Potential of Managing Iron Deficiency In Dry Beans with Interplantings of Annual Ryegrass.

Dry beans are grown throughout the western Great Plains. The high pH, low organic matter, and calcareous soils prevalent in Wyoming can limit availability of iron (Fe) resulting in iron deficiency chlorosis in dry beans. The main objective of this study was to research a cultural method of mitigating Fe deficiency in calcareous, high pH soils. Field studies were conducted at the University of Wyoming Sustainable Agriculture Research and Extension Center near Lingle, Wyoming between 2009 and 2010, to evaluate the effect of interplantings of annual ryegrass to alleviate Fe deficiency in dry beans. Three dry bean market classes including pinto-, black-, and navy beans were grown as monocrops or variously intercropped with four grass species including corn, wheat, oat, and annual ryegrass. Grass intercropping did not increase Fe concentration in bean leaf tissue. Dry bean yield results were not consistent. Yields of dry bean monocultures were 58% greater than grass-intercropped beans in 2009. However, ryegrass-intercropped navy beans had 41% greater yields than navy bean monoculture in 2010. In 2010, grass-intercropped pinto and black beans did not statistically differ in yield compared to bean monoculture. Dry beans tended to exhibit greater chlorosis at the beginning of the season than later corresponding with greater soil and tissue nitrate-nitrogen (NO₃-N) and manganese (Mn) concentrations at the beginning of the season compared to later. Bean monocultures had 4.2 SPAD units of chlorophyll content greater than grass-intercropped beans, which corresponded with 1791 mg kg^-1 and 30 mg kg^-1 less tissue NO₃-N and tissue Mn respectively, in bean monocultures compared to grass-intercropped beans. Nitrate-N and Mn may have interfered with iron uptake and metabolism by bean plants. Further studies are needed to determine threshold NO₃-N and Mn concentration in the soil that can induce economically important Fe deficiency in dry beans.