Cover crop impact on nitrogen availability and dry bean in an organic system

Abstract

Cover crops could play an important role in increasing nutrient availability and crop yield in organic systems. This study had two main objectives, (i) compare the effects of medium red clover (Trifolium pratense L.), cereal rye (Secale cereale L.), and oilseed radish (Raphanus sativus L.) cover crops on N availability and dry bean (Phaseolus vulgaris L.) growth and yield and (ii) compare the use of ion exchange resin and chlorophyll content monitoring with traditional soil KCl extractions for determining soil inorganic N availability. Red clover increased soil inorganic N up to 55 kg ha–1, resulting in delayed maturity and greater grain N in some site-years; population and yield were not affected. Rye reduced soil inorganic N and caused early maturity of bean in some site-years; at maximum dry biomass production (12.8. Mg ha–1) rye reduced dry bean yield. Oilseed radish occasionally increased inorganic N and bean populations; yield was not influenced. Cover crop and weed C/N ratios and C and N content were the most consistent factors influencing soil inorganic N. Soil inorganic N measurements from soil extractions and resin strips were positively correlated, however the use of resin strips may be constrained due to frequent cultivation in organic systems. Correlations were seldom observed among these two direct N measures and dry bean relative chlorophyll content. Overall, planting cover crops did not benefit dry bean yield, however producers may be able to manipulate soil inorganic N by focusing on cover crop quality, depending on their goals and species selection.