Sikuku, P. A., J. M. Kimani, J. W. Kamau, and S. Njinju. “Response of Improved Rainfed Rice Varieties to Low Soil Nitrogen”. New Perspectives in International Plant and Soil Research Vol. 1, Aug. 2019, pp. 129-40, https://stm1.bookpi.org/index.php/npipsr-v1/article/view/319.