**2.2. The roles of soil organic matter on soil fertility**

Organic and low input agriculture are regarded as a procedure to maintain SOM and soil fertility. In Switzerland, a long-term trial biodynamic system was reported to show a stable C content, while a C loss of 15% in 21 years was measured for the conventional system control. In the United States, a field trial showed fivefold higher C sequestration in an organic system (i.e., 1218 kg of C ha–1 year–1) versus conventional management [12,13]. Lal stated that the rate of organic C sequestration in soil with the adoption of recommended technologies depended on soil texture, soil structure, rainfall, temperature, farming system, and its management [14]. He also found that addition of 1 ton of degraded crop organic matter to the soil may increase crop yield by 20-40 kg ha–1 for wheat, 10-20 kg ha–1 for maize, and 0.5-1 kg ha–1 for cowpeas. Apart from enhancing food security, C sequestration also has the potential to offset fossil fuel emissions by 0.4-12 tons of C year–1 or 5-15% of global fossil fuel emissions [14].

Additionally, organic matter has both direct and indirect effects on the availability of nutrients for plant growth. The decay of organic matter liberates these nutrient elements, making them available to the succeeding crop. It is a major source of P and sulfur (S), and essentially the sole source of N through its mineralization by soil microorganisms. Organic matter serves as a source of energy for both macro- and microfaunal organisms. Earthworms and other faunal organisms are strongly affected by the quantity of plant residue material returned to the soil. During the decomposition process of organic tissue, soil particles are attached together as aggregates. SOM enhances the nutrient buffering capacity and the microbial activity, both strengthening soil fertility [15]. Additionally, organic matter contributes 30–70% to the cation exchange capacity, which allows soil particles to hold nutrients, thus preventing them from leaching out. Also, as a buffer, humus exhibits buffering over a wide pH range [16].

Water infiltration and root growth are promoted by lower bulk density, which tends to decrease with organic matter additions [11]. Organic matter has higher water-holding capacity (by 20 times) versus clay. Aggregate stability and water infiltration are increased by organic matter additions. This positive effect on the water-capturing capacity of the soil is likely to increase in importance with climate change, [15] because a higher water-capturing capacity strengthens resilience to droughts and reduces the risk of floods [17]. Thus, the need for irrigation is lowered, which has an additional adaptation and mitigation effect [15,18].

SOM enhances the nutrient buffering capacity and microbial activity, both strengthening soil fertility [15]. The addition of organic matter helps to protect the soil from erosion, acts as a buffer against dramatic changes in acidity, alkalinity, and salinity. The overall effects of organic matter are far greater than the simple analysis of its constituent nutrients; indeed, it is the engine that drives all the biological processes in the soil [19]. Increased SOM and microbial activity in organically farmed soils results from a combination of enhanced C inputs during fertilization and increased grass cover [20].

On-Farm-Produced Organic Amendments on Maintaining and Enhancing Soil Fertility and Nitrogen Availability in Organic or Low Input Agriculture http://dx.doi.org/10.5772/62338/ 293

**Figure 1.** Soil organic matter contributes to soil fertility.

biological properties are based on the soil being a living system; many kinds of organisms are involved in complex biological, chemical, and physical processes. A living soil is regarded as a healthy soil and favorable to plant growth because of the organisms' roles in soil development

Organic and low input agriculture are regarded as a procedure to maintain SOM and soil fertility. In Switzerland, a long-term trial biodynamic system was reported to show a stable C content, while a C loss of 15% in 21 years was measured for the conventional system control. In the United States, a field trial showed fivefold higher C sequestration in an organic system (i.e., 1218 kg of C ha–1 year–1) versus conventional management [12,13]. Lal stated that the rate of organic C sequestration in soil with the adoption of recommended technologies depended on soil texture, soil structure, rainfall, temperature, farming system, and its management [14]. He also found that addition of 1 ton of degraded crop organic matter to the soil may increase crop yield by 20-40 kg ha–1 for wheat, 10-20 kg ha–1 for maize, and 0.5-1 kg ha–1 for cowpeas. Apart from enhancing food security, C sequestration also has the potential to offset fossil fuel

Additionally, organic matter has both direct and indirect effects on the availability of nutrients for plant growth. The decay of organic matter liberates these nutrient elements, making them available to the succeeding crop. It is a major source of P and sulfur (S), and essentially the sole source of N through its mineralization by soil microorganisms. Organic matter serves as a source of energy for both macro- and microfaunal organisms. Earthworms and other faunal organisms are strongly affected by the quantity of plant residue material returned to the soil. During the decomposition process of organic tissue, soil particles are attached together as aggregates. SOM enhances the nutrient buffering capacity and the microbial activity, both strengthening soil fertility [15]. Additionally, organic matter contributes 30–70% to the cation exchange capacity, which allows soil particles to hold nutrients, thus preventing them from

and conservation, specifically nutrient cycling and determining soil fertility.

emissions by 0.4-12 tons of C year–1 or 5-15% of global fossil fuel emissions [14].

leaching out. Also, as a buffer, humus exhibits buffering over a wide pH range [16].

Water infiltration and root growth are promoted by lower bulk density, which tends to decrease with organic matter additions [11]. Organic matter has higher water-holding capacity (by 20 times) versus clay. Aggregate stability and water infiltration are increased by organic matter additions. This positive effect on the water-capturing capacity of the soil is likely to increase in importance with climate change, [15] because a higher water-capturing capacity strengthens resilience to droughts and reduces the risk of floods [17]. Thus, the need for irrigation is lowered, which has an additional adaptation and mitigation effect [15,18].

SOM enhances the nutrient buffering capacity and microbial activity, both strengthening soil fertility [15]. The addition of organic matter helps to protect the soil from erosion, acts as a buffer against dramatic changes in acidity, alkalinity, and salinity. The overall effects of organic matter are far greater than the simple analysis of its constituent nutrients; indeed, it is the engine that drives all the biological processes in the soil [19]. Increased SOM and microbial activity in organically farmed soils results from a combination of enhanced C inputs during

**2.2. The roles of soil organic matter on soil fertility**

292 Organic Fertilizers - From Basic Concepts to Applied Outcomes

fertilization and increased grass cover [20].
