Table 1. Results of Using the Response Surface Method (equation 1).

	independent variablesa			dependent variablesb
run	AN (mg/mL)	UN (mg/mL)	TN (mg/mL)	SRN (mg/mL)
1	19.32	94.40	169.57	55.85
2	22.39	182.81	214.23	9.02
3	20.33	108.10	160.83	32.41
4	25.81	185.76	215.70	4.13
5	21.44	119.94	176.85	35.47
6	27.93	162.18	201.12	11.01
7	24.34	102.22	171.35	44.78
8	30.42	172.00	237.85	35.43
9	22.98	125.83	169.89	21.08
10	30.70	184.83	221.67	6.14
11	21.16	140.57	187.53	25.79
12	29.87	206.35	244.48	8.26
13	33.33	182.81	228.26	12.12
14	16.83	99.31	125.63	9.49
15	22.17	112.08	170.22	35.97
16	25.83	157.13	223.93	40.97
17	14.96	87.49	141.90	39.45
18	33.95	216.17	256.13	6.01
19	47.14	124.82	185.91	13.95
20	25.56	155.30	217.95	37.08
21	20.49	170.00	206.78	16.29
22	28.48	163.16	222.80	31.16
23	23.72	163.09	218.11	31.29
24	26.51	159.18	208.33	22.64
25	25.21	152.36	206.62	29.05
26	25.38	159.20	208.56	23.99
27	26.68	159.18	208.89	23.02
28	23.75	158.18	206.62	24.69
29	21.03	149.41	197.88	27.44
30	24.04	160.22	212.77	28.51

^aAmmonium nitrogen (AN), urea nitrogen (UN), and total nitrogen (TN).

^bSlow-release nitrogen (SRN).