Monday, December 24, 2018

Quality: Potassium Management is Critical for Horticultural Crops

Quality, What is it?
Potassium is frequently referred to as the “quality” nu­trient for plants. Quality has many characteristics and the most important aspects of quality will depend on the spe­cific crop. For example, with citrus, it may be the thickness of the peel and Vitamin C concentration, for apples, sug­ar concentrations, while for tomatoes, the development of uniformly red fruit rich with lycopene. The specific quality parameters for each crop will vary and should be well un­derstood to maximize crop nutritional practices and market profitability (Kumar et al., 2006).

While many “quality” benefits are generally understood, it can be difficult to define and quantify the exact benefits of K (Lester et al., 2010a). Most notably, the lack of quali­ty is frequently observed when the plant K supply becomes
 deficient. An inadequate K supply becomes especially im­portant for horticultural crops where the visual appearance of the fruit and leaves is critical for marketing. Although the total yield may be reduced with insufficient K, it is possible that the entire crop may be unsalable due to poor quality and visual appeal.

The growth and longevity of cut flowers and ornamen­tals can also be diminished by a lack of adequate K. Ship­ping, handling, and freshness are particularly important for ornamental horticulture.

Consumer Preference
Consumers have a strong preference for fresh fruits and vegetables with appealing appearance and texture. Quality and freshness of fruits and vegetables are often cited as the primary characteristics for making purchase decisions.
Potassium plays a critical role in many of the metabolic processes that enhance the quality, nutrition, flavor, appear­ance, and longevity of fresh food crops. These beneficial im­provements clearly are desirable for farmers and will add to the marketability of crops.

 Vitamin C
Application of K to the soil or plant foliage has been shown to increase the concentration of Vitamin C in a va­riety of fruit crops. While citrus is the most frequently cited example, increased Vitamin C has been reported in crops such as cucurbits, cauliflower, onion, banana, guava, and papaya (Imas, 2013). Muskmelon also had higher concen­trations of Vitamin C as a result of foliar K sprays (Lester et al., 2010b).

Nitrate Assimilation and Protein Synthesis

Potassium plays an important role in converting nitrate into amino acids and proteins. An insufficient supply of K may result in both lower nitrate uptake from the soil and slower nitrate assimilation into amino acids and proteins. Potassium deficiency can result in accumulation of low mo­lecular weight sugars and carbohydrates, along with solu­ble-N compounds in the plant.

Nitrate accumulation in K-deficient plants can be a con­cern where limits have been established (such the Europe­an Union nitrate limit for leafy vegetables). When nitrate is rapidly converted to protein, the concern for healthier food is satisfied.

Appearance of Fruits and Vegetables
An adequate K supply has been linked to improved vi­sual appearance of many horticultural crops. For example, banana is a crop that frequently responds favorably to K fertilization. Sufficient K improves banana fruit weight and number of fruits in each bunch, increases soluble solids, sug­ars, and starch. Low K results in thin and brittle bunches with a shorter shelf life. A lack of K has been linked with premature color development and harder, dry fruit sacs in citrus. Potassium-deficient grapes are less firm and have less juice.

An adequate supply of K increased mar­ketability traits of muskmelon fruit (maturity, yield, firmness, and sugars) and quality param­eters (ascorbic acid and β-carotene) (Lester et al., 2010a). The yield, quality, and shelf-life of tomatoes are improved with an adequate K supply. A lack of sufficient K results in uneven ripening, yellow shoulder fruit, and irregularly shaped fruit with poor internal quality (Hartz et al., 2005).

Extending Shelf-life and Reducing Food Waste
Potassium has been shown to have a bene­ficial impact on properties that improve shelf life, storage, and shipping of many fruits and vegetables. Some of this occurs as an adequate K supply generally increases the firmness and strength of skins, allowing greater resistance to damage during trans­port and storage. Extending the longevity of freshness pro­vides immediate benefits to both the farmers and the con­sumers.

The positive impact of K on fruit storage has been re­ported on many crops, including bananas (shelf-life), citrus (decreased post-harvest mold and rot), potatoes (storage longevity), carrots (crispness), pineapple (greater vitamin C leading to reduced browning and rot), figs, and apples.

Disease and Insects
Plants that are deficient in K are likely to be more sus­ceptible to infection and insect damage than when sufficient K is present. In a significant literature review, Perrenoud (1990) examined 2,449 scientific citations and concluded that the use of K reduced the incidence of fungal diseases by 70%, bacterial infection by 69%, insects and mites by 63%, viruses by 41%, and nematodes by 33%. Reducing these pathogens and insects had a large benefit of allowing higher yields to be achieved.

A review by Wang et al. (2013) presented an excellent summary of how optimal K nutrition imparts significant plant resistance to both biotic and abiotic stresses. They re­viewed the important role of K in protecting plants against diseases, pests, drought, salinity, cold and frost, and water­logging.

Consumers are sensitive to the use of plant protection chemicals in production of horticultural crops. This sensi­tivity partially accounts for the growth of the organic farm­ing sector (Mikkelsen, 2007). Whenever possible, providing adequate K should be used as a first line of protecting plant health. Decreased damage to harvested fruits and vegeta­bles from pathogens and stresses will also result in a more attractive, marketable, and hence profitable crop.

Nutrient Composition
Fruits and vegetables are the most important sources of dietary K in the human diet. However, a trend for a decline in the mineral concentration of many foods has been sug­gested for over 75 years (Davis, 2009). A decline of 5% to 40% or more in minerals, vitamins, and proteins has been measured in many foods, especially vegetables. The cause for this decline may be due to dilution, changes through plant breeding, and changes in farming cultural practices. Recent reviews indicate that the decline in nutrient concen­tration of fruits and grain may not be as severe as earlier claimed (Marles, 2017).

Whatever the cause of this dilution, clearly there is a need to reexamine how the K concentration of food can be enhanced to better meet the dietary and health needs of consumers.

Functional Foods
“Functional food” is a term used to describe foods that provide health benefits in addition to the regular vitamins and minerals contained in common foods. Including them in a human diet is often considered to promote health be­yond a more typical diet. Lycopene found in tomatoes, alli­cin present in garlic, and resveratrol in grapes are examples of nutraceutical compounds in functional foods that may provide health benefits.

The concentrations of all these functional food com­pounds listed above have been shown to increase in the pres­ence of an adequate or abundant K supply to plants. The direct metabolic link between K and these functional food compounds is not always clear, but the trends are consistent.

Human Health
Animals and humans have an absolute requirement for K for proper growth and health. Potassium is involved in many essential functions in nerves, biochemical reactions, muscle function, heart health, and water balance. However, almost all human diets are quite low in K compared with the recommendations for health (Weaver, 2013). For exam­ple, in the United States the average daily K consumption is only 55% of the recommended dietary intake.

A diet rich in fruits and vegetables is one of the best ways to increase K intake, with potatoes being one of the highest sources of dietary K. Increasing the K concentra­tion of the harvested portion of fruits, vegetables, and other plant-based products would make an important contribu­tion to improving human health.

Conclusions
Potassium is essential for sustaining both the yield and the quality of many horticultural crops. Enhanced quality is frequently observed in many vegetables and fruits from an abundant supply of K. This quality can be observed in different ways for each species, but includes parameters such as size, appearance, longevity of storage, sugar and acidity, soluble solids, and nutritional benefits. Damage from dis­ease, insects, and environmental stresses are frequently re­duced when adequate K is present. All these considerations combine to underline the importance of maintaining an adequate supply of K for the production of high quality horticultural crops.

References
Davis, D.R. 2009. HortScience 44:15-19.
Hartz, T.K. et al. 2005. HortScience 40:1862-1867.
Imas, P. 2013. Potassium - The quality element in crop production. Intern. Potash Institute: Horgen, Switzerland.
Kumar, A.R. et al. 2006. Agric. Rev. 4:284-291.
Lester, G.E. et al. 2010a. Better Crops 94(1):18-21.
Lester, G.E. et al. 2010b. Plant Soil 335:117-131.
Marles, R.J. 2017. J. Food Comp. Anal. 56:93-103.
Mikkelsen, R.L. 2007. HortTechnology 17:455-460.
Perrenoud, S. 1990. Potassium and Plant Health, 2nd ed., International Potash Institute: Bern, Switzerland.
Wang, M.Q. et al. 2013. Int. J. Mol. Sci. 14:7370-7390.
Weaver, C.M. 2013. Adv. Nutrition 4:368S-377S.

This article originally appeared in IPNI's magazine: Better Crops in 2018.  It is linked here
potassium potash health vegetable fruit quality consumer nitrate shelf waste functional human animal quinic sulphoraphine indole carotenoid echinacoside polysaccharide lignans allicin flavonoids ginsenoside serveratrol quercirtin anthocyanidins lycopene carotenoid beta glucans saporins terpenoids phytic robert mikkelsen rob plant nutrition

Thursday, December 13, 2018

Nanofertilizer and Nanotechnology: A quick look



The word “Nano” means one-billionth, so nanotechnology refers to materials that are measured in a billionth of a meter (nm). A nanometer is so small that the width of a human hair is 80,000 nanometers. The field of nanotechnology has resulted from advances in chemistry, physics, pharmaceuticals, engineering, and biology. The size of a nanomaterial is typically about 1 to 100 nanometers. They can be naturally occurring or engineered. Due to their extremely minute size, they have many unique properties that are now being explored for new opportunities in agriculture.


There are naturally occur- ring nanoparticles that have been previously proposed for agricultural use, such as zeolite minerals. However, engineered nanomaterials can now be synthesized with a range of desired chemical and physical properties to meet various applications.

Nanofertilizers are being studied as a way to increase nutrient efficiency and improve plant nutrition, compared with traditional fertilizers. A nanofertilizer is any product that is made with nanoparticles or uses nanotechnology to improve nutrient efficiency.
Another promising application of nanotechnology is the encapsulation of beneficial microorganisms that can improve plant root health. These could include various bacteria or fungi that enhance the availability of nitrogen, phosphorus, and potassium in the root zone. The development of nanobiosensors to react with specific root exudates is also being explored.

Three classes of nanofertilizers have been proposed:
1. nanoscale fertilizer (nanoparticles which contain nutrients),
2. nanoscale additives (traditional fertilizers with nanoscale additives), and
3. nanoscale coating (traditional fertilizers coated or loaded with nanoparticles)
Nanomaterial coatings (such as a nanomembrane) may slow the release of nutrients or a porous nanofertilizer may include a network of channels that retard nutrient solubility. The use of nanotechnology for fertilizers is still in its infancy but is already adopted for medical and engineering applications.

Another promising application of nanotechnology is the encapsulation of beneficial microorganisms that can improve plant root health. These could include various bacteria or fungi that enhance the availability of nitrogen, phosphorus, and potassium in the root zone. The development of nanobiosensors to react with specific root exudates is also being explored.

Examples of potential nanofertilizer designs  (adapted from Manjunatha et al., 2016)
  • Slow release: the nanocapsule slowly releases nutrients over a specified period of time.
  • Quick release: the nanoparticle shell breaks upon contact with a surface (such as striking a leaf).
  • Specific release: the shell breaks open when it encounters a specific chemical or enzyme.
  • Moisture release: the nanoparticle degrades and re- leases nutrients in the presence of water.
  • Heat release: the nanoparticle releases nutrients when the temperature exceeds a set point.
  • pH release: the nanoparticle only degrades in specified acid or alkaline conditions.
  • Ultrasound release: the nanoparticle is ruptured by an external ultrasound frequency.
  • Magnetic release: a magnetic nanoparticle ruptures when exposed to a magnetic field. 
Many of these nanotechnologies are still in the early development stage for both medical and agricultural uses. However, the next time you hear about nanofertilizers, you will have a better idea of where this field is headed.

Additional Reading
  • Calabi-Floody, M. et al. 2017. Adv. Agron. 147:119-157.
  • Fraceto, L.F. et al. 2016. Front. Environ Sci. 22 March 2016. https://doi.org/10.3389/
fenvs.2016.00020
  • Manjunatha, S.B. et al. 2016. J. Farm Sci. 29:1-13.
  • Tapan, A. et al. 2016. J. Plant Nutri. 39:99-115, https://doi.org/doi.org/10.1080/019041
67.2015.1044012
  • Wang, P. et al. 2016. Trends Plant Sci. 21(8) https://doi.org/10.1016/j.tplants.2016.04.005

The original article can be viewed here:


Fertilizer pollution phosphorus technology mikkelsen soil fertility chemistry advance new nutrition

Wednesday, December 5, 2018

Swapping Organic and Inorganic Fertilizers


Rob Mikkelsen, IPNI
The bickering over the superiority of one source of plant nutrients over another gets tiresome. There are excellent arguments about why organic nutrient sources make valuable contributions to plant and soil health. However, remember that the inorganic fertilizer industry first developed to satisfy farmer’s irreplaceable need for affordable plant nutrients. Yes, both sources of nutrients play essential roles for food production sustainability.


The fundamentals of 4R Nutrient Stewardship remind us to always use the Right Source of nutrient regardless of their origin. Applying 4R principles will always assist in achieving the desired goals of each unique situation.

Predicting N release from mineral fertilizers is relatively simple (see diagram provided). The N release from organic fertilizers depends on the proportion of rapid and extended-release materials. The environmental conditions and field management practices influence the behavior of all nutrient sources applied.

One difference between many organic and inorganic fertilizers is the presence of organic carbon. Addition of organic matter is almost always beneficial for soil health. However, there are at least two ways of adding organic matter to soil: 1) harvest crops from one field,  feed them to animals and humans, and then return the manure to another field, or 2) grow plant-based organic matter directly on the field  (such as cover crops or by returning crop plant residue). Both approaches are effective in increasing organic carbon inputs to the soil.
Predicting nitrogen availability for plants is challenging from organic fertilizers

The decision of using organic or inorganic nutrient sources is often based on the availability of local resources, the economics of hauling and application, and the need to supply balanced crop nutrition. Here are a few considerations to keep in mind:

Potassium (K):  The fertilizer equivalence of K in most organic nutrient sources is quite similar to inorganic sources. Since K is not a structural component of plant cells, it remains soluble in animal manure, urine, and crop residues. The nutrient value of K in animal manures is generally equivalent to soluble K fertilizers.

Phosphate (P):  Phosphorus availability from organic materials for plant nutrition is extremely variable. In animal manure, 45 to 70% of the P is present as inorganic phosphate, the form found in most fertilizers. Most reports indicate that there is no difference in crop growth between P supplied by animal manures and composts or fertilizer P (Prasad, 2009, Zhang, 2002). Phosphorus availability in manure and compost will often range from 60 to 100% of the inorganic P fertilizer equivalent. Conditions controlling mineralization and the presence of additional organic matter can also play a role in P availability.

Some commercially available organic fertilizers have been shown to be unsatisfactory at supplying the immediate P needs of plants. However, with a multi-year perspective, even these slowly available P sources may eventually supply P for crop growth if applied in large quantities.

Nitrogen (N):  Predicting the fertilizer replacement value of N in organic materials is the most challenging of the primary nutrients. The availability of N from an organic material is partially controlled by its chemical and physical characteristics. The N-release rate from organic materials is also impacted by factors such as the site (e.g., soil, climate), soil fertility (existing C and N, turnover rate), crop type (length of growing season, rooting patterns), and multi-year field management practices (placement, tillage).
 
Some organic materials, such as urine, are equivalent to a solution of urea and N will rapidly become available for plant uptake. Other materials, such as aged beef-lot compost will be stable for several years and only begin to release N after many years.

Many organic fertilizers provide both short-term and long-term N release, which consequently requires considerable skill and knowledge to accurately predict the nutrient value. To aid in this prediction, Gutser et al. (2005) developed a chart for comparing the N fertilizer equivalence for a variety of organic materials during the first year of application.
 
Gutser et al (2005) made a chart comparing nitrogen availability from organic materials compared with soluble fertilizer
The selection of any nutrient source should be made so that it simultaneously accomplishes the 4R goals of economic sustainability, environmental protection, and societal acceptance. Whether a farmer primarily uses organic nutrient sources, inorganic fertilizers, or a combination of the two, they must all be managed properly. Let’s not argue about it.

References and Further Reading:
  • Gutser, R. et al. 2005. J. Plant Nutr. Soil Sci 168:439-446.
  • Mikkelsen, R. and T.K. Hartz. 2008. Better Crops 92(4) 16-19.
  • Mikkelsen, R. 2008. Better Crops. 92(2) 26-29.
  • Nelson, N.O. and R. Mikkelsen. 2008. Better Crops 92(1) 12-14
  • Prasad, M. 2009. A Literature Review  on the Availability of Phosphate from Compost in Relation to the Nitrate Regulations SI 378 of 2006. EPA,  Wexford, Ireland.
  • Zhang, H. et al. 2002. Managing  Phosphorus from Animal Manure. Univ. Arkansas. http://animalwaste.okstate.edu/bmps-regulations/ bmps-regulations