**5. Soil organic carbon and nutritional composition of crops grown in organic vs. conventional fertilized soil**

Soil carbon includes both inorganic carbon as carbonate minerals, and organic carbon as soil organic matter. Carbon sequestration is the long‐term storage of carbon in oceans, soils, vegetation (especially forests), and geologic formations. Soil carbon sequestration is a process in which CO2 is removed from the atmosphere and stored in the soil carbon pool. About 35% of CO2 anthropogenic emissions are related to changes in land use [34]. Methane (CH4) and nitrous oxide (N2O) are usually found in the atmosphere at much lower concentrations than CO2. However, these two gases are the big contributors to the greenhouse effect, which is 298 times greater for N2O and 25 times greater for CH4 [35]. Carbon binds to minerals in soil that are just a few thousandths of a millimeter in size, and it accumulates there almost exclusively on rough and angular surfaces [36]. The rough mineral surfaces provide an attractive habitat for microbes that convert the carbon and play a part in binding it to minerals.

Organic wastes are usually rich in carbon and nitrogen, and their addition increases the soil content of labile carbon, accelerates the activity of soil microbes, and increases nitrification and denitrification rates. CO2 emissions from the soil are the result of a combination of heterotro‐ phic and autotrophic respiration, and both processes could have been stimulated by the addition of organic compost [37]. Increases in soil CO2 fluxes in agricultural soils after the disposal of organic wastes are frequently observed [37–39]. De Urzedo et al. [40] reported that the application of organic wastes increased CO2 emissions in the soil, as has been observed in other studies, possibly reflecting the supply of labile C to soil microorganisms, raising the microbial activity and consequently increasing the rate of soil respiration [39]. Cheng et al. [41] studied the impact of fertilizer type (organic or inorganic) on N, P, and K concentrations in runoff water from agricultural field. Although the N, P, and K loss in runoff were low, their concentrations were significantly higher from inorganic fertilizer (Scott's Turf Builder®) obtained from the Scotts Company LLC, Marysville, OH, USA, applied at the manufacturer's recommended rate of 57 kg acre-1 than those treated with organic fertilizer (Nature's Touch® containing enzymes) obtained from Garden Way LLC, Cleveland, OH, USA, and applied at the manufacture's recommended rate of 79 kg acre-1.

a heterogeneous mixture of decomposing vegetable or food waste and animal bedding materials to promote biotransformation of organic waste into organic fertilizer and contribute to sustainable agricultural practices. Researchers, government agencies, and farmers are seeking new ways to manage and utilize agricultural wastes to beneficial use. This way of environmental management could be used as a green technology to bio‐covert plant residues or animal manure residues into nutrient rich in organic fertilizers [29]. Many factors such as available moisture, particle size, and organic content contribute to the growth of earthworms [30]. Earthworms might lose weight and die if they are fed with materials such as rice residues that are rich in lignin, even if the substrate is fortified with nitrogen‐rich amendments to decrease the initial C/N ratio [31]. According to Edwards [32], the basic principle in earthworm breeding systems is to regularly add small batches of wastes in the composting chamber to

Data revealed that earthworm growth was lower in treatments that contained high percentages of cow dung (CD). Results also showed that *E. eugeniae* growth was reduced when the proportion of CD in feed substances was increased. This could be due to the earthworm preference of feed substances that may favor rice straw (RS) than CD, and possibly due to inadequate control of ammonia volatilization, resulting from inadequate pre‐treatment of cow manure to remove urea present in the initial material. Similarly, Chan and Griffiths [33] found that earthworms feed that contained untreated pig manure killed the worms within few hours. This is because of the high sensitivity of earthworms to ammonia and presence of high concentrations of cations in livestock manure. Accordingly, availability of pre‐treated cow manure could be used to enhance the reproduction and growth of *E. eugeniae* for use in

**5. Soil organic carbon and nutritional composition of crops grown in**

for microbes that convert the carbon and play a part in binding it to minerals.

Soil carbon includes both inorganic carbon as carbonate minerals, and organic carbon as soil organic matter. Carbon sequestration is the long‐term storage of carbon in oceans, soils, vegetation (especially forests), and geologic formations. Soil carbon sequestration is a process in which CO2 is removed from the atmosphere and stored in the soil carbon pool. About 35% of CO2 anthropogenic emissions are related to changes in land use [34]. Methane (CH4) and nitrous oxide (N2O) are usually found in the atmosphere at much lower concentrations than CO2. However, these two gases are the big contributors to the greenhouse effect, which is 298 times greater for N2O and 25 times greater for CH4 [35]. Carbon binds to minerals in soil that are just a few thousandths of a millimeter in size, and it accumulates there almost exclusively on rough and angular surfaces [36]. The rough mineral surfaces provide an attractive habitat

Organic wastes are usually rich in carbon and nitrogen, and their addition increases the soil content of labile carbon, accelerates the activity of soil microbes, and increases nitrification and denitrification rates. CO2 emissions from the soil are the result of a combination of heterotro‐

allow worms to process successive layers of waste.

164 Organic Fertilizers - From Basic Concepts to Applied Outcomes

composting and organic agricultural production.

**organic vs. conventional fertilized soil**

Organic systems eliminate synthetic agrochemicals and reduce external inputs to protect and improve environmental quality. The perception among organic food consumers is that organically produced crops possess higher nutritional composition. In fact, the comparisons between organically and conventionally grown crops are not experimentally valid due to the variation in crop varieties, timing in fertilization, and handling and storage after harvesting. Investigators are not in complete agreement about the nutritional composition of crops grown in organic vs. conventional fertilized soils. Some investigators found that fruits of organic crops contain more minerals and vitamins than conventional crops [42, 43]. Worthington [44] compared the nutritional quality of organic vs. conventional crops and concluded that organic crops have significantly greater levels of iron, magnesium, and phosphorus. Whereas several other authors have concluded that very few compositional differences exist, although there are reasonably consistent findings for higher nitrate contents in conventionally produced vegetables [42, 45, 46]. Another investigation found higher nitrate concentrations in organically grown compared to conventionally grown crops [47]. In organic grown carrot, lettuce, and potato, Hoefkens et al. [48] reported that they contained lower nitrate concentrations compared to the higher nitrate levels in organic spinach. The low concentration of nitrate in edible plants has many advantages for human health. This is because high concentrations of nitrate in edible plants may cause many health problems in humans, such as methemoglobinemia (a blood disorder in which an abnormal amount of methemoglobin, a form of hemoglobin is produced), and can cause some types of cancer [49]. Johansson et al. [50] assessed organically and conventionally grown tomatoes for a variety of different attributes. They found no differences in acidity, sweetness, and bitterness, but did find that organic tomatoes were less firm, less juicy, and redder. Hallmann and Rembiałkowska [51] found that bell pepper fruits of plants grown in organic agriculture have significant concentrations of vitamin c, α‐carotene, cis‐β‐ carotene, total carotenoids, and total phenolic acids, such as chlorogenic acid and flavonoids, such as quercetin D‐glucoside, quercetin, and kaempferol, compared to fruits of plants grown under conventional agricultural practices.

Nitrogen (N) is a nutrient element that plants require in amounts larger than that of any other soil supplied element. Most plants can utilize both NH4 + and NO3 - ; however, NH4 + at high concentration can be toxic to plants [52]. NH4 <sup>+</sup> as a sole source of N can result in a variety of negative effects to most plant species. The negative effects include a reduced plant photosyn‐ thetic rate, lower dry weights, reduced root growth, and a reduced rate of water uptake [52– 54]. However, plants differ in their sensitivity to NH4 + toxicity. Onion, a member of the Amaryllidaceae Family, is known to be fairly tolerant to high concentrations of NH4 + [54, 55]. On the contrary, Hippeastrum, a member of the Amaryllidaceae, suffered reduced bulb size when fertilized with NH4 <sup>+</sup> as the sole source of N [56]. Shoot and roots of ornamental shrub, "*Doublefile viburnums*" (*Viburnum plicatum* var. *tomentosum*) contained lower NH4 (ammonium) concentrations when NH4 was supplied alone compared to NH4 supplied with NO3 (nitrate) or a combination of NH4 and NO3 [57]. Al‐Ghamidi et al. [58] found that date palm seedlings grown in a soilless hydroponic media had the greatest leaf area and root weight when NO3 was used as the sole nitrogen (N) source whereas date palm seedlings had a lower root: shoot ratio when NH4‐ or urea‐N were used as N source [58].

Addition of organic matter could affect the adsorption, movement, and biodegradation of pesticides. The addition of organic waste, specifically to agricultural soils, is a practice that has been carried out for centuries, due to its fertilizer properties and contribution to the physico‐ chemical and biological properties of the soil [59, 60], which is a common agricultural practice in diverse countries [61–63]. Addition of organic waste to soil contributes to the enhancement of active humified components, such as humic acid (HA) and fulvic acid (FA) [64], which exert an important role in geochemical processes as sources of nutrients for plants and microorgan‐ isms, in acid–base buffering capacity of soils, and promoting a good soil structure, thereby improving aeration and moisture retention [65, 66]. In agronomic aspects, addition of organic waste enhances biological activity and fertility, because through this addition, nutrients and diverse groups of microorganisms, such as bacteria, fungi, and actinomycetes [67–71] play an important role in the fate of xenobiotic compounds such as heavy metals, aromatic hydrocar‐ bons, and pesticides [72–76].

Some organic wastes are associated with inorganic and organic toxic compounds, such as heavy metals and pesticides [60, 72, 73, 77], that when incorporated into soil, constituting a pollution problem in soils and therefore causing toxic effects on microorganisms and crops [77, 78]. Excessive concentrations of heavy metals in soil can be toxic to microorganisms [79]. On the other hand, soil microorganisms need heavy metals for their growth and activity. Elevated concentrations of heavy metals in soil have shown a reduction in the activity of enzymes secreted by beneficial soil microorganisms. SS contains heavy metals, and the release of these metals into the soil solution and uptake by plants growing in soil amended with SS could be phytotoxic.

The efficiency of some pesticides and their persistence and potential as environmental contaminants depends on their retention and degradation on soil constituents [80]. The OM in soil amendments is reported as a major controller component in the sorption, transforma‐ tion, and transport of many organic pollutants in soil [81]. Soil amendments could be used to intercept pesticide‐contaminated runoff from agricultural fields, and this practice might provide a potential solution to pesticide contamination of surface and seepage water from farmlands. Residues of two of the herbicides commonly used in agriculture, DCPA [1,4‐ Benzenedicarboxylic acid, 2, 3, 5, 6‐tetrachloro‐, dimethyl] ester, and metribuzin [4‐amino‐6‐ tert‐butyl‐4, 5‐dihydro‐3‐methylthio‐1,2,4‐triazin‐5‐one] were monitored in runoff and infiltration water from agriculture fields. Metribuzin was detected in Ohio Rivers and Iowa wells and groundwater [82, 83]. The major mechanism by which metribuzin is lost from soil is microbial degradation. Losses due to the volatilization or photodegradation are not signif‐ icant under field conditions [84, 85]. Sharom and Stephenson [86] also found that metribuzin mobility was inversely related to soil organic matter content. Similarly, soil amended with CM or SS retained DCPA residues up to 99 days compared to NM treatments [87]. Accordingly, soil OM has a major role in the transformation, transport, and adsorption/desorption of most soil organic and inorganic pollutants [81]. Because organic amendments used in agricultural production contain significant amounts of OM, it has been found that this practice (recycling waste and use of organic amendments in land farming) has a significant impact on the fate and transport of pesticides under environmental conditions. On the other hand, the addition of organic amendment to soil normally results in an increase in the microbiological activity due to the availability of simple organic molecules such as sugar and amino acids [88]. The application rate of soil amendments for agricultural soil is proposed according to nitrogen, phosphorus, and potassium requirements. However, a specific rule for animal manure application to soil does not exist, but is proposed through good agricultural practices.

concentration can be toxic to plants [52]. NH4

166 Organic Fertilizers - From Basic Concepts to Applied Outcomes

when fertilized with NH4

bons, and pesticides [72–76].

phytotoxic.

54]. However, plants differ in their sensitivity to NH4

ratio when NH4‐ or urea‐N were used as N source [58].

<sup>+</sup> as a sole source of N can result in a variety of

toxicity. Onion, a member of the

+ [54, 55].

negative effects to most plant species. The negative effects include a reduced plant photosyn‐ thetic rate, lower dry weights, reduced root growth, and a reduced rate of water uptake [52–

On the contrary, Hippeastrum, a member of the Amaryllidaceae, suffered reduced bulb size

"*Doublefile viburnums*" (*Viburnum plicatum* var. *tomentosum*) contained lower NH4 (ammonium) concentrations when NH4 was supplied alone compared to NH4 supplied with NO3 (nitrate) or a combination of NH4 and NO3 [57]. Al‐Ghamidi et al. [58] found that date palm seedlings grown in a soilless hydroponic media had the greatest leaf area and root weight when NO3 was used as the sole nitrogen (N) source whereas date palm seedlings had a lower root: shoot

Addition of organic matter could affect the adsorption, movement, and biodegradation of pesticides. The addition of organic waste, specifically to agricultural soils, is a practice that has been carried out for centuries, due to its fertilizer properties and contribution to the physico‐ chemical and biological properties of the soil [59, 60], which is a common agricultural practice in diverse countries [61–63]. Addition of organic waste to soil contributes to the enhancement of active humified components, such as humic acid (HA) and fulvic acid (FA) [64], which exert an important role in geochemical processes as sources of nutrients for plants and microorgan‐ isms, in acid–base buffering capacity of soils, and promoting a good soil structure, thereby improving aeration and moisture retention [65, 66]. In agronomic aspects, addition of organic waste enhances biological activity and fertility, because through this addition, nutrients and diverse groups of microorganisms, such as bacteria, fungi, and actinomycetes [67–71] play an important role in the fate of xenobiotic compounds such as heavy metals, aromatic hydrocar‐

Some organic wastes are associated with inorganic and organic toxic compounds, such as heavy metals and pesticides [60, 72, 73, 77], that when incorporated into soil, constituting a pollution problem in soils and therefore causing toxic effects on microorganisms and crops [77, 78]. Excessive concentrations of heavy metals in soil can be toxic to microorganisms [79]. On the other hand, soil microorganisms need heavy metals for their growth and activity. Elevated concentrations of heavy metals in soil have shown a reduction in the activity of enzymes secreted by beneficial soil microorganisms. SS contains heavy metals, and the release of these metals into the soil solution and uptake by plants growing in soil amended with SS could be

The efficiency of some pesticides and their persistence and potential as environmental contaminants depends on their retention and degradation on soil constituents [80]. The OM in soil amendments is reported as a major controller component in the sorption, transforma‐ tion, and transport of many organic pollutants in soil [81]. Soil amendments could be used to intercept pesticide‐contaminated runoff from agricultural fields, and this practice might provide a potential solution to pesticide contamination of surface and seepage water from farmlands. Residues of two of the herbicides commonly used in agriculture, DCPA [1,4‐

Amaryllidaceae Family, is known to be fairly tolerant to high concentrations of NH4

+

<sup>+</sup> as the sole source of N [56]. Shoot and roots of ornamental shrub,
