Soybean Response to Phosphorus and Potassium Fertilizers as Affected by Soil Drying
- T. C. Kaspar ,
- D. R. Timmons and
- J. B. Zahler
Soybean, Glycine max (L.) Merr., response to P and K fertilzers can vary with the amount of rainfall received during a growing season, but it is often difficult to determine whether growth is limited by unavailability of nutrients and/or water. A 2-yr study was conducted in a rhizotron at Ames, IA, to determine whether drying of the fertilized, surface soil layer reduces plant growth and utilization of P and K fertilizers when subirrigation replenishes water below the fertilized surface layer. Low, medium, and high fertility levels were established on soil obtained from the upper 0.15 m of a Sparta loamy, fine sand (sandy, mixed, mesic Entic Hapludoll). Two surface-drying treatments, one beginning during late flowering (dR2) and the other after the start of seed fill (dR5), and a control were imposed. Shoot tissue concentrations and dry weights at the fullseed stage (R6) and mature seed yield were measured. Surface drying reduced total shoot accumulation of P and K. Leaf and pod P concentrations were lower for the dR5 treatment than for the dR2 treatment. Shoot K concentrations of the dR2 treatment increased less than those of the other treatments as soil K levels increased. Shoot dry weights at R6 and mature seed yield were reduced at the low fertility level. Surface-drying treatments reduced total shoot dry weight (42.8 and 40.9 g plant −1) compared with the control (49.5 g plant−1) in both years, but yield was reduced only in 1984. This study shows that drying of the fertilized soil layer reduced shoot growth and utilization of applied P and K fertilizers even though water was available at greater depths.
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