According to the Department of Primary Industries of NSW Government Australia (2018), there are numerous benefits of earthworm in relation to soil fertility. Earthworm helps to increase the nutrient availability of soil along with increasing the overall drainage system of soil and making soil a more stable structure. All these help to increase the farm productivity. In relation to nutrient availability, it can be said that the earthworm feds on the debris of plant like the dead roots, grasses, leaves and manure. The digestive system of earthworm is filled with the organic and the mineral constituents of the food which they consume and thus their casts can be cited as a richer available source of nutrients to the soil. The body of the earthworm undergoes rapid decomposition which increases nitrogen content of the soil which increases the soil fertility further. The cast of worm also increases 4 times higher level of phosphorus than the soil itself which increases the nutrient source of the soil. In the domain of regulating drainage system of the soil, it can be said that extensive burrowing and channelling undertaken by the earthworms loosens and aerates the soil and thus improves the soil drainage (Bohlen, 2017). According to Bohlen (2017), soils with earthworms can drain 10-times faster than soil without earthworm. Earthworm also increases the water infiltration rate by 6-times and the tunnels created by earthworm helps the rain water to pass deep inside the soil and increasing the moisture content of the soil and its overall fertility.
Flora and Fauna
Flora is the name given to the collective plant that grows or once grew over a certain area over a period of time and fauna is a collective name given to animal live that thrives on land. Apart from maintaining the ecological balance, floras and faunas of a particular landscape also plays an important role in maintaining the soil fertility. One of the important examples of fauna that increases the soil fertility is the earthworms. Apart the earthworms, other important faunas that contribute towards the increase in soil fertility are the birds (Magurran, 2013). According to Irick et al. (2015), wading bird guano helps in the nutrient enrichment of the soil via carrying marine derived nutrients. They mainly promote increase in the soil fertility in the tree islands of Florida Everglades. The floras that help to improve the soil fertility include the leguminous plants. According to Pankievicz et al. (2015) leguminous plant increases the soil fertility under the action of Rhizobium bacteria which are present in the root knobs of the plant. These bacteria promotes fixation of the atmospheric nitrogen in the soil and thus increasing the overall nitrogen content of the soil and leading to an increase in soil fertility. Thus overall, it can be said the a perfect combination of the floras and faunas help to increase the overall soil fertility along with the maintenance of the ecological diversity which in turn promotes proper cultivation of the crop plants in agriculture.
The soil enzyme increase the rate of reaction at which the plant residues decompose in the soil and thereby increasing the rate of nutrient content in soil. For example, glucosidase, an important soil enzyme cleaves glucoside, one of the common compound produced in plants and thus helps in releasing glucose in the soil. Increase in the glucose content of the soil increases the overall nutrient availability to the plants. Other important soil enzymes include Amidas and it acts upon the carbon and nitrogen compounds leading to the generation of ammonium. Thus it helps to increase the nutrient cycle of the soil and increase in the nitrogen availability of the soil. Other notable soil enzyme are urease, sulfatase and phosphatise. All these enzymes contributes to the nutrient cycling. The main source of the soil enzymes are the microbes either living or dead. Plant roots, plant residues and soil animals are also act as an important source of soil enzyme. The soil enzyme are stabilized in the matrix of the soil or remains accumulated in the form of complex along with the organic matter present in the soil (humus) and humus or clay complexes. They are regarded as useful indicators of soil fertility (Burns et al. 2013).
The detection of the soil enzyme can be done indirectly in the laboratory by the use of biochemical assays. The enzymatic assay reflects the potential enzymatic activity but do not represent true in-situ activity levels of the enzymes. In-situ measurement of enzyme activity present in the soil is regarded as the most realistic method for the detection of the enzymatic activity in the soil. This is regarded as the direct visualization of the ezymatic activity within the undisturbed soil. This is mainly done via the use of electronic microscopic observation of the certain section of soil. At times histochemical staining was also considered as a sensitive method for the detection of the soil enzymatic activity. It is mainly done via alkaline phosphatase enzyme (Burns et al. 2013).
Soil Organic Matter (SOM)
Soil Organic Matter (SOM) is defined as the organic component of soil which consists of both plant and animal residues at different stages of decomposition. The importance of the SOM is it acts as an important source of nutrients to the plants and thus helping to act as a direct indicator of the soil fertility. SOM also helps to increase the water holding capacity of the soil and thus increasing the overall moisture content of the soil. Majority of the soil contain 2 to 10% of organic matter (Paul, 2014). However, Powlson, Smith and Smith (2013) are of the opinion that though SOM is an important source of soil fertility, it can never be regarded as sole indicator for the fertility of the soil. The fertility of the soil depended on the complex interaction of the floras, fauns and the soil micro-organisms with the SOM along with an effective amalgamation of the soil enzyme.
It is never easy to measure the total SOM. However, Walkley Black Method is popularly used to measure the soil carbon content. Since carbon is one of the pivotal sources of SOM, detection of soil carbon content provides an approximate value of SOM. Walkley Black Method mainly uses acid wet oxidation method for the detection of soil carbon content (Powlson, Smith & Smith, 2013).
Bohlen, P. J. (2017). Earthworms. In Encyclopedia of soil science (pp. 701-705). CRC Press.
Burns, R. G., DeForest, J. L., Marxsen, J., Sinsabaugh, R. L., Stromberger, M. E., Wallenstein, M. D., ... & Zoppini, A. (2013). Soil enzymes in a changing environment: current knowledge and future directions. Soil Biology and Biochemistry, 58, 216-234.
Department of Primary Industries of NSW Government Australia (2018). How earthworms can help your soil. Access date: 25th September 2018. Retrieved from: https://www.dpi.nsw.gov.au/agriculture/soils/biology/earthworms
Irick, D. L., Gu, B., Li, Y. C., Inglett, P. W., Frederick, P. C., Ross, M. S., ... & Ewe, S. M. (2015). Wading bird guano enrichment of soil nutrients in tree islands of the Florida Everglades. Science of The Total Environment, 532, 40-47.
Magurran, A. E. (2013). Measuring biological diversity. John Wiley & Sons.
Pankievicz, V. C., do Amaral, F. P., Santos, K. F., Agtuca, B., Xu, Y., Schueller, M. J., ... & Stacey, G. (2015). Robust biological nitrogen fixation in a model grass–bacterial association. The Plant Journal, 81(6), 907-919.
Paul, E. A. (2014). Soil microbiology, ecology and biochemistry. Academic press.
Powlson, D. S., Smith, P., & Smith, J. U. (Eds.). (2013). Evaluation of soil organic matter models: using existing long-term datasets (Vol. 38). Springer Science & Business Media.