- Foliar or soil application- which is better?
- How and why does foliar absorption work? Can I supply all the plantís nutrient needs through the leaf?
- How do microbes fit in with foliar absorption?
- I applied a strong dose of urea-ammonium nitrate foliar nitrogen at the tillering stage to my wheat crop. There were leaf-burn and chlorosis symptoms from the spray which set back yields at harvest. Can you explain what happened, and how to prevent leaf burn when applying nitrogen?
Starter Liquid Fertiliser
- Why is liquid lime quicker to act than limestone or lime-sand?
- Will liquid lime increase the pH of my acid soil?
- We have been unable to grow cauliflowers and cabbage for some time now due to the clubroot disease. We read that the problem is reduced by increasing soil pH with lime, and have tried liquid lime on its own but without success. Can you advise us on how to prevent the clubroot problem?
- Grain analysis, soil analysis, or leaf analysis, which is preferable?
- I usually apply 100 kilograms of urea and 150 kilograms of single superphosphate per hectare before sowing wheat. What is the equivalent amount of nitrogen in Rich Green Liquid N-S fertiliser?
- I would like to harvest around 4 tons per hectare of wheat grain. How much fertiliser do I need to apply?
- Grain analysis of my wheat is showing deficiency in some trace elements. For a 4-ton crop of wheat grain per hectare, what is the minimum amount of Soil & Foliar liquid fertiliser I need to alleviate the deficiency?
- Can I replace soil applied granular fertilisers with liquid fertilisers?
- In addition to fertilisers applied to achieve a certain yield, what other factors should I consider?
- I own a wheat and sheep farm of 6500 hectares in the wheat-belt. Each year I crop around 4000 hectares to wheat, barley, canola and lupins. I treat my crops and pastures with nitrogen and superphosphate, plus I have used the trace elements copper, zinc and molybdenum. I also test my soils each year. However I notice that my crops and pastures are not growing as well as in the past. Yields are down considerably, and I had problems this year from leaf disease and frost. The percentage of small grain at harvest has also increased. Do I need other nutrients such as magnesium, manganese and boron in my fertiliser program?
- Collecting a grain sample at harvest for analysis is easy, but is it as good as a soil sample for improving yields and quality? Is analysis of grain more difficult than soil analysis?
- My cereal and canola crop yields have been severely affected by frost for the past three years. How can I prevent frost damage?
- Under Publications and Nutrition Management on your website, you provided data for grain nutrient levels to characterize nutrient status and for estimating fertiliser needs. This data was collated over a long period of 20 years. Is there a way to collate grain analysis data for rice in a much shorter time frame, say one year?
- On the Adverts page, 'Integrated fertiliser programs way to high yield and quality', is potassium sulphate preferable to potassium chloride in the Super Potash 1:1 fertilizer? Are sodium and chloride nutrients needed for Australian soils? I am surprised to learn that magnesium uptake for a 3-ton/ha wheat crop is about 5 kg/ha of the element. Why is magnesium nutrient not added to most of our broad-acre NPK fertilizers in Australia?
- Under 'Integrated fertiliser programs...', on Adverts page, it is difficult to understand that application of only 2 grams per hectare of molybdenum and 0.2 gram per hectare of cobalt are needed to replace their uptake by 3 tons of wheat grain. Is such small amounts sufficient, and how do I accurately apply such small amounts to crops?
Nutrients are needed in the leaf for the process of photosynthesis. In the long journey from the root surface to the leaf, some of the less mobile nutrients are less likely to reach the leaf surface in sufficient amounts. Direct foliar application of a balanced combination of major and trace nutrient elements, as a fine spray to the surface of the leaf, leads to an enormous increase in the efficiency of photosynthesis (like the fine coating on the surface of a solar heat collector increases its heat absorption). Improved photosynthesis means increased quality and productivity through the formation of quality sugars, carbohydrates and proteins.
It is not possible to supply all of the plantís nutrient needs through foliar application only. A four-ton per hectare crop of wheat grain, for example, removes approximately 82 kilograms of nitrogen in the grain equivalent to 176 kilograms of urea. This large amount of nitrogen (and other major elements) is best applied through both root absorption (fertigation) and foliar absorption.
It is possible to supply all of the plantís trace element needs through the foliar process. However, because plants need trace elements too in the early stages of growth, during and soon after germination and establishment, the modern way is to supply some of the trace elements at seeding (in, or on-the-furrow injection with liquid fertilisers) and some later through the leaf. Grain analysis shows that for trace elements such as manganese (for photosynthesis), molybdenum (for chlorophyll and nitrogen metabolism) and cobalt (for vitamin B12), approximately 240 grams, 2.6 grams and 0.24 grams are removed respectively by 4 tons of grain per hectare. Applying trace elements directly through the leaf increases fertiliser-use efficiency and yields several-fold. Remember in planning fertiliser programs, all nutrients are linked, and a chain is only as strong as its weakest link. Grain analysis of cereals, or analysing small fruit for fruit trees, can identify the weakest link.
I usually apply 100 kilograms of urea and 150 kilograms of single superphosphate per hectare before sowing wheat. What is the equivalent amount of nitrogen in Rich Green Liquid N-S fertiliser?
The analysis values of granular fertilisers such as urea and superphosphate are usually shown as % w/w (per cent weight by weight). The analysis value of urea is usually 46.5% w/w nitrogen, so there is 46.5 kilograms of nitrogen in the 100 kilograms of urea you apply.
The analysis values of liquid nitrogen fertilisers such as Rich Green Liquid N-S are shown as % w/v (per cent weight by volume). The analysis value of Rich Green is 32% w/v nitrogen and 3.5% w/v sulphur. This means that 100 litres of Rich Green contains 32 kilograms of nitrogen and 3.5 kilograms of sulphur. To apply the equivalent amount of nitrogen (46.5 kg) in 100 kilograms of urea, you would then need to apply 100 x 46.5/32 = 145 litres of Rich Green costing approximately $0.30 per litre.
I would like to harvest around 4 tons per hectare of wheat grain. How much
fertiliser do I need to apply?
If you work on the practice of replacing the nutrients removed, you would need to calculate the amount of nutrients removed in 4 tons of wheat grain. This is where the chart showing nutrient content of grains becomes very useful in estimation. Analysis of grains can identify, for example, nutrient deficiencies at depth for deep-rooted crops, eg. copper in canola compared to cereals. From the upper medium concentration range of nutrients in wheat grain, 4 tons of grain removes approximately (as elements):
Grain analysis of my wheat is showing deficiency in some trace elements. For
a 4-ton crop of wheat grain per hectare, what is the minimum amount of Soil &
Foliar liquid fertiliser I need to alleviate the deficiency?
From the nutrients in grain data, you would need a minimum of:
1 litre of Soil & Foliar Copper to provide 20 grams of copper.
6 litres of Soil & Foliar Manganese to provide 240 grams of manganese.
4 litres of Soil & Foliar Zinc to provide 120 grams of zinc.
3 litres of Soil & Foliar Iron to provide 120 grams of iron.
1 litre of Soil & Foliar Boron to provide 30 grams of boron.
4 litres of Soil & Foliar Copper to provide 2.4 grams of molybdenum.
1 litre of Soil & Foliar Iron to provide 0.3 gram of cobalt.
If the deficiencies in the trace elements were identified through grain analysis to be manganese and boron, you would need to apply 6 litres per hectare of Soil & Foliar Manganese and 1 litre per hectare of Soil & Foliar Boron.
Can I replace soil applied granular fertilisers with liquid fertilisers?
As discussed earlier, due to several reasons, the uptake of nutrients by crops from liquid fertilisers are much more efficient than uptake from granular fertilisers. This allows less fertiliser to be used, resulting in considerable savings. As the availability and efficiency of liquid fertilisers improve, it is expected that liquid fertilisers will replace granular fertilisers; although to what extent is not yet known. Long-term trends of liquid fertiliser use in Australia can be expected to follow those set in USA, Canada and Europe. A comparison of nutrient forms used in granular and liquid fertilisers illustrates the efficiencies of liquid fertilisers.
|Nitrogen||Usually made from ammonia
(more expensive to granulate)
|Usually as urea and nitrate
|Phosphorus||Immobile in soil
|Foliar and soil-applied types of P more
|Potassium||Less mobile in soil and prone to fixation in some soil types||Potassium applied direct to leaves is rapidly available for improving photosynthesis|
|Calcium||Immobile in soil
(less available in acid soils)
|Ideal foliar route for availability in leaves, flowers and fruit|
|Magnesium||Less available in acid soils||Ideal foliar route for availability in leaves, flowers and fruit|
|Sulphur||Prone to leaching in soils||Timing of application improves availability and economy|
|Trace Elements||Sulphate forms often used
|Chelation improves uptake several-fold
In addition to fertilisers applied to achieve a certain yield, what
other factors should I consider?
Apart from calculation of the amounts of nutrients needed to achieve a particular yield, using grain analysis data, some of the other factors you should take into account when growing your crop are:
ï Soil pH
ï Soil type
ï Drainage conditions; example waterlogging and salinity
ï Tillage and seed-bed preparation
ï Absence or presence of soil-borne organisms
ï Absence or presence of weeds
ï Fertiliser history
ï Quality of seed and variety
ï Level of organic matter in soil; presence of beneficial microbes and earth-worms
ï Previous type of crop (eg. legumes for nitrogen)
ï Expected rainfall
ï Occurrence of frost.
Many of the problems that occur today in farming systems management and crop quality can often be shown to be related to deficiencies of nutrients; notably trace elements, magnesium and potassium. Management of strongly growing crops with good immunity towards environmental stress makes management a lot easier and rewarding.
I own a wheat and sheep farm of 6500 hectares in the wheat-belt. Each year I crop around 4000 hectares to wheat, barley, canola and lupins. I treat my crops and pastures with nitrogen and superphosphate, plus I have used the trace elements copper, zinc and molybdenum. I also test my soils each year. However I notice that my crops and pastures are not growing as well as in the past. Yields are down considerably, and I had problems this year from leaf disease and frost. The percentage of small grain at harvest has also increased. Do I need other nutrients such as magnesium, manganese and boron in my fertiliser program?
I recommend a grain test for your wheat, barley, canola and lupins after harvest this year to identify the deficient nutrients (see Publications section). I would also recommend 100-hectare yield trials next season using your usual fertiliser plus our Super Energy trace element liquid fertiliser. Use a liquid fertiliser with Super Energy that contains the major elements potassium and magnesium (see Blend-Tech system). Always include a control plot (your usual fertiliser only) for comparison.
The return to cost ratio (profitability) for your farm depends on fertiliser-use efficiency, which also translates to water-use efficiency. Fertiliser-use efficiency is increased greatly by avoiding deficiencies of nutrients. The gross return to nutrient cost ratio is a useful parameter in making fertiliser and management decisions, and can be calculated, as below, for a 4-ton per hectare crop of wheat and nutrients removed (see data above). The low ratio for nitrogen compared to other nutrients indicates a higher per-hectare cost of the nutrient compared to the other nutrients. With the rising cost of oil and industrially fixed nitrogen, farmers should consider improving the nitrogen-use efficiency of crops by using balanced fertilisers.
|Nutrient||Gross return / Nutrient cost|
Collecting a grain sample at harvest for analysis is easy, but is it as good as a soil sample for improving yields and quality? Is analysis of grain more difficult than soil analysis?
Grain analysis can help you to identify whether nutrient elements in the harvested grain are in the low range, medium range or high range for a particular crop. This ability to identify the nutrient elements that fall in the low range is the first crucial step in deciding which elements need to be boosted in fertilisers to increase productivity. If your 100-hectare trials show a considerable improvement in productivity, the deficiencies are confirmed. Grain test results to date have shown some crops to be deficient in up to six elements, alerting farmers to the reason for poor yields and quality.
Grain analysis enables the uptake of a particular nutrient by the crop to be calculated; by multiplying the actual concentration of the nutrient in the grain at harvest with the actual grain yield. From this data, grain analysis can be used to improve the efficiency of fertiliser used, or to help target a particular, higher yield desired for the next crop.
Knowing nutrient levels in soil before sowing a crop is useful, but cannot always be relied upon to predict performance by crops due to various soil conditions which affects plant availability (eg. soil pH, soil type, tillage method etc,). For example, in high alkaline type soils, a high soil phosphorus reading may not guarantee that the crop will receive sufficient phosphorus during its growth. Foliar or soil applied liquid fertilisers containing phosphorus may be needed. Alkaline soils can also tie up manganese, boron and iron, causing deficiency even though a soil test could indicate sufficiency. Acid soils can reduce the uptake of molybdenum. The direct foliar route with liquid fertilisers for these elements is then preferable.
The analysis of grain is no more difficult to accomplish than soil analysis. In many ways grain analysis is easier as the sample is highly homogeneous compared to a soil sample, easy to post, keeps well as it is dry, and nutrient concentrations are much higher than in soil, making analysis more accurate. However choosing a suitable laboratory for analysing grain and soil samples is very important for achieving an accurate interpretation of the results.
My cereal and canola crop yields have been severely affected by frost for the past three years. How can I prevent frost damage?
Throughout the world there are huge economic losses to frost damage reported each year. There are more economic losses to frost damage than any other natural hazard including drought, floods, hurricanes etc. Most countries with temperate climates experience frost damage to crops and even tropical countries can have frost damage at high elevations. When immature crops are damaged, grain yield, drying rate, and grain quality can all be affected; source: Extension Service, University of Minnesota, USA. Shoot tips, and tissue in basal parts of shoots and stems can be irreversibly damaged by frost, curtailing the supply of water and nutrients.
Whether or not frost damage occurs depends on many factors including the plant species, crop variety, cold-temperature hardening, cultural practices including pruning, fertility and irrigation, weather conditions and the presence of ice-nucleation active (INA) bacteria; source: University of California, Davis, USA. Although it would be difficult to completely prevent some frost damage to crops, frost damage can be minimised by applying balanced fertilisers and improving fertility management of problem soils (saline or acid). As you have suffered crop damage by frost for three years in a row, it is most likely that the cause could be severe nutrient deficiencies, in which case I would recommend grain analysis and soil analysis: see: Publications section.
During cold-temperature hardening, plants accumulate protective soluble carbohydrates (glucose, sucrose, raffinose) and proteins in the cell solution, which act as antifreeze solutes. Plants utilise this ability called supercooling to survive freezing temperatures below zero degrees C. Moderate supercooling prevents the formation of ice crystals within the plant tissues, which disrupts plasma membranes causing damage; source: Swedish University of Agricultural Sciences, Uppsala, Sweden.
The soluble carbohydrates and proteins utilised as cryo-protective solutes are synthesised by plants during carbon fixation from atmospheric carbon dioxide (greenhouse gas) for growth and reproduction (see photosynthesis, in earlier discussions). Photosynthesis efficiency by chlorophyll relies heavily on a balanced supply of all the major nutrient elements and trace elements taking part in enzyme-mediated metabolic processes. Some of the functions of the major nutrient elements, of particular importance during photosynthesis are nitrogen (for proteins and enzymes), phosphorus (photosynthesis and energy as ATP), magnesium (for chlorophyll formation), sulphur (for protein); and calcium and potassium to maintain cell wall rigidity and strength to resist frost damage.
The trace elements iron, zinc, manganese, copper, boron, molybdenum and cobalt are all closely involved in plant photosynthesis process and nitrogen metabolism for the synthesis of the carbohydrates and proteins. The ultra-trace element iodine, often used in fertilisers for iodine deficient pastures, is closely associated with chlorophyll function and starch synthesis; and is also important in human and animal nutrition. Utilising grain analysis, replacement of the iodine removed from soil by crops is low; for a 4-ton per hectare crop of wheat being approximately one-half that of cobalt at 0.12 gram per hectare. Farmers would be interested in comparing analysis of grain from frost-free crops and frost-damaged crops. Comparison could then be used in identifying the nutrient needs of frost-damaged crops for treatment.
Under Publications and Nutrition Management on your website, you provided data
for grain nutrient levels to characterize nutrient status and for estimating fertiliser
needs. This data was collated over a long period of 20 years. Is there a way to
collate grain analysis data for rice in a much shorter time frame, say one year?
When farmers sow a crop, whether it is rice, soya bean or wheat, they are usually hoping for a high yield to increase their income. Depending on where the crop is grown, and taking into account costs and investment risks, high-yield targets vary substantially between countries. For example in Australia where irrigated rice yields are very high at 6 to 10 tons per hectare, grain analysis data from crops yielding 6 - 10 tons/ha would be of interest and analysis can then be contrasted against crops with low yields of,say, 2 - 3 tons/ha. Yields of 4 - 6 tons/ha of rice may be considered high and a desirable target yield in some countries.
Provided sufficient samples are taken, reliable and useful nutrient data for fertilizer advice can be obtained for quality crops in a singe season with this method. As more data is collected in future years, the complete nutrient ranges can be fine-tuned and recorded for rice (or soya bean) as has been done here for wheat, canola, barley and lupin crops. I recommend at least six high-yield samples, each harvested from a significantly large area (eg. 1 hectare) from different farms. The accuracy and precision of grain analysis is critical when obtaining this foundation data, so I recommend that the grain sub-samples of the high-yielding crops be sent to at least three independent laboratories for comparison and confirmation.
The recorded data can be used to estimate nutrient status of other crops collected on other farms in the same year. Crops with nutrient level(s) significantly lower than those of the high-yielding crops can be boosted with the deficient nutrient(s) for the next crop to improve yield and quality.
On the Adverts page, 'Integrated fertiliser programs way to high yield and quality',
is potassium sulphate preferable to potassium chloride in the Super Potash 1:1 fertilizer? Are sodium and chloride nutrients needed for Australian soils? I am
surprised to learn that magnesium uptake for a 3-ton/ha wheat crop is about 5 kg/ha of the element. Why is magnesium nutrient not added to most of our broad-acre
NPK fertilizers in Australia?
Super Potash 1:1 is usually manufactured in Australia with potassium chloride (muriate) as a source of potassium, although sometimes potassium sulphate only is used. As chloride in fertilizers is an important nutrient, discussed below, a mixture of potassium chloride and potassium sulphate in Super Potash 1:1 would be preferable for balance. Dolomite, lime and gypsum are natural resources and usually contains some sodium and chloride, so the analysis of these products used for your farm should include sodium and chloride to calculate the applied amounts and keep them within their optimum productivity range.
Sodium and chloride are classified as functional nutrients by plant chemists, instead of as essential nutrients. Functional nutrients have unique roles to play in plant metabolism and helps to increase biomass yields and quality. The sodium cation in healthy plant tissues is usually accompanied by its anion, chloride. It is often assumed that sodium and chloride are always present in plant tissue in sufficient amounts for healthy growth, although this might not always be the case, especially if they are absent in all nutrient inputs. There is also a perception that these two elements should be avoided in fertilizers as they increase the salt index of the fertilizer. There is now increasing evidence from grain analysis that in the majority of grain samples analyzed, there is a shortage of sodium. The analyzed grain samples originate from the general rain-fed broad-acre farms with no salt problems. The optimum analysis level for sodium in wheat grain is about the 0.01- 0.02% level, rather than the less than 0.01% level usually seen. At the 0.01% level of sodium, a three ton/ha wheat crop needs about 300 grams of sodium per hectare. As chloride usually accompanies sodium, chloride requirement for wheat grain should be around 450 grams/ ha for a 3-ton/ha crop of wheat. We will confirm this in a future posting after grain analysis for chloride (Posted below on 3 June, 2010). Calculated from sodium, the replacement level of sodium chloride as sea salt is about 0.75 - 1.0 kg/ha for a 3-ton/ha crop of wheat, and proportionally less is needed for a smaller targeted yield.
In earlier postings under Nutrition Management page (Would sea salt make a good fertilizer?), I have discussed the nutritional needs of crops for sodium and chloride nutrients. Sodium and chloride are particularly important in the nutrition of plants, animals and microbes as they participate in the reactions of a myriad of catalytic enzymes. As the two ions are both smaller than the majority of cations and anions, they can fit into the tight spaces of the large molecules of proteins and enzymes when these are assembled, acting as counter-ions providing ideal distribution of electrical charge. These two elements are particularly important for the critical photosynthesis process which uses sunlight energy, water and carbon dioxide to first synthesize carbohydrates, and then proteins. During the respiration process which follows photosynthesis, complex organic compounds are disassembled into smaller and less complex compounds by plant enzymes, with the release of energy needed by the cell for cellular functions. During disassembly reactions, the chloride anion is a more efficient leaving group than larger anions, for example nitrate and sulphate anions in plants; thus allowing the reactions to take place at a quicker pace because of favorable stereochemistry. As the process of respiration is inextricably linked with the process of photosynthesis in plants, sodium and chloride assists photosynthesis efficiency. Besides photosynthesis, chloride has a function in maintaining water levels in plants, and also diminishes the effects of fungal diseases in plants and grains (chloride crop nutrients: www.americanchemistry.com ). Sodium and chloride are intimately involved as electrolytes and counter-ions in energy releasing reactions involving phosphorus as ATP (adenosine triphosphate), and their inclusion in fertilizers therefore has a positive influence on productivity and quality of crops because of improvements in fertilizer and water-use efficiencies.
Returning to your question on the uptake level and magnesium in NPK fertilizers, magnesium is undoubtedly a very important nutrient. It is the centrally located ion in the chlorophyl a complex and thus central to the photosynthesis process; the pigment imparting its green color to leaves and stems. Magnesium in plants promotes efficient utilization of applied nitrogen, phosphorus and potassium (NPK), increasing photosynthesis efficiency. With regards to magnesium content of our broad-acre NPK fertilizers, there are some difficulties in including magnesium during manufacture as magnesium tends to react with phosphorus during granulation, making granulation costly (see also: Publications; Magnesium's mysteries unravel). Difficulty of adding magnesium to NPK fertilizers is due more to technical problems with its chemistry than availability of this nutrient. Magnesium is needed by crops at a similar level to the all-important sulphur. If magnesium is used as magnesium sulphate heptahydrate, MgSO4.7H2O (epsom salt), about 50 kilograms/ha of epsom salt would be needed to supply 5 kg/ha of magnesium element. Premium quality fertilizers used for horticulture contain magnesium usually as the slow-release magnesium ammonium phosphate compound (magamp). Kieserite granules is a good source of magnesium and sulphur (15% Mg, 20%S).
An NPK fertilizer containing 2% magnesium content would supply only 2 kg of magnesium in an NPK application of 100 kilograms/ha, still far short of the 5 kg/ha needed, unless application rates are increased considerably. The end-result of difficulty and cost of adding magnesium to NPK broad-acre fertilizers is that there is often a high incidence of magnesium deficiency in crops and resultant drops in productivity. NPK fertilizer suppliers should increase awareness of this problem, and if unable to supply magnesium containing NPK fertilizers, should recommend to farmers that dolomite (MgCO3.CaCO3) be spread before sowing. High-quality dolomite at 150 kg/ha supplies about 15 - 19 kg/ha of magnesium. A larger amount than needed is recommended here as it is not as soluble or immediately available compared to epsom salt. In addition to supplying the magnesium needs of a crop, dolomite has alkaline properties and helps to increase the buffering capacity of soils; reduces soil acidity, and improves soil phosphate and potash availability to increase productivity. There is also less risk of losing magnesium through leaching.
Besides magnesium, you should also be aware that many of the compound NPK fertilizers used for broad-acre cropping lacks boron, iron and cobalt trace elements. Although their sodium and sulphate salts are available for use, they should preferably be used together with other trace elements in compound fertilizers for best crop performance and economy. The nutritional importance and interactions of trace elements have been discussed under Nutrition Management and Technical Questions pages (see also: Grain Analysis System Related Products; Soil and Foliar Iron, Soil and Foliar Boron). Super Trace, Super Energy and Super Liquid NPK fertilizers are excellent sources for magnesium and chelated trace elements used as seed coating and for foliar application.
Nutrients accounting and supply, based on grain analysis, is an important innovation by our Company for farmers to secure yields and quality of grains at harvest. Incentive payments to farmers for quality could be increased to encourage increased use of fertilizer. Fertilizer quality and analysis needs special attention by grain growers to maintain sustainability and profitability. Wheat quality is reportedly set to be a major issue for Australian growers in 2010 (Farm Weekly, April 15, 2010 p52). Posted 19 April, 2010
Under 'Integrated fertiliser programs...', on Adverts page, it is difficult to
understand that application of only 2 grams per hectare of molybdenum and 0.2
gram per hectare of cobalt are needed to replace their uptake by 3 tons of wheat
grain. Is such small amounts sufficient, and how do I accurately apply such small
amounts to crops?
Molybdenum and cobalt trace elements occupy the upper boundaries of a range of trace elements classified by chemists as the ultra trace elements. It is not surprising that there is some difficulty in understanding why such small amounts are needed, as the concepts are quite complex . A brief explanation of the analytical chemistry of trace elements and their role in nutrition is therefore needed. Trace elements or micro nutrients derive their name from the fact that they are present only in very small, ìtraceî amounts in agricultural materials such as plant leaves, grains and soils, and are needed by plants, animals and microbes for their metabolism and nutrition.
Laboratory measurements of trace elements in plant tissue and soils advanced rapidly in the late 1950's with the development of a very accurate, precise and sensitive analytical instrument called the atomic absorption spectrometer (AAS) by Australian physicist (Sir) Alan Walsh; AAS was described as the most significant advance in chemical analysis in the twentieth century (New Mexico State University, Department of Chemistry and Biochemistry). This instrument enabled analytical chemists to begin accurate, routine measurements of trace elements in the parts per million range in solutions, which enabled the convenient and routine analysis of the major minerals and trace elements in plants and soils for the first time. For agricultural purposes, the measurement of molybdenum by AAS in plant tissues was still very difficult, but possible in fertilizers after pre-concentration. Scientists announced in the late 1970's that there was still another class of trace elements, the ultra trace elements such as cobalt, vanadium, selenium, iodine etc. which were needed in even smaller amounts than molybdenum for life processes. The ultra trace elements have been discussed to some extent earlier on this website (Nutrition Management and Technical Questions pages). Their uptake levels in 3-tons of wheat grain are in the expected low ranges, ranging from approximately 0.2 gram/ha for cobalt to a low of 0.05 gram/ha for selenium.
Accurate measurement of trace nutrients in fertilizers by AAS allowed measurement of molybdenum, the lowest quantifiable and verifiable nutrient in fertilizers. With the advent of still more sensitive analytical instruments such as the Zeeman graphite furnace atomic absorption spectrometer (Zeeman-GFAAS) and the Inductively coupled plasma - mass spectrometer (ICP - MS), analytical chemists are now able to routinely and accurately measure the levels of the trace and ultra trace elements in fertilizers and plants.
The reason for molybdenum and cobalt being needed in such small amounts is that they perform their functions in plants as single atoms activating large molecules of enzymes. For example, the nitrogen-fixing enzyme, nitrogenase, which helps reduce atmospheric nitrogen to ammonia within the rhizobium nodules ,consists of two protein fractions - an iron protein and a molybdenum-iron protein (The Microbial World by Jim Deacon; The University of Edinburgh). Only a single atom of molybdenum is needed here to activate a very large nitrogenase molecule with a molecular weight of around 200,000 g/mol.
Cobalt as a single central atom activates Vitamin B12 (cobalamin), a large complex molecule with a molecular weight of 1355.37 g/mol. In animals, some of the functions of vitamin B12 are in assisting DNA synthesis, helping in red blood cell production and supporting normal nervous system function. In plants, particularly legumes, cobalt is an essential nutrient for the vitamin B12 nutrition of nitrogen-fixing rhizobia of nodules.
Adding the small amounts of molybdenum and cobalt evenly to granular fertilizers during manufacture would be very difficult, as you could imagine. To give you an idea how small the amounts actually are, the 2.0 grams and 0.2 gram of molybdenum and cobalt needed to be applied to each hectare of farmland are about the weights of 10 granules of urea and 1 granule of urea respectively. One might then think that these amounts of trace elements are so small that they could not possibly perform their important tasks. However, as explained earlier, because they perform their tasks as single atoms activating a much smaller population of large molecular enzymes, they are very effective when applied directly to the seed or leaf.
We can calculate the number of atoms or molecules in a given weight of any element or compound from the extremely useful Avogadro's Number, 6.0221 x 10 (to power of 23)/ mol. Avogadro's Number was confirmed theoretically by Austrian chemist physicist Johann Josef Loschmidt in 1865, and determined experimentally by French physicist Jean Perrin in 1909 (Nobel prize in Physics, 1926) who then named it in honor of Italian chemist Amedeo Avogadro who first proposed it in 1811 (see also: Wikepedia). Each 2.0 gram molybdenum and 0.2 gram cobalt applied per hectare contains 1.26 x 10 (to power of 22) atoms of molybdenum and 2.04 x 10 (to power of 21) atoms of cobalt respectively.
The planning and application technology of fertilizers is particularly important if the objective is for the plant to take up most of the applied nutrients for productivity, without any waste. Grain analysis and calculation of the amounts of nutrients needed in fertilizers, from the levels found in the grain, ensures that all important nutrients are not missed, whilst providing a fully balanced application of nutrients for a targeted yield. Calculations allows full flexibility in planning fertilizer inputs for different crops, for example, double all inputs for double the yield, or halve all inputs to halve the yield; in situations where a higher yield or a lower yield (for less risk or less cost) is desired.
Whilst granular fertilizers are needed to supply the bulk of NPK and secondary nutrients for broadacre cropping, liquid fertilizers are more suitable for trace elements as they can be chelated to remain soluble in solution and active for plant uptake. Chelation of trace elements in granular fertilizers applied to soils would be too expensive. Liquid fertilizers such as Super Energy Seed Treatment applied directly to seeds at 5-litres per ton of seed with about 5-litres of water as diluent ensures quick uptake in the early, crucial stages of germination and root establishment. A good start to the season with excellent crop establishment achieves a higher yield as well as enabling the crop to cope with environmental stress.
As all nutrients take part in the photosynthesis process, application of foliar nutrients direct to the leaves where photosynthesis occurs allows more economical use of expensive fertilizers . Nutrients as carbohydrates and proteins are then translocated efficiently from the flag leaf (cereals) to the nearby developing grain, or from leaves to adjacent fruits. Application rates of water for foliar application is kept low for broadacre crops (about 50- litres/ha), sufficient to coat the leaves evenly. Misting and drift of foliar fertilizers should be avoided by careful choice of spray jets and pressures. Posted 27 April, 2010
The chloride analysis result for a sample of wheat grain was 0.08%, compared to sodium analysis result of <0.01%, which is less than the optimal 0.01 - 0.02% for sodium in wheat grain. With more analyses of grains for chloride in the future, we will be able to advise farmers whether the chloride result for the grain fits in the low, medium or high range in order to manage chloride input. Sodium content here in relation to chloride is surprisingly low, indicating that chloride is present as anion of sodium and potassium, calcium, magnesium cations. If present altogether as sodium chloride, although unlikely, sodium analysis would be around 0.08% x 23/35.5 = 0.05%.
Sodium is an important element for beet and rice cultivation, and application of measured sodium as sea salt or sodium nitrate in addition to potassium chloride increases yields and quality. Vegetable yields, quality, color and taste are also improved by adequate sodium and chloride in fertilizers. Sodium can partly replace potassium in nutrition and enhance conservation of potassium fertilizer, although potassium cannot replace the functions of sodium. Fruits produced only with the potassium chloride form of potash fertilizer, but which lack sodium nutrient altogether, are of lower quality in size, color, taste and weight. Sodium deficit is sometimes unintentionally alleviated by the application of borax (disodium tetraborate) or sodium phosphate in foliar fertilizers.
As discussed above, the small ionic radii and strongly conductive properties of sodium and chloride ions are crucial for promoting enzyme assembly, enzyme function and enzyme kinetics in nutrition. The ionic radius of sodium is 102 pm, compared to a significantly larger 138 pm (picometres) for potassium. Sodium counter-ions can be a better fit between some of the tight spaces in large molecules of enzymes and proteins than potassium. Posted 3 June, 2010