Pamela Henderson Smith
Cotton nutrient management boils down to deciding two things: what you have and what you need.
, Farm Journal Crops & Issues Editor
Let's face it, fertility may be the single highest input investment you will have for cotton. Nitrogen (N) costs this fall already have farmers reeling with sticker shock.
The key to determining what you have begins with a good soil test, says Mississippi State University cotton specialist Darrin Dodds. "Fall is the best time to pull samples,” he notes. "You'll get the results in time to plan a soil fertility program. Correcting a soil fertility problem before planting is much easier and often cheaper than after your crop has been planted.”
Test results give you an indication of plant-available phosphorus (P), potassium (K), magnesium, calcium and a few other ingredients. You will also get an indication of whether you need lime in time to get it applied in the fall.
What you need in fertility is determined by realistic goals for the farm operation. Yield history is a starting point to project future yields. Dodds suggests using average cotton yields from the past three to five years and then tacking on 10% for a realistic projection.
"Since efficient nitrogen use depends on balanced fertility, address liming needs first based on soil test results,” he says.
Obviously every field and region are different. Here are several basic guidelines from cotton fertility specialists.
Lime. Cotton grows best in soil with a pH between 5.8 and 7.0. According to Mississippi State University studies, yield decreases didn't appear until soil pH dropped below 5.5 on sandy loam and silt loam soils and below 5.2 on clay loam soils.
Liming more efficiently uses native nutrients, as well as P and K fertilizers. For best results, incorporate lime into the soil several months before planting.
Impurities in rock formation make it necessary to consider what type of lime is used. Limestone is tested and assigned a calcium carbonate equivalent (CCE) rating. Most soil tests assume a CCE rating of 100.
There are two basic types of lime—calcitic and dolomitic. Either will work, but calcitic contains calcium carbonate and dolomitic contains calcium carbonate and magnesium carbonate. You will need dolomitic if soil tests indicate magnesium levels are low.
- October 2007