Maximizing Corn Phosphorus


Phosphorus soil

Phosphorus (P) is an expensive nutrient but critical for good crop production. Phosphorus is the backbone to the plants genetic code, for ATP (energy transfer/storage) in plants, and for cell division and enlargement. When P is severely limited, plants turn a purple color, which is common on cold wet soils in the spring. However, plants often have a hidden hunger for P which may limit yields.

Chad Penn, Research Soil Scientist for USDA from West Lafayette, Indiana at the Ohio No-till conference; shared recent research on corn P nutrition. Available P in soil varies by soil type and weather conditions. Farmers try to optimize P application, but it varies so much, even within a few inches or feet. Even with extensive soil testing and grid soil sampling, P is often either under applied or over applied. The ARS-USDA research is trying to find a way to put on just the right amount of P so that it maximizes yield.

Chad discussed the two main sources of soil P. The first fraction is the smallest which is the Labile or available P that is not held quite as tightly. This P is what the plant uses. The most common P type is the Non-Labile P which is tightly held but can become Labile slowly. Chad discussed three main processes for P soil cycling. First, soil P is released into solution which means it’s in a form that plants can utilize. Second, when it’s in solution it has to diffuse to the surface and third, P is taken up into the plants by the roots. Often, soil P gets deleted near the roots because it’s being absorbed so quickly, even though their may be more labile and plant available P just a short distance away.

Chad did some interesting experiments in a greenhouse. He used inert sand with no biology and fed the corn with nutrients. The corn was fed and watered and produced a good crop, just like ordinary corn. Using this method, Chad and his team of researchers discovered some interesting facts about corn and P fertilization. He fertilized the corn at various rates. To maximize corn yield, corn needs 580 milligrams (mg) of P per day per plant. However, corn will take up more P than it needs to maximize yield. This is called luxury consumption. If corn takes up too much P, yields may start to decline. The corn puts the excess P in the stems, stalks, and leaves. From 0 to a maximum of 580 mg/day for each corn plant; the P was distributed to maximize yield. From 580 – 730 mg/day, the excess P went to corn stalks and leaves and not yield.

Chad also looked at what happens to other nutrients. Once corn got above 580 -730 P mg/day, the potassium (K), magnesium (Mg), manganese (Mn), and boron (B) also stopped going to corn yield and were stored in the leaves and stalks. Chad’s analysis is that if farmers over apply P, it can cause corn plants to tie up other nutrients (K, Mg, Mn, B) in the corn tissue. Getting P nutrition right is important for maximizing crop yield and utilizing soil nutrients efficiently. Chad also looked at Nitrogen (N), Sulfur (S), and Iron (Fe). All these elements maxed out in the corn grain when P levels reached 580 mg/day/corn plant. When the level got above 580-730 P for corn, all the extra N, S, and Fe was put into the stem. These elements did not increase in the corn for grain so excess soil P seems to cause plants to stop producing higher protein (N, S) in the grain. Too much soil P can thus put a lid on grain quality or keep corn from increasing its nutrient value for feed. The excess nutrients are stored outside the  rain. If used for cattle as silage, these nutrient may still be used, but hogs and chickens and non-ruminants may not get the advantage.

The last category was the impact on zinc (Zn) and copper (Cu). Both Zn and Cu maximized in the grain just like the other nutrients at the critical 580 P mg/day level. Above 730 P mg/day, Zn and Cu and the excess were all stored in the roots and none extra in the grain. It is well known, that excess P ties up Zn and Cu. The plant needs Zn and Cu because they are co-factors to turn proteins into enzymes. Here's where soil biology comes in to help plants in the field. Arbuscular Mycorrhizal Fungi (AMF) supplies crops (corn, soybeans, wheat) with balanced plant available nutrients so that plants can achieve higher yields and higher levels of crude protein.