INCORPORATION OF LIMESTONE INTO NATURALLY COMPACTED SUBSOIL DURING DEEP-RIPPING

Approximately one-half the soil in New Brunswick has naturally compact ed subsoil and can benefit from deep-ripping. These soils are strongly acidic and pose chemical barriers to root proliferation even after de ep-ripping. Therefore we determined the feasibility of placing large q uantities of dry agricultural limestone in the subsoil during a deep-r ipping operation. A gravity-feed applicator was attached to the frame of a commercial heavy duty subsoiler. The applicator released 60% of t he limestone at 0.25 m depth below the soil surface, 25% at 0.55 m and 15% at 0.75 m depth. In the fall of 1991, a research station loam was deep-ripped to a depth of 0.85 m and limestone was applied to the sub soil at 30 and 55 Mg ha(-1). Trenches were dug perpendicular to the di rection of deep-ripping immediately after deep-ripping and 1 year late r. Soil samples were taken on a 0.1 m grid to a depth of 1 m and a wid th of 0.6 m. Chemical analysis of the soils for their acid soluble Ca concentration was used as the criterion to assess the distribution of limestone in the soil profile. The applicator successfully placed lime stone into the highly compacted subsoil; however, large variations in subsoil Ca concentrations occurred. Soil Ca concentrations were not si gnificantly different (P > 0.05) in the 2 years. They were, however, s ignificantly affected by rate of limestone application, horizontal dis placement from the tine and sample depth. The application of 55 Mg ha( -1) resulted in about ten times more subsoil volume with increased Ca concentrations than when 30 Mg ha(-1) was applied. Highest soil Ca con centrations occurred in the 0.5-0.8 m depth layer. Soil Ca concentrati ons were highest near the tine and decreased with increasing horizonta l distance from the tine. Very little enrichment occurred in the 0.2-0 .5 m depth layer.