AGRONOMIC NEWS ITEMS
From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335
Summer 2001, No. 6
Plant tissue analysis is the determination of essential nutrient concentrations in sampled plant tissue. It complements a sound soil testing program and can help identify opportunities for more efficient nutrient use. It is useful in identifying hidden hunger, imbalances or toxicities, the performance of fertilization and nutrient management programs, and the sufficiency of nutrients not evaluated in routine soil tests (e.g. sulfur, zinc, iron, copper, manganese and boron).
Nutrient levels in plants vary with stage of maturity, plant part sampled, hybrid or variety, and environmental or climatic conditions. Most published interpretations of plant nutrient sufficiency levels are based on plant sampling near, or at, reproductive growth. Sampling this late in the season provides more of a “rear-view mirror” look at nutrient sufficiency. Sampling earlier in the season can help identify deficiencies in time to make corrective nutrient applications, to avoid large economic losses. Where soil moisture and rainfall are adequate, many crops can still respond to applications of potassium, sulfur, nitrogen, and micronutrients as late as early reproductive growth (e.g. silking to tasseling for corn, flowering to early pod-filling for soybean, squaring to boll-filling in cotton). Of course, the objective should be to prevent deficiencies before the rapid vegetative growth and reproductive stages.
Plant analysis can be an excellent diagnostic tool early in the season to compare nutritional differences between “normal” and “abnormal” parts of fields. For corn and sorghum, whole above-ground plants can be sampled at the three to four-leaf stage. In young soybeans, the uppermost mature trifoliate leaves can be sampled (often the third to fourth trifoliate below the terminal). For pastures and hay meadows, forage can be cut with a knife, clippers, or scissors above the ground line. Special care is needed to avoid soil contamination, which could confuse analysis for nutrients like iron and manganese. Remember that the concentration of nutrients in young plants should be higher than in plants collected at blooming or silking. Most laboratories can provide an analysis and interpretation for samples collected at different growth stages. However, it is important to communicate with the laboratory before sampling to ensure that appropriate sampling and shipping procedures are followed. Be sure to advise the laboratory of the plant growth stage at sampling, by including that information with your samples.
The results of plant analysis alone should not be used to make fertilizer recommendations. Most diagnosticians prefer to consider plant tissue analysis along with soil test results, a record of lime and nutrient applications (including any manure), cropping history, and recent crop protectant applications. Consider using a laboratory that can demonstrate proficiency in analytical testing and which can provide a reasonable turn-around on the results, with clear interpretation. With today’s express shipping services, modern analytical and communication technologies, results can be in the hands of farmers within four to five days after sampling. Costs may range from $12 to $20/sample, depending on the number of nutrients analyzed.
Contact your analytical laboratory, Certified Crop Adviser, fertilizer dealer, or county Extension agent for more information on plant tissue analysis. Use plant tissue analysis in 2001 to ensure that your crops are getting all the nutrients needed to make good yields for profitable production.