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Both water seeding and dry seeding are utilized in U.S. rice (Oryza sativaL.) 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−15N 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 m2). 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.

Rice (Oryza sativaL.) is widely grown on soils continuously submerged during the annual growing season. Upland crops following rice culture often exhibit chlorosis, extremely slow growth, and low productivity. Phosphorus deficiency induced by drainage following soil submergence was shown to exist in crops following rice. Experiments were conducted to clearly define the problem in terms of crop response to P fertilizer on major California rice soils and to determine the most efficient methods of P fertilization. Three field experiments were conducted on Myers, Willows, and Sacramento soils following variable years of annual rice production. Wheat (Triticum aestivumL.) or barley (Hordeum vulgareL.) were fertilized with P rates of 0, 29, 59, and 89 kg/ha applied as band‐placed TSP, broadcast TSP and band‐placed MAP. Phosphorus sources, rates, and method of application were evaluated by plant responses including seedling dry matter, plant total‐P and 2% HAc extractable PO4‐P, plant total‐N, grain yield, and 1,000‐kernel weight. The differential severity of plant P deficiency between the three soils was Myers ⩾ Willows > Sacramento series. Severe plant P‐deficiency was observed in the Myers soil even though the soil NaHCO3‐extractable P level was 16.8 ppm. Soil submergence and drainage‐induced soil P transformations decreased soil P availability to wheat and barley following flooded rice. The relative efficiency of P fertilizer sources and methods was band‐placed MAP > band‐placed TSP > broadcast‐incorporated TSP. Phosphorus band‐placed 3 cm directly below the seed was more efficient than broadcast‐incorporated P in wheat and barley after rice. Band‐placed P resulted in greater P uptake by plants probably because of less soil sorption of fertilizer P and greater P availability relative to broadcast‐incorporated P.