Tissue Testing: the Crop Check-up

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06 0711 Tissue Testing

Recently an interesting phosphorus (P) question came over our network chat that peeked my interest. Tanner Pollack, an Agri-Coach and owner of Solar Agri Services Ltd in High Prairie made this observation.

“I am working on crop plans for one of my clients. He uses a drill that puts all the fertilizer 1” to the side and 1” below the seed. He has very aggressive yield targets, so we are typically putting down 100+ lb N, 35+ lb P, 20+ lb of K and 20+ lb S per acre on wheat and canola, all as dry product. The peas, typically, do not have any fertilizer applied with them.

I can't help but wonder if this is a great example of how the high N is keeping roots of young plants away from the immobile nutrients in the band.”

I think Tanner answered his own question!YES, the high rates of N as urea or other N fertilizers produce high levels of ammonia-N in the band, which is toxic to roots and limits early season uptake of nutrients from the fertilizer band. This reduces response to P and hence final yield, especially for crops such as canola.

The chemical nature of the fertilizer band can affect nutrient utilization from the fertilizer band, particularly during the seedling stage

The chemical nature of the fertilizer band can affect nutrient utilization from the fertilizer band, particularly during the seedling stage. High concentrations of fertilizer salts and/or high concentrations of fertilizer products such as ammonia can restrict root growth into the fertilizer band and restrict nutrient utilization causing nutrient deficiencies at a very critical growth stage even though sufficient nutrients were added close to the seed or seed-row. In addition, zone acidulation can solubilize relatively high nutrient concentrations, which
can be a good thing in high pH soils but potentially, negative in low pH seedling environments.

It is well known that P fertilization should increase P content of plants during the early to late seedling stages for best yield increases. Table 1 demonstrates how both placement and the chemical nature of P fertilizer bands affect fertilizer P uptake in seedling plants and at flowering and the resultant effects on canola yield.

06 0711 Tissue Testing Table 1

The plants grown with seedplaced P started using the P at emergence, which occurred at 8 days after seeding. Fertilizer P uptake was delayed, in comparison, for all other treatments. Delay in uptake of P was greatest with N (urea) and P dual bands and least with the separate bands. The delay in initiation of P uptake for the separate N and P bands is simply due to time needed for plant roots to grow from the seed row to the P fertilizer band, a distance of about 3”. The large delay in initiation of P uptake for the N (urea) and P dual band was due to:

  • distance between seed row and fertilizer band 
  • high concentrations of ammonia in the band prevented root growth into the band.

Phosphorus banded with nitrogen fertilizers such as ammonium sulphate or ammonium nitrate, result in lower pH in the fertilizer band and/or low or lower concentrations of ammonia that had less adverse effects on root growth. Increasing time between banding and seeding, allowing the N/P band to dissipate reduced the ammonia concentrations, reduced the time to the start of fertilizer P uptake. P uptake from the fertilizer at the later growth stages was not as effective in increasing yield, as was P use from the fertilizer in the very growth or seedling stage. Thus, yield with the N (urea) and P dual band was only 57 % of the yield with P placed with the seed.

It is for those reasons that we usually recommend that the large part of the P requirement be banded with the N at or prior to seeding and a portion applied at seeding with or close to the seed as a “starter”. For crops such as canola, where risk of seed injury is high when P fertilizer rates are higher than about 15 to 20 lb P2O5 /acre, a combination of dual N and P bands and P placed close to the seed is an excellent method of P supplementation. The dual band permits the application of sufficient P for high yields whereas the P placed close to the seed
supplies P to the plant in the early stages and maximizes yield benefit. “Starter” P is very important for canola since delays in initiation in uptake of P from N and P dual bands are greater for canola than for crops such as wheat.

The reason peas aren’t showing low in P or K in the tissue samples in Tanner’s example is two fold:

  1. Fertilizer was not added to create a hostile rooting environment
  2. Peas are very adept at rooting out any P or K available in the soil while canola and cereals are less adept.

Tissue analysis is a great way to check to see whether your crop is making the most of the nutrients you applied and to check up on the crops general well-being. Think of it as an annual physical for your crop – same this as your doctor checking your vital signs – respiration, BP and heart rate - making sure the diet and exercise program are working for you. If you’re like me and hate visiting the Dr., then think of a tissue test like you would your truck’s 51 point inspection just before hooking up to the trailer for your summer vacation.

On the next page is a tissue analysis for a winter wheat field taken earlier this year from an area that for various reasons did not receive adequate fertility at seeding.

06 0711 Tissue Testing Table 2

At this stage in a plant’s growth, for big yields, we would like to see much higher than normal range N levels because this crop still has a long way to go to maturity. While S is in the normal range, when looking at the N/S ratio we see that the ratio is much higher than expected indicating an imbalance between the N and S. In this case, the plant may be unable to take advantage of the available N because of the shortage of S. Tissue P is low as is tissue K and the N/K ratio indicates they are out of balance but because the K/Mg ratio is low if we add more K, we will create a greater K/Mg imbalance if we don’t address the Mg. Looking at the micros, Zn and Fe look good while Mn is low, and B and Cu are very LOW.

At this stage, this wheat crop is losing yield big time!

Now here comes the tricky part. Depending on:

  • the target yield goal
  • early environmental growing conditions (cool wet or cool dry springs will slow down specific nutrient release)
  • fertility program/placements (how much of what was placed where, is manure involved, etc.) 
  • and current yield potential (a good agronomist needs to integrate all of this!)

Depending on the answers to and integration of the above, this field potentially could benefit from:

  • In crop N and S - Streamed, dribble banded or floated to recapture yield potential!

  • Foliar application of P (maybe B) - If this is a big crop this will help us get over a temporary P insufficiency that has been caused by placement and/or environmental issues. Foliar P will help drive roots, (as would foliar B) which often will aid with better access to the K and Mg we know is there from the soil test through expanded rooting depth and soil contact.

  • Foliar micronutrients – because this is winter wheat my focus is on the extremely low Cu with the realization that the best timing is boot/flag stage in most instances. The very low B serves as a warning for next year’s canola crop and I’m going to keep a close eye on Mn in all crops! A follow-up crop check-up tissue test in 3-4 weeks may be warranted, if this crop continues to show larger than yield goal potential.

  • While many use tissue testing as a helpful method to diagnose and correct any immediate deficiencies, tissue testing is especially useful in making long-term fertilizer and seeding system decisions.

So take a tissue test; connect all the dots and find out what your crop is really telling you, you might be surprised!


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