Liming 101

Published: 2023-05-01

Lime application according to our expert: the most frequently asked questions about lime and calcium fertilizers.

STEP 1, OR BRIEFLY ABOUT LIMING

1. FARMER: What are the benefits of liming soil?

Expert’s answer: Liming results in several positive changes in soil characteristics.

Let’s organize them:

– The primary and most important goal is to reduce soil acidity, known as soil pH. Every farmer should know how to test pH and what doses to apply for specific plants. This knowledge is currently essential, and one should not rely solely on information from fertilizer producers, as it is usually too general. Some plants are very sensitive to liming, and knowing how to prepare the soil for a specific crop can result in yield increases of up to 20-60%.
– Proper soil structure is another very important benefit of liming. The key parameters include improving soil granulation structure, better aeration, increased porosity, balance of microbiological systems and living organisms’ activity, better water circulation, organic matter exchange, and improved availability of mineral nutrients. All these processes positively affect soil well-being and help prevent its degradation.
– Liming neutralizes acids of chemical origin, inhibiting their penetration into agricultural products. Most chemicals are neutralized upon contact with lime. One can easily imagine the significant impact this has on the quality of agricultural products, especially those for which consumers require high standards.

2. FARMER: How can I tell if the soil needs liming?

Expert’s answer: Twenty to thirty years ago, scientists recommended identifying soil acidity using so-called bioindicators in fields. These are some wild plant species that prefer highly acidic soils. However, recent research has revealed the considerable inaccuracy of this method. Reliable tests for acidity determination can only be conducted using laboratory methods. The test results allow for a fairly precise determination of the optimal liming range and timing for fields or crops. The pH range for most crops in Poland should be between 5.5 and 6.5. For sensitive plants, pH should range from 6.0 to 7.0. Implementing a systematic and intelligent liming system for individual fields and crops is highly recommended. It requires systematic monitoring of soil acidity (pH) and flexible determination of the lime preparation doses. Detailed dosage tables are always included in the manufacturer’s informational materials. Following such a procedure will result in achieving and maintaining plant well-being – hence, also increasing yields and farmer satisfaction.

3. FARMER: How to test soil pH and where to find information about the appropriate pH for a specific crop?

Expert’s answer: Testing soil pH is not a complicated task. However, not everyone has the knowledge and time to conduct such tests independently. Regarding pH measurement devices, caution is advised. While one can purchase such devices in the market, their reliability is highly questionable; only high-end devices that can be calibrated may show accuracy in measurements. Experiments conducted on cheap devices of this type have shown their complete inconsistency with the actual soil pH. A better solution is to commission such tests to a specialized laboratory – for example, the nearest District Chemical-Agricultural Station.

4. FARMER: What are the types of lime used in agriculture?

Expert’s answer: Three main types of lime with fundamentally different compositions and chemical properties are used in agriculture; these are:

– Quicklime (also known as burnt lime or building lime) with the chemical formula CaO, is obtained artificially by roasting limestone. This lime is highly reactive. There is a real risk of over-limiting the soil because it reacts with water to form calcium hydroxide, which is a strongly corrosive substance.
– Limestone (also known as chalk powder, feed chalk, limestone meal, or lake chalk) with the chemical formula CaCO3, is obtained by crushing and grinding limestone rocks or as a mineral in open-pit mines. Limestone occurs naturally in the form of limestone rocks. The main problem here is the varying degree of purity of the chemical composition. Not all limestone gives good results as a fertilizer! The best limestone fertilizers are those that are finely ground and free from impurities or water. One can easily imagine that buying a product that contains 70% pure content, with the rest being impurities like clay and water, is similar to buying 100 bags of which 70 are limestone, and 30 are water and clay.
– Dolomitic lime (mineral lime, finely crushed lime) is the worst and least reactive type of lime used in agriculture. Its effectiveness in soil de-acidification is often close to zero. Unfortunately, farmers are often deceived and pay large sums for this type of product. Dolomite liming is as effective as spreading ordinary sand because the structure of dolomite is very similar to the structure of quartz, making it a product with a crystalline structure that is completely insoluble in water.

5. FARMER: How often should soil be limed?

Expert’s answer: Until now, liming soil once every few years was recommended. However, such treatments do not prevent soil degradation. The problem here also lies in the subjective, often accidental, size of the lime doses applied to the soil. Currently, more aware farmers realize that systematic use of lime preparations yields better results. Large, even „shock” doses of lime introduced into the soil result in rapid but short-lived changes in soil conditions improvement. Such uncontrolled lime fertilization of fields is usually accompanied by a quick return to unfavorable soil acidity levels.

6. FARMER: When should soil be limed?

Expert’s answer: The method of liming depends on the crop. The best time to spread lime is between crop harvests and late autumn, or even winter. The post-harvest period is typically characterized by good soil moisture, which directly contributes to lime dissolution in the soil. An important aspect here is also the lime activation time, which is longer during this period, as it lasts from crop harvesting to planting. As can be observed, this long period allows for soil tests to be conducted and, a calm selection of the appropriate fertilizer, which ultimately results in the correctness of the entire procedure. Granular fertilizers are particularly recommended here. They do not require as intense mixing with the soil and can also be applied during the winter and early spring on a shallow snow cover (recommended for winter wheat, rapeseed, perennial plantations, and permanent green spaces). Granular fertilizer is also the best form of lime for post-emergence application – crop-saving. In this case, the sowing time may coincide with the plant’s growth stage.

7. FARMER: How much lime should be spread per hectare of soil?

Expert’s answer: Many environmental and agronomic factors influence lime application rates. Therefore, without additional research, it cannot be unequivocally stated how much lime will be sufficient to achieve satisfactory results. pH of the soil and the type of lime fertilizer used are significant factors. Quicklime, limestone, or chalk have different applications for different soils and varied reaction times. The method of liming also influences this. Many farmers believe that liming fields every few years with large doses of fertilizer is sufficient. This is not entirely true, of course. Recent scientific studies indicate that the best results can be achieved by subjecting fields to systematic, annual liming treatments – using smaller doses. Maintaining such an agrotechnical strategy, for most types of soils and plants, doses ranging from 400 to 1200 kg per 1 ha will be sufficient. These doses increase for acidic heavy soils, where lime application needs can be estimated at around 800 to 2000 kg per 1 ha per year. Note: In the case of quicklime, one should not de-acidify too rapidly with large doses, as it may lead to over-limiting or drying out the soil!

8. FARMER: Why do some producers recommend spreading even 10-15 tons of limestone, while others recommend spreading 1-2 tons per hectare?

Expert’s answer: Everything depends on the liming system and soil pH. Spreading granular lime fertilizers is often part of an annual plant feeding system. Hence, smaller doses are used – producers assume that the soil pH is stabilized. Therefore, the lime preparation serves to introduce the necessary lime dose – also incidentally achieving the effect of maintaining the proper soil pH. In the case of powdery limestone fertilizers, the dose is often given to de-acidify the soil for 4-5 years. Hence, the dose is significantly larger. The dose size also depends on the chemical composition of the preparation. There is one rule here: the better the fertilizer, the smaller the doses. In the case of quicklime, the differences in the doses given also result from the CaO content. It can vary between 40 and 80%.

STEP 2, OR ABOUT THE BENEFITS OF LIMING

9. FARMER: Can liming harm plants?

Expert’s answer: In the case of quicklime, there is a risk of over-limiting the soil because an excessive amount of calcium hydroxide, which forms upon contact with water in the soil, can damage crops. On the other hand, over-limiting with limestone is not practically possible. It is a product of natural origin, and its absorption is „controlled” by the plants themselves – they take an appropriate amount of the product from the soil. A good example is soils with shallow limestone rocks. Calcium carbonate can constitute even 20-30% of their mass, i.e., in soil with a field area of ​​1 hectare, about 1000-1500 tons of lime is present! At the same time, only about 1% of the lime present in the soil actively participates in soil processes related to plant nutrition.

10. FARMER: Can lime be mixed with water and used as a spray, for example, for trees or vegetables?

Expert’s answer: As for the effectiveness of using lime as a spray, opinions are divided and often contradictory. This mainly results from confusing two types of lime, namely quicklime obtained artificially (burnt lime, building lime) and natural lime, i.e., limestone. Using quicklime as a spray can have very serious and adverse consequences for plants. Improper doses can even lead to the burning of vegetables or trees. On the other hand, limestone to a limited extent is absorbed through plant leaves. In the case of emergency liming during the plant growth phase, it will be more effective to spread granules to enable faster reaction in the soil.

11. FARMER: How do you apply topdressing lime and what are the benefits of this?

Expert’s answer: Topdressing with lime fertilizers is only possible when using carbonate lime. In the case of oxide lime (burnt, building lime), topdressing with lime will burn the plants and ruin the crop. Granulated carbonate lime fertilizer is particularly recommended for fertilizing plants during growth. It is easily absorbed from the top layer of soil. Of course, it should be noted that not all plants react the same way to topdressing with lime. This depends primarily on their sensitivity to lime. The higher the sensitivity, the more effective the treatment will be. For details, you should consult the producers of the granules.

12. FARMER: What is the best lime for broadcasting?

Expert’s answer: Currently, among farmers, there is still a belief in the effectiveness of broadcasting lime in the form of bulk fertilizer. However, more aware users of lime fertilizers notice significant limitations of such products. These limitations are associated with problems with uniform spreading and resulting product losses. To overcome these limitations, lime granulation has been started – they allow for minimizing the described losses.

13. FARMER: Can lime be mixed with manure, nitrogen, and phosphorus fertilizers?

Expert’s answer: There are many conflicting opinions on this issue. In reality, there are quite simple rules that must be taken into account when liming the soil:

– Oxide lime is not suitable for mixing (in any form) with most fertilizers. The exceptions here are: polyphosphate and phosphate rock. Let’s emphasize once again: other fertilizers cannot be mixed with oxide lime under any circumstances!
– Carbonate lime is not suitable for mixing with manure, ammonium phosphate (granulated), ammonium sulfate (powdery), and Super Phosphate (powdery). Moreover, it is recommended to maintain a gap (4-8 weeks) between spreading lime and introducing the aforementioned preparations into the soil. However, carbonate lime (especially in granulated form) can be mixed with: urea, polyphosphate, Super Phosphate (granulated), phosphate rock, potassium salts, potassium sulfate, and oxide lime.

14. FARMER: What lime to use on heavy and fertile soils?

Expert’s answer: On heavy, fertile soils, oxide lime, carbonate lime, or oxide-carbonate lime can be used depending on the needs. In the case of rapid soil acidification, oxide lime is best suited. However, its use should be minimized in the longer term, as it negatively affects the chemical and physical properties of the soil. Using slower-acting carbonate fertilizers is more effective and safer in the longer term.

15. FARMER: How long does lime „break down”?

Expert’s answer: The rate of lime assimilation by the soil environment largely depends on its physicochemical properties and environmental conditions (moisture, aeration, and soil temperature). For example, oxide lime fertilizers (burnt lime-building lime) react very violently and cause excessive soil drying. In the case of carbonate fertilizers, the most important factor is their fragmentation. The finer the dusty particles, the faster the soil penetration effect and the more effective the fertilizer.

STEP 3, OR ABOUT LIME AND LIME PREPARATIONS

16. FARMER: What do the lime variety designations mean, e.g., variety 04, variety 06a, etc.?

Expert’s answer: The nomenclature of lime fertilizer types is regulated by the Act of July 26, 2000, on fertilizers and fertilization; Journal of Laws No. 89, item 991. The Act clearly describes and classifies lime fertilizer types. The assessment was based on the physical state and chemical composition of lime and the methods of its extraction. From the farmer’s point of view, the most profitable varieties are: 04. A total of 13 types of lime belong to the class of magnesium-free fertilizers, five of which come from the processing of limestone rocks, four from by-product production, and the last four are recognized as minerals. Pay attention to varieties containing magnesium, as they are usually dolomites. The most efficient granulated lime fertilizer is lime variety 04 containing over 50% CaO and over 90% CaCO3. Until now, there was no producer of this type of fertilizer in Poland; only imported fertilizer from Germany and France was sold, which can cost over 2000 PLN per ton. Currently, the only producer of this type of fertilizer is the POLCALC plant in Lubień Kujawski, selling the fertilizer under the trade name POLCALC III GENERACJI, and the price of this fertilizer is about 450 PLN per ton.

17. FARMER: What does converting CaO mean and why is lime denoted in this way?

Expert’s answer: The Act requires producers to inform about the composition of the fertilizer expressed in the quantity of oxide, although the chemical composition of carbonate lime does not contain oxide (CaO) but calcium carbonate (CaCO3). This solution was introduced to easily calculate the amount of fertilizer needed to acidify the soil after pH testing and to easily assess the fertilizing value of lime.

18. FARMER: How to check if the producer does not provide an exaggerated composition? Who to commission the analysis to?

Expert’s answer: Every producer is obliged, at the customer’s request, to present a certificate determining the quality of the sold lime fertilizer. Such documents are issued to producers by District Chemical-Agricultural Stations or the Institute of Crop Production, Fertilization, and Soil Science in Puławy. This information should be found on the packaging of the products sold. In case of any doubts, the product should be tested by the nearest District Chemical-Agricultural Station.

19. FARMER: What are dolomitic limes and how do they differ?

Expert’s answer: Dolomitic fertilizers are produced by crushing sedimentary rocks called dolomites. The microscopic structure of this raw material mostly consists of calcium carbonate and a small amount of magnesium. Therefore, most of them are calcium-magnesium fertilizers. Unfortunately, the natural physicochemical properties of these rocks make them the least efficient fertilizer. They are very poorly absorbed, and the benefits of their use are very doubtful.

20. FARMER: What is lake chalk lime, and how is it different from others?

Expert’s answer: Lake chalk carbonate lime, marked as variety 06a, is a fertilizer with a very fine structure, mostly when it is dried and granulated. However, the low CaCO3 content compared to fertilizers derived from limestone rocks of variety 04 makes it significantly less efficient and effective.

21. FARMER: What about waste lime?

Expert’s answer: There are also waste limes, so-called cellulose, and others, but their agricultural usefulness is questionable, and certainly, the use of such fertilizers can hurt soil and product health. This lime has the highest degree of contamination, which means that only about 30-50% of it is proper lime. The rest are contaminants of uncertain suitability. Such lime must be chemically tested because there is a high risk of soil contamination with highly toxic heavy metals. However, even such caution may be too little. Chemical-agricultural stations determine only the content of two basic heavy metals: cadmium and lead. Other toxic substances are not identified in such tests! The price of such „lime” can range from 1 PLN to 15 PLN per ton.

22. FARMER: How to recognize good carbonate lime?

Expert’s answer: The simplest way is to examine the degree of lime fragmentation. A simple test can be conducted. After pouring two tablespoons of lime into a glass of water, we should obtain a kind of „milk” in suspension. Low-quality products will leave sand or other impurities at the bottom of the glass. Attention should also be paid to the manufacturer’s certificate obtained from the District Chemical-Agricultural Station or the Institute of Fertilization and Soil Science in Puławy. Good carbonate lime should contain over 90% pure CaCO3, which, when converted to oxide mass, gives about 50-55% CaO. It should not contain water or any other additional substances. In the case of lime with magnesium, we will usually deal with dolomite, a product with very weak reactivity.

23. FARMER: What is lime reactivity?

Expert’s answer: Lime reactivity is a factor indicating the quality of the fertilizer. In other words, the higher the reactivity, the better. However, a clear differentiation is required for oxide (burnt-building) lime and carbonate lime. In the first case, reactivity results from the chemical composition of the preparation (CaO content). In turn, the reactivity of carbonate lime (CaCO3) results from the degree of fragmentation of the semi-product. Of course, the finer the fractions, the greater the reactivity.

24. FARMER: What is the composition of granulated lime, what is the active substance? What is its reactivity?

Expert’s answer: Granulated lime is always carbonate lime because oxide lime (burnt-building) cannot be granulated. The chemical formula of such lime is CaCO3, which is often not properly understood by recipients, as producers convert carbonate lime to oxide lime CaO and mistakenly provide the chemical composition as CaO, e.g., 50%. In this case, 50% of the fertilizer consists of pure calcium oxide (CaO) in the total elemental mass. It should be remembered that this is only a mandatory form of presentation imposed by the legislator. However, in reality, good carbonate lime should contain over 90% calcium carbonate CaCO3.

25. FARMER: What are the advantages of granulated lime?

Expert’s answer: The main advantage of granulated fertilizers is their easy assimilation by the soil. As is known, this directly affects crop yields. One should also not forget about the ease and economy of spreading granulated lime. It ensures high work comfort and high precision in the liming process. Especially recommended are highly reactive, granulated lime preparations stored in big-bag bags. They facilitate the transport and use of the fertilizer.

26. FARMER: How to distinguish genuine granules from counterfeits?

Expert’s answer: Many farmers, seeking illusory savings, allow themselves to be deceived and buy so-called „pseudo-granules.” It is just ordinary, finely ground stone. Usually, it is obtained from dolomite, and its utility values ​​are none. At best, producers sell finely ground limestone. Its utility values ​​are very limited. The low chemical activity of such a „product” causes its minimal impact on the soil environment. Distinguishing lime granules from counterfeits is ridiculously simple. To do this, simply pour a sample of the product (e.g., 2-3 tablespoons) into a glass of cold water. If we almost immediately obtain a „milky” suspension, then we are dealing with an original product. If, however, after a while, small pebbles remain at the bottom of the glass, there is no doubt that it is an attempt at fraud.

STEP 4, OR BRIEFLY ABOUT PRACTICE

27. FARMER: Is it worth buying lime with magnesium?

Expert’s answer: Based on research conducted by the IUNG, it can be said that magnesium deficiencies often result from a lack of proper soil pH, and their effective supplementation depends on the specific nature of the soil itself. In other words, first, the soil should be deacidified to increase the availability of magnesium forms already present in it, and only then should magnesium content be tested on the correct soil pH. It follows that in the case of increased soil acidification, it is more effective to use fertilizers without magnesium admixture. Although many producers present on our market indicate that their fertilizers contain highly reactive magnesium, the truth is different. Currently, there is no producer in Poland producing an integrated (calcium-magnesium) granulated fertilizer based on the highest reactivity carbonate variety. Many farmers use multi-component fertilizers in which the necessary amount of magnesium is already present, and in such a case, supplying magnesium along with lime is pointless and increases costs without additional benefits.

28. FARMER: When is the best time to purchase lime?

Expert’s answer: Lime, if its storage conditions allow, can be purchased throughout the year. It is important that during unfavorable weather conditions, it is not destroyed by freezing (for granulated wet lime) or moistening. In the case of good-quality granulated lime, purchases can be made after the season, i.e., in January-February and June-July. Many producers offer seasonal discounts during these periods.

29. FARMER: How to obtain a subsidy for lime?

Expert’s answer: In our country, it is only possible to apply for such funding in certain provinces. It is worth noting that the subsidy within the provinces may change from year to year, and the application submission system changes almost annually. Therefore, it is best to contact the nearest District Chemical-Agricultural Station or the Agricultural Chamber operating in the respective district to obtain full information.

30. FARMER: In what packaging is it worth buying lime?

Expert’s answer: The choice of packaging depends on the consumer’s needs, i.e., the purpose of lime and the possibility of its storage. For large farms, convenient packaging is big-bag containers, with capacities ranging from 500 to 1200 kg. They are equipped with a foil liner to protect against moisture. Purchasing such securely packaged, dry fertilizer allows for significant savings. It is easy to imagine that in the case of lime with a moisture content of 30%, out of 100 purchased bags, 30 contain only water! After adding transportation costs, the initial, low price of such a product becomes significantly less competitive. Therefore, we recommend buying completely dry fertilizers – devoid of water admixture.

31.FARMER: Why is granulated lime more expensive than other forms of lime fertilizers?

Expert’s answer: The price of lime is influenced by many factors. The most important is the quality of the semi-product (raw material) from which the granulate is obtained. Another cost-driving factor is the long and technologically advanced process of granulate production. It begins with the extraction of „raw” rock in open-pit mines. Its subsequent stages involve crushing rocks, purifying the semi-product from troublesome impurities, milling in ball mills, drying, and granulating. Additionally, there are costs of transportation, storage, market servicing, and scientific research to ensure the maintenance of high product quality.

32. FARMER: How is granulated lime stored?

Expert’s answer: Granulated lime, like other granulated fertilizers, should be stored in a dry place, thereby preventing it from getting wet or freezing. Granulated carbonate lime will not change its chemical composition under the influence of water, but it may weaken the structure of the granules.