Soybean leaf tissue analysis involves sampling the top fully developed trifoliates (three leaflets plus petiole) at first flowering. Take at least 20 trifoliates collected randomly from the area in question. Table 1, Interpretation of Plant Analysis for Soybeans, shows expected values at first flower.
It’s important not to contaminate leaf tissue with soil. Do not collect severely damaged or dead leaves. Samples should be shipped fresh if possible or dried in the sun or at low temperatures. Samples must be shipped in paper bags, not plastic to prevent spoilage. Do not sample if foliar fertilizers have been recently applied.
Sampling at times other than first flower may be necessary to diagnose deficiency problems in a field. In that case, take samples from both deficient and healthy areas for comparative purposes. Taking a soil sample from the same area and time as the plant sample will help with diagnostic interpretation. When samples are taken later than first flower nutrient contents may not correspond to the values given in Table 1.
Table 1. Interpretation of Tissue Analysis for Soybeans
| Values apply to the top fully developed leaf (3 leaflets plus petiole) at first flower. | ||
| LEGEND: – = no data available | ||
| Nutrient | Critical Concentration1 | Maximum Normal Concentration2 |
| Nitrogen (N) | 4.0% | 6.0% |
| Phosphorus (P) | 0.35% | 0.5% |
| Potassium (K) | 2.0% | 3.0% |
| Calcium (Ca) | – | 3.0% |
| Magnesium (Mg) | 0.10% | 2.0% |
| Boron (B) | 20.0% | 55.0% |
| Copper (Cu) | 4.0% | 30.0% |
| Manganese (Mn) | 14.0% | 100.0% |
| Molybdenum (Mo) | 0.5% | 5.0% |
| Zinc (Zn) | 12.0% | 80.0% |
| Source: Yin, Xinhua and Tony J. Vyn, 2002 | ||
| 1 Yield loss due to nutrient deficiency is expected with nutrient concentration at/or below the “critical” concentration. 2 Maximum normal concentrations are more than adequate but do not necessarily cause toxicities. | ||