Earthworm effects on crop and weed biomass, and N content in organic and inorganic fertilized agroecosystems

Soil Bid. Biochem. Vol. 29, No. 314, pp. 423-426, 1997

0 1997 Elsevier Science LA. All rights reserved Printed in Great Britain 0038-0717/97 $17.00+0.00 PIk !SOO3?34717(!%)OO@S2

EARTHWORM EFFECTS ON CROP AND WEED BIOMASS, AND N CONTENT IN ORGANIC AND INORGANIC FERTILIZED AGROECOSYSTEMS B. R. STJNNER,‘* D. A. MCCARTNEY,’ J. M. BLAIR; R. W. PARMELEE and M. F. ALLEN’ ‘Departmentof Entomology, Ohio AgriculturalResearch and Development Center, The Ohio State University, Wooster, Ohio 44691, U.S.A., ‘Division of Biological Sciences, Kansas State University, Manhattan,Kansas 66506, U.S.A., and %partment of Entomology, The Ohio State University, Columbus, Ohio 43210, U.S.A. (Accepted I1 January 1996) Summary-Results are reportedfrom an experiment comparing the effects of earthwormmanipulationsand agroecosystem fertility treatments on corn (maize, Zea muys) and weed biomass, and on nitrogen content. The experimental design consisted of inorganic (ammonium nitrate) and organic (cover crop and manure) fertility treatments.Within each fertility treatment,earthwormmanipulationsconsisted of ambient, augmented and reduced populations. Both ambient and augmented earthworm population treatments resulted in greater weed biomass compared to earthwormreductions. Early season crop biomass was significantly influenced by earthworm reductions. Early season crop biomass was significantly influenced by earthwormx N source interactions,with greater maize biomass in the earthwormreduction treatment.In fertilizer and manure treatments,grain yields were higher in the reduced earthwormtreatmentcompared to either augmented or ambient earthwormtreatments. This effect on yields was probably related to interactions with the weeds and damage to the maize by an insect pest. 0 1997 Elsevier Science Ltd

INTRODUCTION The question of how earthworms affect plant growth and soil-plant interactions has been asked for quite some time and has been addressed through numerous

studies, mostly in laboratory or greenhouse pot experiments (Syers and Springett, 19&1; Lee, 1985). Results from laboratory-based experiments conducted over 100 y ago indicated positive effects of earthworms on plant yields (Lee, 1985). Subsequent and more quantitative pot studies have reported a range of earthworm effects on crop biomass production from small to very large [up to a 9-fold increase (Van Rhee, l%S)], depending upon the species of worms and plants and the soil type used in the experiments (Hopp and Slater, 1949). In England, Edwards and Lofty (1980) quantified the influence of Lumbricus terrestris, Aporrectodea longa, A. caliginosa and Allolobophora chlorotica on biomass production in small grams. They found no significant differences in yield, but they did observe proportionately more root biomass and deeper penetrating roots in the earthworm treatments. More specifically, little is known about the quantitative effects of earthworms on maize biomass production, with the exception of a Pakistanian study reporting that the casts of Metaphire posthuma, a non-lumbricid species, increased maize

production over and above the addition of farmyard manure (Khan, 1966, cited in Lee, 1985). Similarly, we found little or no information regarding the effects of earthworms on weed biomass production in agroecosystems. We present the results of a study which quantified the effects of earthworm manipulations and agroecosystem nutrient management on plant biomass dynamics. This work is a component of a larger project investigating the influences of varying earthworm population densities (ambient, reduced and augmented) and agroecosystem fertility management (inorganic, animal manure and legume) on N cycling processes (Blair et al., 1997). The specific objective of this study was to quantify the effects of earthworm and agroecosystem nutrient source manipulations on maize (Zea mays) and weed biomass dynamics, N concentration and N uptake in plant biomass.

*Author for correspondence(tel: 330 263 3737, fax: 330 263 3686). 423

METHODS Site description The study was located at the Ohio Agricultural Research and Development Center in Wooster, Ohio, U.S.A. The site is located on a deep, moderately welldrained silt loam soil (Canfield series - fine-loamy, mixed, mesic Aquic Fragiudalfs). The soil A horizon has a C content of 2.3%. 0.19% N, a cation exchange capacity of 10 meq (100 g)-*, and pH of 6.3. Mean

B.

424 s

fJl 8000

Reduction

R. Stinner et al.

m Ambient

?? Addition

- manure

-

legume

July

Early, Fig. 1. Plant biomass dynamics.

Earthworm

August

mid and

Grain

end-of

Stover

season

Weeds

biomass

and N source effects for July, August and October shown.

monthly temperatures range from -4.8&C in January to 21.2”C in July. The area receives an average of 101 cm of precipitation y-l. L. terrestris and A. tuberculata are the dominant earthworm species at the study site (Bohlen et al., 1995).

sampling.

Means + SD are

biomass of earthworms compared to control (ambient) plots, as determined by handsorting and formalin extraction. The addition treatment had 1.17 times the number of individuals and 1.5 times the amount of earthworm biomass compared to the ambient treatment (Bohlen et al., 1995).

Design The design was a randomized complete block splitplot (four replications). Data were analysed as a twoway ANOVA with interactions. The main treatments were N source [straw-pack cattle manure; legume cover crops - vetch (Vicia villosa) and rye (Secale cereale)] and ammonium nitrate. The manure and chemical fertilizer were applied at 150 kg N ha-’ or approximately equivalent to the amount of N contained within the vetch-rye cover crops. The earthworm manipulation treatments (ambient, reduced and augmented populations) were established as split plots. The nitrogen amendments were applied in the spring and incorporated with disk tillage before planting maize as the main season crop species. Herbicides (Cyanazine, Alachlor and Gramoxone) were used for weed control. No insecticides were applied. An individual N source plot size is 20 m x 30 m, with earthworms being manipulated within 4.5 m x 4.5 m enclosures. Earthworms were manipulated each autumn and spring either by electroshocking (details for this procedure are described in Bohlen et al., 1995) for population reductions or by additions. In 1993, the reduction treatments had 75% fewer individuals and 65% less

Sampling and analyses Maize was sampled by harvesting three plants in each of the three randomly located areas within each enclosure, and weeds from three adjacent 0.1 m2 quadrats. Data are from the 1993 growing season. Maize biomass data are from sampling on 1 July, 1 August and 12 October. Weed biomass data are from sampling on 12 October. Nitrogen content in whole plant biomass was determined with a Carlo-Erba analyser.

RESULTS AND DISCUSSlON

Weed biomass was significantly (P c 0.01) greater under ambient and augmented earthworm treatments, except with mineral fertilizer, compared to earthworm reduction treatments (Fig. 1). We suggest that this effect could have been caused, at least in part, by the earthworms transporting weed seeds into more favourable germination sites. Earthworms can consume significant quantities of seeds (M&ill and Sagar, 1973), digesting less than 30% of the seeds consumed (Grant, 1983). In particular, Shumway and Koide (1994) reported that L. terrestris readily transported seeds

425

Earthworm effects on plant biomass and nitrogen Reduction

??Ambient

?? Addition

5

fertilizer

)

manure

1

legume

j

3 2 1 0

Early,

August

July

mid

Grain

and end of season

Stover

plant

Weeds

N concentration

Fig. 2. Nitrogen concentration in plant biomass. Earthworm and N sourceeffects for July, August and October sampling. Means f SD are shown.

H Reduction

150

??Ambient

‘@ Addition fertilizer

t

)

100 g

50

3l Y V

O 150

manure

E Q) 100 2 8

50

2 2 -

0 150

a

100 50 0

Early.

July

mid

August

Grain

and end of season

Stover

plant

Weeds

N content

Fig. 3. Nitrogen uptake in plant biomass. Earthworm and N source effects for July, August and October sampling. Means f SD a~ shown.

426

B. R. Sinner ef al.

from weeds in the genera Amaranthus and Setaria, which were among the dominant weeds in our study. In July, there was significantly greater (P < 0.02) maize biomass in the earthworm reduction treatments receiving all forms of N (Fig. 1). In August, this trend in maize biomass was observed only for the legume and inorganic fertilizer treatments. Reduced earthworm treatments had greater grain yields (P < 0.01) in October than ambient treatments. These effects of earthworms on grain yields were probably related both to the earthworm effects on the weeds and to the corn rootworm beetle (Chrysomelidae: Diabrotica), a major pest of maize in North America. We measured significantly higher rootworm damage-as indicated by severely lodged plants (plants beyond a 45” angle)for the ambient earthworm treatment (26%) compared to the addition treatment (16%), with the reduction treatment resulting in intermediate damage at 22%. We suggest the following to explain the maize yield results. The earthworm reduction treatment had lower competitive pressure from weeds, an intermediate level of damage by rootworms and therefore the highest yield. The earthworm addition treatment had higher weed biomass, the lowest level of rootworm damage and intermediate yield. The ambient earthworm treatment had higher weed biomass, the most rootworm damage and the lowest yield. There were no significant earthworm effects on N concentration in maize biomass, but we did find a significant (P
to either the ambient or augmented earthworm treatments (Fig. 3). A similar trend was noted in the August data. The N content of weed biomass was also lower in the reduced earthworm treatments, indicating that N content was largely driven by biomass responses to the treatments. Acknowledgements-We thank D. Beam and D. Giroux for their assistance in data collection. This study was supported by the National Science Foundation and the Ohio Agricultural Research and Development Center.

REFERENCES Blair J.M., Allen M.F., Parmelee R.W., McCartney D.A. and Stinner B.R. (1997) Changes in soil N pools in response to earthworm population manipulations under different agroecosystem treatments. Soil Biology & Biochemisrry 29, 361-367. Bohlen P.J., Parmelee R.W., Blair J.M., Edwards C.A. and Stinner B.R. (1995) Efficacy of methods for manipulating earthworm populations in large scale field experiments in agroecosystems. Soil Biology & Biochemistry 27, 993-999. Edwards C.A. and Lofty J.P. (1980) Effects of earthworm inoculation upon the root growth of direct drilled cereals. Journal of Applied Ecology 17, 533-543. Grant J. D. (1983) The activities of earthworms and the fates of seeds. In Earthworm Ecology (J. E. Satchell, Ed.), pp. 107-122. Chapman and Hall, London. Hopp H. and Slater C.S. (1949) Influence of earthworms on soil productivity. Journal of Agricultural Research 78, 325-339. Khan A.W. (1966) Earthworms of West Pakistan and their utility in soil improvement. Agriculture Pakistan 17, 415 434. Earthworms. Their Ecology and Lee K. E. (1985) Relationships with Soils and Land Use. Academic Press, New York. McRill M. and Sagar G.R. (1973) Earthworms and Seeds. Nature 243,482. Shumway D.L. and Koide R.T. (1994) Seed preferences of Lumbricus terrestris L. Applied Soil Ecology 1, 11- 15. Syers J.K. and Springett J.A. (1984) Earthworms and soil fertility. Plant and Soil 76, 93-104. Van Rhee J.A. (1965) Earthworm activity and plant growth in artificial enclosures. Plant and Soil 22, 45-48.