| 1997 total production (Lbs.) | 2007 total production (Lbs.) | 2017 total production (Lbs.) |
| 9,000,000,000 | 13,640,000,000 | 13,530,000,000 |
| 8,650,000,000 | 12,920,000,000 | 13,200,000,000 |
| 8,510,000,000 | 13,270 000 000 | 13,120,000,000 |
| 8,590,000,000 | 13,940 000 000 | 13,490,000,000 |
| 8,910,000,000 | 13,730 000 000 | 13,150,000,000 |
| 8,740,000,000 | 13,370 000 000 | 13,720,000,000 |
| 9,110,000,000 | 12,350,000,000 | 13,010,000,000 |
| 8,630,000,000 | 13,570,000,000 | 13,920,000,000 |
| 8,510,000,000 | 13,380,000,000 | 12,500,000,000 |
| 8,590,000,000 | 13,650,000,000 | 12,680,000,000 |
| 8,940,000,000 | 13,310,000,000 | 14,140,000,000 |
| 8,460,000,000 | 13,720,000,000 | 14,480,000,000 |
| 8,280,000,000 | 12,710,000,000 | 14,170,000,000 |
| 9,010,000,000 | 12,780,000,000 | 14,220,000,000 |
| 8,480,000,000 | 13,150,000,000 | 13,910,000,000 |
| 8,470,000,000 | 13,030 000 000 | 13,160,000,000 |
| 9,180,000,000 | 14,030 000 000 | 13,860,000,000 |
| 8,810,000,000 | 13,870,000,000 | 13,700,000,000 |
| 8,990,000,000 | 13,560,000,000 | 13,150,000,000 |
| 8,610,000,000 | 12,140,000,000 | 12,500,000,000 |
| 8,540,000,000 | 14,210,000,000 | 13,490,000,000 |
| 8,960,000,000 | 13,030,000,000 | 14,300,000,000 |
| 8,990,000,000 | 13,020,000,000 | 12,940,000,000 |
| 9,120,000,000 | 13,120,000,000 | 14,360,000,000 |
| 8,670,000,000 | 12,710,000,000 | 13,160,000,000 |
| 8,520,000,000 | 12,150,000,000 | 12,670,000,000 |
| 8,270,000,000 | 13,730,000,000 | 12,190,000,000 |
| 8,830,000,000 | 13,570,000,000 | 14,010,000,000 |
| 8,950,000,000 | 13,160,000,000 | 13,070,000,000 |
| 8,760,000,000 | 13,340,000,000 | 13,330,000,000 |