including potatoes.

5.2. Farmyard manure

Farmyard manure (FYM) is a decomposed mixture of animal waste products such as dung, urine, litter, and leftover roughages and feed that have been provided to the animals (Suryawanshi & Pagar, 2022). A well-decomposed FYM is an excellent source of organic carbon, which stimulates the biotic life of the soil flora and fauna (Sarker et al., 2022). FYM includes 0.5–1.5% N, 0.2–0.4% P₂O₅, and 0.5–1.0% K₂O, and in comparison to inorganic fertilizers, it is proven to maintain soil productivity longer (Akhtar et al., 2023). FYM has also all macro-and micronutrients needed for plant development including potatoes. If available to farmers, potato exemplifies a crop typically fertilized with farmyard manure, and potatoes are a crop sensitive to soil climate conditions (Hlisnikovský et al., 2021).

5.3. Vermicompost

Vermicompost is the final result of a decomposition process that uses a variety of worm species, often red wigglers, white worms, and other earthworms, to produce a mixture of bedding materials, decaying food or vegetable waste, and vermicast (Mago et al., 2022). Vermicompost really has the ability to physically, chemically, and biologically improve soil fertility (Tammam et al., 2023). Physically, soil that has been amended with vermicompost has improved aeration, porosity, bulk density, and water retention (Das & Ghosh, 2022). For greater crop output, chemical characteristics including pH, electrical conductivity, and organic matter content are also enhanced (Hu et al., 2022).

5.4. Compost

Generally speaking, the most suitable compost for producing potatoes is open-textured, rich in organic matter, high in nutrients (Table 2), and has a neutral pH (Cheyne, 2007). The completed compost can be used in a variety of ways, and it can be put as a soil supplement on top of the soil in the potato field, added to plant and vegetable beds, revitalized indoor plants, or blended with potting soil (Brown et al., 2016).

Table 2. Summary of average nutrient content of organic manures

Organic manures	Nutrient content (%)			Ref.
	N	P2O5	K2O
Farmyard manure	0.5–1.5%	0.2–0.4%	0.5–1.0%	(Adekiya et al., 2020)
Crop residues	34.2–63.4 g N kg^−1	-	>25 kg ha^−1
Organic waste	3.03%	2.63%	1.4%
Green manure	40–60%	2.5%-6.55%	327 mg/kg
Vermicompost	2–3%	1.55–2.25%	1.85–2.25%
Compost	2%	0.5–1%	2%
Biogas slurry	1.4 to 1.8%	1.1 to 1.7%	0.8% to 1.3%

Source: Own data collection and simplification.

5.5. Organic waste

Many producers of organic waste streams now pay for the treatment or disposal of these wastes, which results in the loss of the waste stream’s energy content? (Ddiba et al., 2022). Projects for organic waste diversion process and effectively utilize organic waste, returning nutrients to the land for continued soil fertility and health, and when managed properly, organic waste may produce compost that is nutrient-rich and useful for local communities (Ayilara et al., 2020).

5.6. Crop residues

The vegetative crop material left on the field after a crop is harvested, pruned, or processed is known as crop residue (Yong & Wu, 2022). Farmers are urged to compost crop waste for use as a soil amendment or to incorporate crop residues into the soil as much as possible. Crop waste can enhance soil structure; provide more organic matter, decrease evaporation, and aid in the fixation of CO₂ in the soil (A. Kumar et al., 2022). In agricultural areas, good residue management techniques offer a variety of advantageous effects on soil quality, and crop leftovers can also be utilized to make biofuel (Rather et al., 2022). Under intensive low residue agricultural systems, such as those involving potato-based systems, stagnant crop yields and declining soil health and environmental qualities are common issues (Nyiraneza et al., 2021). Strategies to improve sustainability are important in intensively managed potato systems (Nyiraneza et al., 2015).

5.7. Animal waste

The majority of animal wastes come from cows, pigs, and chickens, and these pollutants, which have the ability to contaminate both surface and groundwater, are of growing concern to both the general public and regulatory agencies (Silbergeld & Nachman, 2008). Manure has been utilized as a fuel source, soil amendment, and fertilizer by those who raise animals and poultry (Samoraj et al., 2022).

5.8. Biogas slurry

A byproduct of the anaerobic fermentation of biomaterials known as biogas slurry has been extensively employed as a fertilizer in agricultural production, and it is both an effective waste material and an organic fertilizer that is kind to the environment (Kaszycki et al., 2021).

A natural fertilizer that may bind soil nutrients and soften hard soil is called bio-slurry (Ambaye et al., 2022). Biogas processing turns bio-slurry into a fertilizer that is higher in nitrogen than phosphate and potassium (Table 2) and it helps soil humification occur more quickly, which in turn slows erosion (Jahangir et al., 2021). Biogas slurry is a superior fertilizer because it enhances soil fertility, structure, and crop yield (Mrunalini et al., 2022).

6. Effect of combined application of organic manure and inorganic nitrogen fertilizer on the growth, yield, and quality of potato

Increased radiation interception and canopy expansion might both be used to explain why nitrogen fertilizers promote growth (Getahun et al., 2020). The most important factor influencing biomass increase under variable nitrogen supply is how well crops capture light. According to nitrogen and water management are the two most important elements affecting potato yield and tuber quality (Badr et al., 2012). Effective nitrogen fertilizer management and irrigation practices enable water conservation and minimize nutrient loss (X. Liang et al., 2013). The mineral nutrient nitrogen is most frequently lacking in agricultural soils, which reduces potato yield (Muleta & Aga, 2019). The positive effects of chemical fertilizers on plant cell division, increased root hairs, and root elongation, which allow the plant to explore a wider area for nutrient absorption and result in a higher nutrient concentration in the plant, may be attributed to the increase in nitrogen content with inorganic nitrogen (Richardson et al., 2009). Nitrogen promotes plant development, increases the number and length of internodes, and causes a gradual increase in plant height (Kwon et al., 2019). Moreover, the root biomass, plant height, root length, and root diameter all greatly increased when nitrogen fertilizer was used. Potato has a high nitrogen demand for ideal development and output; as a result, when grown on soils low in nitrogen, reports showed significant yield losses (Mijena et al., 2022). However, if nitrogen fertilizer is applied in excess or below the crop needs, the entire physiology of the crop will be disturbed, resulting in decreased potato output (Ullah et al., 2019). Although experts discussed the negative effects of applying a large amount of nitrogen fertilizer, others report contrasting theories that claim using a large amount of nitrogen fertilizer would increase yield (Wubet et al., 2022). Soil analysis is not properly carried out before or after nitrogen fertilizer application to potato fields, particularly in developing nations such as Ethiopia for appropriate nitrogen fertilizer recommendation. Even the majority of nitrogen recommendations for potato growing and production are blanket and do not take individual site conditions into account (Zelleke et al., 2019).

In addition to macronutrients such as nitrogen (N), phosphorus (P), and potassium (K), organic manures also have micronutrients such as copper (Cu), manganese (Mn), and zinc (Zn) (Gorfie et al., 2022). Thus, although the numbers are small, all nutrients that plants need are provided by organic manure. It also helps to maintain the carbon to nitrogen ratio (C: N) in the soil and improve soil fertility and productivity (Gautam et al., 2022). The influence of phosphorus and potassium combinations with nitrogen fertilizer increased the yields of potato tubers by 32–93%, and farmyard manure enhanced the yields of potato tubers by 38–82% depending on fertilizer combinations (Baniuniene & Zekaite, 2008). Generally, the availability and percentage of nitrogen present in inorganic fertilizer (Urea) is 46.6%, option (C) is correct while, in organic manure the availability is estimated about 3.03 percent. The average nutrient content of poultry manure are 3.03% N, 2.63% P₂O₅, and 1.4% K₂O, and concentrated organic manures have higher nutrient contents than bulky organic manures (Srivastava & Ngullie, 2009). Poultry manure also contains higher nitrogen and phosphorus levels than other bulky organic manures, and the greatest concentration of NPK of all animal manures is found in chicken manure, which is also utilized as an organic fertilizer, particularly for soils with low levels of nitrogen (Masarirambi et al., 2012). Organic manures, however, have a dual benefit of improving the physical environment for better plant and tuber growth in addition to supplying nutrients. Although manures are inadequate sources of nitrogen for maximizing potato yield, they do increase the soil organic carbon status. Increased yield and improved environmental safety are two social advantages of using manure instead of commercial fertilizer (less nitrogen loss and lower greenhouse gas emissions) (Massé et al., 2011). Potato producers will secure the availability of micronutrients which are essential for a good output of potatoes by employing manure and compost (Atanaw, 2021).

Despite having an abundance of animal waste resources, Ethiopia has inadequate waste management practices, especially in its rural smallholder societies (Yigrem et al., 2008). As a result, manure availability is a result of the raising of livestock (particularly dairy and beef cattle) in Ethiopia’s urban areas. Ethiopia has the largest livestock population in Africa, with 70 million cattle, 42 million sheep, 52 million goats, 8 million camels, and 56 million chickens (Tadesse & Negash, 2022). However, the availability of manure is not only explained by the population of livestock, rather the feeding skills and waste management experiences of the community. Fluctuations in the starch and dry matter contents of potato tubers produced with farmyard manure were less pronounced than those of potatoes cultivated without farmyard manure (Tein et al., 2014). According to scenarios on the effects of organic manure, high-efficiency organic fertilizers can increase tuber yield without depleting soil quality, making their application a means of supporting both long-term food security and environmental preservation. Depending on the type of fertilizers combined (inorganic and organic fertilizers), farmyard manure increased the average yield of potato tubers by 38–82% (Harraq et al., 2022). The development of large-sized tubers and the rise of tuber numbers per plant increases potato yield.

Systematic fertilization not only increases crop yield but also changes its quality and leads to a higher buildup of nutrients in the yield (Khoshgoftarmanesh et al., 2010). Organic and mineral fertilization also improves the physical properties of light-textured soils and their water and warmth regimes. Manure, ground-up animal parts (blood meal, feather dust, leather dust), and seed meals are the greatest organic sources of nitrogen (soybean meal, cottonseed meal) (Rynk et al., 2022). Approximately 70–80% of the nitrogen (N), 60–85% of phosphorus (P), and 80–90% of the potassium (K) contained in feeds are expelled in the manure, which is rich in nutrients and trace elements required for crop growth, and of all solid fertilizers, urea has the largest nitrogen concentration (46% N) (Khoshgoftarmanesh et al., 2010). Several types of nitrogen are combined to make urea, ammonium, and nitrate (UAN) solutions, such as 28% and 32% liquid nitrogen, and 28% liquid nitrogen is 50% urea, 25% ammonium, and 25% nitrate (H. Wang et al., 2020). Continuous application of chemical fertilizer causes a drastic reduction in the concentration of organic carbon, whereas the addition of farmyard manure in combination with nitrogen fertilizer helps maintain the original organic matter status of the soil (Singh et al., 2001). This increase in vegetative growth of plants as a result of the combination of inorganic fertilizer and organic manure may be attributed to this. Moreover, organic manure such as cow dung raised the pH of the soil, which made it easier for plants to absorb nutrients (F. Wang et al., 2022). According to the research conducted in Iran in 2015, farmyard manure (FYM) and nitrogen fertilizer affect some potato characteristics. The highest dry matter content (23.92%), total dry weight (241.2 g), and plant height (70.11 cm) was recorded from the combined application of 40 tons of FYM and 300 kg of nitrogen fertilizer (Asghari et al., 2015). Moreover, the maximum average tuber weight (97.44 g) and average yield (40,080 kg) was obtained from 40 tons of FYM and 200 kg of nitrogen fertilizer. Hence, the findings of this study indicated that the integrated application of FYM and nitrogen fertilizer significantly maximizes the yield of potato.

In parallel, a study conducted in India to determine the effect of nitrogen and farmyard manure on potato (Solanum tuberosum L.) productivity, nutritional content, and quality reported that potato tubers responded positively to increasing rates of FYM and nitrogen fertilizers (Bashir & Qureshi, 2014). This might be explained by the increased metabolite synthesis into useful components. Furthermore, the combined application of 24 tons of FYM/ha and 180 kg of N/ha resulted in the highest tuber yield (26.36 tons/ha). The interaction effects of FYM and nitrogen fertilizers revealed the highest mean yield of potato than the yield harvested from the separate application of FYM and nitrogen fertilizer. The balanced C: N ratio increased the organic matter content, microbial activity, and improves the soil property (Z. Liang et al., 2022). All of these factors might increase the metabolic processes, and the resulting good photosynthesis and translocation of photosynthates from sink to source.

A research conducted in 2016 at Jimma District of Ethiopia to assess the effects of different rates of organic and inorganic fertilizer on the growth and yield components of potato (Solanum tuberosum L.) reported that the combined application of farm yard manure (20 tons/ha) and nitrogen fertilizer rates (70 kg/ha) gave the highest plant highest (128.8 cm) and leaf diameter (5.0 cm) (Asfaw, 2016). Asfaw (2016) described that as the amount of farmyard manure increased, the leaf area of potatoes also increased, and this may be due to the positive role of farmyard manure on soil fertility. Additionally, subsequent studies done on the application rates of cow dung and nitrogen fertilizer rates reported the highest plant height (Chen, 2006).

In addition, a study conducted in 2020 in the North Shewa Zone of the Amhara Regional State of Ethiopia to estimate the effect of organic and inorganic fertilizers on the growth and yield of irrigated potato (Solanum tuberosum L.) reported the highest potato fresh weight (904.5 g/plant), tuber numbers (13.7/plant), and marketable yield (36.9 ton/ha) (Alemayehu et al., 2020).

Integrated use of organic and inorganic fertilizers is the best method for maintaining the soil fertility and applying compost and nitrogen fertilizer together results in better yield than separate application (Bayu et al., 2006).

A field experiment was conducted in 2018/2019 to study the effect of integrated nutrient management on the vegetative growth, yield, and quality of potatoes in India reported that the maximum yield of potatoes (27.9 tons/ha) was obtained from the integrated use of 75% recommended dose of NPK + 50 tons/ha farmyard manure +10 kg/ha phosphorus solubilizing bacteria (PSB) (Prativa & Bhattarai, 2011).

Moreover, a field experiment that assessed the impact of nutrient management in potatoes through vermicompost and urea was conducted in farmers’ fields for two consecutive years (2003 and 2004) in India. The results showed that the integrated use of plant nutrients in potatoes through vermicompost and urea had a significant effect on growth, productivity, nutrient uptake, economics, and soil nutrient reserve (Bordoloi, 2021). The addition of 40–60% of the necessary nitrogen dose from vermicompost and the remaining from artificial fertilizers resulted in the greatest growth, yield characteristics, and quality components in potato. The outcomes demonstrated that the output of potatoes was greatly influenced by the combined use of inorganic and organic sources of nutrients.

Researches were conducted to study the effect of nutrient supply and management on potato production and reported that combined use of FYM (18.75 tons/ha) and NPK (25:25:25 kg/ha) significantly increased the total tuber yield (26.9 tons/ha) (Islam et al., 2013).

7. Comparative advantage of organic manure over inorganic fertilizer

Organic fertilizers and materials enhance soil texture, allowing the soil to retain water for a longer period of time and boosting microbial and fungal activity, thereby benefiting the soil in addition to the plants (Kocsis et al., 2022). On the other hand, synthetic fertilizers deprive the soil of its nutrients, rendering it useless. Over time, organic fertilizers improve the soil capacity to retain water and nutrients by releasing nutrients as they decompose, and they also make the soil and plants healthier and more resilient (Brust, 2019).

In comparison to synthetic fertilizers, organic manure adds much more humus to the soil and the nutrients could be absorbed by the plants slowly. Experts’ recommend to use an integrated nutrient strategy and this is important for maintaining soil fertility and availability (Stewart et al., 2020).

8. Organic manure and soil environment

The application of organic manure improves soil fertility and structure and creates a more stable system by promoting soil fauna and flora (Sofo et al., 2022). To compensate for the lack of mineral fertilizers, nutrient and energy cycling is carried out, and the soil capacity to retain nutrients and water is improving. Low-cost organic manure helps in preserving and enhancing soil quality and productivity (Choudhary et al., 2022). By maintaining a balance between organic matter and soil microflora, the physical, chemical, and biological properties of the soil could be improved, and this contributes to the soil health.

9. Organic manure and soil microbes

Long-term application of manure to the field increases the number of soil microbes and the microbial community (Hou et al., 2022). They also found that the microbial taxonomic composition greatly differed between organic manure treatment and inorganic fertilizer treatment. High levels of organic manure in the soil improve the network communication between beneficial nematodes and microorganisms (Liu et al., 2022).

10. Constraints of organic manure and chemical fertilizers

The inability of organic fertilizers to provide enough levels of vital nutrients such as NPK (nitrogen, phosphorus, and potassium), even if these minerals are available in manure-based fertilizers, which are still recognized as organic, is one of the biggest problems with utilizing organic fertilizer (De Corato, 2020). Several natural fertilizers, such as dung, seaweed, and fish oil, have disagreeable aromas and should not be used on indoor plants since they take some time to transform into the nutrients that a garden in growth needs (Awogbemi et al., 2022).

Overuse of chemical fertilizers can cause soil acidification and soil crust, which lowers the amount of organic matter, humus, and beneficial organisms in the soil, and stunts plant growth, and triggers the release of greenhouse gases (Pahalvi et al., 2021).

In addition, since chemical fertilizers prevent the plants from absorbing adequate water, they might result in root burn or fertilizer burn (Fageria et al., 2009). Chemical fertilizers include a lot of nitrogen salts, and when the nitrogen is absorbed by the soil too rapidly, it causes the plant to become dehydrated and dry (Ammar et al., 2022). Long-term chemical usage can change your soil’s pH balance and result in a hazardous buildup of some nutrients (Abd–Elrahman et al., 2022). Chemical fertilizers have a large negative influence on the ecosystem and the two environmental consequences that must be reduced include GHG emissions and environmental contamination (Tyagi et al., 2022). A number of problems, including major soil deterioration, nitrogen leaching, soil compaction, reduction in soil organic matter, and loss of soil carbon, have been brought on by excessive use of chemical fertilizers (Weifeng et al., 2022).

11. Review gaps and future lines of work

Researches done on integrated nutrient managements (INM) are still inadequate, and a lot of work remains to be done and need to be studied. The burden of nutrients deficient in climate change and the influence of sustainable development are not addressed. Nutrient management models should be designed and integrated with systematic and predictive agronomy approaches. It is also important to investigate the physio-morphological and biochemical changes that nutrients cause in agricultural crops. Furthermore, it is important to look into the transcriptome and protein expression levels of agricultural crops under nutritional stress that are relevant to biochemical and physiological alterations.

12. Summary and conclusions

Organic manure and inorganic fertilizers (nitrogen) are a valuable source of nutrients for smallholder farmers worldwide. Organic manures are popular for their humus content and possess nitrogen, phosphorus, and potassium nutrients in minimum amounts. A variety of organic manures (farmyard manure, biogas slurry, animal waste, crop residues, green manure, compost, and vermi-compost) are extensively utilized by smallholder farmers. However, inorganic fertilizers (nitrogen) are taking the highest share of world fertilizer utilization. Both organic manure and inorganic fertilizers affect potato growth, yield, and quality. However, in terms of environmental impact and sustainable development, organic manures have a paramount importance over inorganic nutrients.

Currently, there are few instances of integrated application of both organic and inorganic fertilizers in different parts of the world. The techniques are widely applied in developing countries, including Ethiopia. The major challenge to sustain this practice is the large requirement of organic manure per hectare basis (recommendation), and it is quite difficult for potato producers to generate and apply organic manure for their potato production because of the enormous volume that is suggested for hectares. The lack of manure production technology is also another constraint. Whatsoever, in order to maximize the potato yield and maintain the safety of the environment and realize sustainable development, there is no option than using both organic and inorganic fertilization in an integrated approach.

Significant research work has been carried out on the integrated nutrient management effects on potatoes during the past several years. However, still a lot of work remains to be done and need to be studied.

Authors’ contributions

Analysis, synthesis, drafting, write-up.

Availability of data and materials

The dataset that supports the findings of this review is included in the article.

Acknowledgments

The author acknowledges the anonymous reviewers for their valuable input on the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author.

Additional information

Funding

No funding was received for this manuscript.

Notes on contributors

Yohannes Gelaye

Yohannes Gelaye is a lecturer and researcher in the Department of Horticulture, Debre Markos University. He did Master’s degree in Horticulture at Bahir Dar University, Ethiopia. He has taught various Horticulture courses at Debre Markos University, Ethiopia since December 2014 (Such as vegetable and fruit crops production, Ornamental plants production, Plant physiology, Coffee production and quality control, Design and agricultural experimentation, Weeds and its management, Nutrition sensitive agriculture). His area of research interest is horticulture crops improvement, Postharvest handling and management, Food safety, Soil fertility management, Nutrition and food security.