Phosphorus and Potassium Uptake by Corn in Conservation Tillage Systems

In conservation tillage systems surface application of P and K fertilizers and the annual return of corn residue to the soil surface can result in the stratification of these two nutrients in the topsoil. The extent to which this changes P and K uptake patterns of corn ( Zea mays L.) has not been investigated. The objectives of this field study on a Chalmers silty clay loam (Typic Haplaquoll) were to compare the degree of stratification of P and K after 9 yr under conventional, no‐till, and ridge till systems, and to use this data along with root measurements in a model to calculate P and K uptake patterns by corn under these three tillage systems. Under conventional tillage Bray P 1 ‐P and exchangeable K were distributed evenly throughout the topsoil (0–275 mm). Stratification of P and K, however, had occurred in the ridge till and no‐till systems after 9 yr. Of calculated P and K uptake from 30 to 47 d after planting, only 18 and 23%, respectively, came from the upper 75 mm under conventional tillage, compared with 52 and 58%, respectively, under no‐till for the same period. From 30 to 77 d, 39 and 52% of calculated P and K uptake, respectively, was from the upper 75 mm under no‐till compared with only 28 and 26%, respectively, under conventional tillage. Some deep placement of fertilizer P and K may be desirable after several years of continuous no‐till cropping, to provide P and K to roots growing deeper in the soil.