Potential of Managing Iron and Zinc Deficiency in Dry Beans with Interplantings of Annual Ryegrass and Increased Bean Density

Potential of Managing Iron and Zinc Deficiency in Dry Beans with Interplantings of Annual Ryegrass and Increased Bean Density

Summary

The project is based on a farmer’s observation in 2002 that pinto beans intercropped with annual ryegrass did not exhibit iron-deficiency chlorosis and produced better than beans grown without the ryegrass intercrop. The purpose of this project is to determine if an annual ryegrass-pinto beans intercrop can mitigate iron deficiency in the high pH calcareous soils that are prevalent in the State of Wyoming. The study will also investigate recent observations that iron deficiency chlorosis can be overcome by more resistant cultivars of dry beans, close bean plant spacing, and low levels of nitrate-nitrogen in these soils. In addition, the project will determine if interplantings of annual ryegrass can mitigate zinc deficiency in acidic soils in western Kenya.

Objectives/Performance Targets

1. To determine the effectiveness of intercropping annual ryegrass with pinto beans in mitigating iron deficiency in calcareous soils. Built within this objective will include: – A comparison with pinto beans intercropped with wheat, as a grass known to exude compounds capable of chelating iron – An assessment of the effect of selective herbicide in facilitating machine harvesting of dry beans – An assessment of the effect of close spacing and high plant density – An assessment of the role of nitrate-nitrogen plays in mitigating iron deficiency To determine the effectiveness of intercropping annual ryegrass with dry beans in mitigating iron deficiency in calcareous soils in a controlled environment. Built within this objective will include: – A comparison of annual ryegrass intercropped with two bean varieties known to be more susceptible to iron deficiency chlorosis such as ‘Nodak’ pinto beans, black beans and soy beans – A comparison of two bean varieties susceptible to iron deficiency chlorosis intercropped with oats and wheat as grasses known to exude compounds capable of chelating iron To determine the effectiveness of intercropping annual ryegrass with pinto beans in the field in mitigating zinc deficiency in acid soils. This will be compared to pinto beans intercropped with wheat, as a grass known to exude compounds capable of chelating zinc, and with millet, a hardy cereal food crop popular in western Kenya.

Accomplishments/Milestones

Preliminary results from this study were presented as a poster at the Western Society of Crop Science meeting held at the Hawaii Preparatory Academy in Waimea, Hawaii, on June 16-18, 2008.

Analysis of the samples collected from the study is still underway in the UW Soils Lab and we hope to have those results within the next month. However, we can report that the pinto beans we planted in the plots at the SAREC Station did not exhibit substantial iron deficiency chlorosis as anticipated. Though minor iron deficiency chlorosis symptoms were observed in the pinto beans during the first month after planting, the plants were able to overcome these symptoms as the season progressed. This may be a normal response of the particular cultivar we planted. There may also have been external environmental conditions that stimulated this response in the beans. We hope to reduce the potential for our beans overcoming the iron deficiency chlorosis we are trying to study.

During the course of the study, we observed that both soybeans and black beans planted by another researcher in nearby plots exhibited more iron deficiency chlorosis than did our pinto beans. While it is not yet possible to provide a definite explanation for this observation, it is possible that the reason for it is the requirement for iron is much higher in soybeans and black beans than in pinto beans. A review of the literature has not shed any light on this, though we will continue to look for an explanation.

In spring 2009 we will establish a greenhouse study that will assess the effect of intercropping annual ryegrass with ‘Nodak’ pinto beans, soybeans, and black beans as an improved model system to see if annual ryegrass will produce a more significant difference in these beans. Results from this study will provide justification to carry out a second expanded field study at SAREC in the summer of 2009 using black beans, ‘Nodak’ pinto beans as well as ‘Marquis’ pinto beans we used in 2008. We will also establish a hydroponics study to see whether the results obtained in the field can be replicated under the highly controlled conditions of the growth chamber.

In the course of carrying out the study, we learned that some scientists at the University of Minnesota are exploring the possibility that iron deficiency chlorosis in soybeans may be related to high levels of nitrate-nitrogen in soils with high levels of salt and free calcium carbonate. This may interfere with the metabolism of iron in the plant and, therefore, chlorophyll synthesis (Christensen and Johnson, 2008). Studies by John Lamb at the University of Minnesota Extension (unpublished) have shown that growing an inexpensive competition crop, for example oats, with soybeans makes less nitrate-nitrogen available to the soybean plants and mitigates iron deficiency chlorosis (Christensen and Johnson, 2008). As a result, we will perform additional analyses of nitrate levels and availability on our soils in our 2009 experiments.

Impacts and Contributions/Outcomes

Conventional control of iron deficiency in dry beans is achieved by multiple foliar applications of 1% iron sulfate solution applied at 20-30 gallons per acre, or similar applications of the more expensive iron chelates at approximately half the rate of iron sulfate (Stevens and Belden, 2005). A non-chemical cultural practice, such as this project hopes to recommend, would be a welcome alternative for organic and natural bean producers and would also provide a more sustainable and potentially more affordable solution for conventional bean growers. It also provides an opportunity for more conventional farmers to adopt sustainable and/or organic farming.

Conventional control of zinc deficiency in dry beans is achieved by multiple foliar applications of 0.5-1.5% zinc EDTA applied at 20-30 gallons per acre, or similar applications of the more expensive zinc chelates at approximately half the rate of zinc sulfate (Stevens and Belden, 2005). Recommendations from this project will be especially useful to Kenyan farmers as it not only provides them with an alternative to expensive chemicals, but it fits in with their small-scale hand-labor farming practices. The study has the potential to both save on the costs of farming as well as increase yields.

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