**4. Organic manures**

Traditional agricultural practices include applying organic manures at agronomic rates for plant nutrition delivery and advantageous impacts on physical qualities [55]. Due to a growing interest in the disposal of the enormous volumes of organic waste being generated over the past few decades, the impacts of organic manures on soil qualities have attracted new attention.

### **4.1 Effects of organic manures on physical and chemical properties of soil**

According to Liu [56], organic manure has an impact on the soil's bulk density, stability, aggregation, pH, buffer capacity, cation exchange capacity, soil encrustation, water infiltration, soil penetrability, moisture content, drainage, tilth, aeration, soil temperature, as well as the supply and availability of nutrients for plant growth.

### *4.1.1 Soil bulk density*

The physical qualities of the soil are improved by the addition of organic manures because it increases the amount of organic matter in the soil and the activity of its microbial population [57]. As a result of net increases in soil organic C, there is a direct correlation between changes in bulk density and water-holding capacity in the soil [58]. Because the denser mineral portion of the soil is diluted by the addition of organic manures, the bulk density of the soil falls. Organic manures have larger and more numerous pores and are less thick [59]. The humic components of organic manures reduce the flexibility, cohesiveness, and stickiness of clayey soils, causing the development of stable aggregates in the soil [60]. After the lag phase that occurs after adding organic manures to soils, the amount of microbial biomass increases. The physical entanglement of fungal hyphae and the synthesis of extra-cellular polysaccharides, which connect soil aggregates and hence boost aggregate stability, occur in conjunction with an increase in the microbial biomass pool [55]. In comparison to fresh organic manures, composted organic manures cause a slower, more gradual rise in aggregate stability [57].

#### *4.1.2 Soil pH and cation exchange capacity*

Cations like calcium, potassium, and magnesium are held in exchangeable forms by humus colloids so that they can be used by plants and are not washed away by water. According to Ampong et al. [60], "Organic matter also provides much of the pH buffering capacity in soils through its cation exchange capacity and acid and base functional groups." According to Fang et al. [59], applying organic manure caused the pH of the soil where composted organic materials had been mixed into acidic soil to rise. However, neutral or basic soils did not yield the same findings. Masmoudi et al. [61] demonstrated the high CEC of soils treated with organic manures. When compared to clay soil, the CEC on sandy soil rose by a ratio of 5–10.

#### *4.1.3 Soil water content and soil water holding capacity*

By increasing infiltration capacity and hydraulic activities, the addition of organic manures to the soil reduces surface crusting, reduces soil particle displacement by raindrops, reduces runoff water, reduces water lost through evaporation, improves drainage, and enhances root penetration [57]. By adding organic manures to soils,

#### *Effective Microorganisms (EM): A Potential Pathway for Enhancing Soil Quality… DOI: http://dx.doi.org/10.5772/intechopen.114089*

soils can hold more water, which is regulated by the number, size, and distribution of pores. At low tensions, an increase in the quantity of tiny pores is principally responsible for an increase in water-holding capacity. The amount of surface area and the thickness of the water films on these surfaces dictate the soil moisture content at higher pressures where practically all the pores are air-filled [58]. The addition of organic manures to soils also expands the soil's specific surface area and boosts its ability to hold onto water under higher pressures [62].

#### *4.1.4 Soil nutrients*

Micronutrients, phosphorus, sulfur, nitrogen, and other elements are contained in organic manures and are gradually released through mineralization. The degree to which organic manures are mineralized is greatly influenced by their quality. As a result, N mineralization and immobilization, which, in turn, are regulated by C: N, lignin: N, polyphenol: N, and (lignin + polyphenol): N ratios, lignin and polyphenols, N% of the organic manure used, and moderate N release from organic materials [63]. In the early stages of decomposition, mineralization or immobilization processes will predominate depending on the chemical makeup of the organic manures, particularly the C: N ratio. The rate of material decomposition and subsequent soil turnover of decomposed C and N determine how much inorganic N is released from organic manures into the soil [63]. According to Ndambi et al. [64], the amount, kind, and duration of manure utilized all affect how successful it is as a source of nutrients for plants. Long-term addition of low-quality organic inputs can boost soil organic C build-up without necessarily boosting output. For instance, cropping system research in India found that using wheat straw and urea together significantly lowered yields, but using Sesbania green manure and urea together increased yields when compared to using urea alone [65]. According to Adekiya et al. [57], low-quality organic manures have low concentrations of soluble C and N, which are necessary to boost the activities of the soil's microbial pool and, thus, reduce crop output. Numerous crop wastes and animal manures can temporarily immobilize nitrogen (N) and have low-quality nitrogen contents that vary from 1.8 to 2.0%. Several crops have been produced using fresh organic manures as well as composted organic manures as a source of nutrients, with varied degrees of success. The results of adding organic manure to a soil depend on the quality of the manure and the characteristics of the soil. Manure application rates of 5.5 to 11 t ha−1 for field crops and double that amount for plants needing more nutrients have been recommended for South Africa [66]. The precise amount of organic manure required for optimal crop production is difficult to predict since it depends on the type of manure used, the type of soil, the needs of the crop, and the current environmental circumstances. Small-holder farmers in South Africa's Eastern Cape Province apply manure at rates that range from 0.3 to 18.2 t ha−1 [67]. However, manure is applied at rates of 25–100 t ha−1 [68]. Manure may be harmful in high concentrations to humans, animals, and plants [69]; hence, care must be taken to limit any negative consequences. According to Reimer et al. [70], 100 t ha−1 of compost added annually is sufficient to alter the physical properties of the soil and boost output. Numerous studies have shown that applying both organic manures and inorganic mineral sources together has a greater positive impact on growth and production than applying either one alone. This can be because organic manures do not have enough of all the necessary plant nutrients. When inorganic fertilizers are mixed with organic manures, their soluble minerals will mix with the organic portion because inorganic fertilizers are quickly leached. The nutrients will then be gradually released over time in the form of microbial pool by-products and under the influence of organic acids [57].

#### **4.2 Types of organic manures**

You can use organic manures on soil as compost or right out of the bag. Fresh organic materials have higher net N mineralization rates and higher inorganic N concentrations than composted manure, according to Cambardella et al. [71]. According to Paul and Beauchamp's study from 1994, plants treated with fresh organic manure showed more dry matter in their first growth season than plants treated with composted manure.

#### *4.2.1 Compost*

As organic materials are broken down, decomposed, and stabilized by natural microorganisms in a moist, warm, aerobic environment, carbon dioxide, water, minerals, and stabilized organic matter are produced, and pathogenic microbes are eliminated by enzymatic combustion and the heat generated [72]. Organic waste can be recycled by composting and used as a soil amendment. Composting organic waste has been shown to improve soil fertility, soil structure, and plant growth. According to Cambardella et al. [71], applying un-composted trash or compost that has not been stabilized to soil might cause phytotoxicity and nutrient immobilization.

#### *4.2.2 Animal manures*

Animal manure is used in Africa to improve soil fertility, and its advantages are well known. Animal food modifications, collection methods, and storage methods all affect the nutrient content of animal dung. Before the development of mineral fertilizers, manure and other livestock waste products were the only methods of increasing soil productivity. Animal manure application is a frequent practice in Zimbabwe, and it has been discovered that the quality of manure as a source of plant nutrients varies greatly in terms of chemical composition [73]. The most frequent manures used in southern Africa are those produced by goats, sheep, cattle, and chicken, with cattle producing two-thirds of the total amount of manure utilized and sheep and goats producing the remaining third. Species, animal diet, mineral particle content, and storage conditions all have a significant impact on the nutritional makeup of animal manures [66]. However, in the Eastern Cape Province, the nutrients in animal manures fall within the ranges recorded for manures in West African nations and range from 9.9 to 16.7 g N, 2.0 to 3.6 g P, and 17.2 to23.7 g K kg−1 [68]. The manures have a low P content, though. The differences in animal diet that affect how nitrogen is divided between feces and urine cause the nutrient content of manures to vary. When animals are fed high-quality food, N is lost by volatilization and expelled through urine [74]. The amount of nitrogen (N) excreted in feces is thought to rise when diets with a significant number of tannins are consumed. N in manures from animals given a diet high in tannin is particularly resistant to mineralization in the soil, according to a study by Halvorson et al. [75]. According to Mkile's [68] analysis of the nutritional content of various manures in the Eastern Cape region of South Africa, goat manure had the highest levels of N, P, and K, whereas sheep dung had the lowest levels.

## **5. Conclusion**

Through the rapid proliferating of their constituents, more advantageous microorganisms, and subsequent suppression of soil-borne harmful organisms, the *Effective Microorganisms (EM): A Potential Pathway for Enhancing Soil Quality… DOI: http://dx.doi.org/10.5772/intechopen.114089*

application of various brands of EM has been demonstrated to boost crop growth and quality, lowering the occurrence of pests and diseases. They may also effectively mineralize organic soil matter, which enhances nutrient availability and is how EM might boost soil health and crop growth. It has been well documented that EM has positive benefits on agricultural output by promoting plant germination, blooming, fruiting, and ripening. However, several studies have not consistently demonstrated the positive effects of EM on yield, indicating that the findings are not repeatable.
