2.2. Corn planting method
Bright Jean Number 7 corn was used for the planting test. Having yellowish kernels, Bright Jean Number 7 is heat-tolerant, moisture-resistant, lodging-resistant, and pest-resistant. Moreover, the corn is suitable for the hot and humid climate of Nantou, Taiwan. An area of approximately 30 m2 was used for the planting tests, which were conducted from December 2011 to October 2013, throughout four rounds of corn planting. The first round began in December 2011 and ended in May 2012 (137 days), and the second round was from June 2012 to August 2012 (84 days). The corn grew rapidly in the second round because of high temperatures. The third round began in February 2013 and continued until June 2013 (103 days). The fourth round was from July 2013 to October 2013 (84 days). Prior to each planting round, a sample of surface soil (depth, approximately 30 cm) was collected, crushed, and mixed evenly using a soil mixer. The mean distance between each row of corn was approximately 30 cm, and the plants were spaced at intervals of approximately 20 cm. After the corn was planted, 5 g of instant compound fertilizer Number 4 (Taiwan Fertilizer Company), which contained 14% nitrogen, 28% phosphorus anhydride, and 14% potassium oxide, was applied to each plant. When the corn began to tassel, 5 g of the Number 4 fertilizer and 3 g of potassium chloride were applied. Fig. 1 depicts photographs of the corn planting at various stages.