Submitted to: Better Crops
Publication Type: Trade Journal
Publication Acceptance Date: 6/15/1999
Publication Date: N/A
Technical Abstract: Variability in nutrient quantity may be significant when considering the variation in root zone depth across a Mexico silty clay loam (Mollic Endoaqualf) soil landscape. Research was initiated to (1)evaluate the relationship between topsoil thickness (depth to Bt horizon) and phosphorus (P) and potassium (K) nutrient availability, and (2) determine the responsiveness of crops to added P and K fertilizer as affected by topsoil thickness. From 90-cm depth soil samples taken from 80 separate locations within 16 claypan soil fields, topsoil thickness and sampling depth were significant in explaining P and K variability, but model fitness values were relatively low. Many locations with deep topsoil had higher surface soil-test P levels, likely a result of soil erosion and deposition downslope of sediment and organic matter. In a second study, 108 P and K response plots were established in 1996 at different topsoil-depth locations within a single field. Soybean yields in 1996 and 1998 ranged from 3 to 4.5 Mg/ha but were not affected by topsoil depth or soil-test P and K. Corn yield in 1997 varied from 2.5 to 10.0 Mg/ha, mostly explained by topsoil thickness and soil-test K level (R2=0.80). The greatest positive benefit with increasing soil-test K occurred where the topsoil was thin. Because plant K nutrition plays such an important role in water regulation and plant response to water stress, higher levels of soil-test K were needed in thin topsoil areas of the field where crop water stress was highest. Accounting for subsoil nutrients has the potential for greatly improving efficiency of crop nutrient inputs.