Soil and leaf analysis of coffee
Soil testing can be used to assess pH, organic matter content and cation exchange capacity (CEC), thereby indicating nutrient availability and the nutrient retention characteristics of the soil.
It can be used to assess levels of soil potassium and phosphorus and also to provide an indication of likely cationic imbalances, e.g. K:Mg:Ca ratios. However, it is not a good indicator of nitrogen requirement. Therefore, soil testing alone does not provide enough information to ensure accurate nutrition.
Leaf Tissue Analysis
Leaf tissue analysis helps monitor crop needs throughout key periods of growth. Seasonal analyses – carried out at the same growth stage – will help the producer build up a clear picture of nutrient status and needs, and highlight where adjustments need to be made to current fertilizer programmes.
Leaf tissue analysis should also be used to diagnose or confirm nutrient deficiencies, particularly where visual symptoms are confusing, not visible, or where multiple nutrient deficiencies occur. It is important to ensure that tissue analysis follows standard procedures. Pre-flowering is the preferred sampling time, but more frequent sampling is desirable to check and adjust nutrient status during periods of active growth.
In practice, the third and fourth leaf pairs down from the tip on an active primary branch, from a bearing crop, are most commonly sampled. Samples should consist of around 100 leaves selected in random from around 40 trees within the same 2-4ha block. Tables 1 and 2 give nutrient standards for macro and micro-nutrients based on plant tissue analyses.
Nutrient Ratios
Soil and leaf tissue analyses should also be used to assess nutrient imbalances. Where the critical values for any one of potassium, magnesium and calcium are exceeded, then uptake of other cations can be affected. For example, productive growth occurs when the K:Ca ratio in the leaf is around 1.7-2.1. Nutrient ratio tables can be an important guide to ensure nutrients are well balanced, but they should not be used as the main determinant for fertilizer rate.
