Response of rice cultivars to phosphorus supply on an oxisol

Genotypic differences in absorption or utilization of P might be exploited to improve efficiency of fertilizer use or to obtain higher productivity on P-deficient soils. The objective of this study was to evaluate responses by 75 genotypes of upland rice (Oryza sativa L.) to two soil P levels in two field experiments. In the first experiment, soil P levels (Mehlich 1) were 1.5 mg kg^–1 and 5 mg kg^–1, and in the second experiment, 3 mg kg^–1 and 4.7 mg kg^–1 of soil, respectively. Rice cultivars differed significantly in shoot dry matter production at flowering, grain yield, and plant P status. Based on a grain yield efficiency index, cultivars were classified as P-efficient or P-inefficient. Shoot dry matter was more sensitive to P-deficiency but was not related to grain yield. Phosphorus use efficiency was higher under the low P treatment. Phosphorus uptake was significantly correlated with dry matter, P concentration and P-efficiency ratio. Results of this study indicate that genetic differences in P-use efficiency exist among upland rice cultivars and may be exploited in breeding programs.Contribution from National Rice and Bean Research Center of EMBRAPA, Goiania, Goias, Brazil and Appalachian Soil and Water Conservation Research Laboratoy, Beckley, WV, USA.     

Screening wheat and other small grains for acid soil tolerance

Aluminum (Al) toxicity in acid soils is a major growth-limiting factor for cereal crops in many parts of the world. The most striking effect of high Al concentration in acid soils is stunting of the root system. Liming reduces Al toxicity in surface soils; however, cereal breeders must be prepared to develop cultivars that have tolerance to soil acidity. A 4 day root bioassay, originally used to identify Al toxics soils, was adapted to evaluate tolerance to soil acidity of cereal species and genotypes. Acid soil tolerance was related to the extent of inhibition of root elongation in an Al-toxic soil (pH 4.2) relative to root elongation in the same soil treated with lime (pH5.2). Of the entries, 18% were tolerant or moderately tolerant, and 48% were susceptible or moderately susceptible when 75 bread wheat (Triticum aestivum L.) genotypes were tested. None of the 22 entries of durum wheat (Triticum durum Desf.) were tolerant or moderately tolerant, indicating much lower adaptability to soil acidity than bread wheat. The following ranking of acid soil tolerance of cereal species was obtained: rye (Secale cereale L.) #62;oats (Avena sativa L.) #62;millet(Panicum miliaceum L.) #62;bread wheat (Triticum aestivum L.) #62;barley (Hordeum vulgare L.) #62;durum wheat (Triticum durum Desf.). Variation in tolerance within the other cereal species was much lower than within bread wheat species. The root bioassay method is relatively quick, simple and inexpensive. The method can also be used to screen early-generation populations because assayed seedlings are still viable and can be transplanted for growing until harvest.