Phosphorus Stratified Soil Management

Reduced tillage systems teamed with surface applications of fertilizer phosphorus (P) often results in an accumulation of P in the surface soil and depletion of available P deeper in the soil profile. Research workers at the University of Kentucky and Kansas State University conducted a three-year study of tillage and P nutrient management on soils with a stratified level of available P. Four P management methods were studied with three tillage systems.

Fertilizer P was applied at a rate of 40 pounds per acre of phosphorus pentoxide (P₂O₅) in a 2x2-inch band, surface broadcast, banded 5 to 6 inches deep on 28-inch centers, and compared with a no-P control and three tillage systems (no-till, disk and field cultivation, and initial moldboard plowing followed by reduced tillage). Phosphorus uptake and grain yields were evaluated for corn, wheat, sorghum and soybeans.

Early-season dry-matter yield was higher for all crops when the soil was moldboard plowed prior to minimum tillage compared with no tillage, but final grain yields were inconsistent. Subsurface placement of P improved grain yield of corn and sorghum but had little effect on soybeans. Differences in crop response to deep- placed P may result from root architecture and ability to extract P from the first few inches of soil. Of the crops studied, soybeans responded best to P fertilization, while sorghum responded least. The authors suggest that growers should consider subsurface applications of P fertilizer if soil test P is highly stratified within the surface 0 to 6 inches and if the soil from the top 6 inches of the soil profile tests medium or below for available P. 

Source: Agron. J. 98:430-435 (2006)

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