Agriculture Reference
In-Depth Information
Mineral soil
+
OM (food) inputs
Physical
breakdown
comminution
GAPs
(grinding in
gizzard,
microbial
activity)
Mucus, enzyme
production,
pH changes
(Bio)chemical
breakdown
Fresh casts
CAPs
(microbial
activity and
soil chemical
changes)
Compact
Decompact
Aging casts
Nutrient
“protection”
Nutrient
release
Breakdown
Plant nutrient spatio-
temporal availability
Root growth and
development
FIGURE 2.7
Diagrammatic representation of ways by which earthworms can positively affect plant growth
via chemical changes in the soil environment induced by gut-associated processes (GAPs) and cast-associated
processes (CAPs).
Most of the reported increases in uptake of nutrients (especially N and P) by plants in response to
earthworms has been related to increased P and N mineralization rates and their availability in castings,
earthworm burrow linings, and earthworm-worked soils (e.g., Graff 1967; 1970; Aldag and Graff 1975;
Lee 1985; Lavelle et al. 1992; Lpez-Hernndez et al. 1993; Brossard et al. 1995; Chapuis-Lardy et
al. 1998; Barois et al. 1999; Rangel et al. 1999). This is particularly important because N and P are
commonly the most limiting nutrients in soils for optimum plant productivity. Because cast production
rates can reach large quantities, ranging from a few tonnes per hectare in temperate arable land up to
more than 1000 t ha
−1
in tropical savannas with a predominance of geophagous endogeic earthworm
species (Lavelle 1988), the amount of nutrients cycled and made available to plants by earthworm
activity can be enormous, ranging from a few up to several hundred kilograms of mineral N per hectare
and tens of kilograms per hectare of plant-available P (Lee 1985, Hauser 1993).
Because of the enhanced rates of nutrient release and availability in the drilosphere, plants
grown in the presence of earthworms often have more nutrients, particularly N and P (e.g., Atlavinyte
and Vanagas 1982; McColl 1982; Graff and Makeschin 1983; Spain et al. 1992; Blakemore 1994;
Baker et al. 1997; Stephens et al. 1994a; Tomati et al. 1996, etc.). Greater availability and rates of
