Crop Scene Investigation - 55 Solved: 'Death on the knolls'

Sunday, March 8, 2015

Corn plants on the sandy knolls in Dave's cornfield were dying because of a cause-and-effect relationship tracing back to the extremely acidic conditions on the sandy knolls. The corn plants were dying due to micro-nutrient deficiencies, which were caused by extremely low soil pH levels.

Pioneer agronomist Aric Bos' instincts were correct when he suspected the dying corn plants in the field were likely deficient in magnesium, sulphur and other key micro-nutrients. Bos had initially ruled out micro-nutrient deficiency because of the strength of Dave's fertility program and the fact that the farmer had limed the field in the fall in an effort to maintain pH levels.

Bos' soil tests, however, revealed how low the pH levels had fallen on the knolls. "Typically, you want pH to be in the 6.8 to 7.2 range. But the soil test revealed that levels on the knolls had sunk all the way to 4.5, despite Dave's' fall lime application," explains Bos.

"A pH level that low effectively ties up micro-nutrients in the soil, making them unavailable to the plant," he adds, noting that tissue tests revealed the dying plants scored very low for magnesium and sulphur.

Bos says farmers can learn several lessons from this situation. The first thing is the importance of regular soil testing, especially on farms with sandy knolls.

"In a field like Dave's, it's important to identify management zones and sample them accordingly. It's also important to understand that you can't fix low pH soils with one lime application, especially when you run into excessive fall rains and spring moisture as he did. It will take several years of liming to fix that field."

Congratulations to Randy Hentz, Wallacetown, for his correct answer. BF