Webster gives a definition, "to endure without failing or yielding, to bear up under."

Sustainable agriculture is a method that will continue agriculture for 10,000 years, 100,000 years, till the end of the earth.

Study the formation of soil. A large amount of time is needed; therefore erosion must be prevented to save the soil.

Elements needed to grow plants - nitrogen, phosphorus, potassium and minor elements - have cycles in nature. They're taken from the soil by plants, and after going through animal life or other processes, are returned to the soil to be used by plants again. Some cycles are complex. Farmers should study biology, botany and zoology to understand the importance of the cycles.

If the cycles are broken, the elements are not returned to the soil and agriculture may not be sustainable for 10,000 years.

Manure is not a waste. It's part of the sustainable cycle. Manure should be returned to the land where the crop was grown to sustain the element cycle.

The effort to increase foreign sales of crops without return of manure is not a sustainable cycle.

If corn is made into ethanol, do we have something to return to the soil? If straw is made into wallboard, is there anything to return to the soil?

Soil needs humus, which comes from plant life. Commercial fertilizer is not likely to add humus to the soil.

Commercial fertilizer produces good crops. But do we have a supply of phosphorus and potassium that we can (use to) make commercial fertilizer for 10,000 or 100,000 years without returning something to the soil?

Farmers, environmentalists and politicians should understand the cycles of nature and plan for agriculture to continue for a long time. James Jackson Carlisle, IN

Save Butterflies An item in the December issue can't pass unchallenged.

Regarding Bt corn products on page 6 (News and e-news), EPA says "widespread cultivation of Bt crops may have a huge benefit for monarch butterfly survival."

As a person who has used Bt corn seed and finds it to be effective, I quit using it when I read allegations that monarch butterflies were dying because of Bt corn pollen. I will not use it again until my fears are alleviated. I frankly don't see it happening.

Some years ago, when my kids were 7-9 years old, they loved buterflies. Butterflies were abundant.

The last couple of years I have marveled at the dearth of butterflies. I realize that milkweeds have been drastically reduced by herbicides, and that can account for some of the reduction in the number of monarchs. But it doesn't account for the dearth of swallowtails, mourning cloaks, cabbage and other butterflies.

I have used pesticides for 50 years, starting with 2,4-5T and DDT. They didn't kill me, but we all know they contaminated our environment, tragically, as Vietnam War veterans found. Russell Graham Beresford, SD