NCDA& CS Agronomic Division 1040 Mail Service Center, Raleigh NC 27699- 1040 ( 919) 733- 2655 www. ncagr. com/ agronomi/
Understanding the Plant Report for Cotton
www. ncagr. com/ agronomi/ uyrpws. htm Steve Troxler, Commissioner of Agriculture
Leaf and petiole analyses can detect nutrient defi ciencies up to two weeks before symptoms appear. Timely diagnosis makes
it possible to optimize yield and quality through precise fertilizer management.
Leaf blade tissue is analyzed for major nutrients ( N, P, K), secondary nutrients ( Ca, Mg, S) and micronutrients ( Fe,
Mn, Zn, Cu, B) ( Table 1). These essential nutrients are required in specifi c concentrations for optimum growth and yield.
Results are reported as percent values for major and secondary nutrients and in parts per million for micronutrients.
Nutrient index values are also provided for interpretation of laboratory results ( Figure 1, Table 2). The optimum index
range is 50– 74. The critical value is the point at which there is a 5– 10% yield loss. Below this value potential loss increases
proportionately. High index values ( 75– 99) may indicate overfertilization and, in some cases, reduced crop quality. With
index values of 100+, there may be growth problems due to nutrient imbalances or micronutrient toxicity.
Petiole analysis for NO3- N best indicates the amount of soil N currently available for plant uptake. It is highly correlated
with yield, especially early in the season ( Figure 2). Apply additional N at the recommended rate if NO3- N falls below the
adequate level for the sampled growth stage ( E4— early growth, week 4; B1 to B4— bloom, weeks 1 to 4; F5 to F8— fruit,
weeks 5 to 8). Excessive NO3- N can lower cotton quality and increase potential for disease and insect pressure.
When tissue analysis indicates nutrient defi ciency, any corrective action should take into account fertilization history,
soil type, environmental conditions, overall crop potential and insect/ disease pressure. During the growing season, foliar
applications of micronutrients are effective. Soil applications of macronutrients are most effective early in the season when
the root system is most active. Soil application of N and/ or K to correct defi ciency is effective only through the 2nd or 3rd
week of bloom. After that time, foliar application may increase yield until about the 5th week of bloom. Soil testing along
with tissue analysis provides information for the best long- term corrective action.
Table 1. Abbreviations
N Nitrogen
P Phosphorus
K Potassium
Ca Calcium
Mg Magnesium
S Sulfur
Fe Iron
Mn Manganese
Zn Zinc
Cu Copper
B Boron
Mo Molybdenum
Cl Chloride
Na Sodium
Ni Nickel
Cd Cadmium
Pb Lead
NO3- N Nitrate N
Figure 1. Leaf interpretation Figure 2. Petiole interpretation
Table 2. Response to nutrient applications *
Index Interpretation Crop Response
0– 24 Defi cient High
25– 49 Low Medium
50– 74 Suffi cient Low
75– 99 High None
100– 124 Excess None
* Fertilizer history, environmental conditions, stress
factors and growth stage will affect ultimate response.
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