18.3.3 Cover Crops or Green Manure
As previously outlined, in organic soil fertility management, there is a need to supply
nutrients from mineralized organic sources. Cover crops and green manures have
thus been widely promoted in organic agriculture and these are cereals, annual or
perennial grasses or legumes used to cover the soil for a certain period and then
ploughed under to contribute organic matter and nutrients to the soil (Gaskell and
Smith 2007). Cover crops play an important function in soil fertility management as
they capture residual nutrients during crop production and sequester it in plant
biomass for subsequent supply to the next crops during decomposition. Furthermore,
other green manure crops are grown mainly due to their ability to fix atmospheric
nitrogen into organic nitrogen which is an important nutrient source in organic
agriculture.
18.3.4 Mineral Organic Fertilizers
There is a shift towards classifying nutrient sources that are of natural origin as
suitable sources of nutrients in organic agriculture. This has seen the acceptance of
natural unprocessed mineral nutrient sources such as rock phosphate (source of
phosphorus), dolomitic limestone (raises the pH of soils that are low in magnesium),
sulphur (lowers soil pH), greensand (supplies potassium and several micronutrients)
and Epsom salts (provide rapid release of magnesium) in organic agriculture
(Mupambwa and Mnkeni 2018; Lavison 2013; Edwards et al. 2010; Chianu et al.
2012). Mineral fertilizers are used mainly for soil pH control, as well as for the
supply of nutrients like phosphorus, potassium and magnesium but none of these
provides any nitrogen (Green 2019). Unlike synthetic inorganic fertilizers, the
nutrients on mineral fertilizers require natural soil chemical processes to make
them bio-available for plant uptake; hence, the rate of nutrient release is also slow
when directly applied to soil. However, processes such as vermicomposting can be
used to further enhance the bio-availability of nutrients in the mineral fertilizers
(Mupambwa and Mnkeni 2018).
18.3.5 Compost Leachates and Human Urine
Unlike solid nutrient sources identified before, several researchers have looked at the
possibility of extracting nutrients from solid composts by leaching them with
water thus producing liquid nutrient sources called leachates or using liquid excreta
(urine) from animals and humans (Gutierrez-Miceli et al. 2008; Mnkeni et al. 2008).
The leachates from composts have been reported to be high in macro- and
micronutrients and also contain essential humic acids which are important in
18 Some Perspectives on Vermicompost Utilization in Organic Agriculture
305
As previously outlined, in organic soil fertility management, there is a need to supply
nutrients from mineralized organic sources. Cover crops and green manures have
thus been widely promoted in organic agriculture and these are cereals, annual or
perennial grasses or legumes used to cover the soil for a certain period and then
ploughed under to contribute organic matter and nutrients to the soil (Gaskell and
Smith 2007). Cover crops play an important function in soil fertility management as
they capture residual nutrients during crop production and sequester it in plant
biomass for subsequent supply to the next crops during decomposition. Furthermore,
other green manure crops are grown mainly due to their ability to fix atmospheric
nitrogen into organic nitrogen which is an important nutrient source in organic
agriculture.
18.3.4 Mineral Organic Fertilizers
There is a shift towards classifying nutrient sources that are of natural origin as
suitable sources of nutrients in organic agriculture. This has seen the acceptance of
natural unprocessed mineral nutrient sources such as rock phosphate (source of
phosphorus), dolomitic limestone (raises the pH of soils that are low in magnesium),
sulphur (lowers soil pH), greensand (supplies potassium and several micronutrients)
and Epsom salts (provide rapid release of magnesium) in organic agriculture
(Mupambwa and Mnkeni 2018; Lavison 2013; Edwards et al. 2010; Chianu et al.
2012). Mineral fertilizers are used mainly for soil pH control, as well as for the
supply of nutrients like phosphorus, potassium and magnesium but none of these
provides any nitrogen (Green 2019). Unlike synthetic inorganic fertilizers, the
nutrients on mineral fertilizers require natural soil chemical processes to make
them bio-available for plant uptake; hence, the rate of nutrient release is also slow
when directly applied to soil. However, processes such as vermicomposting can be
used to further enhance the bio-availability of nutrients in the mineral fertilizers
(Mupambwa and Mnkeni 2018).
18.3.5 Compost Leachates and Human Urine
Unlike solid nutrient sources identified before, several researchers have looked at the
possibility of extracting nutrients from solid composts by leaching them with
water thus producing liquid nutrient sources called leachates or using liquid excreta
(urine) from animals and humans (Gutierrez-Miceli et al. 2008; Mnkeni et al. 2008).
The leachates from composts have been reported to be high in macro- and
micronutrients and also contain essential humic acids which are important in
18 Some Perspectives on Vermicompost Utilization in Organic Agriculture
305