Lumbanraja, Jamalam and Evangelou, V.P. (1992) Potassium Quantity-Intensity Relationships in the Presence and Absence of NH4+ for Three Kentucky Soils. Soil Science, 154 (5). pp. 366-376. ISSN 0038-075X

Nugroho, Sutopo Ghani and Yoshida, Shigekata and Kuwatsuka, Shozo (1992) Concurrent observation of several processes of nitrogen metabolism in soil amended with organic materials: V. Effects of long-term application of farmyard manure and nitrogen fertilizer on N cycling processes in upland field soil. Soil Science and Plant Nutrition, 38 (4). pp. 619-629. ISSN 0038-0768