Organic farming practices favor bacterivore and fungivore nematodes as compared to plant-parasitic nematodes S.S. Briar1,2, P.S. Grewal1,2, Deborah H. Stinner1, and S.A. Miller2 1Dept. of Entomology & 2Dept. of Plant Pathology, The Ohio State University, OARDC, Wooster, OH 44691-4096, USA Abstract A primary objective of nematological research is to identify farming strategies that increase multiplication of free-living nematodes that contribute to nutrient cycling but reduce that of plant parasitic nematodes that reduces crop yield. We hypothesized that the organic farming system would be dominated by bacterial and fungal feeding nematodes but not by plant parasitic nematodes. Therefore, we compared nematode communities for a four-year period (2000-2003) in a field transitioning to organic farming with that under low tillage conventional management. Conventional plots had corn and soybean rotation and received synthetic inputs. Organic plots had corn, soybeans, oats and hay rotation and received beef and poultry manure. Organic farming favored the population of bacterivore, fungivore, omnivore and predatory nematodes over the 4 years as compared to conventional farming system. Nematode structure, maturity, diversity, richness, basal, enrichment, and channel indices showed no significant differences among the farming systems. However combined maturity index (based on both free living and plant parasitic nematodes) was higher in conventional farming as compared to organic farming system. The conventional farming system had significantly higher populations of total plant parasitic and the root lesion nematode Pratylenchus crenatus, compared to the organic farming system during most of the study period. Nematode faunal profile based on enrichment and structure indices revealed that the food webs were highly enriched and moderately to highly structured, and the decomposition channels were predominantly bacterial in both the farming systems. Introduction Methods ¦Nematode communities play a significant role in a Experimental design: Split block design (Plate 2) Plot size 60’x50’ nutrient cycling in the ecosystem. Treatments: Organic and conventional farming systems ¦ Various nematode indices such as maturity, Conventional Farming system (1): structure and diversity indices are considered as •Rotation: Corn-Soybeans indicators of ecosystem health. •Application : Synthetic fertilizers and insecticides ¦ Nematode faunal profile (Plate 1) which provides a •Tillage: Every alternate year framework of the soil food web can be used as a Organic farming system (2): diagnostic tool to measure the health of soil in agro- •Rotation: Corn-Oats-Soybeans-Hay ecosystems (Ferris et al., 2001). •Application: 12 T/A raw straw pack beef manure + 1.25 T/A Day-Lay poultry compost in corn and 8 T/A raw straw •Disturbed pack manure + 0.8 T/A DayLay poultry compost in oats •N-enriched Enriched •Maturing •Low C:N •N-enriched •Tillage: Twice a year y r •Bacterial •Low C:N o t c •Bacterial e A B j •Regulated Ba1(3.2) ra t t Farming System 1 N Farming System 2 n e Conventional Corn (C ) Transitional Corn (T ) Transitional Oats (T ) m c C o h ic Conventional Soybean(C ) Transitional Soybean (T ) Transitional Hay (T ) r •Degraded Structured B B H n Rep 1 Rep 2 Rep 3 E Fu2(0.8) •Depleted D C •Matured 1-1 1-2 1-3 2-1 2-2 2-3 3-1 3-2 3-3 •High C:N C T T C T T T T C •Fungal •Fertile B C O B B H B O C F •Mod. C:N 1-4 1-5 1-6 2-4 2-52-6 3-4 3-5 3-6 u •Conducive 431 ’ 2 •Bact. /Fungal C T T C T T T T C (0 C H B C C O H C B B .8 Basal a ) •Suppressive 2 Rep 4 Rep 5 Rep 6 (0 .8 Ca Om Om 4-1 4-2 4-3 5-1 5-2 5-3 6-1 6-2 6-3 Basal ) 2(0.8) 4(3.2) 5(5) Ca3(0.8) TH TB CB CB TH TO CC TB TH condition Ca4(3.2) Ca5(5) Fu3(1.8) Fu4(3.2) Fu5(5) 4-4 4-5 4-6 5-4 5-55-6 6-4 6-5 6-6 Ba5(5) 60’ Ba3(1.8) Ba4(3.2) TC TO CC CC TB TC CB TC TO Structure trajectory 25’ 60’ 854’ Plate 2. Layout map of field crops organic transition experiment. Plate 1. Conceptual Model relating nematode community to soil food web health. Bax, Fux, Cax, Omx (x=1-5): functional guilds of nematodes that are bacterivores (Ba), fungivores (Fu), carnivores (Ca) and omnivores (Om) where the guilds have the character indicated by Sampling: Three soil cores (2 cm dia. X 15 cm depth) were x on the cp scale (Ferris et al., 2001). collected from each plot in spring & fall from year 2000-2003. Nematode extraction: Nematodes were extracted from 10-g sub sample of soil using Bearmann funnel technique. Hypothesis Nematode Identification and counting: All nematodes were identified to genus level and assigned to a trophic group: plant ¦ Organic farming system would be dominated by parasitic, fungivore, bacterivore, carnivore and omnivore beneficial bacterivore and fungivore nematodes but not according to Yeates et al (1993). Colonizer persister value (c-p plant parasitic nematodes. value) were also assigned to each genus according to Bongers (1990). Nematode indices: Nematode abundance, enrichment, structure, Objectives maturity and species diversity indices were calculated using ¦ Determine the long-term effects of organic farming standard formulae (Ferris et al., 2001;Yeates et al., 1993). and low tilled conventional farming systems on soil Statistical analysis: Repeated measures analysis of variance nematode community. (PROC GLM, SAS Ver. 9) was used to obtain F-values for the split block experimental design using the appropriate error terms ¦ Compare population of free-living and plant parasitic in the model, to compare between the farming systems over the nematodes between the two farming systems. years. Results and Discussion 90 ¦ Population of bacterivore (P < 0.01) (Fig. 1A) and Quadrat A Quadrat B 80 8 3 fungivore nematodes (P < 0.1) (Fig. 1B) over the 4 years 5 3 5 1 70 7 8 2 was significantly higher in the organic as compared with 4 6 2 4 the conventional farming system (Fig. 1 and 2). 60 6 7 ¦ Abundance of plant parasitic nematodes (P=0.03) 1 50 (Fig. 1E) and migratory endoparasitic Pratylenchus 40 crenatus (P=0.01) (Fig. 1F) was significantly lower in Enrichment Index Quadrat D Quadrat C organic than conventional farming system. 30 Organic Conventional ¦Nematode maturity, diversity and richness indices 20 showed no significant differences among the farming 10 systems (Fig. 1). However combined maturity index 10 20 30 40 50 60 70 80 90 (based on both free living and plant parasitic nematodes) Structure Index was higher in conventional farming as compared to organic farming system (P=0.01) (Fig. 2A). ¦Nematode faunal analysis revealed that the food webs were highly enriched and moderately to highly Fig. 3: Comparison and temporal progression of food web indicated by nematode faunal analysis in organic and conventional farming structured in both farming systems (Fig. 3). Also systems.. Numbers 1-8 represent the progression of changes in the decomposition channels in both systems were bacterial fauna in each farming system from spring 2000 to autumn 2003. driven. ¦Proportion of free-living nematodes was negatively 0.95 correlated (r=-0.60, P=0.0001) with abundance of plant r = -0.60 parasitic nematodes (Fig. 4). P = 0.0001 0.75 2.8 0.55 (A) (B) 2.2 2.6 2.0 0.35 2.4 1.8 Maturity Index Maturity 2.2 Combined MaturityIndex Proportion of free-living nematodes free-living of Proportion 1.6 0.15 3.6 4.0 (C) (D)(D) 3.4 50 100 150 200 250 300 350 3.5 Plant-parasitic nematodes 3.2 3.0 3.0 Fig. 4: Correlation between proportion of free-living nematodes 2.8 Plant parasiticindex and plant parasitic nematodes. 2.5 2.6 Richness index (Margalef) 3.0 (E) (F) ) ) 1.2 J' H+ Conclusions 2.5 1.0 ¦ There were significantly more bacterivore and fungivore 2.0 0.8 nematodes in the organic farming than the conventional Organic Organic 1.5 0.6 farming system. Conventional Evenness index (Pielous Conventional Shannon DiversityIndex ( 0 2000 200 2001 2002 2003 n-2001 n-2003 2002 ng- ng- ¦Farming systems did not differ significantly in diversity, ri ring- ri ring- ing-2002 p p tum p p tum pring-2001 S S u S utumn-2002S u Spring-2000 S Spr utumn- Spring-2003utumn-2003 Autumn- A A A Autumn-2000 Autumn-2001 A A richness and evenness of nematode community. Figure 2: Comparison of nematode community indices between organic and conventional farming system from spring 2000 to autumn 2003. A) Maturity; B) Combined maturity; C) Plant parasitic; D) Richness ¦ Organic farming showed a significant reduction in total Index ; E) Shannon diversity (H’) and F) Evenness indices. plant parasitic nematodes and migratory endoparasite Pratylenchus crenatus populations as compared to conventional farming system. (A) (B) 300 60 ¦ The food webs were highly enriched and moderately to 200 40 highly structured and the decomposition channels were 100 20 bacterial driven in both the farming systems. Fungivore nematodes Fungivore Bacterivore nematodes 50 (C)15 (D) ¦ Abundance of plant parasitic nematodes showed a negative 40 correlation with abundance of free-living nematodes 30 10 suggesting competitive exclusion. 20 5 Omnivore nematodes 10 Predatory nematodes Acknowledgements 0 0 30 200 (E)(E) (F) We thank Dr. Ganpat Jagdale for help with nematode identification 25 and suggestions. 150 Organic 20 Organic Conventional Conventional References 15 100 10 Bongers, T.