@article{icrisat7097,
           title = {Agronomic evaluation of two unacidulated and partially acidulated phosphate rocks indigenous to Niger},
       publisher = {Soil Science Society of America},
          author = {S H Chien and J Henao and C B Christianson and A Bationo and A U Mokwunye},
           pages = {1772--1777},
            year = {1990},
          volume = {54},
         journal = {Soil Science Society of America Journal},
          number = {6},
             url = {http://oar.icrisat.org/7097/},
        abstract = {A field study was conducted on a sandy soil in Niger to evaluate the agronomic effectiveness of various P fertilizers for millet production during 1985 to 1987. The P fertilizers tested were two finely ground phosphate rocks (PR) indigenous to Niger (Tahoua and Parc W rocks), PR partially acidulated with H2SO4 at 50\% acidulation level (PAPR), single superphosphate (SSP), and triple superphosphate (TSP). In 1985, application rates were 0, 6.5, 13.0, and 19.5 kg P ha?1 for each of the P fertilizers. In 1986, half of the plots received the same rates of P as in 1985 and half of the plots received no additional P. In 1987, P additions were repeated only in half of the plots that received P during 1986. A significant (P = 0.05) millet response to P was observed in all the trials. The major findings of this study were: (i) finely ground Tahoua PR was more effective than Parc W PR because of its higher reactivity and was 82 to 91\% as effective as SSP for millet production in both the initial and two subsequent seasons; (ii) partial acidulation of Parc W PR can significantly increase its agronomic effectiveness in the first year, but not in terms of residual effect; (iii) partial acidulation was not a desirable technology for increasing the effectiveness of Tahoua PR, because its high Fe2O3 plus Al2O3 content resulted in a product containing relatively low amounts of water-soluble P; and (iv) over a period of 3 yr, one initial application of a large dose of P fertilizer was found to be more effective than three small annual applications in terms of total grain production}
}