Phosphorus – What do we do with it and what does it do?

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Published April 14, 2020 | By Mike Petersen


Image Above:

The index finger is touching the 2nd most important nutrient for many crops we grow. Phosphorus


Last blog I spoke about placement and the wiser way to put it in a band right in the pathway of the row crops root system.


When you as a farmer place P & K and maybe some other elements such as S and Zn with a strip till rig we are putting it in something of a concentrated zone.  A caveat here – you do not have to apply the same amount as one would if broadcasting the material whether dry or liquid.  How much less you ask?  We have seen a reduction as much as 40% (ie: 90lb/ac or 100kg/ha reduction to 54lbs/ac or 60kg/ha) when banded at 6.5 inches deep (160mm). Today’s price at $19.50/cwt {dry 11-52-0} or $390/ton that can be a savings of 40% or a savings of approximately $7.00 per acre.  And that is just for the phosphorus.  Now folks that does not say it is the exact right thing for you if you are new to deep banding with a strip-till tool.  A good approach is to incrementally ratchet this down first year and so forth in the next season and so on.  Hundreds of seasoned Strip-Tillers have told us at Orthman, they can reach that goal of 40% in three years and maintain depending upon replacement or satisfying plant use needs with both tissue and soil tests.


A question for you.  As you hitch up the planter, are you using a Phosphorus component in your starter products? I ask this because the plant usage of P in the first days after the coleoptile erupts through the seed coat to 15-20 days after emergence N,P,K and other elements consumption is not much.  For P, it might be ~2 pounds per acre.


But where it is, is just what the realtor tells any one of us if we a buying a new home; location, location, location!  Nearest to the seedling root and the best products you can give that infant plant the better.  A salt laden fertilizer – bad idea!  I say that because that brand new tissue that erupted out of the seed is a lot like an infant human child’s skin.  Tissue burns, cellular breakdown, toxicity, pain – it all happens to this infant plant if we burn that seedling root.  Cooper and MacDonald back in 1970 published in Crop Science, that the preautotrophic stage in maize is 14 to 26 days after germination, that time frame is dependent upon air and soil temperatures.  After that short period maize becomes autotrophic, that is when photosynthesis plus root absorption do it all in the way of feeding the plants engine.  But during that time maximum number of leaves is determined and a certain number of other genetic switches are flipped on.  Soil temperatures after 20 days are warming along with daytime ambient temps.  Bacteria and fungi growth and activity is so minimal unless you supercharge it with a biostimilant that it is pretty imperative to have some nutrients close at hand.  This is dependent upon soil pH in the upper 10 inches (250mm) for the soil solution with inorganic or organic forms of P to be readily available.  Phosphorus is most available in pH’s of 6 to 7.  There are those that will tell you that starters are too expensive and they do not give a decent return or yield bump.  I like to say and do, “When your baby boy or daughter was fresh from the hospital did your wife quit feeding him or her?”  Didn’t think so, I ask again; does placement of nutrients have value/importance?  You bet your last dollar you bet on your college football team to win by 6 points over its archrival.


So what does P do in the plant?

Phosphorus in even the very first days out of the ground is beginning to start photosynthesizing.  Light energy is being used to split water to produce molecular O2, reduced nicotinamide adenine dinucleotide phosphate and adenosine triphosphate (Yoshida, 1981) which sends these NADP and ATP through the leaf to enlarge the plant, make it grow to a 12 foot (300cm) tall plant with an ear and kernels.  Note phosphate in those molecules – IMPORTANT!  Thus, phosphorus is essential for the general health and vigor of all plants. Some specific growth factors that have been associated with phosphorus are:


– Stimulated root development

– Increased stalk and stem strength

– Improved flower formation and seed production

– More uniform and earlier crop maturity

-Increased nitrogen N-fixing capacity of legumes

– Improvements in crop quality

– Increased resistance to plant diseases

– Supports development throughout entire life cycle


Another set of scientists from British Columbia, our neighbors to the north of us in the States, state this; “Phosphorus is important for all photosynthesis, maintenance and transfer of genetic code, development and growth of all new plant cells, and formation of seed.”  To me that is pretty doggone important.


As I reiterated last week in the Precision Tillage blog, early P consumption is minimal but by the time the sixth leaf collar is exposed the plant starts consuming P.   At what kinds of rates, about 0.42lbs/acre/day by the time it reaches tassle or VT.  Then during the VT to R2 stage the plant ramps up again and calls down to the roots or maybe by a foliar application for more phosphorus.  Nearly all of that rushes to the ear and all the kernels, putting on bushels or tonnes.


By R6 when we are near full starch line and drying down the maize plant has used phosphorus to grow cells of stalk, leaves, collars, tassle tissues, pollen, pollen tubes, cob full of kernels and god ole my favorite ROOTS.  Follow us along as I delve into Potassium in the coming weeks.  K is the big sister to nitrogen, remember that.


Definition of autotropic – An organism, such as a maize plant capable of synthesizing its own food and cellular growth from inorganic substances using light or chemical energy.


References I used in writing this article:

Fageria, N.K., Baligar, V.C., Clark, R.B., 2006;  Physiology of Crop Production., 345pp, Haworth Press, Birmingham, NY

Cooper, C.S., and MacDonald, P.W., 1970; Whole plant physiological and yield responses of maize to plant density., Crop Sci., 10:136-139

Yoshida, S., 1981; Fundamentals of Rice Crop Science. Los Banos, Phillipines: International Rice Research Institute


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