Subsoil Shattering and Subsoil Liming for Crop Production on Claypan Soils

E claypan soils represent a large area of relaJ. tively level agricultural land throughout the central states region. They are characterized by poor internal profile drainage and a low level of fertility. . Although relatively level and not subject to excessive erosion, these soils are considered droughty and unsuited to the growth of cultivated row crops, such as corn. Numerous studies have been made on the improvement of these soils through deep tillage, tile drainage, and deep placement of fertilizer (3). Evidence obtained from recent studies and experiments suggests that a solution is being obtained to the problem of growing corn on these soils. The problems of soil management on claypan soils provoked this project initially under the leadership of Miller, et al. (2) and received their first physicochemical attack from Bradfield ( i) . The design of the experiment for which the data are reported in this paper was prompted by some studies which showed that in the claypan horizon the pore space of the soil is filled with water af a moisture tension represented by the field capacity (5). These studies also showed that the clay when immersed in water reaches a limited degree of hydration of about 40% moisture by weight. The unworkable plastic condition of the clay was observed to disappear and to be replaced by a stable granular condition during periods of drought when legume crops, such as sweetclover, lespedeza, and soybeans, occupied the land. While in this semi-dry condition the claypan is susceptible to shattering by deep tillage. These observations and facts suggested that if the clay were shattered mechanically'while in a semi-dry condition the water-holding capacity and the aeration of the soil should be improved. In addition to the undesirable physical characteristics associated with the subsoil horizon of the claypan soils, chemical studies reported by Whiteside and Marshall (4) showed that the soil layers beneath the surface plow depth were less than 50% saturated with exchangeable bases. Lime must be added to correct this acid condition of the subsoil. Unreported data from the Missouri Experiment Station show that lime and fertilizer injected into the subsoil through a tube on the rear of a Killefer pan breaker remained unweathered for a period of 10 years in a small band at the bottom of the silt cut by the deep tillage machine. These results suggested that the lime should be well distributed through the subsoil in order to be effective. PROCEDURE