surprising since it is the most abundant mineral nutrient in fibers. Most of the carbohydrate for fiber cellulose synthesis comes from the leaves subtending the cotton bolls. K deficiency affects cotton leaf photosynthetic capacity by inhibiting carbohydrate synthesis and the carbohydrate transportation rate. Therefore, K deficiency affects cotton fiber properties by inducing a carbohydrate acquisition difficulty represents a good entry point for exploring the mechanisms underlying this process.
If making a supplemental K application, one should also evaluate nitrogen (N) and boron (B) needs. N demand picks up through early flowering and is high at peak bloom. Similarly, peak demand for B occurs during flowering and extends through boll filling.
Conditions Leading to Potassium (K) Deficiencies
K mobility in soils is intermediate between N and phosphorus (P) but is not easily leached because it has a positive charge (K+), which causes it to be attracted to negatively charged soil colloids. In soils that are K deficient, chlorosis may be a result of this deficiency. The reason this often does not appear sooner in the season is due to cotton's demand for K is relatively low until squares appear at which time demand begins to increase.
Dry weather can cause K deficiency to appear if there is minimal moisture in the soil profile for the plant to take up water and K. In this situation you may have more than adequate soil test levels of nutrients.
Low pH soils (i.e. below 5.8) can result in restricted root growth to some degree. Restricted root growth will limit the area from which the plant can take up water and nutrients.
In some cases, a transient nutrient deficiency is caused because the plant may need more K than it can physically take up from the soil. This may be the case where cotton is blooming and is maintaining a heavy fruit load.
Desired Potassium Tissue Test Values
The desired tissue test levels for youngest mature leaf are 1.5 to 3% K during early bloom and 0.9 to 3% for late bloom. In high-yielding cotton varieties it is preferred to be at the top end of sufficiency levels entering early bloom, because as much as three-fourths of the K is partitioned to fruiting structures (bolls), so there is heavy draw of K moving from the leafs to developing bolls.
Key Application Timings and Rates
To maximize the effectiveness of supplemental K application it is important to make the applications during and right before peak demand. The best practice is to make applications between match-head square and early to peak bloom. Later applications effectiveness is varied and will depend on the fruit load and cotton varieties. Application options include side-dress, foliar and fertigation through flood, drip of pivots.
- BRANDT® EnzUp® K DS
Nutrient(s) Deficiency Pictures
K deficiency often appears initially as interveinal chlorosis following by red coloration of leaf tissue on older leaves. After peak bloom, similar deficiency symptoms appear but tend to appear on new growth. If deficiency symptoms become severe enough, leaves can curl downward and/or appear thickened. In extreme cases, cotton will begin to defoliate itself due to potassium deficiency.
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