The Effect of Intercropping Annual Ryegrass with Pinto Beans in Mitigating Iron Deficiency in Calcareous Soils

Dry beans are grown extensively throughout the western Great Plains. The high-pH soils prevalent in this region limit the availability of many micronutrients, especially iron. In 2002 a Goshen County, Wyoming farmer observed that pinto beans intercropped with annual ryegrass did not exhibit iron-deficiency chlorosis and produced higher yields than beans grown without the ryegrass. Field studies were conducted on the same farm in 2006 to determine if a ryegrass intercrop results in increased iron concentration in pinto beans. Treatments included bean-ryegrass intercrop, beans planted in ryegrass residue incorporated in the soil, and beans planted alone. Soil iron concentration increased for all treatments (p0.10) over the first 76 days of the experiment. There was also significantly more soil organic matter and significantly lower soil pH (p0.10) in plots with ryegrass compared to beans alone. Iron concentration declined, though not significantly, in bean leaves over the study period with a steep decline over the first sampling interval in the monoculture plots compared to bean-ryegrass plots.