Is anyone else missing the Christmas carols? Because we’re in the midst of the 12 Days of Christmas, and because the lack of seasonal music has me feeling a little deflated, I’m going to borrow the theme of the beloved Christmas carol “The 12 Days of Christmas,” and turn it into the 12 days of crop nutrients.
Partridge in a Pear Tree – or Phosphorus (P)
The alliteration here demands that we feature phosphorus first.
Phosphorus is an essential plant nutrient and very important for numerous plant processes and crop production. It is a vital component of DNA and RNA, the building blocks of proteins and protein synthesis. The adenosine triphosphate molecule (ATP) molecule is responsible for storing and transferring all of the energy produced and needed by the plant. At the core of this ATP molecule are phosphates, responsible for all of the activity of ATP. Phosphorus also plays a major role in the stimulation of new root growth.
So, P is Important
Our crops clearly need phosphorus to thrive. So, what do we need to worry about when supplying P? “Tie up” within the soil is the primary concern with phosphorus fertilizers. In acidic soil conditions, P will tend to get tied up by iron, aluminum, and manganese. In basic soil conditions, calcium will be the major component of phosphorus tie up.
Phosphorus is most available to the plant in a soil pH range of 6.3-6.8. Common liquid fertilizers, such as ammonium polyphosphate (10-34-0) and orthophosphate (9-18-9), applied in the early spring will also have a likely chance of being tied up if a gypsum application was made in the fall.
Choosing a phosphorus fertilizer that is protected from tie up will ensure that you get the most out of your fertilizer investment and that your crop will receive the required amount of phosphorus needed.
Available P versus Usable P
Not to mention, applying phosphorus as a crop nutrient can be tricky. Just because phosphorus was applied to the soil does not mean that it is doing what you want it to do: feed the plant! AgroLiquid founder, Douglas Cook, was known to say that all applied fertilizer is available, but not all applied fertilizer is usable. Sounds funny, but it’s true. What’s the difference? All fertilizer is available to plants — it’s right there for the taking. But it may not be usable. In order for a nutrient to be usable, it must be close to the roots and it must be in a form that the plant can absorb.
Nutrients like nitrogen can be lost to leaching or volatility before absorption. Potassium can be strongly held by clay in the soil and not able to be taken up by roots since it is not in the soil solution. Phosphorus can also become unusable. Phosphate is negatively charged and can react with, or be fixed, by positively charged elements in the soil (cations). Plants cannot take up these compounds of calcium phosphate, aluminum phosphate or iron phosphate. Estimates are that the crop will utilize only around 20% of applied phosphate fertilizer during the season after application, and in following years, the amount becomes progressively less as it reverts to mineral forms. Again, the nutrients are there and available, but they are not always usable.
Out of Sight, Out of Mind
You cannot actually see the fate of phosphate molecules in the soil, so it’s not necessarily something growers are thinking about. If only a small percentage of your planted seed came up, you would probably be mad because you can see that loss. Similarly, only a small percentage of the applied phosphate is usable. However, you cannot see this, so it is not a concern. But it should be.
Placement is Key
Phosphate fertilizer works best if it is placed close to the seed at planting. In the picture at the left, it is apparent that phosphate fertilizer placement is affecting growth. Five rows of the plot had 5 gal/A of Pro-Germinator applied through the planter, and the sixth row had no planter fertilizer.
The rows with the In-furrow placement are tasseling, whereas the 2×2 placement has yet to tassel. Close inspection shows that the corn with the 2×2 placement is taller than the row with no fertilizer, but it is behind the rows with the in-furrow placement. This shows that phosphorus placement for earliest root access affects plant growth and yield. Additional testing at the North Central Research Station has shown that in furrow placement can out-yield 2×2 placement by almost 5 bu/A.
In order for phosphorus fertilizer to be most effective, it needs to be usable. Usability is increased by placement close to the seed row and protection from fixation losses. Pro-Germinator is the only fertilizer that does both.
Common phosphorus deficiency symptoms:
- Stunted plants
- Leaves may be darker green or begin purpling
- Leaves may curl upward
- Maturity can be delayed
- Poor seed set
- Poor fruit quality