Cropping intensity and organic amendments in transitional farming systems

• 2007 annual report

The procedure of using quantitative real time polymerase chain reaction (Q-PCR) to quantify Pseudomonas fluorescens (P. fluorescens) from soil samples were developed. This allowed us to answer three questions:
1. What is the effect of field treatments on the amount of P. fluorescens;
2. What is the effect of P. fluorescens on disease levels?
3. What is the change of amount of P. fluorescens through out the years of transition?

It is found that both the “cropping system” as the fixed effect for whole plot factor and “organic amendment” as the fixed effect for sub-plot factor did not have significant effect on the amount of P. fluorescens.

Also, the effect of P. fluorescens on disease levels of both greenhouse and field results is inconclusive with the statistical analysis we performed so far.

However, the amount of P. fluorescens increased significantly after transition, which indicate that the transition does have impact on soil microbes.

Introduction:

Organic matter amendments to soil, in the form of preceding crop residues, cover crop residues, or direct organic matter applications, have been shown to affect levels of root and foliar diseases in several crops. Suppression of soilborne plant pathogens has been observed following additions of certain types of organic matter to soils. In some cases the mechanism of suppression in these systems has been found to be associated with increased microbial activity resulting from the influx of carbon and nitrogen supplied by the incorporated organic matter. Specific cropping systems have been shown to alter the associated soil microbial communities, and in some cases the population levels of known biological control agents have been enhanced. Foliar disease levels have been shown to be affected by applications of soil orgniac matter, even for diseases caused by pathogens that do not have a soilborne phase in their disease cycles. Possible mechanisms suggested for this type of disease suppression include changes in plant's nutrient status and the phenomenon known as systemic acquired resistance or induced systemic resistance. Based on this information, it seemed likely that differences in the disease suppressiveness of plots in the organic transition study would vary as a result of the cropping system and organic amendment treatments. We evaluated the diseases suppressiveness of the soil to soybean root diseases in greenhouse bioassays on soil samples taken over the course of the study, and we monitored disease development on the crops in the plots to evaluate the impact of the treatments on disease development in the field. In 2007, natural-occurring diseases, bacterial pustule and wild fire, were evaluated by percentage of leaf area infected in mid-August. These bacterial diseases were confirmed using the ooze-test and isolated on nutrient agar. Soil samples were taken and assayed in the greenhouse with infestation of R. solani and F. solani on soybean. Pseudomonas population was quantified with non-culturing method, real-time polymerase chain reaction (PCR). The working hypothesis is field treatments had an effect on Pseudomonas population and disease suppression.

Our short-term goal was to characterize and compare the effect of selected cropping systems and organic amendments in transitional farming systems on soil Pseudomonas population, and understand the links between plant disease suppression and Pseudomonas population.

Our intermediate-term goal was to develop relevant, accessible outreach and educational products for organic producers.

The long-term goal was to establish an interdisciplinary, cross-institutional organic farming systems research and education program, guided by an active partnership between organic producers, researchers, and extension educators, that improves the performance of organic farming systems and enhances the ability of North central region organic producers to meet the growing local and regional demand for organic produce.