Agriculture Reference
In-Depth Information
3.The effects of Lumbricidae could be a consequence of the burial of large organic particles
mixed with ingested soil, because it is commonly recognized that the incorporation of
litter into soil has significant effects on soil physical parameters (Springett 1983; Aina
1984; Oades 1984; Kladivko et al. 1986; Shaw and Pawluk 1986; Joschko et al. 1989;
Kooistra 1991; Wolters 1991).
MEDIUM-TERM EFFECTS: EXPERIMENTS INOCULATING
EARTHWORMS INTO CROPPING SYSTEMS OF THE
HUMID TROPICS
Three-year experiments have been conducted at two tropical sites, Lamto (Cte dÔIvoire) and
Yurimaguas (Peru). Annual cropping systems were inoculated with populations of endogeic species
of earthworms, and the dynamics of the system were compared with those of noninoculated systems
for six successive crops over 3 years (Pashanasi et al. 1996; Gilot 1997).
At Yurimaguas, the C and N contents of soil decreased significantly with time. After six
cropping cycles, the C contents had decreased from 16.8 to 1.36 and 1.51 mg g
in systems
1
inoculated with earthworms and in the control, respectively ( Figure 8.4 ) . Although systems
inoculated with earthworms tended to have less C after the fourth cropping cycle, the observed
differences were not significant at the end of the experiment. Changes in N content during the
experiment showed similar trends: N concentrations increased initially in both systems as a result
of N outputs after burning and incorporation of ashes in the soil. During the first three cropping
cycles, N contents were higher in the earthworm-inoculated systems. From the fourth harvest,
the N contents were lower in the earthworm-inoculated treatments, but differences were not
significant. Earthworms did not affect soil nutrient contents for the first five cropping cycles: Ca,
Mg, K, and P contents increased first after burning and incorporation of ashes and thereafter
decreased steadily. By the last harvest, cation contents were slightly higher in the earthworm-
inoculated systems, but the differences were significant only for K contents. Similar trends were
observed for pH and Al saturation.
At Lamto, similar results were obtained. After four cropping cycles of maize, the C contents
in the upper 10 cm of soil decreased from 13.37 mg g
at time 0 to 9.75 and 9.64 mg/g in the
control and earthworm-inoculated systems, respectively, with the differences observed between the
last two treatments insignificant. In spite of these results, some differences in the quality of organic
matter seemed to exist. Physical fractionation of SOM using the Feller (1979) method showed
some evidence of protection of the coarse organic particles in the inoculated systems (Gilot 1997).
Furthermore, laboratory respirometric tests showed a significant increase in soil respiration rates
where earthworms had been active (Tsakala 1994).
Experiments by Gilot (1997) showed that the effects of earthworms in protecting coarse organic
fractions were significant only in soils that had been sieved previously. In this case, reaggregation
of soil by earthworms had positive effects on SOM protection. In soils that had not been sieved,
large aggregates, resulting from earthworm activities in the natural soil, were conserved in the no
earthworm treatment conditions during the 3 years that the experiment lasted. Thus, the effects of
protection linked to aggregation were retained, although no earthworms were present.
1
LONG-TERM EFFECTS OF EARTHWORMS: MODELING AND
OBSERVATION OF SUCCESSIONAL PROCESSES
In the absence of long-term experiments, evidence for effects of earthworms at scales from 10 to
100 years or more has been sought from simulation modeling and the observation of time sequences
in successional processes.
 
Search WWH ::




Custom Search