several factors, including temperature, soil moisture, soil properties and organic
fertilizer characteristics. Laboratory incubation studies can be important for evaluating N mineralization mechanisms but relating incubation results to mineralization
under actual field conditions can be difficult. Mineralization increases with increasing temperature under conditions found in agricultural soils. Mineralization is
greatest when soil moisture is near field capacity and declines with soil drying.
Growing degree day, which is a function of temperature, has been used to predict N
availability from applied composts. In this case, it is important to understand post
field temperature and moisture conditions post compost application. Fields should
preferably be managed to minimize ammonia loss following application, hence
tillage practices post compost application should be minimal.
18.5.3 Economic Benefits of Organic Fertilizers
To encourage the use of vermicomposts on both conventional and organic agricultural production, it is important that there be a thorough understanding of the
benefits. Koelsch (2017) states that, organic fertilizers such as vermicomposts derive
their economic value, from improvements in soil quality, increases in yield and
replacement of purchased nutrients required for crop production. Compared to
commercial inorganic fertilizers, organic fertilizers contain organic carbon, which
is the key to maintaining soil health, including the characteristics of cation exchange
capacity, soil tilth and water holding capacity. Targeting fields requiring supplemental P produces the largest economic value from organic sources. As mentioned
previously, most nutrients in organic fertilizers are slowly released over a longer
period than is obtained from most inorganic fertilizers. Soil organic matter has an
added benefit of preventing nutrients from leaching or loss through increasing the
soil CEC. The organic matter in organic fertilizers plays an important role in nutrient
cycling, which provides food for soil organisms and facilitates the formation of
aggregates that maintain the soil as a habitat favourable for beneficial soil organisms.
The value of nutrients in organic fertilizers like vermicomposts is therefore more
than the accumulated value of the individual nutrients. The residual effects of
composts last for at least three seasons; therefore, farmers could benefit from its
residual fertility in subsequent seasons providing nutrients to crops for several years.
Also, addition of organic fertilizers can help to buffer the soil against pH changes,
hence saving on liming costs on acidic soils.
18.5.4 Organic Fertilizer (Vermicompost) Quality
Though vermicomposts can be optimized in terms of degradation efficiency and
nutrient content, there has been very limited information on product standards and
indicators or compost quality parameters to govern their marketing and field application (Fan et al. 2016; Brinton 2000). This is unlike inorganic fertilizers that have to
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H. A. Mupambwa et al.
fertilizer characteristics. Laboratory incubation studies can be important for evaluating N mineralization mechanisms but relating incubation results to mineralization
under actual field conditions can be difficult. Mineralization increases with increasing temperature under conditions found in agricultural soils. Mineralization is
greatest when soil moisture is near field capacity and declines with soil drying.
Growing degree day, which is a function of temperature, has been used to predict N
availability from applied composts. In this case, it is important to understand post
field temperature and moisture conditions post compost application. Fields should
preferably be managed to minimize ammonia loss following application, hence
tillage practices post compost application should be minimal.
18.5.3 Economic Benefits of Organic Fertilizers
To encourage the use of vermicomposts on both conventional and organic agricultural production, it is important that there be a thorough understanding of the
benefits. Koelsch (2017) states that, organic fertilizers such as vermicomposts derive
their economic value, from improvements in soil quality, increases in yield and
replacement of purchased nutrients required for crop production. Compared to
commercial inorganic fertilizers, organic fertilizers contain organic carbon, which
is the key to maintaining soil health, including the characteristics of cation exchange
capacity, soil tilth and water holding capacity. Targeting fields requiring supplemental P produces the largest economic value from organic sources. As mentioned
previously, most nutrients in organic fertilizers are slowly released over a longer
period than is obtained from most inorganic fertilizers. Soil organic matter has an
added benefit of preventing nutrients from leaching or loss through increasing the
soil CEC. The organic matter in organic fertilizers plays an important role in nutrient
cycling, which provides food for soil organisms and facilitates the formation of
aggregates that maintain the soil as a habitat favourable for beneficial soil organisms.
The value of nutrients in organic fertilizers like vermicomposts is therefore more
than the accumulated value of the individual nutrients. The residual effects of
composts last for at least three seasons; therefore, farmers could benefit from its
residual fertility in subsequent seasons providing nutrients to crops for several years.
Also, addition of organic fertilizers can help to buffer the soil against pH changes,
hence saving on liming costs on acidic soils.
18.5.4 Organic Fertilizer (Vermicompost) Quality
Though vermicomposts can be optimized in terms of degradation efficiency and
nutrient content, there has been very limited information on product standards and
indicators or compost quality parameters to govern their marketing and field application (Fan et al. 2016; Brinton 2000). This is unlike inorganic fertilizers that have to
314
H. A. Mupambwa et al.