Low K, B and S in Tissue Samples

Tissue testing is in full swing this summer and at a rapid pace. More growers and agronomists are evaluating tissue tests to learn more about the effectiveness of their fertility programs. There are some common areas of concern arising this year. As the ALGL agronomy staff review and approve tissue test data before delivery to the customer, a trend for low sulfur, potassium, or boron is developing. The calls from growers and agronomists about these nutrients confirm that they are seeing this trend as well.

Tissue tests are very good at validating whether the crop can access the nutrients in the soil. When a tissue test comes back low for a nutrient the first question becomes, is the nutrient in the soil and the plant cannot access it, or is the nutrient deficient in the soil? Therefore, a soil sample, taken in conjunction with a plant tissue sample, is very useful.

One likely reason explaining low tissue test results for these three nutrients is a deficiency in the soil. Our annual average soil test values for these nutrients have been decreasing over the past 20 years. Less nutrient in the soil increases the probability that plants may not be able to access adequate quantities. Potassium soil test levels have been decreasing at an average rate of 0.5 ppm/year over the last 23 years. Sulfur soil test levels (measuring plant available sulfate) has declined at an average rate of 0.5 ppm/year and boron has declined on an average of 0.02 ppm/year over this same 23-year time span. This may not seem like much, but the soil test values of sulfur and boron are approximately half of what they were 20 years ago. These declines are being attributed to crop removal and/or leaching, out pacing nutrient application.

The second challenge leading to limited plant access to nutrients is weather related. Dry soil conditions can reduce the movement and uptake of all three of these nutrients in the soil, and we have seen those conditions in portions of our trade area recently. Reduced root exploration of the soil due to soil compaction is also a contributing factor in many fields. Soil compaction from traffic and tillage of wet soil the past few years have led to compaction layers restricting root growth. Heavy rains can leach both sulfur and boron, and sometimes potassium in specific situations, below the resulting shallow root zone.

Soil testing is valuable tool in ensuring you have the need foundational soil fertility for a productive crop, but tissue testing identifies if the crop can access and utilize this fertility.