Renewable Farming

Still time to foliar feed if leaves signal they’re low on chlorophyll

Many Midwest cornfields are signaling, with a slightly lighter green leaf color, they’re running low on nitrogen. Low chlorophyll levels show before the bottom leaves start firing. The firing signals that the stalk is cannibalizing nutrients in bottom leaves.

August 3, 2018 — A quick, low-cost scouting tool that makes an objective measurement of leaf “green-ness” is the atLEAF meter shown below. At around $250, the basic instrument is considerably less expensive than the price of the more upscale Minolta SPAD meter, which sells online for $1,000 to $3,000 depending on source and model. Yet, SPAD leaf readings have shown near-identical values with the atLEAF in careful comparisons.

In corn, leaf readings below an index of 50 indicate nutrient shortage. That’s most likely low nitrogen in counties like north central Iowa with incessant April-July rains. In previous years, we’ve sprayed a gallon or two of slow-release nitrogen plus WakeUP Summer on corn late in the season, and saw a yield nudge over 10 bushels.

Crop consultant Bob Streit offers more detail in his latest weekly scouting summary:

“When scouting fields the last three weeks, I have been using my Minolta SPAD meter to take measurements and recording them for the grower. The instrument reads the degree of greenness in the leaves to infer the level of N and chlorophyll. The readings are given on a 1 to 80 scale with bigger being better. If the readings get down to 50 or below, yields will be reduced.  If they remain in the mid to high 50s or above the plants have enough N to produce maximum yields. I checked plants July 29 in fields that were somewhat yellow and they registered in the 40 to 50 range. The quite yellowed fields are under 30 with plants in the worst spots registering around 25.

“Too often the equipment and budget to remedy the situation were not available years ago. Buying one of the less expensive SPAD meters to permit growers to do their own monitoring of their fields is something that needs to happen.”

More thorough tissue testing helps zero in on other nutrient shortages which might contribute to early die-down, but the leaf meter is a handy tool to carry in your pickup or tractor. Several atLEAF models range from $249 to $399 depending on data recording options.


Corn leaf below: Definitely short on nutrients, with a greenness reading of 41.1 !