Both water seeding and dry seeding are utilized in U.S. rice ( Oryza sativa L.) cultural systems. Early season N applications are soil incorporated or deep placed prior to planting with water seeding, but are broadcast on the soil surface just prior to permanent flooding with dry seeding. Field studies were conducted on a Crowley silt loam (Typic Albaqualf) and a Sharkey clay (Vertic Haplaquept) to determine the effects of seeding method and time of application on the recovery of urea− 15 N by rice (var. Lemont). A total rate of 100 kg N/ha was added as (i) a single preplant (water seeded) or preflood (dry seeded) application, or (ii) a split with an initial application (preplant or preflood) of 67 kg N/ha and a topdressing of 33 kg N/ ha broadcast into the floodwater at midseason. Nitrogen‐15‐labeled materials were utilized in microplots (0.255 m 2 ). The plant recovery of preplant N with water seeding (41.7% of the applied N) was significantly greater than the uptake of preflood N with drill seeding (30.2%). Water seeding also increased total N uptake and dry matter production, but grain yields were unaffected by seeding method due to a higher harvest index (HI) for drill‐seeded rice. Topdressed N was taken up with equal efficiency (45.8% recovery) in either seeding method. Soil recovery of labeled N was unaffected by seedling method; differences in total recovery of labeled N in the soil‐plant system at harvest (ranging from 40.0 to 57.7% of the application rate), therefore, primarily reflected differences in plant uptake. Overall, differences between seeding methods reflected a stimulation of early season growth and N uptake characteristics on the part of water seeding.
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Westcott et al. (1986) studied this question.