Even if enough Fe is in the soil, deficiency can occur under the following conditions: poorly drained soil, high Ca, high Mn, high pH, high P, high heavy metals, oxygen deficiency. Deficiency symptoms General: Yellow or white areas on youngest leaves. Older leaves remain green.
The Bt corn can produce unpredictable toxins and allergens into food plants and therefore into the final product. Also the Bt corn can be considered unstable as the number of copies of an inserted gene changes through later generations of the Bt corn. The low tillage is also a prime spot for a monoculture in the fields. A monoculture is where all of the crops are the same, so with this it is a perfect situation for weeds.
Commercial corn today is 100% hybrid corn. This means that the seed corn is produced by cross-pollinating two inbred lines. Because corn plants have both male (tassels) and female (silks) reproductive parts, a seed corn field has to be altered in order to keep the plants from pollinating themselves and therefore just producing more inbred seeds. This is done by detasseling the 'female' rows of corn.