Understanding the plant analysis report

NCDA&CS Agronomic Division 1040 Mail Service Center, Raleigh NC 27699-1040 (919) 733-2655 www.ncagr.com/agronomi/ Understanding the Plant Analysis Report WWW.ncagr.com/agronomi/pwshome.htm Steve Troxler, Commissioner of Agriculture 100 - 2 13 >h ь- o -5 о 6 25 50 75 Nutrient Index Value 100 124 Healthy plants contain predictable concentrations of the elements (nutrients) required for normal growth and development. Plants need primary nutrients (N, P, K) in greatest quantities, secondary nutrients (Ca, Mg, S) in lesser quantities and micronutrients (Fe, Mn, Zn, Си, B, Mo, Cl) in very small amounts (Table 1 ). Plants get all these nutrients from fertilizer and/or the soil. Three other elements that plants need — hydrogen, oxygen and carbon — come from water and the atmosphere. Standard plant analysis measures concentrations of 1 1 essential elements (N, P, K, Ca, Mg, S, Fe, Mn, Zn, Си, B). Additional tests can be requested to measure Cl and Mo. Concentrations of primary and secondary nutrients are reported as percentages; micronutrient concentrations are reported in parts per million (ppm). The plant analysis report also presents results as index values that make it easy to interpret results in terms of plant health and productivity. The concentration for each element is converted into an index value (0-124), which falls into one of five interpretative categories (Figure 1 ). An index of 50-74 indicates that the nutrient concentration is sufficient for optimum growth and yield. Low (25-49) and deficient (0-24) index values indicate that the nutrient concentration is below the desired level and may be contributing to reduced growth, yield and/or quality. In such cases, supplying that nutrient to the crop at the optimum time and under optimum environmental conditions will result in an increase in growth and/or yield (Table 2). Values in the high range (75-99) are not normally detrimental to growth or yield but, under some circumstances, may negatively impact crop quality. When values are in the excess ( 1 00+) range, growth problems may result due to nutrient imbalances or, in the case of micronutrients, toxic reactions. Values above 75 may indicate overfertilization and poor allocation of resources. The critical value indicates the point at which a nutrient shortage causes a 5 to 10% loss in yield or growth; the point of mild toxicity indicates the same degree of loss due to nutrient excess. As the index decreases below the critical value or increases above the mild toxicity point, growth or yield will continue to decrease proportionately. The N:S, N:K and Fe:Mn ratios listed on the report indicate degree of balance among some essential elements. Figure 1. Nutrient Index Interpretation Scale Table 1. Nutrient abbreviations N Nitrogen Fe Iron Cl Chloride P Phosphorus Mn Manganese Na Sodium К Potassium Zn Zinc Ni Nickel Ca Calcium Cu Copper Cd Cadmium Mg Magnesium В Boron Pb Lead S Sulfur Mo Molybdenum NO,-N Nitrate nitrogen Table 2. Expected response to nutrient applications Index 0-24 25-49 50-74 75-99 100-124+ Interpretation Deficient Low Sufficient High Excess Crop Response High Medium Low None None May 2006