**3. Soil health, rhizosphere microbes and sustainable crop growth**

The concept of soil health has a long history. Attention was much given to soil health in well developed countries initially. This may probably be due to increasing concern of global food security in terms demand for high quality food and feed as a result of exponential growth in population and to keep in check the state of the soil health in general.

According to some studies, some authors are of the opinion that SH has to have inherent components before it can be termed as healthy soil, considering the biological physical and chemical qualities. Health of the soil is a function of its environmental sustainability [59, 60]. There are certain properties to look out for to determine 'healthy soil'. One of the inherent elements of a healthy soil is the ability to be adapted to diverse ecological resources in an optimally balanced condition. It also has to be self-purifying from soil pollutants through elution or biotransformation and thirdly, it has to be suppressive of harmful biota (phytophytogenic) maintaining beneficial soil microbes [60].

While a variety of definitions to the term 'soil health' have been suggested, this chapter will use the definition suggested by Semenov et al. [60] that, soil fertility was traditionally defined as the ability of soil to provide plants with mineral elements, water, air and overall ability to live in favorable physical and chemical environment. Organic fertilizers when used solely, serves as biological control against harmful organisms. Similarly, exclusion of chemical pesticides and using genetically modified organisms in organic farming system offers improved physical and chemical soil properties. The report established that organic farming increases soil health and microbial biodiversity by limiting mass development of pathogenic microbes.

According to Soil Science Society of America (SSSA), soil quality is the ability of the soil to function within the limits of the ecosystem to preserve its biological productivity and quality, ensuring healthy plants and animals. It was further established that methods and parameters have been developed, including portable devices and sets of tools (Environmental Box Kit Soil quality) for the determination of the quality of the soil. These kits are essential in determining soil conductivity, its pH, resistance during plowing, density, organic carbon, carbon microbial biomass, humidity, moisture capacity, nitrate content, soil respiration rates, etc.

Increasing agricultural production to feed the snowballing population in sub-Saharan Africa (SSA) is very challenging [59]. These results due to poor soil quality resulting from soil degradation, unsustainable management practices, and available arable land for mass production to feed the ever-increasing population of subsistence farmers and non-agricultural population. Han et al.'s [61] report on organic and inorganic/chemical fertilizers established that both have their positives and negatives on plant growth and soil in general. Chemical fertilizers/inorganic fertilizers according to their study are reasonably affordable, very rich nutrient contents, and could easily be assimilated by plants. Despite these beneficial effects, chemical fertilizers when used excessively could affect both the plant and the soil

*Enzymatic Processing of Pigeon Pea Seed Increased Their Techno-Functional Properties DOI: http://dx.doi.org/10.5772/intechopen.101406*

community through nutrient loss, surface water and groundwater contamination, soil acidification or basification, reductions in useful microbial communities, and increased sensitivity to harmful insects.

On the other hand, organic manure similarly has several positive effects owing to the stable supply of both essential nutrients and micronutrients, improved microbial activity due to amplified nutrient availability resulting from breakdown of harmful elements, improved soil structure and root development and sufficient soil water for physiological activities [61]. Organic manure is said to be produced from the decomposition of animal byproducts which are utilized to overcome environmental degradation and low plant productivity resulting from excessive utilization of chemical fertilizers. Organic manure is cost-effective and environmentally friendly particularly when waste from livestock industries is recycled which in turn promote agricultural productivity.

In a recent development, Fasusi et al. [45] have shown that nodule formation is enhanced by the low availability of nitrogen, but microorganisms that produce an enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase, have the potential to degrade 1-aminocyclopropane-1-carboxylate before its conversion to ethylene and may also enhance the formation of a nodule. Such formation is part of a common strategy developed by leguminous plants and Rhizobiaceae bacteria to decrease the concentration of oxygen to which the nitrogenase is exposed due to the inhibitory effect of oxygen on nitrogenase activity.

## **4. Conclusion**

This study set out to review in detail the available information on enzymatic processes in pigeon peas and related legumes like the allelopathic inhibition of nitrifying microorganisms by root exudation of phenolic compounds, legumes' tolerance to drought stresses, high biomass productivity, relationship between plant growth promoting bacteria (PGPB) and plant growth promoting rhizofungi (PGPF) and general soil health towards sustainable crop production. This study has examined the peer reviewed literature on pigeon pea among others legumes as having huge untapped potential for improvement of both in quantity and in quality of production in Africa. The most obvious finding to emerge from this study is that pigeon pea requires lesser amount of nitrogen (N2) compared to other crops like maize. Secondly, pigeon pea has extensive roots which could grow through hard layers of soil aggregates, increasing soil porosity and aeration which in turn improves soil fertility. Taken together, these findings suggest a role for pigeon pea in promoting crop yield. The present study is important in furthering our understanding of the role pigeon pea and related legumes play in boosting yield when mixed cropping is practiced. This is the first study to report an association between underutilized African legumes, enzymatic processes involved in mutualistic association of PGPR (rhizobacteria) and PGPF (arbuscular mycorrhizae fungi) and nodule formation to bring about increases in growth, nutrient uptake potential, and yield of the plants. The study is limited by the lack of information on pigeon pea and accurate state-of the art about the enzymatic processing of pigeon pea seed in promoting its technofunctional potentials. The strengths of the study included the in-depth analysis of Role of Plant Growth-Promoting Bacteria (PGPR) and Fungi (PGPF) in Sustainable Agriculture, Neglected and Underutilized Legumes in Sub-Saharan Africa and general Soil Health for Sustainable Crop Growth. Further research should be undertaken to explore how the mechanism of enzymatic processing of pigeon pea works for sustainable food security.
