Influence of tillage and compost on communities of phytoparasitic nematodes

INFLUENCE OF TILLAGE AND COMPOST ON COMMUNITIES

OF PHYTOPARASITIC NEMATODES

INFLUENCE DU TRAVAIL DU SOL ET DE L'APPORT DE COMPOST

SUR LES PEUPLEMENTS DE NÉMATODES PHYTOPARASITES

The pH was also less acidic when compost was applied annually. The effect of tillage on the physical and chemical characteristics of the soil was not significant.

The phytoparasitic nematodes community was mainly composed of four species: Scutellonema cavenessi, Helicotylenchus dihystera;

Tylenchorhynchus gladiolatus and Pratylenchus pseudopratensis.

CHARACTERISTICS OF THE NEMATODE

COMMUNITIES IN THE DIFFERENT TREATMENTS During the cultural cycle, between sowing and harvesting; the density for each of the species has been quite constant. Only the number of

T. gladiolatus decreases considerably after the harvest in all the

treatments. The final number of H. dihystera especially declined in the treatment P4, P5 and P6 at the harvest.

The nematofauna of plot 1 distinguished itself amongst the other plots by its high density (over 6,300 phytoparasitic nematodes per litre of soil) linked essentially to a high abundance of S. cavenessi.

The maize production was low on all plots. This is mainly due to a water deficit during the year of the study. However, differences between plots were recorded. The worst yields were obtained from plots P2 and P3; those which did not receive any compost and with tillage.

INTRODUCTION

Demands for agriculture are constantly increasing in the Sudano-Sahelian region of Africa.

These demands can not be satisfied because of the deterioration of the cultivated soils in this zone. This process is mostly a result of two phenomenons: erosion and the lowered organic matter content of the soils (Pieri, 1990). On the other hand, the parasitic pressure, especially that of the phytoparasitic nematodes, is high and limits the food production.

In the Senegalese groundnut fields (Sudano-Sahelian zone), the nematicides are efficient in decreasing phytoparasitic nematodes populations of the soil, which engenders important increases of the millet and groundnut yields (Baujard, 1994), although alternatives have to be found for these methods of chemical battle, as their long term use could be harmful to man and the environment.

OBJECTIVES

In the areas where the soil deterioration is a worrisome phenomenon, the use of techniques that improve the organic matter content of soils and allow simultaneously the control of the nematodes' pathogenicity would be particularly interesting. To evaluate this opportunity, the effect of the different tillage practices (limiting the run-off) and the application of compost in different amounts on some physical and chemical soil characteristics and on the communities of phytoparasitic nematodes, was tested in the southern part of the Senegalese peanut basin.

EXPERIMENTAL DESIGN

The treatments intersect soil tillage (no weeding, pulling up of weeds, nor

loosening of the soil) and compost supply (0, 5 or 10 tDM ha-1_{); they were}

implemented for six years on a millet-peanut crop rotation.

The after-effects of these treatments were evaluated the seventh year during a maize cultivation. So, the treatments were not applied during this seventh year.

PHYSICAL AND CHEMICAL CHARACTERISTICS OF THE SOIL AFTER THE SIXTH YEAR AND MAIZE YIELD

The soil texture in the different plots was homegenous and very sandy (between 82 and 84% of sand).

The amendment of compost, in plots P4, P5 and P6, induced a significant increase of the cation exchange capacity (as measured by the cobaltihexamin method) due to the increase of the exchangeable Ca and Mg content (by 100%).

0 0 25 50 75 100 0 25 50 75 100 P6 P5 P4 P3 P1 P2 sowing flowering harvesting sowing flowering Scutellonema cavenessi Helicotylenchus dihystera 0 250 500 750 1000 1250 0 25 50 75 100 Tylenchorhynchus gladiolatus 500 1000 1500 2000 2500 3000 3500 P1 P6 harvesting 0 500 1000 1500 2000 2500 3000 3500 4000 P2 P3 P1 P6 P5 P4 days 0 250 500 0 25 50 75 100 Pratylenchus pseudopratensis days numbers of nematodes / dm3 of soil

numbers of nematodes / dm3 of soil numbers of nematodes / dm3 of soil numbers of nematodes / dm3 of soil

P1 P2 P3 P4 P5 P6

Aerial parts (kg/ha) Grains (kg/ha) 1 0 0 3 0 0 5 0 0 7 0 0 % clay 4.2 4.3 4.0 4.6 5.1 4.9 % silt 13.9 13.5 12.5 13.2 11.8 12.4 % sand 82.0 82.3 83.5 82.4 83.1 82.8 ‰ MO 3.4 3.9 3.3 4.5 4.2 4.5 P-ppm 7.5 9.2 7.5 8.6 9.8 12.7 Ca (cmol/kg) 0.4 0.4 0.4 0.7 0.7 0.9 Mg (cmol/kg) 0.2 0.2 0.1 0.3 0.4 0.5 K (cmol/kg) 0.1 0.1 0.1 0.1 0.1 0.1 Na (cmol/kg) 0.0 0.0 0.0 0.0 0.0 0.0 S 0.6 0.6 0.6 1.1 1.1 1.5 CEC 0.7 0.7 0.7 1.2 1.2 1.7 pH 5.6 5.6 5.5 6.1 6.3 6.3 P6 P5 P4 P3 P1 P2 weeding chiseling

weeding compost 5 tDM/ha chiseling compost 5 tDM/ha chiseling chiseling compost 5 tDM/ha compost 5 tDM/ha slope 1,6% runoff collector 1 0 m 5 m 5 m

area for plant sampling

area for soil sampling

+ tillage + organic amendment

+ + + + + + + + + + weeding ridging weeding weeding ridging TREATMANTS: Experimental design

Soil characteristics after 6th harvest (0-10 cm de plh) Maize production

Evolution of the nematode densities during the cropping cycle

(1) Centre ORSTOM, BP 1386 Dakar, Sénégal.

(3) Institut sénégalais de recherches agricoles (ISRA), Bel-Air, route des hydrocarbures, BP 3120 Dakar, Sénégal. (2) Centre de coopération internationale

en recherche agronomique pour le développement (CIRAD), BP 5035, 34032 Montpellier cedex 1, France.

REFERENCES

Baujard, P. (1994) Nématicides, nématodes phytoparasites et rendements des cultures pluviales dans la zone sahélienne de l'Afrique de l'Ouest.

Afro-Asian Journal of Nematology 4, 129-146. McSorley, R. (1996). Impact of crop management practices on soil nematode populations. Soil and Crop Science Society of Florida Proceedings 55, 63-66.

Norton, D.C. (1979). Relationship of physical and chemical factors to populations of plant parasitic nematodes. Annual Review of Phytopatology 17, 279-299.

Seinhorst, J.W. (1962). Modifications of the elutriation method for extracting nematodes from soil. Nematologica 8, 117-128.

Sene, M. and Perez, P. (1994). Contraintes et possibilités de valorisation des ressources naturelles dans le sud du bassin arachidier (Sine Saloum, Sénégal) in Reyniers et Netoyo (Eds), Bilan hydrique agricole et sécheresse en Afrique tropicale. AUPELF-UREF, John Libbey Eurotext, Montrouge, 217-234.

Villenave, C. and Cadet, P. (accepted for publication). Interaction of Helicotylenchus dihystera, Pratylenchus sefaensis and Tylenchorhynchus gladiolatus on two plants from the soudano-sahelian zone of West Africa. Nematropica.

Where no weeding was done (P1), the density of S. cavenessi,

H. dihystera and P. pseudopratensis was significantly higher

(respectively multiplied by 2, 4 and 13 on average on the cultural cycle) as compared to the cleaned and weeded plot (P2). The total nematodes density increased from P2 to P5, mainly because of the increase of

H. dihystera whilst the density of S. cavenessi remained constant.

But, more than the abundance of phytoparasitic nematodes, the specific composition of the community was modified by the treatments. The proportion of H. dihystera increased from P2 to P6, representing up to 60% of the nematodes community in the latter case, while, in the absence of tillage and compost amendment, the community was dominated by S. cavenessi representing 60% of the phytoparasitic nematode fauna (P2). The factorial analysis showed the opposition between S. cavenessi and H. dihystera on the first axe.

CONCLUSION

The application of compost tilled in the soil modified its chemical properties as well as the relative and absolute abundance of the phytoparasitic nematodes species. The best crops yields were obtained in the treatments P1, P5, P6 and to a less extend in P4 (the control and the plots which received compost); the species H. dihystera was the most abundant in these treatments. These results obtained in the field corroborate with others recorded under controlled conditions which show that, with millet, the presence of H. dihystera limited the pathogenicity of the other species of the communities (Villenave and Cadet, in press). In the control treatment, the nematodes can develop preferentially on weeds which are more appetant, and less on cultivated plants being therefore less affected by their attacks. This could explain the good yields obtained.

The phytophageous nematodes are parasites which feed on the plants that they attack and therefore create damage by limiting their root growth. The plants have defence mechanisms to limit the damage; however, certain phytoparasitic nematodes attacks engender a stimulation of the root developpement which can lead, depending on the soil and the cultural practices, to an increase of the growth of its above-gound parts. This can happen when the phytoparasitic nematodes are not very abundant (pathogenicity threshold) or depending on the abundance of certain species, particularly H. dihystera.

The incorporation by tillage of compost improved the soil organic matter content in comparison with the other treatments and, by consequence, favoured plant growth. On the other hand, these cultural practices modified the structure of the phytoparasitic nematodes community. The effects of tillage combined with organic matter supply have to be further investigated.

T. gladiolatus P. pseudopratensis H. dihystera S. cavenessi 0 20 40 60 80 100 P1 P2 P3 P4 P5 P6 %

increase of H. dihystera proportion

de crease of S. cavenessi proportion 0 2000 4000 6000 P1 P2 P3 P4 P5 P6 nematodes/ dm3

increase in the density

of H. dihystera

density of s. cavenessi quite constant

-1 -1 Principal axis 1 SC D HD PP TG 1 1 P1 P4 P5 Principal axis 2 Scutellonema cavenessi Ditylenchus sp. Tylenchorhynchus gladiolatus Helicotylenchus dihystera Pratylenchus pseudopratensis P6 P2 P3 Correspondence analysis Structure of the nematode communities

(mean of the three sampling dates before harvesting)

Nematode densities (mean of the three sampling dates before harvesting)