Urea, superphosphate and potassium chloride were fixed at maximum rates to supply 225 kg/ha of N, 112.5 kg/ha of P2O5, 225 kg/ha of K2O, resulting 12 treatments in an optimum regression design.

• 尿素、过磷酸钙和氯化钾最大用量确定为225公斤N/公顷、112.；5公斤P2O5/公顷、225公斤K2O/公顷，产生出最优回归设计的12个处理。