_____________________________________________________________________________________________________ *Corresponding author: E-mail: asherikalala@yahoo.com; Advances in Research 7(5): 1-12, 2016, Article no.AIR.26368 ISSN: 2348-0394, NLM ID: 101666096 SCIENCEDOMAIN international www.sciencedomain.org Response of Rice to Phosphorus and Potassium Fertilization Based on Nutrient Critical Levels in Plants and Soils of Kilombero Valley A. M. Kalala 1,2* , N. A. Amuri 1 and J. M. R. Semoka 1 1 Department of Soil and Geological Sciences, Sokoine University of Agriculture, P.O.Box 3008, Tanzania. 2 Tumbi Agricultural Research Institute (ARI- Tumbi), P.O.Box 306, Tabora, Tanzania. Authors’ contributions This work was carried out in collaboration between all authors. Author AMK designed the study, wrote the protocol, wrote the first draft of the manuscript, managed the literature searches and all laboratory analyses. Authors NAA and JMRS involved in site selection, edited the data, reviewed and edited the protocol and manuscript. All authors read and approved the final manuscript. Article Information DOI: 10.9734/AIR/2016/26368 Editor(s): (1) Prabhakar Tamboli, Director International Training Program, Department of Environmental Science & Technology, University of Maryland, USA. Reviewers: (1) Zacharie Segda, Agronomic and Environmental Research Institute, INERA, Burkina Faso. (2) Birol Tas, Uludag University & Bursa, Turkey. (3) Alie Kamara, Njala University, Sierra Leone. (4) Usman Monday, Federal College of Education (Technical) Potiskum, Yobe State- Nigeria. Complete Peer review History: http://sciencedomain.org/review-history/15265 Received 13 th April 2016 Accepted 17 th June 2016 Published 2 nd July 2016 ABSTRACT Phosphorus (P) and potassium (K) optimization is crucial for achieving high yields of rice. This study objective was to establish optimum rates and critical concentrations of P and K in soil and rice shoots using soils from Kilombero district, Tanzania. Two-screen house experiment was carried out from December 2013 to May 2014 at Sokoine University of Agriculture (SUA), each using 10 soils collected from different sites in Kilombero valley. The first experiment had varied levels of P, namely 0, 40 and 80 mg kg -1 soil and the second with varied levels of K, namely 0, 200 and 400 mg kg -1 soil. Absolute control treatment was included in both experiments. Rice (variety TXD 306) was grown in pots arranged in a randomized complete block design with three replications. The results showed that soil critical concentration of P was 8.0 mg kg -1 and the shoots- P critical concentration was 0.16%. Established critical concentration of K in soil was 0.2 cmol (+) kg -1 and the shoots- K concentration was 1.4%. Grain yield increased significantly for rice grown in Short Research Article