Supercharging your phosphorus fertilizer Does it work? Plant requirements for P Phosphorus dynamics in the soil

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1 Supercharging your phosphorus fertilizer Does it work? Dr. Cynthia Grant, Agriculture and Agri-Food Canada, Brandon Research Centre, Box 1000A, R.R.#3, Brandon, MB R7A 5Y3 Plant requirements for P Phosphorus fertilization is a major input in crop production, as many soils lack sufficient P to optimize crop production (Nyborg et al. 1999). Effective phosphorus management requires that nutrients be available to the plant in adequate amounts when needed by the crop. With P, ensuring that the nutrient is available to the plant early in the growing season is of particular importance. Phosphorus is critical in the metabolism of the plant, playing a role in cellular energy transfer, respiration and photosynthesis (Glass et al. 1980). Light energy absorbed by chlorophyll during photosynthesis is stored in adenosine triphosphate (ATP) and serves as the primary source of energy for energy-requiring biological processes. Phosphorus is also a structural component of the nucleic acids of genes and chromosomes and of many coenzymes, phosphoproteins and phospholipids. An adequate supply of P is therefore needed from the earliest stages of crop growth to support cell division, growth and establishment. Symptoms of P deficiency include decreased plant height, delayed leaf emergence and phasic development, and reductions in tillering, secondary root development, dry matter yield and seed production (Glass et al. 1980; Grant et al. 2001; Hoppo et al. 1999). Early season limitations in P availability can result in restrictions in crop growth, from which the plant will not recover, even when P supply is increased to adequate levels. Crops utilize and remove relatively high amounts of P. A 45 bu/acre spring wheat crop removes about 24 lb P 2 O 5 acre -1 in the seed, with an additional 10 lb acre -1 taken up but recycled in residue, giving about 34 lb acre -1 needed for growth. A 40 bu acre -1 canola crop removes about 38 lb P 2 O 5 acre -1 in the seed, and needs around 58 lb P 2 O 5 acre -1 for growth. All of the P does not have to come from fertilizer application in a given year as the plant can access P from the soil. In the long-term, P inputs should be balanced with P removal in the harvested crop to avoid P accumulation or depletion. Phosphorus dynamics in the soil Phosphorus is present in the soil in both organic and inorganic forms (Figure 1). Plants absorb P from the soil solution, mainly as inorganic orthophosphate ions, although a limited absorption of soluble organic phosphates may also occur (Schlegel and Grant 2006). As with N, mineralization of organic matter can release inorganic P while immobilisation can convert inorganic P to organic forms. The P in the soil solution reacts with the surfaces of secondary soil minerals and other compounds through adsorption and precipitation, reducing the concentration of inorganic P in the soil solution. Phosphorus is lost from the soil systems through crop removal. Phosphorus bound to soil particles can be lost from the system through erosion while P in the soil solution can move through surface runoff. These paths of loss are greater for P situated near the soil surface. Leaching of P may also occur, particularly in highly manured systems in regions where heavy P applications have been made and in areas of high precipitation (Sanchez Valero et al. 2007). However, from a fertilizer management perspective, the major factor leading to loss in P use efficiency is the fixation of P. Phosphate fertilizer reacts with calcium (Ca) and magnesium (Mg) to form Ca and Mg phosphates in high ph soils and with iron (Fe) and aluminium (Al ) oxides in low ph soils to form Fe and Al phosphates (Sample et al. 1980). The reaction products formed over time are less soluble than the fertilizer products added, reducing the plant availability of the applied P. It is commonly suggested that the use efficiency of fertilizer P by crops ranges from 10 to 30 percent in the year that it is applied. However, the recovery of P in the long-term can be substantially higher, since the P can be also be accessed by the crop in subsequent years (Syers 2008).

2 Phosphate Fertilizer Soil Solution P Plant Uptake Primary Minerals (Apatite Lower Availability Organic matter Adsorption on Mineral Surfaces Secondary Ca and Mg phosphates Figure 1: Phosphorus forms and reactions in the soil 140,000 P2O5 (tonnes) 120, ,000 80,000 60,000 40,000 20,000 P Removed P Added Source: Johnston 2006 Figure 2: Balance between P inputs as fertilizer and manure and P removal in the harvested crop for Manitoba between 1965 and 2005.

3 Principles of P Management Effective P management for crop production requires that a growing crop can access adequate amounts of available P when the P is required for optimum crop growth. Phosphorus supply during the first 2 to 6 wk of growth tends to have a large impact on final crop yield in most crops; therefore, it is important that P fertilizer applications are managed in a way that ensures early season access of the fertilizer by the growing crop. Where the supply of plant-available P in the soil is high, the soil may supply sufficient P to the plant to optimize economic crop yield (Nyborg et al. 1999). If P supplied from the soil and seed reserves is inadequate to support optimum crop yield, fertilizer applications can supply P to the plant. Specific plant factors as well as environmental factors such as soil temperature, moisture, and compaction, will all influence the ability of the plant to absorb sufficient P to support optimum growth. In the Canadian prairies, soil ph is generally high (greater than 7.0), with the exchange saturated by calcium and magnesium and so P will react to form sparingly soluble calcium and magnesium phosphate compounds that are less available to the plant than the fertilizer. Therefore, P will not move very far from the fertilizer granule, with the reaction zone generally being significantly less than one inch in diameter. Placing the band in a position where the soil does not dry out early in the season avoids having the fertilizer "stranded" on the surface of the soil where the roots cannot use it. Many plants are able to proliferate their roots when they contact a concentrated source of P, such as a fertilizer reaction zone (Strong and Soper 1974a; Strong and Soper 1974b). In addition, placing the P in a band in or near the seed-row allows the highest possible concentration of roots to contact and utilize the band soon after emergence. This allows the plant to effectively extract the P from the band, utilizing the P efficiently. Therefore, fertilizer P is most efficiently used when seed-placed or placed in a band close to the seed. Placement near the seed-row is most important in soils with low P where plant demand for P can outstrip its ability to take up P from the soil. In P-deficient soils with a high P fixation capacity, the optimal method of supply P for early crop growth is generally by banding the fertilizer near to or with the seed, during the seeding operation (i.e. use of Astarter P@). In particular, P availability may be low with cold soil temperatures because of slower diffusion rate, reduced root growth, less availability of native soil P, possibly greater relative physiological demand for P. Therefore, crops are more likely to benefit from starter P placed near the seed when soils are cold than when soils are warmer. The rate of P fertilizer must be high enough to allow each seedling access to a P granule or droplet early in the season. Cutting the fertilizer rate too low may restrict plant access to P because there are not enough fertilizer granules or droplets to provide physical proximity each germinating seedling ( accessed December 20, 2010). The physical distribution of the fertilizer in relation to the seed will be

4 Grain yield, bu/acre affected by seed-bed utilization (SBU), so a higher fertilizer rate may be needed with a greater SBU to ensure fertilizer-seedling contact. Effectiveness of Various Phosphorus Fertilizers The most common form of phosphorus fertilizer used in the Canadian prairies is monoammonium phosphate (MAP), which provides P in the form of orthophosphate. The most common fluid form is ammonium polyphosphate (APP), which provides both polyphosphate and orthophosphate forms ( Both MAP and APP also contain ammonium, which increases the availability of the P for crop uptake. Therefore, both of these fertilizers are good forms of available P for plant uptake. Plants take up P in the orthophosphate form, however polyphosphate converts rapidly in the soil to the orthophosphate form. Half of the polyphosphate in APP is usually converted to orthophosphate within a week, although the conversion may be slower if soils are cool and dry ( Under field conditions, there is normally no difference in effectiveness between P supplied as orthophosphate or polyphosphate (Figure 3) a b Simplo t M AP or Omex plus TP A Alpine Alpine AVA

5 Figure 3: In field studies conducted by Tom Jensen near Brandon, MB, there was no significant yield advantage of fluids over granular or orthophosphate over polyphosphate (values under the same red line are not statistically different). Phosphorus can be applied in fluid forms such as APP or Alpine formulations or in dry forms such as MAP or DAP. Research in Australia has shown greatly improved efficiency by using fluid formulations such as APP or even dissolved MAP solutions instead of dry granular fertilizer (Bertrand et al. 2003; Bertrand et al. 2006; Holloway et al. 2001; McBeath et al. 2005; McBeath et al. 2007). These studies were conducted on dry, highly calcareous soils where precipitation of P with Ca was rapid. The reason for the improvement in effectiveness with fluid fertilizer sources was proposed to be that soil moisture moving towards the dry fertilizer granule carried Ca that rapidly precipitated the P, limiting the size of the fertilizer reaction zone and the ability of the plant to access the P. With fluid sources, the fertilizer was not precipitated as rapidly and the size of the reaction zone was larger, increasing the fertilizer availability. While similar reactions have been reported on Manitoba soils (Racz and Soper 1970; Racz and Soper 1967) a similar difference in crop response to fluid versus dry sources has not been observed (Figure 3Figure 4). In the Australian studies the soils were much more highly calcareous than we see in Manitoba and the growing conditions tend to be drier, which could be the reason for the differing results.

6 Figure 4: Effect of fluid ammonium polyphosphate (APP) as compared to granular monoammonium phosphate (MAP) applied at 20 kg P 2 O 5 ha -1 on grain yield of wheat on a clay loam (CL) and silty clay (SiC) soil, averaged over three years (Grant unpublished). Avail is an additive, maleic-itaconic co-polymer, that can be applied to either granular or liquid P fertilizer ( It is designed to sequester antagonistic metals in the soil around the fertilizer granule to reduce the tie-up of phosphorus and keep it in a plant-available form throughout the growing season. Numerous studies on corn, winter wheat and potatoes conducted in the United States as well as studies with wheat in Alberta report benefits of using Avail with band-applied P ( accessed December 20, 2010). A study conducted by AgQuest in western Manitoba also reported a benefit of using Avail with canola (Table 1). There is little published information on the benefits of Avail, however, and much of the unpublished research conducted in the prairie provinces shows little benefit with use f the product (Figure 5, 6 and 7). Research is continuing to better assess the potential for use of this product under prairie conditions.

7 Grain yield, bu/acre Table 1: Effect of monoammonium phosphate fertilizer and Avail on tissue P concentration and seed yield of canola (soil ph 7.6 Research by Ag. Quest) ( (November 29, 2007) Avail + Avail Phophorus rate, lb P 2 O 5 /acre Figure 5: Yield of wheat in 6 site years of trials conducted on the prairies was similar with MAP, with and without Avail application (Karamanos Unpublished).

8 Potato Yield (cwt/acre) Control Sideband 20 Sideband 40 Sideband 80 Avail 40 Broadcast 40 Figure 6: Potato yield in trials conducted at Portage and Carberry between 2007 and 2009 was improved by side-banded MAP but was not affected by addition of Avail (Gaia Consulting accessed December 20, 2010) Figure 7: Effect of MAP with and without Avail and a polymer coated MAP product on wheat grain yield on a CL and SiC soil, averaged over 3 study years (Grant Unpublished).

9 Polymer coatings may control the release of P into the soil solution to slow the formation of sparingly soluble P compounds and increase the supply of crop-available P. Controlled release monoammonium phosphate (MAP), diammonium phosphate (DAP) and ammonium polyphosphate were simulated under greenhouse conditions by making small, periodic additions of fertilizer P. The plants rapidly depleted the supplied P from the soil solution, minimizing the potential for precipitation (Nyborg et al. 1998). Where the P was gradually supplied to the plant over several weeks, P fixation was reduced and P uptake increased as compared to a single application of P at the start of the growing period. Polymer and shrink wrap coatings could be used to slow the release of P from MAP and DAP under greenhouse conditions. Coating MAP improved P uptake, fertilizer efficiency and barley dry matter yield (Table 2), but the performance of DAP was not consistently improved (Pauly et al. 2002). Under field conditions in Manitoba, there was no significant benefit of using coated MAP as compared to uncoated MAP increasing grain yield of wheat (Figure 7). While studies are underway evaluating controlled release phosphate fertilizers, there is little published Canadian information from evaluating enhanced efficiency P fertilizers under field conditions. Table 2: Barley dry matter yield, P uptake and net fertilizer P efficiency after 52 days of growth in pot trials as affected by application of uncoated or coated monoammonium phosphate fertilizers (Pauly et al. 2002) Dry Matter Yield P Uptake NFPE Treatment g pot mg P pot %-- Control NA Uncoated Thin-coated Thick-coated LSD A note of caution should be used while interpreting the results of field studies on P. Often, the annual response to P application is relatively small and it could be difficult to reliably identify minor influences of products on P availability against background field variability. That being said, if effects on availability are small, the economic benefit of using the products are likely to be small as well. Microbial Products Two major microbial products are marked in western Canada as a method of influencing P availability. Jumpstart (Penicillium bilaii) is a P-solubilizing fungus that occurs naturally in agricultural soils and is said to improve the availability of fertilizer and soil P. Laboratory and greenhouse studies have shown enhanced P uptake with the use of Provide (Kucey 1988; Kucey and Leggett 1989). However, in studies conducted under field conditions on the Canadian prairies, grain yield responses to use of Provide have been limited. In nine site years of study with wheat in Manitoba and Alberta, there was no significant increase in grain yield due to use of Provide (Figure 8). Similarly, there was no yield benefit of using Provide on flax in nine site years of study in Manitoba (Figure 9). In 47 site years of study in wheat and 20 in barley across the prairies provinces, there was no benefit in application of Provide in increasing grain yield (Figure 10). However, research in continuing to further assess the potential for benefits from Provide in canola.

10 Grain Yield (bu acre -1 ) Grain Yield (bu acre -1 ) Control 20 P Provide Brandon Minnedosa Rosebank Figure 8: Effect of Provide and MAP fertilizer on yield of durum wheat (averaged over 9 site years in Manitoba and Alberta, and averaged over 3 site years on a Newdale Clay Loam soil near Minnedosa) (Grant et al. 2002) Control Provide alone Provide + 10 lb P 20 lb P 40 lb P Mean Minnedosa Figure 9: Effect of Provide and MAP fertilizer on seed yield of flax at three sites in Manitoba, averaged over three years ((Grant et al. 1999).

11 Wheat Yield (Bu/acre) Barley Yield (Bu/acre) P alone P + P.bilaii P Rate (kg/ha) P alone P + P.bilaii P Rate (kg/ha) Figure 10: Effect of Provide and MAP fertilizer on yield of barley (20 site years of data) and wheat (47 site years of data) in the Canadian prairies (data courtesy of Rigas Karamanos) Mycorrhizae are an association between fungi and the plant root. The plant provides photosynthate to the fungus and the fungus provides nutrients and possibly water to the plant. The external hyphae of arbuscular mycorrhizae extend from the root surface to the soil beyond the P depletion zone and so access a greater volume of undepleted soil than the root alone (Grant et al. 2005). Some hyphae may extend more than 10 cm from root surfaces (Jakobsen et al. 1992) which is a hundred times further than most root hairs. Also, the small

12 -Colonization- % diameter of hyphae (20 50 μm) allows access to soil pores that cannot be explored by roots. Therefore, a root system that has formed a mycorrhizal network will have a greater effective surface area to absorb nutrients and explore a greater volume of soil than nonmycorrhizal roots. Mycorrhizae are naturally present in soils and extremely important in natural ecosystems, but their populations can be reduced by summerfallow and excess tillage, P fertilization and by following a non-mycorrhizal crop such as canola or sugar beet. Some crops such as corn or flax are more dependant on mycorrhizal associations that crops such as wheat or barley and can show a negative response when grown after a non-mycorrhizal crop such as canola (Grant et al. 2009). Inoculation with a mycorrhizal fungus may be able to increase mycorrhizal colonization, especially under conditions where the background level of mycorrhizal spores are low. Inoculants are commercially used in horticulture and forestry as well as in organic production systems. Data on the effectiveness of mycorrhizal inoculation under field conditions in the prairies is limited. In trials conducted over three years at two locations near Brandon and one near Lacombe, mycorrhizal colonization of wheat roots was increased by application of a mycorrhizal inoculant (Figure 11), but biomass production was reduced and grain yield unaffected by inoculation (Figure 12 and 13). It may have been that wheat did not require the mycorrhizal association to access adequate P, so colonization resulted in a detriment to the plant. Crops such as corn or flax, that tend to be more reliant on mycorrhizae may possibly show more of a benefit to inoculation when soil levels of inoculum are reduced by tillage, fallow or crop sequence Lacombe MCDC Maziers P Fertilizer Control Myc Figure 11: Mycorrhizal colonization of wheat roots at 6 weeks was increased by mycorrhizal inoculation and decreased by P application (averaged over three years) (Grant and Monrea Unpublished)

13 Figure 12: Biomass yield at heading was increased by P fertilization and decreased by mycorrhizal inoculation (averaged over three years) (Grant and Monreal Unpublished) Figure 13: Biomass yield at heading was increased by P fertilization and not affected by mycorrhizal inoculation (averaged over three years) (Grant and Monreal Unpublished)

14 Summary An adequate amount of phosphorus is required by crops early in the season to support plant growth and optimum yield. Phosphorus use efficiency in the year of application is relatively low, but the phosphorus not used by the current year s crop will remain in an available form for the crop to use in future years. When viewed over time, inputs of P fertilizer and off-take of P in the harvested grain are relatively well-balanced in non-manured fields in Manitoba. Little difference occurs in efficiency between orthophosphate and polyphosphate or between fluid and granular forms of P under Manitoba conditions. Similarly there has been little observed benefit with enhanced efficiency products or microbial applications in prairie studies. Reducing the rate of P application too low may reduce the proximity of seedlings to P fertilizer reactions zones, limiting early season uptake. Therefore, banding an available form of P near the seed at a rate high enough to balance off-take over time will generally optimize crop yield and avoid excess or depletion on non-manured soils. References Bertrand, I., Holloway, R. E., Armstrong, R. D. and McLaughlin, M. J Chemical characteristics of phosphorus in alkaline soils from southern Australia. Australian Journal of Soil Research 41(1): Bertrand, I., McLaughlin, M. J., Holloway, R. E., Armstrong, R. D. and McBeath, T Changes in P bioavailability induced by the application of liquid and powder sources of P, N and Zn fertilizers in alkaline soils. Nutrient Cycling in Agroecosystems 74(1): Glass, A. D. M., Beaton, J. D. and Bomke, A Role of P in plant nutrition. Proceedings of the Western Canada Phosphate Symposium: Grant, C., Bittman, S., Montreal, M., Plenchette, C. and Morel, C Soil and fertilizer phosphorus: Effects on plant P supply and mycorrhizal development. Canadian Journal of Plant Science 85(1):3-14. Grant, C. A., Bailey, L. D., Harapiak, J. T. and Flore, N. A Effect of phosphate source, rate and cadmium content and use of Penicillium bilaii on phosphorus, zinc and cadmium concentration in durum wheat grain. Journal of the Science of Food and Agriculture 82(3): Grant, C. A., Dribnenki, J. C. P. and Bailey, L. D A comparison of the yield response of solin (cv. Linola 947) and flax (cvs. McGregor and Vimy) to application of nitrogen, phosphorus, and Provide (Penicillium bilaji). Canadian Journal of Plant Science 79(4): Grant, C. A., Flaten, D. N., Tomasiewicz, D. J. and Sheppard, S. C The importance of early season phosphorus nutrition. Canadian Journal of Plant Science 81(2): Grant, C. A., Monreal, M. A., Irvine, R. B., Mohr, R. M., McLaren, D. L. and Khakbazan, M Crop response to current and previous season applications of phosphorus as affected by crop sequence and tillage. Canadian Journal of Plant Science 89(1): Holloway, R. E., Bertrand, I., Frischke, A. J., Brace, D. M., McLaughlin, M. J. and Shepperd, W Improving fertiliser efficiency on calcareous and alkaline soils with fluid sources of P, N and Zn. Plant and Soil 236(2): Hoppo, S. D., Elliott, D. E. and Reuter, D. J Plant tests for diagnosing phosphorus deficiency in barley (Hordeum vulgare L.). Australian Journal of Experimental Agriculture 39(7): Jakobsen, I., Abbott, L. K. and Robson, A. D External hyphae of vesicular-arbuscular mycorrhizal fungi associated with Trifolium subterraneum L. 2. Hyphal transport of 32P over defined distances. New Phytologist 120(4): Kucey, R. M. N Effect of Penicillium bilaji on the solubility and uptake of P and micronutrients from soil by wheat. Canadian Journal of Soil Science 68:

15 Kucey, R. M. N. and Leggett, M. E Increased yields and phosphorus uptake by Westar canola (Brassica napus L.) inoculated with a phosphate-solubilizing isolate of Penicillium bilaji. Canadian Journal of Soil Science 69: McBeath, T. M., Armstrong, R. D., Lombi, E., McLaughlin, M. J. and Holloway, R. E Responsiveness of wheat (Triticum aestivum) to liquid and granular phosphorus fertilisers in southern Australian soils. Australian Journal of Soil Research 43(2): McBeath, T. M., McLaughlin, M. J., Armstrong, R. D., Bell, M., Bolland, M. D. A., Conyers, M. K., Holloway, R. E. and Mason, S. D Predicting the response of wheat (Triticum aestivum L.) to liquid and granular phosphorus fertilisers in Australian soils. Australian Journal of Soil Research 45(6): Nyborg, M., Malhi, S. S., Mumey, G., Penney, D. C. and Laverty, D. H Economics of phosphorus fertilization of barley as influenced by concentration of extractable phosphorus in soil. Communications in Soil Science and Plant Analysis 30(11-12): Nyborg, M., Solberg, E. D. and Pauly, D. G Controlled release of phosphorus fertilizers by small, frequent additions in water solution. Canadian Journal of Soil Science 78: Pauly, D. G., Nyborg, M. and Malhi, S. S Controlled-release P fertilizer concept evaluation using growth and P uptake of barley from three soils in a greenhouse. Can J Soil Sci 82(2): Racz, G. and Soper, R Solubility of phosphorus added to four Manitoba soils with different calcium and magnesium contents. Plant and Soil 32(1): Racz, G. J. and Soper, R. J Reaction products of orthophosphates in soils containing varying amounts of calcium and magnesium. Can J Soil Sci 47(3): Sample, E. C., Soper, R. J. and Racz, G. J Reaction of phosphate fertilizers in soils. In: Sample, E C and Kamprath, E J, editors The Role of Phosphorus in Agriculture, American Society of Agronomy Madison, WI: Sanchez Valero, C., Madramootoo, C. A. and Stämpfli, N Water table management impacts on phosphorus loads in tile drainage. Agricultural Water Management 89(1-2): Schlegel, A. J. and Grant, C. A Soil Fertility. Pages Dryland Agriculture. ASA- CSSA-SSSA, Madison, WI. Strong, W. M. and Soper, R. J. 1974a. Phosphorus utilization by flax, wheat, rape, and buckwheat from a band or pellet-like application. I. Reaction zone proliferation. Agronomy Journal 66: Strong, W. M. and Soper, R. J. 1974b. Phosphorus utilization by flax, wheat, rape, and buckwheat from a band or pellet-like application. II. Influence of reaction zone phosphorus concentration and soil phosphorus supply. Agronomy Journal 66: Syers, J. K Efficiency of soil and fertilizer phosphorus use : reconciling changing concepts of soil phosphorus behaviour with agronomic information / by J.K. Syers, A.E. Johnston, D. Curtin. Food and Agriculture Organization of the United Nations, Rome :.