The potential of managing iron and zinc deficiency in dry beans with interplantings of annual ryegrass.

摘要

Dry edible beans are grown all over the world and are a major source of protein and calories for millions of families, especially in developing countries. Dry bean production faces many challenges including diseases, insect pests, and nutrient deficiencies. The main objective of this study was to research a cultural method of mitigating iron (Fe) and zinc (Zn) deficiency in calcareous, high pH soils in Wyoming and highly weathered acidic soils in western Kenya. Field studies were conducted in western Kenya in 2006 and near Lingle, Wyoming between 2008 and 2010, to evaluate the effect of interplantings of annual ryegrass to alleviate Zn and Fe deficiency in dry beans in acidic and alkaline soils, respectively. Growth chamber and greenhouse studies were also conducted to test the field study hypotheses in a controlled environment. Three dry bean market classes including pinto-, black-, and navy beans were grown as monocrops or variously intercropped with five grass species including millet, corn, wheat, oat, and annual ryegrass. Although annual ryegrass increased soil zinc concentration when interplanted with pinto beans in the Kenya study, bean yields were not determined because of hailstorm damage at harvest time. In Wyoming, grass intercropping did not increase iron concentration in bean leaf tissue. Dry bean yield results were not consistent. There were no statistical differences in bean yield between ryegrass-intercropped beans and pinto bean monoculture in 2008. 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 monoculture. Mean dry bean yield was equivalent to 2,324 kg ha-1 in 2010 compared to 1,623 kg ha-1 in 2009. In field studies in 2009-2010, dry beans exhibited greater chlorosis at the beginning of the season than later in the season 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. Grass intercrops, including annual ryegrass, may have reduced available NO3-N and Mn from the soil thereby limiting their uptake and interference with iron metabolism in bean tissues. 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.