The Effect of Different Tillage Methods and Crop Residue Management on the Population of Plant Parasitic Nematodes in the Wheat (Triticum aestivum L.), Barley (Hordeum vulgare L.) and Cotton (Gossypium hirsutum L.)Rotation System

Conventional tillage-based farming systems had negative effects on the quality of essential natural resources including soil, water, and plant biodiversity. In the recent decades, Conservation Agriculture (CA) farming systems based on the three interlinked principles, namely: no or minimum mechanical soil disturbance, crop residue retention and crop rotation introduced and adopted as an alternative to conventional agriculture. However, the influence of conservation agriculture practices on the population of soil-borne plant pathogens including plant parasitic nematodes is not well studied. This study was performed to determine the effect of different tillage methods and different levels of residue management on the population of plant parasitic nematodes in the wheat-barley-cotton-wheat rotation system during five consecutive cropping seasons (2012-2017) at the Gonabad Agricultural Research and Education Organization.

The experimental design was split-plot layout based on a randomized complete block design with three replications. Three tillage methods (such as conventional tillage, minimum tillage, and no-tillage) were assigned to main plots and three levels of residue retention (no residue retention, 30% of residue retention, and 60% of residue retention) were assigned to sub plots. The planting area of each subplot was 450 m2 (30 m length and 15 m width) and the total are of each main plot was 4050 m2 (9×450 m). To compare the population density of plant pathogenic nematodes in different crops, a combined soil sample from each experimental plot was collected. The nematodes were extracted from soil samples using sieving and centrifugal-flotation technique and were identified to genus or species level using relevant systematic references. The data were analyzed using MSTAT-C statistical software package. The Duncan multiple range tests were applied to separate the differences between means.

Plant pathogenic nematodes including root lesion nematode (Pratylenchus thornei), pin nematode (Paratylenchus spp.), spiral nematode (Helicotylenchus spp.), Geocenamus spp., stem and bulb nematode (Ditylenchus spp.), Boleodorus spp., Tylenchus spp. and Filenchus spp. were identified in different treatments. Based on the results of analysis of variance, the effect of tillage methods, residue retention and the interaction between tillage × residue retention was not statistically significant on the population of most plant parasitic nematodes but the interaction between tillage × residue retention was significant on the total number of plant parasitic nematodes and the population of Tylenchus spp. and Geocenamus spp. In average the highest density of plant pathogenic nematodes was related to the no-tillage system with 30% of residue retention and the lowest density was related to the minimum tillage system with 30% of residue retention. The results of this study indicated that different tillage systems and different levels of residue retention under the wheat-barley-cotton-wheat rotation system do not affect dramatically the population density of important species of plant pathogenic nematodes including the root lesion nematode (Pratylenchus thornei). Some other studies reported that reducing tillage intensity was associated with reducing population densities of plant pathogenic nematodes, which was contrary to the results of this study.

The results of this study indicated that conservation agriculture under the wheat-barley-cotton-wheat rotation system in temperate climatic zone of Khorasan Razavi (Gonabad) does not significantly affect the population of plant pathogenic nematodes and increases the risk of crop damage by this group of plan pathogens.AcknowledgementsThis study has been financially supported by the Agricultural Research, Education and Extension Organization (AREEO) and the Seed and Plant Improvement Institute (SPII) (project number 17-43-03-9154-91002).The authors would like to thank AREEO and SPII for their financial and administrative supports.The excellent technical and laboratory assistance of A. Rastegar Paymani and A. Ahmadian Yazdi from the department of plant protection is acknowledged.