Phosphorus seed coating and soaking for improving seedling growth of Oryzasativa (rice) cv. IR66

In view of the large influence which phosphorus (P) can have on early seedl ing growth and the fact that many rice growing soils are P deficient, appro priate methods of P application to enhance the efficient use of P fertilize r for early plant growth need to be investigated. The objective of the stud y was to determine the effect of coating and of soaking rice (Oryza sativa) seed with various P fertilizers at increasing concentrations, on early pla nt growth. Treatments comprised: control; seed coated with single superphosphate (SSP) , rock phosphate (RP), monoammonium phosphate (MAP) and potassium phosphate (PP); and seeds soaked in three levels of KH;PO, (PP), or NaH2PO4.2H(2)O ( SP) solutions (5, 10, 20% w/v), each with three replicates. Amounts of P ap plied to the seeds by coating or soaking were as follows (mg P seed(-1)): C ontrol, 0; Coating-SSP, 3.8; Coating-RP, 1.2; Coating-MAP 3.4; Coating-PP, 3.7; Soaking-PP (5-20%), 0.05-0.17; Soaking-SP (5-20%), 0.05-0.21. Seedling emergence was depressed by 40-60% when seeds were coated with SSP, MAP or PP or soaked in PP or SP solutions. By contrast, seed coating with RP did not affect final emergence compared to the untreated control althoug h it delayed seedling emergence by 2-3 days. At 20 and 40 days after sowing (DAS), soaking in P solutions had no significant effect on plant growth. A t 20 DAS, coating increased shoot dry weight but decreased root dry weight of plants. The effect of coating treatments persisted to 40 DAS and at this stage, seed coating increased root length and dry weight and increased sho ot dry weight by 400-870%. Although plant growth responded to coating seeds with SSP, MAP or PP, these seed treatments initially depressed seed emergence and may therefore not b e acceptable to farmers. Coating rice seeds with RP may be more promising f or stimulating early rice growth on low P soils. Rock phosphate when applie d at 1.2 mg P per seed or 0.5 kg RP per kg of seed was not harmful to final seedling emergence but quadrupled shoot and root growth of rice.