May 20, 2011

Nematode, soil health challenges can’t wait

My work with Michigan soils and nematodes started 21 years ago with a three-year sweet cherry tree decline project with plant pathologist Alan Jones and nematologist George Bird. We established that soil pH was the driving factor of the syndrome.

Since 1994, my program’s focus has been on understanding nematode/plant/soil/nutrient interactions at the organism and ecosystem levels. Despite the best of efforts, we have witnessed the challenges associated with managing plant-parasitic nematodes (PPN, or herbivores) in vegetable and other cropping systems nationwide. In this article, I will discuss the conceptual challenges to realizing the strategy of managing nematodes and soil health. Biological and scientific issues will be addressed in a second part in the future.

PPN continue to be a problem because of: a) the multitude of FQPA and environmentally driven restrictions, b) their broad host range, rendering rotations ineffective, c) the lack of an agro-biologically integrated understanding of soil biology, and d) more emphasis on short-term fixes and less on long-term solutions.

Under these circumstances, the concept of integrated soil health management that treats PPN and beneficial nematodes as part of a soil ecosystem is appealing and probably necessary. Talks with stakeholders, growers, academics and industry leaders, however, indicate that it may not be easy to implement without strategic understanding of the conceptual challenges. Hence, before accepting, being indifferent to, or rejecting the concept of managing all nematodes and soil health, it is important to consider several pertinent questions.
Are FQPA and related restrictions likely to increase or decrease with time? The chances are more likely to increase than to decrease because of the changing consumer awareness and global issues driving the restrictions. A blend of short- and long-term integrated research priorities and investments will likely be needed to develop economically and environmentally sustainable management alternatives for biotic yield-limiting factors.

What is soil health and why is it important? Healthy soil refers to a soil whose biological, chemical, nutritional, physical and water use properties are uncompromised. The traditional focus had been on the latter four components of soil health. As knowledge of soil biology mounts, the significance of microbes and soil organisms to biological processes that are central to biodiversity, soil food-web and maintaining all forms of life has increased. This knowledge allows us to read the integrated biological pulse of a soil and maintain desired levels in space and time.

Why is managing all nematodes important? It generally accepted that PPN represent about 10 percent of nematodes. The rest of them include bacteriovores, carnivores, fungivores, omnivores and predacious trophic groups. As many studies have shown, analyzing the composition of all nematodes provides information on succession, changes in decomposition pathways, nutrient cycling, fertility and acidity of soils, response to environmental stresses and decision criteria for conservation and remediation of the prevailing soil conditions.

What have we learned about PPN biology that is relevant to soil health management? In simple terms, soil-dwelling PPN cause yield and quality loss by destroying root tissue and disrupting water and nutrient uptake, leading to cascading physiological changes manifested in leaf chlorosis, stunting and poor yield. We have accumulated considerable knowledge based on understanding nutrient-nematode-soil interactions; nematode adaptation and parasitic (genetic) variability (look the same, act differently); challenges associated with multi-purpose biofumigants; and agro-biological, economic and environmental efficiency of soil amendments.

We have developed scalable models that enable us to identify what amendment works where, why and/or how.
Why worry about PPN in minor crop A while growing major crop B? This will only work if crops A and B are not hosts to the same problematic PPNs and if they are not grown in the same soil. Otherwise, it will be a costly misconception because the PPNs are being provided with a buffet line. An example worth mentioning in the Great Lakes region is a production system that includes carrot, celery, onions, peas and potatoes and root-lesion, northern root-knot and stem and bulb nematodes. A soil health-centered management strategy is most likely to be effective across crops for such complexes.

Does managing all nematodes and soil health apply to my cropping/production system? While the levels and/or types of management parameters may vary by soil types, the principles apply to all cropping systems. For example, it is reasonable to assume that conditions in a muck soil will be different from that in a mineral soil, as will the impact of planting a root crop (e.g. carrot) and non-root crop (e.g. celery) on a given soil.

Can soil health management be established in a pesticide-intensive production system? When it comes to pesticide use, limited resources, economics and environmental issues, common ground is often the victim. The realities are that we have a limited landmass that has been subjected to the chemical era for a better part of a century. Therefore, soil health and pesticide use are not and should not be mutually exclusive; they need to be handled simultaneously. Dealing with pesticide use restrictions and developing sustainable and profitable alternatives are not events, but processes whose timeline may take generations to accomplish. The sooner we start on it, the better.

Isn’t soil health management a long-term strategy? It is a short-term and a long-term strategy because any biological, chemical and/or mechanical inputs and disturbances that are part of a production system induce short- and long-term changes in the soil.
What if we don’t do anything about soil health and nematodes? This will simply mean kicking the problem down to the next generation of growers and researchers.

It will always be difficult to fight soil-dwelling enemies without understanding their biotic and abiotic environments. It may take time, but I firmly believe it is doable.

By Haddish Melakeberhan