Five field experiments were conducted from 1986 to 1989 to compare broadcast and band P fertilization of crisphead lettuce (Lactuca sativa L.) on Histosols. Rates of P were 0, 50, 100, 200, and 300 kg P/ha applied broadcast or banded. Broadcast P was surface-applied and disked into the soil 1 day before bedding and planting. Banded P was placed in strips 8 cm wide, 5 cm below the lettuce seeds at planting. Lettuce yields were significantly(P < 0.01) increased by P rate in all experiments. However, significant rate-by -placement interactions indicated that response of lettuce to P varied by placement. Lettuce yields were generally optimized with a band P rate one-third of that required with broadcast placement. Analysis of soil samples collected in the lettuce bed after fertilization indicated that banded P increased available P in the lettuce root zone compared to broadcast fertilization. Lettuce leaf P concentration increased with P rate and generally was greater when P was banded. The critical concentration of P in lettuce leaf tissue at the six- to eight-leaf stage was 0.37%. Banding P fertilizer did not reduce the availability of other essential nutrients, as indicated by tissue analysis.
C.A. Sanchez, S. Swanson and P.S. Porter
C.A. Sanchez, M. Lockhart and P.S. Porter
Five field experiments were conducted from 1986 through 1988 to evaluate the response of radish (Raphanus sativus L.) to rate and source of P (triple superphosphate and phosphoric acid) and to rate of K (KC1) on Histosols. Marketable radish root yields increased with P fertilization when the soil tested <13 mg P/dm3 using a test for water-soluble P. No significant differences were due to P source. Results of leaf tissue analysis suggested that the critical concentration of P in radish leaves was 0.45%. Radish did not respond to K fertilization in any of the five experiments, even though preliminary soil-test K levels ranged from 20 to 102 K/dm3. Histosols used for crop production in Florida rarely test below 20 mg K/dm3; thus, radish rarely would require supplementary K fertilization for optimal yield.