Forage radish cover crops increase soil test phosphorus surrounding radish taproot holes

Cover crops can influence nutrient cycling in the agroecosystem. Forage radish (FR) (Raphanus sativus L. var. longipinnatus) is unique in terms of P cycling because of its high tissue P concentration, rapid growth in the fall, and rapid decomposition in winter and spring. In addition, FR produces a taproot that decays during the winter and leaves distinct holes in the surface soil. This study measured P uptake by FR and cereal rye (CR) (Secale cereale L.) cover crops; the Mehlich 3 P concentration (M3P) in bulk soil following FR, CR, and no cover crop (NC); and M3P in soil within 3 cm of FR taproot holes. Cover crop treatments of FR, CR, and NC were established at two sites each fall for three subsequent years in a cover crop-corn (Zea mays L.) silage rotation. Cover crop shoot P uptake ranged from 5-9 to 25 kg P ha^-1 for FR measured in the fall and from 3.0 to 26 kg P ha^-1 for CR measured in the spring. The greatest cover crop effect on bulk soil M3P was observed at the 0- to 2.5-cm depth after 3 yr of cover crops, with M3P values of 101,82, and 79 mg P kg ^-1 after FR, CR, and NC, respectively. Soil within 3 cm of FR taproot holes had greater M3P than FR and NC bulk soil. Further studies should be conducted to determine if FR could increase P removal rates in excessively high P soils or increase P availability in low P soils.