Published April 8, 2020 | By Mike Petersen
In the last Agronomic blog I here at PrecisionTillage.com, I began a conversation to look into plant use and efficiency of phosphorus in a fertilization scheme in high production Agriculture. Phosphorus is ‘the’ second most important nutrient to plant growth for nearly every crop we grow behind nitrogen.
Fig. 1. Estimated cumulative P uptake for maize as a function of grow¬ing degree days (GDDc on the Y-axis) for maize growth with vegetative (V) and reproductive (R) stages shown for “modern hybrids” (adapted from Bender et al., 2013a) and “older hybrids” (adapted from Ritchie et al., 1997).
Fig. 1. Estimated cumulative P uptake for maize which I will explain throughout this article.
What I am aiming to accomplish in this part, is to offer to the Phosphorus discussion is: smart placement of said P products, and why we scientists see P placement important in affecting plant growth and ultimately yield be it grain, forage or fiber. Some of you already know my perspective that roots are such an emphasis to me personally in this discussion, which zone of the rooting profile extracts/takes-up the nutrients (in this case P) and how we can enhance that use and uptake efficiency with the methodology of Strip-Till.
As you observe in this graphic (Figure 1.) to your immediate left in maize that older hybrids dropped off in P uptake at the V10 stage to a small degree and the newer, more recent breeding and selectivity of maize characteristics has given rise in thinking when later P fertilization gives desired outcomes are a little later. As new longer cellular life functions are bred into the maize hybrids, the P uptake curve changes into latter parts of the plants life. Early on in the life of the maize plant the uptake of P is (<5lb/ac) now known to be slightly less than observed before (prior to somewhere around 1996-2000) just when genetic modifications were really getting off the ground. With the successes here in the United States of 400, then 500+ and now {2019} >600 bushels per acre (10.9T/hectare to 13.6T/ha to 16.3T/ha) the P needs and P uptake curve has been altered. Growers should be changing their thinking and what should be their P fertilizer recommendations. In some instances the step-by-step approach of incrementally fertilizing for P looks daunting compared to the big juggernaut load prior to planting. Loading up front with P and the propensity of soil systems to tie-up P appears to me an inefficient way to feed this crop, maybe any row crop we grow. Especially as you look at V10 and then R2 stages (see black solid line in Figure 1). I try to wrap my agronomic mind around that amount of maize coming from one hectare or one acre when I think of those kinds of yields – Wow!
Figure 2. Early corn root system with 1st nodal roots emerging with banded nutrients with planter and deeper placed with 1tRIP tool (yellow blotches)
Back to considering Figure 1 folks, I ask this age ole question: have we been carrying out our Phosphorus fertilization practices to feed the soil, the organic matter complex in the soil, as well the unfortunate calcium tie up mechanisms in our Western U.S. soils or – are we seeking to best feed the plant? Okay, you are giving that some thought, which is good. Let us next consider the earlier root system of the maize plant (seedling root to Nodal system 1 and then extending to the beginning of nodal stage 2 development). Where one places nutrients via broadcast and using tillage to mix to feed the very limited number of roots and root hairs, the surface area of all roots in the first 15 days after emergence could make an incredible difference in those days of growth and future days ahead. [See figure 3] Then as you consider the placing those nutrients including P as a starter mix in the seed trench or along either side of the trench, associate that with pre-plant placing P by 1tRIPr tool is seen in Figure 2. In this depiction (Figure 2) the roots can run into an initial amount of addition of nutrients and then as the deeper seedling root obtains the deeper placed materials the root can proliferate and take in another dose. I will chance repeating myself here; roots have to physically run into nutrients whether liquid or dry for osmosis, diffusion and mass flow to gain access to them. The two dark background images (Figures 2 & 3) are what one observes at 15-18 days after emergence stage as the soils are beginning to warm above 55 degrees F. at 6 inch depth. As soils warm at the depth of 6 to 9 inches (15 to 23cm), bacteria and mycorrhizae that live on and in roots do rapidly populate and fungi infect roots. Both bacteria and fungi gain activity, access and breakdown for the plant what we add of nutrients and then the plant roots absorb. Numerous scientific articles from worldwide research studies (Netherlands, UK, India, Pakistan, Australia, United States to name a few) have looked in depth at how hundreds of bacteria species along with mycorrhizae do feed the plant hosts through the root system. Mycorrhizae are of prime importance in absorbing P and feeding its host plant very efficiently of which maize is dependent upon.
Figure 3. Early corn root system with 1st nodal roots emerging, colored dots depict nutrient products after surface broadcast & mixing
The maize plant may have 85 to 110 square inches of root-to-soil surface area which I have done the measurements (look again at Figures 2 & 3) at this V3-V4 stage for absorbing water and nutrients. It is very important that the P products are placed right near the root system to efficiently and effectively supply nutrients to the fast growing plant. I have to remind myself, that plant roots do not grow upwards towards the surface where broadcast fertilization drops N,P,K etc. Gravity pulls roots downward – you physically place said products in the pathway of the root growth – Violá!
As the soil temperature warms to 63° then up to 75° the bacteria are ramped up to a near frenzy and are working on converting inorganic P source products or taking it off the organic complex right in that zone of 6 to 9 inches below the surface – back to Figure 1, we are right in the steep up-climb of the maize plants needs. We see the roots that are in this zone with their symbionts of fungi and billions to trillions of bacteria working in harmony together. Up near the soil surface the soil temperature is rising into the 90 degree range and bacteria die back and the fungal hyphae shrivel and die. Why we to think the plant roots will be effective at gaining access to surface applied and lightly mixed to roots that are dying due to heat and desiccation? It is about placement folks into where an abundant root system will proliferate and using a tool that helps the grower conserve moisture, allow residue to protect and insulate the soil surface, water to infiltrate better, feed the biological life, use less fuel to prepare the seedbed and a host of other benefits.
All of it works together so beautifully folks. The amounts of N,P,K we place is your choice. Fertilizing as a pre-loading the soil up with broadcast rates in a strip till system approach is not the most wise, you are becoming more efficient with strategic placement, please be smart about this. May this article be helpful to you as you get after it this spring and into the future. I will be getting Potassium info ready and up and running so you will reading that in the coming weeks.
References I used for preparation of this article:
Battini, et.al, 2017, Facilitation of phosphorus uptake in maize plants by mycorrhizosphere bacteria. Scientific Reports in Nature Publishing Group, Scientific Report 2017; 7:4686
2. P.S. Bindraban, et.al. 2019, Exploring phosphorus fertilizers and fertilization strategies for improved human and environmental health., Biology and Fertility of Soils 56:299-317
3. D.P. Schachtman, et.al., 1998, Phosphorus uptake by plants: from soil to cell. Plant Physiology 116:447-453
4. A.E. Richardson et.al., 2005, Utilization of soil organic phosphorus by higher plants. Organic phosphorus in the Environment. CABI-Wallingford 165-184
5. Schnepf, et.al., 2008, Impact of growth and uptake patterns of arbuscular mycorrhizal fungi on plant phosphorus uptake – a modelling study. Plant Soil, 312:85-89
6. M.J. Harrison et.al., 1995, A phosphatic transporter from mycorrhizal fungus Glomus versiforme. Nature 1995; 378:626-629
7. S.M. Kaeppler, et.al., 2000, Variation among maize inbred lines and detection of quantitative trait loci for growth at low phosphorus and responsiveness to arbuscular mycorrhizal fungi. Crop Science 2000; 40:358-364
8. G. Hopkins & Niel Hansen,2019, Phosphorus Management in High-Yield Systems., Journal of Environmental Quality, 48:1265-1280
