Amnat Suwanarit, Nualchavee Roongtanakiat, Jarong Rungchuang, and Somporn Thongdaeng. 1996. “15N-Aided Studies on Effects on Maize and Balance Sheets of Different Form of N Fertilizer”. Agriculture and Natural Resources 30 (2). Bangkok, Thailand:232-40. https://li01.tci-thaijo.org/index.php/anres/article/view/241152.