**6. The impact of organic carbon on yield**

According to research, it was found that the high yield of crops is a result of soil organic carbon. 2% soil organic carbon is critical to the threshold [23, 45]. A value below 2% may have a negative influence on the structural functionality and the asymptotic relationship that exist between soil organic carbon and yield [12, 20]. In other words, the critical threshold for productivity may not be relevant if there is sufficient mineral fertilizer to support crop production [3, 15, 43]. Mineral fertilizer was found to be effective at increasing maize yield [16, 21]. It was reported that mineral fertilizer increases SOC. It improves crop yield and promotes entire growth [2, 11, 31]. It was also found that long-term application of mineral fertilizer significantly increases the SOC content in the 0 – 20 cm soil layer [16, 27, 50]. However, the use of mineral fertilizer is not as effective as the use of straw on farmland [16, 17, 40]. It was discovered in an experiment that the use of straw provides a metabolic substrate for soil microorganisms. Soil porosity and water movement were influenced by straw input [3, 17, 30]. It was also recorded that the use of animal–plant residue increases the SOC content. Straw carbon transformation activates and enhances microbial communities such as bacteria, archaea, protozoa, fungi, and viruses [11–13]. These organisms distribute organic carbon in the complex terrestrial environment [6, 11, 33, 51]. Betaproteobacteria and Gammaproteobacteria were the main genera of *Janthinobacterium*, *Massilia*, *Variovorax*, *Xanthomonas*, and *Pseudomonas* in the early stage of carbon transformation of wheat straw [22, 45, 47]. A positive correlation was recorded relative to SOC to soil microbial structure and diversity. The quality and quantity of SOC are subjected to the metabolic action of the microorganism in the ecosystem [12, 17, 47]. The abundance and structure of microorganisms are generally considered to be essential for the fixation, transport, and accumulation of SOC [17, 22]. They are widely involved in soil processes and functions. Soil microorganisms are effective with the use of organic matter [5, 9].

#### *Restoration of Soil Organic Carbon a Reliable Sustenance for a Healthy Ecosystem DOI: http://dx.doi.org/10.5772/intechopen.100188*

It supports and shapes the global carbon cycle. It enhances the mechanism that increases SOC and limits the impact of climate change [2, 7, 37]. A limiting factor for straw application is moisture [17, 30]. In cold weather, the accumulation of straw in the soil does not easily decompose. Straw deposition in this case may result in phytotoxic [20, 21, 27]. The use of soil organic carbon is not sufficient enough to influence sustainable intensification to reduce the harm caused by inorganic fertilizer due to eutrophication and greenhouse gas emissions [17, 23, 41]. There is a positive relationship between soil organic carbon and yield starting from the 2% threshold [25, 45, 51]. It provides a reduction in nutrient runoff, drought resistance, and yield stability **Figure 3** [22, 23, 45].

In a finding, the cultivation of maize and wheat uses less than 2% soil organic carbon to area and harvest [2, 12]. It was also found that a continuous cropping system and grazing may result in carbon loss if not properly managed [1, 5, 9]. This practice in other words may improve the yield of maize and wheat due to a large amount of soil organic matter from animal waste [33, 39]. The reduction in nitrogen fertilizer plays a significant role in agricultural land and the ecosystem [16, 20]. It minimizes soil emission of nitrous, eutrophication of water, and efficiency of greenhouse gas [1, 4, 9, 44]. However, as much as soil organic matter is significant to providing nutrients to the soil. This cannot be a direct substitute for mineral fertilizer [16, 20, 40]. The efficiency of soil organic carbon varies between 0.5% and 2.0% to soil properties, climate, and the type of input applied at a point in time [8, 51]. The agricultural input differs in its potential. This efficiency ranges from farmyard manure to sewage sludge to mineral fertilization [13, 20, 27]. It was however concluded that soil organic matter and nutrient provision from agricultural input may be cut down the use of nitrogen fertilizer as input to a large extent [1, 4, 9]. Higher soil organic carbon enhances N input to produce a high yield. Likewise, essential macro and micronutrients are provided through the application of higher levels of soil organic matter [13, 16, 40, 51]. This compensates for soil with limited soil organic carbon concentration [16, 40].

**Figure 3.** *Carbon pool and straw application sourced from [17].*
