Beans (Phaseolus spp. L.) are extensively grown throughout the western Great Plains. However, high pH soils prevalent in this region limit the availability of many micronutrients, especially iron and zinc. Iron deficiency in high pH soils results in interveinal chlorosis in beans and a higher susceptibility to insect and disease damage, thereby reducing yield and quality. A Wyoming farmer observed that dry beans grown with an intercrop of annual ryegrass (Lolium perenne L. ssp. multiflorum (Lam.) Husnot) did not exhibit any iron-deficiency chlorosis and produced better than beans grown without the ryegrass intercrop. We conducted field studies in Goshen County, Wyoming, in 2006 to test the hypothesis that an annual rye intercrop may result in increased iron availability in a pinto bean field. Treatments included beans planted in annual rye residue incorporated in the soil, bean-annual rye intercrop, and beans planted alone as a control. There was significantly higher soil iron and zinc availability in the bean-annual rye intercrop compared to beans alone. Iron concentration in bean leaves declined in all treatments but at a lower rate in the bean-annual rye intercrop and beans-annual rye residue when compared to the control, though this difference was not significant.
Over the last five years, the value of dry beans in Wyoming has averaged $12,700,000 making it the fourth most valuable crop in the state after hay, sugarbeets, and barley. Nationally, Wyoming ranks fourth in pinto bean production (USDA NASS, 2006). Micronutrient availability can be a critical limitation on bean production and overall plant health (Jones and Jacobsen, 2003). In Wyoming, high pH, low organic matter, and calcareous soils limit the availability of many micronutrients, especially iron (Stevens and Belden, 2005). Iron deficiency under these conditions is not a result of absolute iron deficiency in the soil but rather of low iron availability (Mengel and Geurtzen, 1986). Conventional management of iron deficiency in 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 would therefore 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. Studies have shown that some grasses have the ability to extract micronutrients from the soil through exudates of phytosiderophores. This mechanism has been extensively studied in maize (Zea mays L.), wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), and oats (Avena sativa L.) (Singh et al., 2005). Annual ryegrass has not been reported in the literature as a known phytosiderophore releasing plant. We hypothesize that phytosiderophore-derived iron chelate introduced to the soil by annual ryegrass may explain the observation that dry beans grown with an intercrop of annual ryegrass did not exhibit iron-deficiency chlorosis and yielded better than beans grown without the ryegrass intercrop.
The objective of the study was to determine the effectiveness of intercropping annual ryegrass with pinto beans in mitigating iron deficiency in calcareous soils.
Materials and Methods
We established a field experiment at Mike and Cindy Ridenour’s farm in Goshen County, WY, at 42°05′N, 104°23′W and an elevation of 1,390m asl. The selected field had not been previously planted with annual ryegrass. Field preparation and planting was done between May and June 2006.
The study consisted of 0.6 x 6 meter plots in a randomized complete block design with six replications. Treatments included 1)‘Nodak’ pinto beans planted with ‘Gulf’ annual ryegrass residue incorporated in the soil; 2) ‘Nodak’ pinto beans intercropped with ‘Gulf’ annual ryegrass; and 3) Monoculture of ‘Nodak’ pinto beans as the control treatment. Pinto bean planted into incorporated annual ryegrass residue was included to determine if the same effect as intercropping would be observed. This would be convenient for machine harvesting as rapid growth and establishment of annual ryegrass could make it difficult to machine harvest beans. Irrigation was provided by means of drip tape and weeding was performed manually.
Bean leaf and soil samples were randomly collected from each plot for tissue analysis at plant establishment, mid-season, and maturity. In each case, 2 to 3 of the youngest fully matured leaves were collected from an average of 15 plants per plot, in accordance with Hue et al. (2000). Leaf samples were oven-dried, finely ground, and analyzed for Fe, Zn, Mo, P, Mn, and Cu. Soil samples were air dried, ground and sieved through a 2-mm screen in accordance with Hue et al. (2000) and tested for P, K, pH, Organic Matter, Fe, Zn, Mn, Cu, Mo, and EC. Beans were harvested by hand between August 7 and October 28, 2006, air-dried, threshed, winnowed and weighed, and yield data recorded.
Analysis of variance (ANOVA) of the Fe and Zn availability was done using the MIXED and GLM procedures in SAS (SAS Institute, 1999-2000). Treatment differences determined using Fisher’s protected LSD (a= 0.10). A two-group TTEST procedure in SAS (SAS Institute, 1999-2000) done without the bean-ryegrass incorporated treatment (included in this study for machine harvesting convenience).
1. Beans on one plot in which annual ryegrass failed to germinate and had interveinal chlorosis (Fig. 1A) recovered one month after re-seeding and establishment of ryegrass (Fig. 1B)
2. ANOVA of the Fe availability showed no significant differences between the three treatments. The results however showed a general trend in favor of bean-ryegrass intercrop (Fig. 2, 3, and 4).
3. Soil organic matter (SOM) in the treatments with ryegrass was significantly higher than the control plots (a=0.10; p=0.086) suggesting that the extensive rooting system of the annual ryegrass may have contributed to higher below ground biomass (Fig. 5).
4. The pH of the control plots was marginally higher (a=0.10; p=0.01) than the other treatments suggesting that the higher SOM in the ryegrass plots may have helped to slightly reduce the pH on those plots (Table 1). However, there was no significant correlation between soil Fe and soil Zn with SOM.
5. There was a significant negative correlation between pH and the concentration of Fe and Zn in the soil suggesting that as the soil pH decreased, Fe and Zn availability increased (r2 = 0.65, p<0.0001).
6. A two-group T-TEST procedure to compare the intercropped plots with the control treatment showed that soil Fe in the bean-annual ryegrass intercropped treatment was significantly higher (p = 0.0631) than in the control (Table 2).
1. Strong negative correlation between pH and the concentration of Fe and Zn in the soil suggest that something else, other than the increased organic matter in the intercropped plots, contributed toward increased iron and zinc availability. There is therefore a need to investigate further the possible role that root exudates from annual ryegrass may play in increasing micronutrient availability in the soil.
2. These results suggest that intercropping annual ryegrass with beans has the potential to increase deficient micronutrients in the soil.
Benefits or Impacts on Agriculture
As stated in the introduction above, conventional management of iron deficiency is through the use of foliar sprays. Foliar feeding is expensive, and organic alternatives are often not available for larger scale operations. Therefore, using annual ryegrass provides an alternative, natural means to manage iron deficiency. Further research is necessary to determine the feasibility of using annual ryegrass to ameliorate iron chlorosis in commercial bean production. Dr. Smith and Mr. Omondi will be conducting further research at the University of Wyoming’s Sustainable Agriculture Research and Education Center (SAREC) in order to further the work started through this project.
We are not able to predict at this time the degree of adoption among producers until further work is completed in future years by Dr. Smith and Mr. Omondi.
Reaction from Producers
We have begun to informally discuss the results of this project and the potential benefits with sustainable and organic producers within the region. Interest is high amongst this producer group although many are still awaiting the further work at SAREC to determine the best means of potential integration into their operations.
Recommendations or New Hypotheses
1. A common problem in the development of new cultural practices in agriculture is that a single growing season on a limited scale is not adequate to fully prove the viability of the idea. It would be more ideal if the FRG program could be structured in such a way as to provide funding over three to five years. Additionally, the cap on these grants is too small to scale up to a large enough study to truly prove the concept.
2. In the review process, it was apparent that at least some of the reviewers do not believe farmers and ranchers are able to write scientifically as evidenced by the comments, which directly accuse the Technical Advisor of writing the proposal (which was not true). Western SARE may want to consider the changing educational levels of the new generation of farmers and ranchers when reviewing proposals.
3. The continuing research at SAREC by Dr. Smith and Mr. Omondi is being funded by Western SARE. We believe this provides a nice example of how ideas at the farm level (with support from Western SARE FRG program) can become “seeds” for new farming practices.
4. With respect to this project, approval of our grant came relatively late in the season. Ideally, we should have started preparations for planting about one month earlier. Other projects that require planting crops may benefit from an earlier notification date.
Dr. Smith and Mr. Omondi presented the results of this work through the poster session at the ASA-CSSA-SSSA conference in New Orleans, LA in November, 2007. As the results of the continuing work become available, additional opportunities to present will be studied. A copy of the poster is provided with this report.
Additionally, SAREC holds several field days each year, at which they present their research projects to local producers. Thus, the large number of pinto bean growers in this region will be exposed to this alternative cultural practice.