Kun-Jun Han, Alison, Jr, Montgomery W. "Wink"
Kun-Jun Han and Montgomery W. “Wink” Alison Jr.
Daikon radish (Raphanus sativus) is known for developing a long taproot that may reduce soil compaction and immobilize excess soil nutrients. The vegetative part of the plant can be used for high-quality forage. On-farm research trials were established on four private farm sites in Louisiana to evaluate the agricultural value of daikon radish when overseeded into warm-season perennial grass pastures over two growing seasons. Two sites each on private beef farms in Franklin and Washington parishes were overseeded with daikon radish or radish plus annual ryegrass (Lolium multiflorum) along with a non-overseeded area. Overseeded crops were planted into the warm-season grass sod using a no-till drill in the fall. Overseeded crops were treated as cover crops and not disturbed during the growing season by grazing or harvest. The goal was to quantify effects of overseeding approaches on soil properties and determine potential benefits to warm-season grass pasture.
Overall, overseeding with radish or radish/ryegrass mixture did not appear to have a definitive effect on the physical or chemical properties of the pasture soils. Overseeding warm-season grass pastures with radish or a radish/ryegrass mix for two consecutive years did not reduce soil bulk density from the initial level or affect bulk density compared to areas not overseeded. Overseeding treatments did not result in an increase in water infiltration rates, and soil organic matter in the pastures was not different when comparing non-overseeded and the two overseeded areas after two years of overseeding. There was also no difference detected among the treatments concerning soil nutrient levels.
The effect of the overseeding treatments on warm-season grass production was measured by a harvest following two years of overseeding. Nutrient levels were also determined from forage samples collected. Forage dry matter production did not differ among treatments except at one location in Franklin Parish where production following radish/ryegrass overseeding exceeded production from other treatments. Plant nitrogen levels did not differ among the treatments at any location, but the plant potassium level was slightly higher following the overseeded treatments at one location.
The hypothesis for conducting these trials was that the radish would develop a relatively deep taproot system, thus improving soil physical condition and providing nutrients to enhance early season growth by the perennial warm-season forage crop. The lack of influence by the overseeding treatments could be attributable to several factors. One is lack of survival of the daikon radish through the winter. Although initial stand counts were not taken in the fall after emergence, visual observation indicated a high percentage of the plants did not survive into the following spring. It is also well understood that cool-season forages exhibit limited growth in fall and early winter when overseeded into warm-season perennial grass sods compared to planting on a prepared seedbed. The overseeded crops in this study had limited growth in fall and early winter, and the surviving radish plants began reproductive growth in late winter before substantial plant development. These conditions resulted in a sparse stand of small radish plants with little root development (Figure 1).
Results indicate daikon radish will provide minimal forage production and not affect soil characteristics when overseeded in the fall into a warm-season perennial grass sod. Similar responses were obtained in plantings at LSU AgCenter locations over the past three years. These results contrast with expectations and with reports of improved soil characteristics from daikon radish growth on some cropland fields, indicating that cover crop and soil health benefits of this plant do not extend to pastures with perennial grass sod.
Kun-Jun Han is an associate professor in the School of Plant, Environmental and Soil Sciences, and Montgomery W. “Wink” Alison Jr. is an associate professor at the Scott Research and Extension Center, Winnsboro, Louisiana.
(This article appears in the fall 2020 issue of Louisiana Agriculture.)
Figure 1. Daikon radish plants in spring following fall planting in a perennial warm-season grass sod. Photo by Kun-Jun Han