English

Abstract

Alluvial soils in the Upper Coastal Plain soil resource area in the state of Mississippi occur in narrow floodplains. Prime farmland soil was collected in 4 foot increments to a depth of 16 ft. Soil collected from Kirkville and Oaklimiter sites was placed in 5 gallon pots in the greenhouse with five replications. Soil fertility (P, K, Ca, Mg and CEC) increased (P<0.05) as depth increased indicating that deep alluvial subsoils have a greater productive capacity. Soil pH was acidic (4.5 to 5.2) and tended to be similar with depth from the Oaklimiter site, but decreased curvilinearly to a depth of 12 ft from the Kirkville site. Pearl millet was planted in the summers of 2005 and 2006 followed by annual ryegrass in the winters of 2006 and 2007. Soil was remixed and limed with 2 tons dololmite per acre after year one. Pearl millet growth in 2005 increased linearly (P < 0.05) as subsoil depth increased at both sites. Manganese (Mn) levels in pearl millet increased linearly as subsoil depth increased from both soils to greater than 2000 ppm but was apparently not toxic to pearl millet. Ryegrass growth increased curvilinearly to a depth of 12 ft from Oaklimiter subsoils but decreased linearly as depth increased from Kirkville due to elevated Mn levels in ryegrass. Mn levels above 500 ppm were toxic to ryegrass. Liming increased pH to as high as 7.6 in soil from Kirkville and to 7.2 from Oaklimiter and had a neutral impact on pearl millet growth. Ryegrass growth following lime was greater as depth increased from Kirkville subsoils and was similar in Oaklimiter. Mn levels in both pearl millet and ryegrass were reduced to non-toxic levels following lime indicating that lime ameliorated subsoils would be suitable as topsoil.