A Review of the Agronomics Related to the Use of Polyhalite as a Major Fertilizer Product in World Agriculture

Transcription

1 A Review of the Agronomics Related to the Use of Polyhalite as a Major Fertilizer Product in World Agriculture Submitted by: Kim R. Polizotto, Ph.D. President, KRP Agronomic Consulting To: North Moors National Park Authority This report represents the agronomic review of the supplied documents related to the use of polyhalite as a major fertilizer material. Comments and observations are based on the author s expertise as an agronomist and over 26 years experience in the fertilizer industry as the Director of Agronomy for a major potash producer. As described, polyhalite is a multi-nutrient fertilizer material containing 14% potassium (potash) as K 2 O, 19% sulfur (S), 6% magnesium as MgO, and 12% calcium (Ca). As such, the fertilizer analysis of polyhalite is S-6Mg-12Ca. In my opinion there is no debate regarding the fact that polyhalite contains four plant essential nutrients and is an acceptable fertilizer material. In the fertilizer industry polyhalite would be considered a multi-nutrient fertilizer but not a balanced fertilizer. The industry term balanced fertilizer refers to a fertilizer that contains plant available nutrients in the approximate ratios needed by crops or an analysis that closely supplies nutrients in the ratio recommend by soil test or crop removal information. The analysis of polyhalite does not approximate either of these criteria. Potash Submitted reports indicate differences of opinion regarding whether polyhalite would be considered a viable substitute or competitor with muriate of potash (KCl. MOP), sulfate of potash (potassium sulfate, SOP), and/or sulfate of potash magnesium (SOPM). In my opinion polyhalite could not compete head to head with MOP or SOP as a main source of potassium (K) simply because the K 2 O content is not high enough. If polyhalite were used as the sole source of K for direct application, or in blends or compound fertilizers, the sulfur content would be extremely high. A routine application of 125 kg/ha of K 2 O would require applying 893 kg/ha of polyhalite. This application rate would result in applying 170 kg/ha of S. On soils considered

2 low in sulfur, a normal application rate would be in the range of kg/ha so you can see this is an extreme over application of S. To my knowledge there are no agronomic or environmental consequences to over application of S, however. Polyhalite is also touted for its absence of chlorine (Cl). First, it needs to be noted that Cl is itself an essential plant nutrient. Although some crops are sensitive to Cl, these do not represent large acreages and SOP is a known product in these markets. Also, for crops where Cl adversely affects storage or processing characteristics, it needs to be noted that in many parts of the world farmers are not paid based on these factors. Only in the developed countries do farmers concern themselves with the potential effects of Cl on non visible quality factors. Another consideration is the tremendous difference in application rates of polyhalite compared to conventional potash fertilizers. For example, to get 125 kg/ha of K 2 O from various sources would require applying 208 kg/ha of MOP, or 250 kg/ha of SOP or 893 kg/ha of polyhalite. Farmers, fertilizer dealers, blenders and manufacturers are all very aware of the time and money involved in transporting, storing and applying fertilizer and do not look favorably on low analysis fertilizers or high application rates. The negatives associated with handling unnecessarily large volumes of fertilizer cannot be overemphasized. I have not included SOPM in this discussion because SOPM producers and the industry in general consider this product to be a magnesium source. In the markets I am familiar with, it is sold as such. SOPM is used alone and in blends and compound fertilizers as a Mg source. K requirements are then adjusted to the desired levels using MOP or SOP. Sulfur is just considered a bonus nutrient and S is credited toward S fertilizer if required. SOPM is not considered a first choice for S as it is an expensive source. Based on its Mg content, polyhalite would compete better against SOPM than MOP and SOP, but as pointed out in one of the reports, the SOPM market is pretty small and growth potential is not imminent. Most soils have fairly high levels of Mg compared to crops needs. Also, in areas where dolomitic limestone is used to maintain soil ph, high levels of Mg are attained. The ADAS report spent a considerable amount of time and space discussing crop requirements and rates of nutrient removal for the different nutrients in polyhalite. Reports indicating that potash removal in harvested crops is greater than the amount applied as fertilizer can be very misleading. The mass balance approach of calculating nutrients removed compared to fertilizer applied is only useful in small geographic areas with known soil test values. Doing mass balance analyses for large areas cannot take into account differences in soil mineralogy and naturally occurring nutrients. For example, in the western United States, Western Canada, Mexico and Argentina, K in crop removal is significant, but potash fertilizer use is minimal because of inherently high soil potassium levels. Calculating fertilizer need based on a mass balance approach would indicate an under fertilization of potash in these areas when, in fact, potash is really not needed. Based on what we have seen charting potassium levels in these soils for many years, it will take many more years to pull the soil potassium levels down to the point

3 where potash fertilizer is widely needed. Sulfur, magnesium and calcium mass balance calculations are equally inaccurate and misleading. For these reasons, although the information presented is factual, in my opinion it is not pertinent to this discussion. The actual growth of world fertilizer markets is very debatable and subject to many factors that have been amply discussed. The market for K will indeed grow, probably at or near its present rate, but the fact of the matter is that present potash production capacity far exceeds demand and new projects to develop greenfield facilities and expand production at existing facilities are on the drawing board. Presently, major Western Canada potash producers are operating their mines and plants at 50% to 60% of total production capacity, so new mines do not appear needed in the near future. To my knowledge, there is no particular need for increased capacity in sulfur, magnesium or calcium fertilizers, either. Sulfur Based on the fertilizer analysis of polyhalite, it would seem to be best suited as a sulfur source. It could be used directly as polyhalite or in blends or compound fertilizers to supply sulfur to any crop. The major question(s) with regard to its future as a major source of S for these purposes are: 1. How big is the S fertilizer market and what are its growth projections? 2. How are sulfur fertilizers presently sourced in different parts of the world? and 3. What are the present and future export, shipping, storage and distribution opportunities and obstacles? A problem involving sulfur fertilization, however, is that farmers, fertilizer dealers, agronomists, and university and government researchers cannot accurately predict when sulfur fertilization is necessary. We are all in agreement that soil sulfur levels are lower today as a result of increased crop removal and less atmospheric deposition resulting from more rigorous emission standards. We are also in agreement that we are seeing more sulfur deficiencies in crops and more responses to sulfur fertilization. The uncertainty with S fertilization is in interpreting soil tests for S, and making subsequent S fertilizer recommendations. To illustrate this point, I refer to research at the University of Illinois (USA). Researchers identified 85 fields with low to very low S soil test levels ranging from, 0 to 7 ppm S as SO 4. They then applied S as SO 4 to all of the fields at a rate of about 24 kg/ha prior to planting corn. Of the 85 fields fertilized with S, there was a positive yield response in only 5 test sites. Unfortunately, these research results are consistent with many other similar experiments around the world. The reasons why S soil tests are not good predictors of sulfur fertilizer needs are varied. First, sulfate sulfur (SO 4 ), the form taken up by plants, and the form analyzed for in soil tests, is very mobile in soil. As a negative anion it is free to move with soil water up and down in the soil profile. Since there is often a several month delay between soil testing and crop growth, sometimes soil tests just do not represent the true amounts of S available during the growing

4 season. Also, mineralization of soil organic matter can supply significant amounts of S to crops but not be detected in soil tests. The reason I have gone into this much detail with regard to sulfur soil testing and fertilizer recommendations is to emphasize the point that it is very hard to predict the future demands for sulfur fertilizers based on the concepts of soil content, crop use, and crop removal. In my opinion, a great deal of the sulfur fertilizer being sold today in the developed countries is being sold as an insurance policy against S deficiency. As long as farmers are making good profits, they accept this cost with little concern. In developing countries, farmers are less knowledgeable and more susceptible to a sales pitch promoting S as absolutely essential. Regardless of how these scenarios play out, the market for sulfur fertilizers is not nearly as large as the market for potassium, nitrogen and phosphorus. The CRU report states that sulfur is required by crops in the same amounts as nitrogen and this is incorrect. Sulfur requirements of the major world crops range from 20 to 30 kg/ha, a number significantly less than N, P and K needs. Sulfur removal in harvested crops is also significantly less in most crops, as compared to N, P and K. I think some of the projections for growth in sulfur fertilizers are based on incorrect understanding of crop requirements for S and overly optimistic assumptions about its impact on crop yields. Using polyhalite as a source of sulfur in physical blends will require production of the proper size and uniformity to make it compatible with granular nitrogen, phosphate, and potassium fertilizers with which it will most likely be blended. Particles differing in size and uniformity by more than 10% will segregate during handling, storage, bagging, shipping and application. This could be a major consideration in its acceptance as a blend ingredient. Polyhalite would seem to be a good choice for sulfur in both physical blends and compound fertilizers. At issue would be the total market for these fertilizers and the market for compound fertilizers containing S and Mg. Compound fertilizers are generally made to analyses approximating the requirements of specific crops. Based on how inaccurately we can predict S needs, it would seem problematic that compound fertilizers would be made to routinely contain S. Also, as soil testing becomes more available and blend plants become more common, in my opinion physical blends will begin to displace compound fertilizers. Rightly or wrongly, as farmers adopt soil testing they tend to gravitate toward a prescriptive approach to fertilization. Soil test levels and crop removal are assessed as well as nutrient requirements for the next crop to develop specific fertilizer recommendations for individual fields and crops. Experience and local knowledge are also important in this process. Locally produced physical blends can be made in infinite nutrient analyses and components of the blends can be easily sourced. Storage space for blend components is a consideration at most blend plants, so polyhalite will have to compete with other fertilizers for space, however. Significant questions with regards to

5 polyhalite are 1. how much of these fertilizers will include S and 2. is it going to be more convenient to store and supply a different source of S. If polyhalite can be made to proper size and uniformity standards, it could probably compete favorably with ammonium sulfate (AS). In markets I am familiar with, granular AS is not universally available and is sold as a premium product. Yield Enhancement The CRU report based part of their analyses on the assumption of a 10% and 20% yield increase for the use of polyhalite. In my experience, it is extremely rare that we see differences in yield related to the source of plant nutrients. Plants take up nutrients in very specific forms and cannot differentiate among the many sources of those nutrients. The data presented in the report was from greenhouse and field trials that mostly measured plant growth, not yield. An actual yield improvement of 10% due to changing a fertilizer source would be groundbreaking. A 20% yield increase from a product change would be miraculous. We just do not see these levels of yield improvement in today s agriculture. I would totally disregard any consideration of yield improvement in making a decision on the value of polyhalite. Organic Fertilizer Today an organic fertilizer is basically any fertilizer that is approved by a government or growers group as approved for use in organic crop production. It does not have to be an organic compound itself. Polyhalite would qualify as an organic fertilizer and would be a pretty good source, as organic potassium fertilizers are scarce. Polyhalite is approved as long as there are no extraneous chemicals used in the production process. These would include chemicals used for the separation of polyhalite from other minerals or clays during the production process. Also, any non-approved material added to polyhalite to reduce dusting and prevent caking would preclude it from being approved as an organic fertilizer. The demand for organic fertilizers is growing, but it is still a very small market. Neutrality and Salt Index Claims of neutrality and relative salt index values for polyhalite compared to other fertilizers are of no consequence. All of the fertilizers they are using in comparison to polyhalite are pretty much the same. Also, neutrality and salt content of fertilizers is a non-issue in the industry. Summary In summary, I agree that polyhalite is a legitimate fertilizer product that contains plant available K, S, Mg and Ca. As it is a low analysis K fertilizer, I think it will have a very hard time competing with traditional potash products like muriate of potash and sulfate of potash, regardless of the price. In analysis, polyhalite resembles SOPM fairly closely. SOPM is primarily marketed as a Mg source and the market for this product is relatively small. Of the

6 options, polyhalite as a primary source of sulfur is the most logical. It would seem to be a good candidate as a stand alone S fertilizer and for inclusion into physical blends and compound blends where S and Mg were needed. Existing SOPM manufacturers sell their product at a premium to other MOP and SOP fertilizers. Since York appears to have a very low cost of production for polyhalite, they should be able to develop sales for this product. The big question is just how large the market is for S and perhaps Mg, and what is a realistic potential for growth. I suspect that it is not nearly as large as their marketing studies are projecting, however.