ag, seeds, organic farming, propagating seeds

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Seeds of Change: What’s in your Packet of Certified organic seed?

By Dr. Wesley Chun Ph.D., Grower's Secret, Chief Science Officer

Abstract

There are three reasons for using certified organic seed to produce organic crops. First, the National Organic Program (NOP) guidelines recommend use of organically produced seed for organic crop production. Second, it is good for your conscience since organically produced seeds inherit environmental conservation and pollution reduction benefits. Third, organic seeds are claimed to be healthier (more resistant to pathogens and pests), and better adapted to grow under organic cropping systems. NOP guidelines, and environmental sustainability benefits are compelling factors for using certified organic seed. The third reason is highly dependent on the seed producer and the source of the seed. Most plant varieties were bred under conventional agricultural systems. However, there are now university and private breeders who are breeding new varieties using organic growing methods. While organically bred varieties are available, the performance of these varieties may be regionally limited. Seed selection should be based on production needs and environmental growing conditions first, and then organic if it is available. Check the facts when organic seeds claim to be healthier, pest- and pathogen-resistant, and pesticide-free.

organic farming

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Organic Versus Conventional Foods: Fifty Shades of Green
By Dr. Wesley Chun Ph.D., Grower's Secret, Chief Science Officer

Introduction

Organically produced food is an essential form of food production that has existed since the dawn of agriculture. It resided with the Green Revolution but has regained popularity since the rebirth of the organic movement in the 1940s. Once only available in organic stores, three out of four stores now carry organic products. From 2010 to 2019, organic food sales increased 4.6 to 12.2 percent annually. In 2018, total US organic sales reached $52.5 billion, a 6.3 percent increase from 2017. US organic food sales accounted for $49.7 billion, a 5.9 percent increase from 2017. This year organic produce sales as a result of the COVID pandemic jumped 22 percent in March, leading to a first-quarter rise of 8 percent for 2020. 

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By Dr. Wes Chun Ph.D. 
Grower's Secret, Chief Science Officer

Applying fertilizers pre-plant and at-planting are beneficial practices to restore soil fertility and grow a successful crop.  Pre-plant fertilizers are applied before planting seeds or seedlings into the field or into nursery potting media.  At-planting fertilizers are applied during planting.  These practices provide ready access to nutrients that are vital for seedling establishment and health.  Proper fertilizer choice and placement are essential for maximizing the benefits of pre- and at- planting fertilizers

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By Dr. Wes Chun Ph.D. 
Grower's Secret, Chief Science Officer

For many crops, post-harvest (the period after harvest and before leaf senescence) fertilization can play an important role in the following season crop. In many tree crops, it is one of the best times of the season for uptake of nitrogen and potassium. Trees are still active, and the roots and foliage readily absorb applied nutrients. These nutrients become reserves for the following growing season.  While there may be little difference in tree productivity between fall and spring fertilizer applications, it may be better to fertilize in the fall. Fall applications are more efficient since trees are still actively taking up nutrients, cold and wet conditions in the spring can delay dormancy break, and spring-applied fertilizers are subject to leaching and runoff.

fertilizer, nickel, elements

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Ferti-Facts:  Nickel, It Just Makes Good “Cents”

Introduction

Nickel (Ni) is the 24th most abundant element in the Earth’s crust with concentrations ranging from 80 to 125 ppm. Combined with the estimated 20% Ni content of the Earth’s core, nickel jumps to the fifth most abundant element by weight after iron, oxygen, magnesium, and silicon. In pure form Ni is a lustrous silvery white metal with a gold tinge. Nickel is a group 10 member of the Periodic Table of Elements. Nickel’s position in the Periodic Table places it in a group of transition metals (Mn, Fe, Co, Cu, and Zn) that serve as essential micronutrients for plants.

Nickel is the most recent element to be added to the essential element list for plants. Its presence in plant tissues (ash) was used for biogeochemical nickel prospecting in the mid 1900’s. In 1946 broad beans, potatoes, and wheat grown in the Romney Marsh area in England responded well to applications of nickel, as well as boron, copper, iron, manganese, and zinc. In 1975, nickel was identified as an essential component of the plant enzyme, urease when tissue cultured soybean plants could not grow when urea was supplied as the sole nitrogen source unless nickel was supplied. Other researchers soon demonstrated that a nickel deficiency severely impacted growth of other plants when urea was the sole nitrogen source. In 1983-84, nickel was shown to be essential for nitrogen fixing plants such as legumes. In 1987, it was shown that barley could not complete its life cycle in the absence of nickel, even if a non-urea nitrogen source was provided. Other researchers showed that a nickel deficiency depressed growth of oats and wheat.These findings met the requirements defining essential elements for plants. By 2004, nickel was added to the USDA list of essential plant elements and recognized as an essential micronutrient by the American Association of Plant Food Control.

Nickel in Plants

Nickel concentrations in leaves of plants range between 0.05 to 5 mg/kg dry weight.  However, nickel concentrations between 0.1 to 10 mg/kg dry weight are adequate for most plants.  Different plant tissues as well as certain plants are considered Ni accumulators. Accumulators are able to tolerate higher soil Ni concentrations and usually have higher Ni content in their tissues. For example, 100 mg/kg is the critical concentration of Ni needed for seed germination in barley; shoot growth in oats, barley, and wheat; shoot growth of urea-fed tomato, rice, and zucchini; and for pecan crop production. In Ni sensitive plant species, Ni concentrations of 10 mg/kg dry weight is toxic. In moderately tolerant plants, Ni concentrations greater than 50 mg/kg can be toxic. There are approximately 150 plant species that are known to be Ni accumulators that can have Ni concentrations at least 1000 mg/kg dry weight without exhibiting toxicity symptoms. Some plant tissues are able to accumulate Ni as high as 50,000 mg/kg.

Nickel is mobile in plants so deficiency symptoms appear in older leaves first. This can create a spatial Ni concentration gradient within a plant.  For example, up to 70% of the Ni content in a plant’s shoots can be transported to seeds. Uptake mechanisms of Ni may share some similarities with other metal elements since copper and zinc are effective competitors of nickel.  There are two regulatory systems that manage Ni uptake. There is a low affinity system that can absorb Ni at concentration of 4.4 ppb (0.6 ounces of Ni per million gallons of water), and a high affinity transport system that can absorb Ni at 1.8 ppm (237.7 ounces Ni per million gallons of water. Nickel is readily re-translocated within the plant, probably as a complex with organic acids, such as citrate at pH < 5, or with an amino acid, such as histidine at pH > 6.5.

Nickel in Soils

Nickel is widely distributed in soils originating from soil forming processes, plant decomposition, and pollution. Only the ionic form, Ni2+ is available to plants.  Since these may be chelated to other compounds, total soil Ni concentrations may not be reflective of actual Ni availability. Other ions such as copper and zinc compete directly for carrier sites with nickel.  Other ions such as iron and cobalt compete indirectly. These competitive ions are also Ni limiting in soils.

The lowest amounts of Ni are found in low nutrient acidic soils, sedimentary rocks such as limestone (<5 mg/kg), sandstone (20 mg/kg), and shale (90 mg/kg).  Highest concentrations of nickel are found in basic igneous rocks (2,000 to 6,000 mg/kg) and lands impacted by industrial wastes. Nickel concentrations normally range from 3 to 1000 mg/kg in agricultural soil.  Some of the higher recordings may be due to fertilizer introduced nickel. Healthy productive soils have nickel concentrations ranging from 1 - 20 mg/kg. Deficient levels of Ni are found in low nutrient, acidic soils such as the Romney Marsh in England and in the southeastern United States. Average Ni concentrations run around 50 mg/kg, and range from 5 to 500 mg/kg in most soils. High nickel concentrations have been found near metal refineries (24,000 mg/kg) and in dried sewage sludge (53,000 mg/kg).

Nickel Deficiency Symptoms

Nickel should be at sufficient levels for agriculture since Ni is fairly ubiquitous and continually being deposited from atmospheric pollution generators. Although rare, nickel deficiencies are known to occur in a number of perennial plant species grown in the low nutrient, acidic soils of the southeastern United States, soils with high Ni binding capacity, high pH soils (>pH 6.7), and high lime soils. It can also occur under tightly controlled conditions such as tissue culture. Nickel deficiencies, can appear after three years of tightly controlled fertilization that prevents Ni introduction. The current trend for cleaner air, better fertilizers, and greenhouse and tissue culture based production, may also impact and lead to Ni deficiencies.

Nickel deficiencies can be induced by excessively high levels of zinc, copper, manganese, iron, calcium or magnesium in the soil through the use of fertilizers and zinc and copper containing fungicides. Nickel deficiencies can also be induced by root-knot nematode damage, and by dry or cool soils at the time of bud break.

Nickel deficiency symptoms result from decreased urease activity leading to the buildup of toxic levels of urea which causes  leaflet tip necrosis. In nitrogen-fixing plants receiving nitrate and ammonium fertilizers, Ni deficiency is observed as leaf tip necrosis on pale green leaves. A nickel deficiency can result in a reduction in shoot growth of barley, oats, and wheat. Tissue analyses will show a reduction of tissue iron and malate concentrations. In pecan and in certain other woody perennial crops (e.g., plum, peach and pyracantha, and citrus) Ni deficiency is characterized by early-season leaf chlorosis, dwarfing of foliage, blunting of leaf or leaflet tips, necrosis of leaf or leaflet tips, curled leaf or leaflet margins, shortened  internodes, distorted bud shape, brittle shoots, cold-injury such as  death of overwintering shoots, diminished root system with dead fibrous roots, failure of foliar lamina to develop, rosetting and loss of apical dominance, dwarfed trees, and tree death.

For woody perennials, chlorosis similar to that of iron or sulfur deficiency has been noted as an early indicator of Ni deficiency. Other more severe symptoms that have been observed in pecan trees include a rounding or blunting of the leaflet tips, and dwarfing of foliage to produce what has been termed “mouse ear” or “little leaf” in the southeastern US. This rounding of leaf tips is associated with buildup of urea to toxic levels. With severe Ni deficiency, leaf deformation is often most prominent at the top of the tree canopy. Affected foliage is thicker, less pliable, tends to be brittle, and may exhibit cupping or wrinkling. Severe Ni deficiency results in plant stunting and abnormal growth patterns.

In graminaceous species, deficiency symptoms include chlorosis which appear similar to that induced by iron deficiency, including interveinal chlorosis and patchy necrosis in the youngest leaves. Nickel deficiency also results in a marked enhancement in plant senescence and a reduction in tissue-iron concentrations. In monocotyledons and in dicotyledons, the accumulation of urea  in leaf tips is diagnostic of nickel deficiency.

Fertilizing with Nickel

Fertilization with nickel is usually not needed. Soil plant available Ni or deposition from the air is usually sufficient to meet the critical requirements for most plants.  Trace amounts of Ni are also present in some commonly used fertilizers. However, situations where Ni is deficient, or with crops that have a high requirement for Ni such as pecans, Ni supplementation would be useful if not necessary.

Anhydrous nickel sulfate (NiSO4) or nickel sulfate NiSO46H2O can be used for tissue culture or to address nickel deficiencies when used as a foliar spray (0.03 to 0.06 ppm). Municipal sewage sludge is another good source for Ni. Other Ni containing fertilizers include nickel nitrate (Ni(NO3)2 •6H2O), nickel chloride (NiCl26H2O), nickel EDTA complex (NiC10H16N2O2), and Nickel Plus. Application of foliar sprays of 0.05 to 0.06 ppm Ni, or 0.5 lbs Ni per acre is all that is needed.

Crop Responses to Nickel

Crop responses to nickel are the absence of Ni deficiency symptoms. Approximately 0.03 mg/kg dry weight in leaves for most plants are sufficient. Sufficient Ni has been reported to produce significant increases in nodule weight and seed yield of soybean. Nickel is needed in barley to yield viable seeds. In pecans, Ni alleviates mouse ear symptoms and may be associated with reduced resistance to certain diseases. In other plants, Ni has been associated with increasing disease resistance due to a direct phytosanitary effect of Ni on the pathogens or possibly increased host plant resistance. Nickel is absolutely essential for rice, soybean, and tobacco tissue culture.

Nickel Toxicity Symptoms

Until the recognition of Ni as an essential element, attention was focused on the toxicity of nickel in plants especially lands impacted by industrial pollution. In sensitive plant species (>10 mg/kg dry weight), moderately tolerant plant species(>50 mg/kg dry weight), impaired root and shoot growth without any remarkable defining characteristics can be observed. This can occur in serpentine soils, sewage amended soils, or soils subject to contamination from industrial pollution.  Nickel toxicity symptoms usually occurs in plants grown in soils with high concentrations of iron, zinc, and chromium, or an unfavorable ratio of magnesium to calcium. Severe toxicity results in complete foliar chlorosis with necrosis advancing in from the leaf margins, followed by plant death.

In early or incipient stages of nickel toxicity, no clearly visible symptoms develop, though shoot and root growth may be suppressed. Acute nickel toxicity results in symptoms that have occasionally been likened to iron deficiency (interveinal chlorosis in monocotyledons, mottling in dicotyledons) or zinc deficiency (chlorosis and restricted leaf expansion).

Summary

Nickel is the latest element to be classified as essential for plant growth in both laboratory and field conditions. Nickel plays an important role in nodulation and nitrogen fixation so it is an essential nutrient in leguminous nitrogen fixing plants. Nickel deficiencies are usually observed when soil pH is greater than 6.7, or in soils that have received excessive application of Ca, Cu, Fe, Mg, Mn, or Zn. Common symptoms are leaflet tip necrosis or “mouse-ear” leaves. Deficiencies can be remedied with foliar sprays such as NiSO4 or other soluble Ni fertilizers. Municipal biosolids can also be effectively used to address soil Ni deficiencies.